caspain geology

Hydrocarbons of the South Caspian Basin: How Exploitation Depends on the Understanding of the Neogene Paleoclimate

Hydrocarbon exploration is moving forward at an accelerated pace in the Neogene section of the South Caspian basin, driven by development of the giant "megastructure" field in the South Caspian basin and recent gas discoveries at Shah Deniz. In addition, there are large recent discoveries in the older strata of the North Caspian basin. As a result, major oil companies as well as national governments in the region are pushing plans for major export pipelines to the world market. This is a very opportune time to take at look at some of the remarkable aspects of the geologic history of the South Caspian basin that make it such an attractive petroleum province. Would you have guessed that Neogene paleoclimate is one such factor?The latitude of the South Caspian basin put it in a "Mediterranean" zone where the climate has oscillated from wet to very dry every 20,000 years, in response to insolation changes driven by variations in the Earth’s orbit (Milankovitch cycles). This land-locked sea responded by major changes; the "sea"level changed probably more than 100 meters vertically and shorelines migrated probably several hundreds of kilometres laterally during each cycle. About a dozen such cycles occurred just during deposition of the Pereriva Suite, implying that there are (at least) an equal number of internal unconformities within just this interval of the reservoirs of the Productive Series. In addition, there is a major unconformity at the base of the Pereriva. There are probably about 50 unconformities within the Balakhany Suite. At first glance, this may induce a development geologist to just give up and apply some geostatistial tool to ‘get around’ the problem. A look at the sedimentology of outcrops and cores of the Productive Series, however, offer a lot of hope that the complexity can be resolved by understanding the architecture of the individual depositional sequences that resulted from these climate and ‘sea’ level oscillations. The Caspian database also reveals that some fundamental paradigms in sequence stratigraphy require major revision before they can be applied to predict lacustrine reservoir architecture. Among these is the observation that the sequence boundary (lowstand exposure surface) essentially coincides with the maximum flooding surface because there is hardly any clastic sediments deposited in an enclosed lake during lake level fall - there is no fluvial discharge to get them there. Also, sequence boundaries in the South Caspian have no time relationship to those formed by global eustasy; they are neither in- nor out-of-phase. This is because levels of the Caspian Sea are driven by low-latitude insolation, which is mostly controlled by 20,000-year precession and 100,000-year eccentricity cycles. In contrast, global eustasy is controlled by polar ice volumes, which change in response to high-latitude insolation that is heavily influenced by obliquity changes on 40,000-year time scales. So, don’t attempt to date the Neogene section of the Caspian using global sea level charts.Caspian reservoir architecture is not random; few things in geology ever are. Before order can be discerned and used effectively in exploitation, however, the factors controlling sedimentary architecture must be understood. Although

many factors interact in the Caspian as elsewhere, the first-order control was the Neogene paleoclimatic cycles.

Productive Series in the South Caspian basin: Depositional environment and cycles of sedimentation at rapid sea level changes

Elmira G. Aliyeva, e-mail: e_aliyeva@yahoo.com, Institute of Geology of Academy of Sciences, Azerbaijan, Dep/Inst. of stratigraphy, lithology, geotectonics

David J. Hinds, e-mail: d.hinds@abdn.ac.uk, University of Aberdeen, United Kingdom, Dep/Inst. of geology and petroleum geology

Keywords: Closed basin, Rapid sea level changes, High order cycles

The Caspian Sea being a closed basin is characterized by very great instability of its level. Amplitude of its small time scale sea-level cycles (decades, centuries) can be compared with amplitude of millennial and longer stages of the World Ocean fluctuations. Besides long-term stages of fluctuations of the sea level there exist high-frequency cycles in the Caspian Sea level changes. They are still playing a key role in the formation of sedimentary series and architecture of major hydrocarbon reservoir units. Object for the study- the Balakhany suite of Lower Pliocene Productive Series (PS), the large thickness of which (about 5  km) was formed during 2  Ma (5.5  Ma - 3.5  Ma). PS consists of 9 suites and Balakhany suite represents the key production interval in the South Caspian basin The outcrops observation were combined with subsurface data (gamma ray and SP logs). On the background of long- time sea level rise from the base of the Balakhany suite( horizon X) to the top of this one (horizon V), one can observe rapid fluctuations of the sea level expressed in the formation of several high order cycles. Deposits of lower portion of the Balakhany suite are interpreted as predominantly braided fluvial deposits with numerous lateral extended amalgamated channels. Cross-bedding with fining upward foresets are common depositional patterns. However, it is also possible to observe the different types of paleoenvironment- the front of the delta; the delta plain with good lateral communication and restricted vertical connection of sand layers. One can say, that only in horizon IX of the Balakhany suite there were recorded 7 cycles of a high order and 4 stages of sea level fall . In the upper part of Balakhany suite the fluctuations of the sea level are not so dramatic. Sedimentation at proximal and distal delta front dissected by channels is the predominant depositional feature. During the formation of horizons VIII-V only 5 complete cycles of the sea level fluctuations took place. For the upper horizons of the the Balakhany suite a tendency of a stable sea level rise and uninterrupted development of the accommodation space are typical. Thus, during the accumulation of only one suite of PS- the Balakhany suite- there were exist 13 cycles of the sea level fluctuations with its highest intensity in the lower horizons.

Hydrocarbon migration and entrapment at Shah Deniz: A few clues for the South Caspian

Greg Riley1, Neil Piggott1, Mark Osborne1, and Norman Oxtoby2. (1) BP Azerbaijan, BP, Building C, Chertsey Road, Sunbury-on-Thames, TW16 7LN, United Kingdom, phone: 44

1932760210, fax: 44 1932760267, RileyGR@bp.com, (2) Department of Geology, University of London, Royal Holloway, Egham, Surrey, TW20 0EX, United Kingdom Data acquired from the Shah Deniz (SD) gas-condensate discovery suggest that phase and quantity of petroleum in South Caspian Basin (SCB) structures are a consequence of the interplay between structural timing, sand connectivity (allowing depressurisation) and timing of depressurisation events. SD is located in the SCB within the High Pressure (HP) PaleoVolga playfairway. This play fairway is HP due to compaction disequilibria resulting from rapid Pliocene sedimentation. Hence, in general, water-wet sands at SD are overpressured by up to 5,000 psi. In contrast, gas-bearing reservoirs are at significantly lower pressures. These lower pressures are interpreted to result from basin margin uplift and erosion of laterally extensive reservoir sandbodies. Less extensive sandbodies remain overpressured. Early oil emplacement is recorded in oil inclusions, which isochore modeling suggests occurred at near-lithostatic pressures, prior to depressurisation. Maturity indicators from both gases and liquids from DST samples indicate that the upper, Balakhany reservoirs trapped an earlier less mature hydrocarbon charge than the deeper Pereriv reservoirs. A fill model for the trap is proposed as follows: 1) At approximately 2.0 – 3.5 Ma oil migrated through the reservoirs. Because of near lithostatic pressures there was no effective seal. 2) Later, uplift of onshore structures resulted in pressure depletion of the Balakhany. This pressure decrease created an extremely effective seal (overlying, overpressured mudstones) and permitted gas entrapment. 3) Continued uplift resulted in the pressure depletion of deeper Pereriv reservoirs. Depletion of Pereriv pressures resulted in creation of an effective trap and stopped gas migration to the Balakhany.

EXECUTIVE SUMMARY

This report presents the results of a joint study between the Geology Institute of the Azerbaijan Academy of Sciences (GIA) and the BP and Statoil Alliance to investigate the remaining prospectivity within the essentially Pliocene "Productive Series" succession of Azerbaijan.

The South Caspian Basin contains prolific hydrocarbon reserves. An estimated 26 billion barrels (oil equivalent) have been found to date and some yet to find estimates are as high as a further 30 billion barrels oil equivalent. 99% of known reserves are within reservoirs of the Productive Series. However, hydrocarbon production in Azerbaijan is currently in decline and new reserves need to be located. This study therefore addresses the question of what prospects remain for finding more hydrocarbons within the Productive Series, and in particular, for locating them in regions outside of the main area of structures which have already been drilled and which have been producing hydrocarbons for many years.

Two case studies are presented, one looking at the potential of the Lower Kura region (particularly in the relatively unexplored Lower Productive Series); the other considering the prospectivity of the Mugan Homocline region (south-west of the Kura Valley), where pinch-out of the Productive Series provides a series of underexplored plays.

To supplement these case studies and to build on previous collaborative studies between the GIA and the BP and Statoil Alliance, field work and various sample analyses have been carried out. This field work has concentrated on two aspects of Productive Series geology: firstly, the upper part of the Productive Series, which was relatively unexamined during our earlier joint work; and secondly, localities outside the Apsheron Peninsula region, which allow for a comparison of the sedimentation styles, petrography and prospectivity of the Palaeo-Kura and Palaeo-Volga river systems which were the prevalent depositional controls during Productive Series sedimentation. Detailed sedimentological logging, followed by petrographic and biostratigraphic analyses have improved our understanding of the depositional environments, stratigraphy, reservoir connectivity, reservoir architecture and reservoir quality of the Productive Series and thus provided major insights into the future hydrocarbon prospectivity of Azerbaijan.

CONTENTS

(i) Executive summary (ii) Contents List

1. INTRODUCTION 1.1 Aims and Scope of the Study 1.2 Methods 1.3 Report Organisation 1.4 Roles and Responsibilities

2. SEDIMENTOLOGY 2.1 Introduction 2.2 Outcrop Sedimentology 2.3 Petrography and Reservoir Quality 2.4 Conclusions

3. FAULTING WITHIN THE PRODUCTIVE SERIES 3.1 Introduction and Objectives 3.2 Kirmaky Valley 3.3 Balakhany Quarry 3.4 Balakhany Foreshore 3.5 Aktapa Bridge 3.6 Conclusions

4. BIOSTRATIGRAPHY 4.1 Introduction 4.2 Results of Outcrop Studies 4.3 Conclusions

5. PROSPECTIVITY WITHIN THE PRODUCTIVE SERIES OF THE LOWER KURA VALLEY 5.1 Introduction 5.2 History of Exploration and Production 5.3 Lithofacies Characterisation 5.4 Depositional Environments 5.5 Future Prospectivity

6. ROSPECTIVITY WITHIN THE MUGAN HOMOCLINE REGION 6.1 Introduction 6.2 History of Research 6.3 Lithostratigraphy 6.4 Structure and Tectonics 6.5 Future Prospectivity 6.6 Conclusions

7. SELECTED BIBLIOGRAPHY

APPENDIX 1: Graphic Logs APPENDIX 2: Petrographic Analyses APPENDIX 3: Reservoir Quality Tables

APPENDIX 4: Biostratigraphic Data

A TECTONIC MAP OF THE ABSHERON PENINSULA

Scale 1:100,000

I. When analysing the geologic map of the Absheron peninsula, one established that the main structure elements of Western Absheron are:

1. The West-Absheron rise (K2-N1); 2. The Nasosni-Binagadi downdip block (P-N1); 3. The Kurdakhany-Mashtagi rise (Pl-Q).

II. The zone of the Late Pliocene-Anthropogene superimposed troughs and plateau: 4. The Chuvaldag (Karadag) plateau (Pl3); 5. The Gezdeck plateau (Pl3-Q); 6. The Baku trough (Pl3-Q); 7. The Bina-Gousan trough (Pl1-Q); 8. The Dubendi-Zira trough (Pl1-Q); 9. The Interblock overfault structures.

III. The study of the distribution of mud volcanoes on the Absheron peninsula has shown , that all the volcanoes form strict parallel rows stretching in the north-eastward direction.

1. The volcanoes Beyuk-dag, Keireki, Zigil-Piri, Gekmaly, Bozdag, Kirmaki, Sulutepe, Bog-Boga, Shonkar and etc. form a single line. We have called this line of volcanoes the Sangachal-Nardaran fault zone. This fault (which is 2,000-2,500 m below the lower segment of the productive series) is a result of sinking of the coast of the Caspian Sea.

2. The Karadag-Gurganian N.–E. fault starting at Karadag runs through the volcanies Lok-Batan, Bibi-Eibat, Zykh and Pirallakhi.

IV. We have separeted the bellow written rows of volcanoes westwards to the Sangachal-Nardaran zone of faults up to Sumgayit-city:

3. Kosmaly-Kalagy; 4. Novkhany-Tashgyl; 5. Nagdaly-Sumgayit North-Eastern fault.

V. The deeply sunk coastal zone of the Late Pliocene-Antropogene superimposed troughs and plateaux is located between the Sangachal-Nardaran zone of faults in the west and the Karadag-Gurganian North-Eastern fault in the east. From the Sangachal-Nardaran fault, up to Sumgayit, all the territory of the Western Absheron is cut by the North-Western faults (the Akhtarma-Shonkar, Shubany-Karakush, Gousan-Geradyl and Kalinski faults). The Karadag and Gezdek plateaux, Baku trough are separated by the above-mentioned faults. The overfault oil bearing structures such as Lock-Batan, Bibi-Eybat, Shubany and others are linked to the North-Western Shubany-Karakush fault. The Baku through is separated from the Bina-Gousan through by the Gousan-Geradil North-Western fault, which gave a rise to the Zykh, Kara-Chukhur, Surakhany, Ramany, Zabrat, Sabunchi and Balakhany oil-bearing structures. The Bina-Gousan through is separated from the Dubendy-Zirya trough by the North-Western Kalinski fault, above which the oil-field Azizbekovneft came into being.

The Apsheron oil-gas province is the oldest on Earth, where the first productive oil wells were drilled onshore in 1847 (Bibi-Eibat) and off-shore in 1922 (north of Pir-Allagi island).

The database contains a complete information on 12 of the major onshore and offshore fields of the Apsheron oil-gas region.

Onshore Offshore

Buzovna-Mashtagi Darvin bankasi

Gala Pir-Allagi

Surakhani Neft Dashlari

Qarachukhur-Zykh Gum-deniz

Bibi-Eibat Bakhar

Lokbatan  

Garadag  

For each field, the following data is available: structural map, geological profile, stratigraphic section as well as the following data in tabular form: discovery year, fold sizes, deposit type, productive suites, well discharge, oil density, formation pressure and temperature, carbonate content, porosity, etc.

We have the possibility of operative including the analogous information into the database on following onshore and offshore fields of the Apsheron oil-gas region.

Onshore Offshore

Gushkhana-new Gurguan-deniz

Kergez Djanub

Shongar Khali

Puta Djylov adasy

Lokbatan-southern Hazi Aslanov

Atashnya-Shabandag-Yasamaly valley Palchyg-pilpilyasi

Binagady-Chakhageyar-Sulutepe Guneshli

Balakhany-Sabunchi-Ramany Chirag

Zyrya Azeri

  Kepaz

E.ShikhalibeyliSome Problematical Questions of Geological Structure

and Tectonics of Azerbaijan

Summary

The data, received by author was brought to this issue in the process of his personal long - term research - works with the drawing of new detailed geological maps of the Southern Slope of the Greater Caucasus, Eastern part of the Lesser Caucasus (eastwards from Shamkhor chai river up to lower flow of Araks river), reconnoitering researches of the rest territory of Azerbaijan (with the exclusion of Talysh), including the Southern Daghestan in the North and the Nakhichevan AR in the South with the usage of all the geophysical research results in Azerbaijan, and also the literature on geology of Azerbaijan and contiguous areas of Iran, Turkey, Georgia, Caspian, Black and Mediterranian Seas. His works made available to reveal new magmatic bodies and bound with them minerals' outcrops, prospectivity of them was further confirmed.

The author's opinion about the recasting of the granitic layer of the interior seas' earth in the process of long - term sagging and the influence of basic magma are confirmed now by research data of the Black Sea, Kura depression troughs', and superdeep Saatly - well data . The detailed investigations of multyannual seismogramms of the Northern Caucasus had confirmed the author's sayings about the connection of mantle Earthquakes of Caucasus with the North - Eastern faults, which cut the transversal rises. The author was the first to reveal the binding of Mud Volcanoes of Apsheron peninsula with the knots cross overings of North - Eastern Riphean faults (Upper Proterozoic - Lower Cambrian) with north - western Alpine faults .

The existing scheme of tectonic division into districts of Apsheron peninsula had been drawn before along the cover of Supra Kirmaki Horizon of Productive Series, i.e. here were not taken into stock, created in Middle Pliocene - Anthropogene age. The new scheme is drawn by author with the account of participation of all the sediments of peninsula in the process of folding, and along with it the structures apportioned in the first scheme of tectonic division into districts. Although, there is not taken into consideration the role of faults in structures' creation, had made sunk step - by - step the peninsula in Eastward direction, but by Sangachal - Turkanian North - Eastern fault the coastal strip, beginning from the age of Upper part of Productive Series, was sunk for 1,5-2,0 km and here was created the strip of superimposed troughs, imposed by Upper Pliocene - Anthropogene depositions. The North - Western faults cutting the strip of superimposed troughs for separate links created Karadag, Gusdek, Baku, Gousan, Zyrya - Dubendy troughs. The same North - Western faults in Western Apsheron created the risen and sunk blocks, and created overfault structures of Productive Series in separated by these faults in inter - trough spaces with richest outcrops of oil (Bibi - Aibat, Lock - Batan, Shubany, II - Zykh, Karachukhur, Surakhany, Ramany, Zabrat, Sabunchu, Balakhany, Kirmaki, Fatmai, III - Kala).

Due to author's opinion, the coastal strip of Apsheron peninsula is sinking now and with time passed because of heaviness of super laying depositions from under the troughs the oil would be ousted into the structures of old outcrops. So it is necessary to conduct constant supervising on increase of well's output even if on one deep well in every outcrop.

Thus, the edition of this publication has a great scientifical and practical value for the understanding of deep structure of Republic's territory and revealing of new outcrops of hydrocarbon raw material and hard minerals.

Contents

Introduction. Chapter 1. The main Alpine deep faults of Azerbaijan. Chapter 2. The transversal "Anti Caucasian" faults of Azerbaijan of ancient deposition. Chapter 3. A new tectonic map of the Apsheron peninsula. Chapter 4. The causes of juncture, disappearance or extinction of the Caucasian folded System by the approaches to the Caspian Sea.

Chapter 5. The role of riff formation and long sagging and disappearance of the Earth's crust granitic layer in the interior and marginal seas (on examples of the Yevlakh-Agdjabedy trough of the Kura depression and the Black sea). Chapter 6. The deep earthquakes of the Caucasus in the neotectonic stage. Chapter 7. The Kura depression (new data about depression structure). Chapter 8. The ophiolite association of rocks establishment mechanism in the Lesser Caucasus troughs. Chapter 9. The matter of the Benyoff - Zavaritsky zone presence along the Northern flank of the Kura depression in Azerbaijan.

GAS OF AZERBAIJAN

Azerbaijan is one of the world's unique regions where as from the old times people have used natural gas blowouts to burn limestone and cook meal.

The application of gas in Azerbaijan for heating steam-boilers dates back to 1859. In the year 1902 to 1906 six gas lines made of cast iron running from the wells in Surakhany to the settlement of Balakhany were laid to use the gas for heating.

In the 30's in Azerbaijan a work was launched for the regional power stations, oil processing facilities, industrial boiler-houses, etc., to be switched over to using gas as a fuel.

In 1848 in the former Soviet Union the putting of a closed oil/gas well exploitation system into practice was begun for the first time. It allowed to minimize gas losses.

A new era in the history of the republic's gas upstream industry started in 1954 by discovering a gas-condensate deposit in the Karadag field. The discovery was followed by striking gas and gas condensate in the Kalmas, Zyrya, Duvanny, Yuzhnaya, Bakhar, Duvanny-deniz, Bulla-deniz areas and others. The discoveries showed that Azerbaijan's bowels of the earth were rich in not only oil but gas.

The following figures say about the pace of development of the republic's gas upstream industry : if in 1922 only 26 million cubic meters of gas were produced, as early as 1940 the output hit 2.5 billion cubic meters, in 1965 gas production rose to 6.2 billion cubic meters and in 1982 the production level edged up to 14.9 billion cubic meters.

A high rate of gas production and the construction of main gas lines enabled to gasify Azerbaijan's towns, villages and industrial enterprises. In 1988 in the republic more than 1.3 millions of apartments were provided with gas , including 900,000 accommodations were supplied with natural gas. Gas flew to the mountainous regions of Azerbaijan. More than 750 production facilities and about 13,000 social and municipal enterprises providing public utilities used natural gas as feedstock and fuel.

Unfortunately, because of hostilities in Azerbaijan's provinces bordering on Armenia and the occupation of a part of the republic's territory, the works have been suspended.

Slathers of gas reserves found in the republic gave a great incentive to the development of the republic's oil upstream and downstream industry. The questions of the combined use of natural gas were decided in the 60's. The process was launched with the construction in the 60's of the Azerbaijan gas processing plant and the commissioning of a petrochemical facility in Sumgait. A joint processing of gas and instable condensate allowed to supply the republic's new chemicals producing facilities with valuable feedstock, on the basis of which the output of tens of kinds of chemicals was built up.

For reliable gas supply of the country's population and power stations especially in the fall/winter season of every year it is necessary to lay in a stock of gas. For this purpose two underground gas storage facilities have been built in the areas of Kalmas and Karadag and they are now operational.

But that given all of the gas/condensate deposits currently in production were developed without paying attention to a fall of the reservoir pressure to nothing and new deposits have not been entered since 1983, domestic gas production started to drop. Only 5.6 billion cubic meters of gas were produced in 1998.

After the Chirag contract area offshore was put into operation in November 1997 and the capacity of a gas compressor station built by Pennzoil company in the Neft Dashlary field was increased from 4.2 to 5.6 million cubic meters of gas handled per day, the gas delivery onto shore rose from the oil fields of Guneshli and Chirag through the undersea gas pipelines. The domestic gas production was maintained at the same levels and even somewhat stepped up in current year. As a result, SOCAR's two production associations for the first time in recent years surpassed their gas production targets more than planned.

This year a well in the Shahdeniz contract area offshore was drilled to a record depth from the Istiglal and Dada Gorgud semi-submersible drilling rigs. It reached and opened up the eight and tenth horizons of the Balakhany Suite and Pereriv Suite. The mammoth gas and condensate reserves (and probably there is an oil fringe as well) have been proved by testing the exploratory well. These deposits will enable for many years not only to meet the republic's internal needs but to export natural gas in large quantities to world market, above all, Turkey. It should be suggested that large reserves of gas/condensate can also be stricken in the lower lying horizons of the field.

Given a find of significant gas reserves in the fields of Shahdeniz, Chirag, Azeri and Guneshli and the results of testing appraisal wells drilled in the Karabakh, Ashrafi and Dan Ulduzu areas as well as an increased chance of their hitting in the promising structures both on land and in a significant part of the Azerbaijan sector of the Caspian Sea, one may speak with confidence that in the next few years Azerbaijan is able to sharply boost gas production and become one

of main suppliers of the kind of this fuel in the region. It will give a great impact on development of many industries in Azerbaijan.

In accordance with an instruction given by Azerbaijan President Heydar Aliyev when discussing the test results from the exploratory well drilled in the Shahdeniz field, SOCAR in conjunction with another organizations concerned are to work out soon a long-term program for the streamlined use of gas reserves in the unique field and all the republic as a whole.

R.Dadashev, in charge of oil

and chemistry department for Azerbaijan's Cabinet of Ministers,

Dr. of Geology and Mineralogy Science.

THE KUR DASHI PROJECTThe Exploration and Development Production Sharing Agreement for the Kur Dashi exploration block was signed on 2 June, 1998 and became effective on 30 July.

Parties to the Agreement are Agip Azerbaijan B.V. (the Exploration and Production subsidiary of ENI, the Italian oil and natural gas company, operating in Azerbaijan), which is the Operator and holds a 25 per cent interest: Mitsui Kur Dashi Exploration, with a 15 per cent interest; Repsol Exploracion, with a 5 per cent interest; SOCAR Oil Affiliate, with a 50 per cent interest; and Turkish Petroleum Overseas, holding the remaining 5 per cent interest. The EDPSA structure is the standard one for Azerbaijani Agreements.

The commitment during the exploration period is to shoot a 3D of 550 square kilometres and drill three wells.

Geological backgroundThe block is located in the offshore extension of the Lower Kura Basin, which is a prolific hydrocarbon basin with a number of discoveries onshore. The onshore part of the basin is little explored, but contains numerous prospects. Seepages of hydrocarbons from the sea floor are known to occur in the area. In particular, the Kur Dashi block is located on the offshore continuation of the Neftchala-Khilli-Garabagli-Kurovdag trend, along which a number of oil and gas fields were discovered in the past and are still producing. The block contains three known anticlines: Kur Dashi itself, Araz Daniz and Kirgan Daniz. The water depth in the area ranges from a few meters (actually a small islet, which represents the culmination of a mud volcano, is present in the block) to more than 600 meters.

The targets contained into the pliocenic "Productive Series", whose base in the block ranges from less than 4,000 to more than 6,000 meters below sea level. The main sandstones should be represented by sandstones of the Pereryv, Balakhany and Surakhany formations., which were deposited in a fluvio-deltaic to marginal marine environment.

The main "source rocks" of the area are represented by the Maykop formation (Lower Miocene to Upper Oligocene in age) and the "Diatomite shales" (Mid-Upper Miocene in age). Hydrocarbon migration is likely to have started in the Upper Pliocene, thus during, or right after, the main tectonic phase which have generated the structural traps. Vertical migration of hydrocarbons has been probably controlled by the presence of mud volcanoes, which have

acted as preferential pathways.

Seismic activity was conducted in the past over the block, and resulted in the identification of the three anticlines. Only a number of geotechnical shallow wells, were drilled. Consequently, the block must be considered as attractive exploration acreage.

Environmental issuesThe delicate ecosystem of the region of the Caspian Sea in which Kur Dashi is located, renders the environmental issues a critical one, and a priority for the Operator.

The Gizilagac environmental reserve, with its fish spawning and birds nesting areas, and the Kura river delta, another spawning area for sturgeon, with fish hatcheries and fish farms, are both in the vicinity of Kur Dashi. Fishing activities are an important feature of the local economy. We have taken a commitment that such a delicately balanced environment shall not be altered by the conduct of Kur Dashi operations. To assure that, detailed environmental procedures whose principles are already contained in the EDPSA are being agreed with SOCAR and appropriate authorities.

Activity planThe 3D seismic acquisition is started in November, preceded by an Environmental Impact Assessment. A campaign to collect samples of water, sediments, flora and fauna was conducted in October: these samples are being analysed and studied and results will be used in preparing the environmental guidelines for future operations.

Due to the scarcity of drilling rigs in the Caspian Sea, Agip has entered, together with other operators, into an agreement to build a new jack-up rig to be used in the Kur Dashi operations. A large part of the construction is going to take place in Azerbaijan, with tangible benefit to the local economy. The rig, whose completion is foreseen in 2000, will be the first to be built from scratch in Azerbaijan.

The water depth in the block requires also the use of a semi-sub rig and opportunities are actively pursued to satisfy this need. The Operator will be technically ready to start drilling activities in mid-1999: drilling will start as soon as a rig becomes available.

Conceptual development planA first Conceptual Development Plan for a possible commercial discovery was prepared. The Plan is based on a tested and classic development scheme with well-heads and processing platforms and subsea completions.

According to the Plan, the three prospects will be developed in a phased sequence, starting with the Kur Dashi prospect, the nearest to shore (15 kilometers) and in around 50 meters of water, and closing with Kirgan Daniz, in the deepest waters (350 meters).

In the first phase two drilling/wellhead platforms would be used, one of which should also function as a Central Processing Platform (CPP), where the production will be collected from the whole field and processed for the onshore export. Each platform will have two drilling rigs in order to minimize drilling time. The Processing Platform will process up to 130,000 bbl/d of oil and 100 Mscf/d of gas. It will also host the power generation station (18 MW) for all the field (inclusive of the ESP required on the wells and the gas compression), the accommodation module, the flare boom, the helideck and all other ancillary facilities required offshore. Production would be sent offshore via two pipelines with a diameter, respectively, of 18 and 24 inches.

The second development would be Araz Daniz, located in a water depth ranging between 125 and 150 meters. Also in this case the Plan foresees two platforms with facilities very similar to the Kur Dashi topsides. The Processing and Drilling Platform would process all the field production, which would be sent to the Kur Dashi CPP, where the hydrocarbons will enter the existing export pipeline to shore. The start-up of Araz production would be optimized in order to cover the natural Kur Dashi decline and to have a longer production plateau.

Kirgan Daniz would be the last field to be exploited. The water depth is 350 meters. the Plan foresees the drilling of eight subsea wells linked to Araz Daniz. Again, production start-up would be optimized to cover Araz Daniz decline. The main practical problems foreseen in the Conceptual Development Plan are related to the procurement of major items (compressors, turbine pumps etc.) and the timely fabrication of jackets and decks, due to the current construction capacity of the yards in the area.

ConclusionThe Parties in the Kur Dashi EDPSA are at the beginning of an exciting venture in a portion of the Caspian Sea which has seen so far limited exploration. Kur Dashi offers challenges which can be overcome utilising the best technology and resource available and with the co-operation of all concerned parties and Authorities. It is true that – as in any exploration venture – the outcome is not guaranteed. However, we think that it is not excessively optimistic to class Kur Dashi as a first class exploration acreage.

The Caspian Basins have a long history of exploration and oil production, which has increased in recent years as a result of the arrival of Western investment.  Improved offshore 2D/3D seismic and knowledge gained from key exploration and appraisal wells has given a valuable new insight into previously frontier areas to the petroleum geology and basin development, influencing an operator's investment strategy. 

This conference aims to reflect on the subsurface lessons learned and will focus on the offshore and nearshore Caspian region, by illustrating 

the varied regional petroleum geology and its potential           the use of modern concepts and techniques in exploration, appraisal and

production           the insights from academic research into regional and field-scale structural and

stratigraphic issues

Themes:   Exploration strategy           SHallow geology variation and its interpretation           Regional and semi-regional structural understanding - application of modern

techiques           Understanding clastic reservoir development at basin and field scale           Carbonate reservoirs - variety and potential           Reservoir performance and rehabilitation           Hydrocarbon systems - from surface oil seeps to deep gas/condensate - evaluation of

potential (opportunity?)

Conference Supported by:Convenors

Neil Pigott, BP: piggottn@bp.com          Mark Allen, CASP: mark.allen@casp.cam.ac.uk         Adrian Tizley, Statoil: tizley@statoil.com

For further details contact: Helen Wilson or Clair Parks Address: The Conference Office, The Geological Society of London, Burlington House, Piccadilly, London, W1J 0BGTel: + 44 (0)20 7434 9944Fax: + 44 (0)20 7494 0579Email: helen.wilson@geolsoc.org.uk or clair.parks@geolsoc.org.ukWeb: http://www.geolsoc.org.uk

Miocene/Quaternary Sequence Stratigraphy of the Caspian Sea Region: Interplay of Deltaic Systems and

Climatic Control on Non-Marine Depositional Sequences

Vitor Abreu1, Dag Nummedal2, Paul Ware3, Roger Witmer3, and Dan Self3. (1) ExxonMobil Upstream Research Company, P. O. Box 2189, Houston, TX 77252-2189, phone: 713-431-7214, v9abreu@upstream.xomcorp.com, (2) Institute for Energy Research, University of Wyoming, P.O. Box 4068 Laramie, WY 82071-4068, (3) Unocal, Sugarland, TX 77478 The interplay of the paleo-Volga, paleo-Amu Darya, and paleo-Kura deltas is the most important factor for lithology distribution in the southern Caspian. The three deltaic systems exhibit differences in depositional style. Progradation of the paleo-Amu Darya delta occurred from Pereryva to Surakhany (Lower Pliocene) on the Turkmenistan shelf during a lake-level rise. During the same time, aggradation was the primary pattern in the paleo-Volga delta at the Apsheron sill. In the Central Caspian, the paleo-Volga delta is marked by transgressive stratal patterns. In the paleo-Kura system, on the southeast margin of Azerbaijan, a transgressive trend occurred during the uppermost Miocene to Lower Pliocene (Lower Productive Series to the mid-Balakhany), with onlap of these units over Miocene and Cretaceous rocks. A downlap surface developed in the paleo-Kura during mid-Surakhany time, which correlates to the upper part of the progradational phase of the paleo Amu-Darya delta. A paleo-Kura prograding wedge developed during the Upper Pliocene (Surakhany and Akchagylian) on the Azerbaijan margin. Climatic fluctuations exerted a dominant control on the sedimentation in the South Caspian basin, along with sediment supply. The Productive Series reflects the Pliocene "golden climate" when the earth was much warmer than today. On a shorter time scale, the stratification is controlled by high-frequency climatic cycles. Lowstand deposits are dominated by aggradational braided streams and braid deltas. Transgressive and highstand deposits are extensive lake shales interbedded with silts and sands. The transgressive shales can act as pervasive seals and permeability barriers and baffles within the

SEPM: Eustatic, Tectonic and Sedimentary Control on Depositional Sequences: Relative Importance - I AAPG Annual Meeting 2002: Our Heritage-Key to Global Discovery Technical Program AAPG Annual Meeting 2002: Our Heritage-Key to Global Discovery Main Page to: Registration and Exhibit Information

Andrei Belopolsky, Rice University

Introduction

Central Asia, in particular the Caspian Sea area, is one of the oldest oil-producing regions in the world. Surface oil seeps in what is now Azerbaijan were known since 4 B.C., when Alexander the Great’s soldiers used oil from shallow hand-dug wells (Abrams and Narimanov, 1997). The first oil well in history was drilled by a Russian engineer, F. N. Semyenov, in the Bibi-Eibat area of the Apsheron Peninsula in Azerbaijan in 1848 (Narimanov and Palaz, 1995). The first true offshore well was also drilled in Azerbaijan in 1924 from a wooden platform not far from Baku (Narimanov and Palaz, 1995).

Azerbaijan had the leading role in oil production in the former Soviet Union. Oil and gas exploration continues off the Azerbaijan coast and also in Kazakhstan and Turkmenistan. The discovery of large oil fields in the Caspian Sea and giant oil fields such as Tengiz and Karachaganak in Kazakhstan in the mid- and late 1980s showed that despite 150 years of oil production, the Central Asian region still contained significant amounts of oil and gas. It still does today.

In this study, we focus on the different geological basins located both directly within the Caspian Sea and in the surrounding areas. From the geological point of view, the territory of the Caspian Sea belongs to two different basins, the North Caspian and South Caspian (Figure 1). The Pricaspian Basin (alternative spelling, Precaspian) is another name for the North Caspian Basin. It includes the northern part of the Caspian Sea and the territory north of it, and is adjacent to the Volga-Ural province. The North Usturt Basin occupies the territory between the northern part of the Caspian Sea and the southern tip of the Ural mountain belt. The Mangyshlak Basin is located directly east of the Caspian Sea and south of North Usturt. The Amu-Darya Basin occupies eastern Turkmenistan and western Uzbekistan (Figure 1).

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The South Caspian Basin

The South Caspian geological basin contains the largest proven oil and gas resources in the Central Asian countries of the Caspian region. Azerbaijan, Kazakhstan, and Turkmenistan have territory in the South Caspian Basin. Exploration activity in the basin started in the middle of the 19th century, and the geology of the basin is relatively well established.

The South Caspian Basin is 400 km across in the northwest-to-southeast direction and 900 m deep. It occupies the central part of a broader depression that includes the Kura Trough to the west and the coastal lowland of Turkmenia to the east. Two main folding ranges, the Great Caucasus and the Lesser Caucasus-Talesh-Elburz arc, surround the basin (Figure 1). The northern boundary of the basin is formed by the Apsheron-Balkanian sill, below which a periclinal termination of the Great Caucasus is buried. It can be traced to the eastern coast of the Caspian Sea to the Great Balkan Mountains, where Jurassic shales are exposed.

The South Caspian Sea basin is considered a Tertiary back-arc basin (Zonenshain & Le Pichon, 1986). The basin does not have a low-velocity crustal (granitic) layer. An oceanic-type crust underlies a sedimentary package 20 km thick. The relatively low geothermal gradient (about 1.5 C per 100 m) provides favorable conditions for the preservation of hydrocarbons at significant depths (up to 10 km).

Drilling on the South Caspian shelf in Azerbaijan and Turkmenistan revealed that thick (2,500-3,000 m) shallow-water sediments accumulated from the Late Jurassic to the Early Pliocene (Alikhanov, 1978). In Azerbaijan, shales and sandstones comprise most of the section, with flyshlike deposits found at two levels, in the Valanginian and Campanian-Maastrichtian. Tertiary deposits are represented by shales, including Eocene carbonate shales, carbonate-bituminous shales of the Maikopian suite (Oligocene-Lower Miocene), Middle and Upper Miocene shales and marles, and Meotic and Pont (Lower Pliocene) shales (Figure 2). This section of the Turkmenistan shelf consists mainly of basinal shale facies with local evaporites.

Significant change in sedimentation is observed in the Middle Pliocene with the accumulation of the oil-productive red suite. In Azerbaijan, these deposits lie

transgressively on the Pont (Lower Pliocene) deposits. This oil-bearing suite is made of sandstones and siltstone that are probably deltaic deposits of the paleo-Volga River (Alikhanov, 1978). The buried paleo-Volga valley of has been disclosed by seismic surveys in the central part of the Caspian Sea (Clarke, 1993). The thickness of the oil-productive suite varies from 1,500 to 3,500 m. It is overlapped by Upper Pliocene and Quaternary deposits up to 2,000 m thick (Figure 2). They comprise mainly clastics brought in by the Volga and small mountain rivers.

Seismic reflection profiles allow us to estimate the thickness of the units in the deeper parts of the basin where they have not been recovered by drilling (Figure 3). The reflector at the bottom of the Bakinian bed (Middle Pleistocene) is very distinct and can be traced across the basin. The thickness of the deposits overlying this bed varies from 0.5 km at the crest of anticlines to 2 km over synclines. The thickness of Upper Pliocene-Quaternary deposits over the oil-productive series varies between 3 and 6 km. The thickness of the oil-productive series is 5 to 6 km. The remaining 8 to 10 km of sediments are pre-Middle Pliocene.

Seismic profiles also show considerable deformation within the sedimentary package. A fold system that runs north/northwest-south/southeast and is 100 to 120 km wide occupies the western part of the South Caspian Sea basin. The folds are penetrated by numerous mud volcanoes.

Most of the known hydrocarbon fields in the South Caspian basin (Figure 4) are contained within silisiclastic reservoirs within structural traps. Structural traps range from anticlinal folds to monoclines with various degree of reverse faulting and fracturing. Many structures are penetrated by mud diapirs and mud volcanoes. Most of the structures are located along clearly identifiable trends associated with underlying deep-seated faults that were inherited from the Mesozoic and reactivated during Cenozoic. Most hydrocarbons are located within fluvial-deltaic Middle Pliocene sediments (Productive series).

The Productive series can be subdivided into two distinct groups, early and late (Ruehlman, Abrams, & Narimanov, 1995). The early series is dominated by quartz and minor sedimentary rock fragments typical of the Paleo-Volga province to the north. The late contains less quartz, more feldspar, and sedimentary and volcanic rock fragments more typical of sediments of Paleo-Kura in the west. Oil is also found in the Miocene Chokrak clastics and fractured Oligocene-Miocene Maikopian shales (Klosterman et al., 1997).

The unconsolidated nature of the Neogene sediments prevents extensive core recovery. By studying the sedimentary succession in the outcrops, it is possible to complement the core, well log, and seismic data (Reynolds et al., 1998). Traditionally, the Productive series is divided into a number of successions, or suites. The Kalin Suite is only known from subsurface samples and consists of coarse-grained sediments more than 300 m thick. The pre-Kirmaky Sand Suite lies directly over the Kalin Suite and is over 150 m thick. It has a thickness of 250-300 m and can be divided into a lower sand-prone unit and an upper argillaceous unit. The post-Kirmaky Suite is about 150 m thick, its base comprised of sandstone 35 m thick. The basal sandstone passes upward into a succession of gradually coarsening parasequences of mudstones, siltstones, and sandstones. The post-Kirmaky Clay Suite consists of mudstones and siltstones with thin sandstone beds. These rock types are arranged into stacked successions 9-15 m thick that coarsen toward the top (Reynolds et al., 1998). The Pereriva Suite is one of the most important producing intervals in the subsurface. It is particularly important in the Azeri, Chirag, and Guneshli fields, where its thickness is up to 110 m. Sandstones with conglomeratic sandstones at the base comprise the suite. Sandstones are

characterized by poor sorting and giant cross-stratification indicating unidirectional southward paleocurrents. The rocks are interpreted as being deposited in a major fluvial or distributary channel system. The dramatic basal erosion surface is thought to reflect a major drop in base level and is considered a major sequence boundary.

The Balakhany Suite forms the main reservoirs of the fields located on the Apsheron Peninsula and is a major producing interval offshore. The sediments consist of fine-grained sandstone intervals and intervals of interbedded siltstone and sandstone. The Sabunchi Suite is an argillaceous succession over 190 m thick and characterized by decimeter-thick beds of mudstone, siltstone, and sandstone. The Surakhany Suite I is the uppermost lithostratigraphic subdivision of the Productive series and typically consists of more than 400 m of mudstones, siltstones, and very thin, fine-grained sandstones.

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The North Caspian (Pricaspian) Basin

The North Caspian (Pricaspian) Basin is located on the southeastern margin of the Russian Platform and extends to the northern coast of the Caspian Sea (Figure 5). The topographic elevations are below sea level and can be as low as -24 m. Russia and Kazakhstan claim the territory within the North Caspian basin. A large part of the Russian Caspian shelf (southern part of the basin), however, is off limits for exploration because it is a sturgeon spawning ground.

The North Caspian is a pericratonic depression of the Late Proterozoic-Early Paleozoic age. It is bounded to the east by the Hercynian Ural Mountains and to the southeast and south by other orogenic belts. In the north, the basin is separated by the Voronezh Massif in the west and by the Volga-Urals Platform high in the north.

The North Caspian basin contains two supergiant fields, Tengiz and Karachaganak, and a large number of smaller fields. Tengiz and Karachaganak are isolated carbonate platforms (Figure 6) that consist of stacked sequences of Devonian-Middle Carboniferous and Devonian-Lower Permian carbonates, respectively (Cook, Zempolich, Zhemchuzhnikov, & Corboy, 1997).

The depth to reservoir of the Karachaganak, Tengiz, Astrakhan, and Zhanazhol fields varies from 3 to 5.2 km (Bagrintseva & Belozerova, 1990). The reservoirs qualify as shallow-water carbonate facies and reef buildups. The upper productive unit of the Zhanazhol field has a permeability up to 2 Darcies and a porosity of 25-28%. At Tengiz, the porosity is up to 18.6% for the pore-type reservoirs. The Karachaganak reservoirs are similar to those of Tengiz. Porosity varies from 7.5 to 18.7% and permeability varies from 1 to 98 md. The porosity of the Astrakhan field is 8-15% and permeability is 1-8 md. The complex facies architecture of the Tengiz and Karachaganak fields results in abrupt changes in porosity and permeability, a patchy distribution of reservoirs, and significant thickness changes within the reservoirs. Many reservoirs have fractured or microfractured porosity. The bedded shallow-water carbonates of the Zhanazhol field display reservoir properties in the subsurface that are easier to predict. The intensive karstification in the upper part of the section caused the development of high-capacity cavity porosity.

Subsalt Paleozoic carbonates are widely distributed in the North Caspian depression and consist of Middle Devonian, Upper Devonian-Tournaisian, Upper Visean-Lower Bashkirian, and Moscovian-Lower Permian sequences (Figure 8). The overall thickness is estimated at 1.7 km (Golov, Komissarova, & Nemtsov,

1990). Within the depression, carbonate platforms or banks occur on basement highs on the northern, eastern, and southern edges of the basin. An exception is the Devonian (Famennian)-"Middle" Carboniferous (Russian time scale) carbonate complex of the Karaton-Tengiz zone of highs that is located on the northern border of the Lower-Middle Paleozoic South Emba downwarp. The Paleozoic carbonate sequences are characterized by large, high relief (800-1,000 m) reefs or atolls that are reservoirs for Karachaganak, Kenkiyak, Zhanazhol, Tengiz, and possibly Astrakhan fields.

There is another ringlike belt of zones of probable hydrocarbon accumulation towards the interior of the basin (Golov et al., 1990). It is also most likely related to the large Paleozoic highs.

Most of the subsalt highs existed prior to the deposition of the Permian Kungurian salt. Maximum uplift movements were during the Late Carboniferous. The amplitudes were estimated as 300-400 m for the Karachaganak-Koblandin arch, about 500 m for the Yenbek and Zharkamys arches, 150-200 m for the Karaton-Tengiz zone of highs, and about 600 m for the Astrakhan arch.

The main hydrocarbon migration paths were updip from the more quickly subsiding parts of the depression. The reservoir fill occurred in multiple stages. First, the oil pools formed at the end of Paleozoic. Later, with further subsidence of the basin, gas was generated and entered oil-filled traps, changing the pools into gas-oil, gas-oil-condensate, and gas. The northern, western and southwestern parts of the depression are gas prone, while the east and southeast are oil prone.

Field studies in the Karatau Mountains of Kazakhstan (Cook et al., 1997) describe rock sections that can be used as analogs for producing fields. They have defined several rock units.

The Frasnian and Famennian platforms (about 1,500 m thick) are reef-rimmed algal-stromatoporoid boundstones and rudstones. The platfrom interiors contain mud mounds, carbonate sands, cryptalgal laminites, and evaporitic laminites that are 10-100 m thick, and regionally extensive breccia that are 90 m thick. Basin margins contain carbonate turbidites and debris flow aprons. Tornasian carbonates up to 1,000 m thick form ramps of brachiopod-crinoid biostromes; ramp interiors have abundant tidal flat facies. Seaward ramp settings contain mud mounds 100 to 200 m thick and bioclastic turbidite aprons.

The Visean and Serpukhovian platforms (up to 1,500 m thick) consist of slope mounds and grainstone-rimmed margins. The mounds consist of sponge-bryozoan-Tubiphytes-algae boundstone and cementstone (100-500 m thick); some mounds are interbedded with carbonate turbidite aprons. Grainstone-rimmed platform margins are characterized by cross-bedded ooidal-bioclastic sands, and platform interiors contain ooid, bioclastic, and phyloid algae sands and muddy facies. Bashkirian carbonate contain slope mounds of algae-brachiopod boundstone and cementstone (500 m) and platform margins and interiors of ooid, bioclastic, and phylloid algae sands.

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The North Usturt Basin

The North Usturt Basin has an area of 240,000 km2 and is bounded on the north by the North Caspian Basin, on the northeast by the Mugodzar and Chelkar downwarps, on the east by the Aral-Kyzylkum zone of highs, and on the south by the Mangyshlak-Central Usturt system of highs (Figures 1, 9). On the west, the basin opens into the Caspian Sea.

Seismic data and drilling revealed folded basement in the North Usturt Basin covered by a package of sedimentary rocks up to 12 km thick. Several rock sequences have been defined within the sedimentary cover.

Carboniferous-Lower Permian carbonates and clastic rocks are found in the eastern part of the basin and are about 1,000 m thick. Lower Triassic redbeds and local volcanoclastics are 3,000 m thick on the Buzachi Peninsula. The section contains argillites within the redbeds that may serve as regional seals for lower reservoirs. The Middle Triassic section is mainly clastic with a thickness of up to 2 km. Two reservoirs with porosity up to 20% are present in the Kalamkas area. The Upper Triassic section is made of clastic rocks up to 600 m thick. They are similar to the Upper Triassic of the Prorva area of the North Caspian basin.

Overlying sediments have the following thickness: Jurassic , 150 m; Cretaceous, 2,500 m; Paleogene, 1200 m; and Neogene, 500 m.

The Triassic oil and gas play is composed of alternating sand-silt and clay beds 3 to 5 km thick. Sandstone reservoirs have up to 17% porosity and up to 30 md permeability. Oil has been found in the Triassic sediments in the Koltyk area.

The Middle-Upper Jurassic play is made of clays, argillites, siltstones, and sandstones with thickness varying from 200 to 1,000 m. Siltstone and sandstones form reservoirs and have 28-32% porosity and 1.5-2 darcies permeability. An Upper Jurassic clay-carbonate unit forms a seal. Commercial discoveries in the Jurassic have been made in the Karazhanbas, Severo-Buzachi, Kalamkas, Arman, Arystan, Karakuduk, Koltyk, Komsomol, and Vostochno-Karaturun fields.

The Lower Cretaceous (Neocomian) play is interbedded sands, silts, and clays that range in thickness from 150 to 850 m. The reservoirs are largely siltstones, and Aptian clays act as a seal. Commercials amounts of hydrocarbons have been discovered in the Karazhanbas, Severo-Buzachi, and Kalamkas fields.

The Eocene play is in the upper part of the Kuma Horizon and is represented by marls, siltstones, and clays. The reservoirs are siltstones that display porosity of 36% and 30 md permeability. The thickness is 10 to 30 m, and Eocene clays form the seal. Gas has been found in the five fields of the Chumyshty-Bazay group.

The distribution of reserves among the plays is the following: Middle-Upper Jurassic rocks contain over 60% of the oil and gas, Triassic rocks, 10%; the Lower Cretaceous section, 21%; and Eocene rocks, 8%.

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The Mangyshlak Basin

The Mangyshlak Basin (Figure 1) is located on the western part of the Turan epi-Paleozoic platform. Tectonic activity in the Riphean-Vendian era led to crustal tension and rifting, particularly the development of the Central Mangyshlak and Tuarkyr-Karaaudan rift systems (Murzagaliyev, 1996).

The Central Mangyshlak rift formed in Early Paleozoic time. Deep drilling showed that Paleozoic sediments consist of the Lower Permian and Carboniferous carbonate rocks and Upper and Middle Devonian and Lower Carboniferous clastics. The rift zone probably experienced some compression during pre-Permian times and then tension during the Late Permian and Early Triassic. The Mangyshlak and Usturt plates collided with the eastern European continent during the Early Cimmerian tectonic event. Tangential compression in the collision zone

led to the formation of inversion highs with upthrust-overthrust activity. The result was a series of linear mega-anticlines and megasynclines. The rocks of the Permo-Triassic age are strongly deformed.

The Tuakyr-Karaaudan rift probably formed in the Early Paleozoic. Middle Paleozoic deposits are strongly deformed and contain basic and ultrabasic rocks of Devonian and Early Carboniferous age (Murzagaliyev, 1996). These ophiolites are probably fragments of older oceanic crust. They are overlain by red Permo-Triassic molasse composed of conglomerates and tuff and lava beds. The total thickness of the molasse is 4-5 km.

Exploration activity in the 1980s in the Mangyshlak Basin was aimed at Triassic and Jurassic rocks of the Zhetbay-Uzen structural step and Triassic rocks of the Peschanomys-Rakushech, Karadin, and Zhazgurlin tectonic zones of South Mangyshlak. Exploration targets were mainly anticlinal structures identified on seismic. Despite years of exploration in the central part of the south Mangyshlak basin, no significant hydrocarbon discoveries have been made. Exploration activity since 1990 has been targeting the Upper and Middle Triassic in the eastern part of the Sedendyk depression and the northern part of the Karagin saddle (Popkov, Rabinovich, & Timurziyev, 1992). Paleozoic rocks also may contain oil. A commercial discovery was made in Paleozoic reservoir rocks in the Oymash area. Other areas of the basin, such as the eastern Mangyshlak, the Uchkuduk depression, Buzuchi Peninsula, and the continuation of the Mangyshlak basin off the Caspian shore, have not been explored for oil and gas. Exploration in the eastern Mangyshlak and South Usturt has been disappointing; only one gas field (Kansuy) was discovered. Thick Jurassic and Cretaceous reservoirs and seals are disrupted at the crests of anticlines; the Triassic section is also strongly deformed.

Recent seismic surveys showed a connection between the Uchkuduk depression and the Zhazgurli depression of the southern Mangyshlak. This suggests that the Uchkuduk depression contains Middle and Upper Triassic oil and gas reservoirs similar to those in the southern Mangyshlak (Popkov et al., 1992).

There is an increasing amount of interest in the northern part of the Buzuchi Peninsula and offshore on the Caspian Sea shelf. Seismic surveys demonstrate that many onshore structures on the Buzuchi Peninsula extend into the Caspian Sea. A large, favorable structure of the Jurassic-Cretaceous age has been identified north of the Kalamkas anticlinal zone and west of Karazhanbas (Popkov et al., 1992).

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The Amu-Darya Basin

The Amu-Darya Basin extends over an area of 370,000 km2 of eastern Turkmenistan and western Uzbekistan; another 57,000 km2 are situated in neighboring countries, in particular northern Afganistan (Figures 1, 10). The southwestern border lies at the base of the Kopet Dag, an Alpine mountain range. The Amu-Darya Basin lies within the Turanian plate, a feature that extends into the Caspian Sea and farther west into Europe as the Scythian platform. On the north, the basin is connected with the West Siberian platform through the Turgay depression.

The sedimentary section of the Amu-Darya Basin consists of Lower and Middle Jurassic coal-bearing clastics; Callovian-Oxfordian carbonates, including reef facies and Kimmeridgean and Tithonian carbonates and evaporites; Lower and Upper Cretaceous clastics; and Paleogene carbonates and clastics (Clarke, 1994).

This section is commonly referred to as intermediate complex, and its thickness can be up to 10 km.

The Amu-Darya Basin has a complex tectonic structure (Figure 10). The Bukhara structural step occupies the extreme northeast of the basin and has a blocky shape created by large uplifts. The Permian-Triassic intermediate-complex rocks are absent here, as is the Kimmeridgean salt. The Chardzhou structural step also has a blocky shape as a result of the intersection of a northwest-trending Hercynian structure in the basement and a northeast-trending Alpine structure. Southeast of the Chardzou step is the Beshkent downwarp, where the thickness of the sedimentary is 6 km. It is bounded on the east by a system of overthrusts of the southeastern spurs of the Gissar Mountains.

The Khiva downwarp has a 4 to 5 km thick sedimentary rock cover, beneath which lies a graben filled with 3 km of Permian-Triassic deposits. The Beurdeshik structural step is located to the west of the Khiva downwarp and is a transitional feature to the Central Kara Kum arch farther west. This arch is interpreted as a microplate caught up in the Hercynian orogenic belt (Clarke, 1994).

The Malay-Bagadzha saddle is a structural high located between the Zaungiz downwarp on the west and the Karabekaul downwarp on the east. All three features are characterized by large uplifts. The Vostochno-Unguz zone of highs is a segment of the north-south Ural-Oman tectonic zone, a system of faults beneath which lie horsts and grabens. The central part of this system is the Aral-Murgab zone of rifts, which is more than 1,000 km long. The Rapetek arch is a narrow zone 12-15 km wide that extends 450 km across the Amu-Darya Basin and is associated with the Repetek-Kelif regional fault. Domes of Jurassic salts form the cores of anticlines located along this arch. In places, salt has reached the surface.

The Mary-Serakh zone of highs and the Uch-Adzhi arch are separated by the Bayram-Ali arch. These three structural elements are sometimes united into the Mary-Uch-Adzhi monocline, which dips southward and forms the north flank of the Murgab depression, a structural zone that also includes the Sandykachi zone of downwarps and the Severo-Karabil downwarps. The Badhyz-Karabil zone of highs is located immediately to the south. It is followed by the Kalaimor downwarp, which is largely in Afghanistan.

The Murgab depression occupies the space between the Repetek-Kelif regional fault on the north and the Badkhuz-Karabil zone on the south. The Bakhardok monocline south of the Central Kara Kum arch is a transitional feature that dips south into the Cis-Kopet Dag foredeep.

More than 130 gas, gas-condensate, and oil fields have been discovered in the Amu-Darya Basin. Of these, 60% are in western Uzbekistan and 40% in eastern Turkmenistan. There are three regional plays: Lower-Middle Jurassic clastic, Upper Jurassic carbonate, and Lower Cretaceous carbonate-clastic. There are also two local plays: Upper Cretaceous carbonate-clastic and Paleogene carbonate.

The Lower-Middle Jurassic play consists of sandstones, siltstones, argillites, and thin coal beds. Their thickness varies from 100 to 400 m. The reservoirs are not continuous and in general have low porosity. Seals are localized and are not favorable for large hydrocarbon accumulations. Fifteen gas and gas-condensate pools have been discovered on the Bukhara, Chardzhou, and Beurdeshik structural steps, and some oil pools have been found in this part of the section. This play is assessed as containing 15% of the undiscovered resources of the province and essentially is unexplored.

The Upper Jurassic play is made of limestones with a wide range of porosity and permeability. The thickness of the pay zones varies from 10 to 60 m. The thick Kimmeridgian evaporites form the seal. Beyond the margins of the evaporite, argillaceous rocks act as seal, or in their absence, the hydrocarbons have migrated upward to form pools in the Cretaceous or to escape entrapment. Gas fields have been found on the Beurdeshik, Khiva, Zaunguz, and Chardzhou structural features. This play is assessed as carrying 56% of the undiscovered petroleum resources of the province.

The Lower Cretaceous-Cenomanian play includes carbonate-clastic deposits of the Neocomian-lower Aptian and predominantly clastic deposits of the upper Aptian, Albian, and Cenomanian. The section consists largely of sandstone 20-60 m thick, rare carbonates, and clays 10-200 m thick. Total thickness of the sedimentary package ranges from 700 to 1,600 m. A regional seal for this play is an upper Albian clay unit 100-130 m thick. In the central part of the basin, the Shatlyk Horizon of the upper part of the Hautervian Stage carries 90% of this play’s discovered gas. The reservoir rock is a red sandstone that has good porosity and permeability. The reservoir beds of the hydrodynamically sealed, supergiant Dauletabad-Donmez gas field belong to the Shatlyk Horizon. This play hosts more than 50%of the discovered gas of the basin and 20% of the undiscovered petroleum resources.

A few small discoveries have been made in the Upper Cretaceous play of the Bukhara tectonic step and Central Kara Kum arch. Small pools have been found in Maastrichtian limestones in the Badkhyz-Karabil zone of highs. Four thin pays zone are recognized in the Upper Cretaceous of the Central Kara Kum arch in the Cenomanian and Turonian stages. They consist of fine-grained sandstones. Very large pools are present in the Upper Cretaceous in the Gazli field. Two gas-bearing horizons in the Cenomanian rocks contain 70% of the reserves of the field.

Small amounts of oil have been found in carbonates of the Paleogene play in the Karabil field of the Badkhyz-Karabil zone of highs. Reservoirs are both carbonates and sandstones, and the seal is an Eocene clay. The play is assessed to contain less than 10% of the undiscovered petroleum resources of the basin.

The Amu-Darya Basin is gas prone. Oil is found only as small pools in the Chardzhou and Bukhara gas-oil regions. Of the total assessed hydrocarbon resources in the basin, 4% is oil, and 96% is gas. The same ratio is assumed for the undiscovered resources.

The Yashlag area in the central part of the Murgab region is the most promising area for oil and gas exploration. The Late Jurassic basin here has adequate source beds and similar conditions to those of the northern basin’s margin, where the Kukdumalak field has been discovered. O’Connor and Sonnenberg (1991) assess the undiscovered resources of this area at 120 trillion ft3 of gas, 7 billion barrels of condensate, and 3-4 billion barrels of oil.

The northern part of the Chardzhou structural step potentially contains structural traps. Here the Lower Cretaceous deposits rest on an erosional surface above the Kimmeridgian-Tithonian beds. Facies changes and pinch-outs could be acting as potential reservoirs that trapped hydrocarbons migrating from deeper parts of the Jurassic basin of deposition.

There are a number of undrilled structures in the Bakhardok monocline and northern margin of the Cis-Kipet Dag foredeep. Three main plays are recognized here: Oxfordian, Tithonian, and Valanginian, with Tithonian being the most promising. The Lower-Middle Jurassic, Triassic, Permian, and Carboniferous section also may contain commercial amounts of hydrocarbons. New discoveries

are also possible in the Mesozoic section in the Central Kara Kum arch despite the mature stage of exploration in the area. Southeastern Turkmenistan may contain significant gas and condensate reserves in the Upper Jurassic, both below and above the Upper Jurassic evaporite in the Murgab region.

According to the report by Ulmishek and Masters (1993), the entire Amu-Darya Basin contains 0.7 billion barrels of oil in identified reserves and 3 billion in undiscovered reserves. For gas, the cumulative production is 86 trillion ft3; identified reserves are 200 trillion, and undiscovered reserves are assessed at 75 trillion. Seventy-five percent of these gas reserves are found in Turkmenistan , and 25% in Uzbekistan.

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Comparison of the Caspian Region Oil and Gas Reserves

to the World Hydrocarbon Reserves

Fossil fuels have been an inexpensive energy source for the entire 20th century. Crude oil is now the source of 38% of the world energy. Coal and natural gas provide 25% and 22% of world energy, respectively. All three fossil fuels (oil, gas, and coal) are nonrenewable resources and have been created through geologic time from solar energy.

The estimates of the world ultimate crude oil recovery range from 1,650 to 3,200 billion barrels, with most of the estimates between 2 and 3 trillion barrels (Edwards, 1997). According to the study by Petroconsultants (Marbo, 1996), the world is running out of cheap oil. The midpoint of world oil production is estimated to be around the year 2000. The world will then face a shortfall in supply and a permanent increase in the price of oil. By 2050 world oil production will be down to the 1950 level of 18 million barrels a day (Marbo, 1996).

Estimated world crude oil reserves were 1111 billion barrels of oil on January 1, 1994 (Energy Information Administration, 1995). World Oil (1997) estimated proven world total oil reserves at the end of 1996 at 1,160,102.6 million barrels. About 300 billion barrels of these reserves are suspect, added principally by Middle East OPEC producers from 1987 to 1990 to justify their production quotas (Ivanhoe, 1995). Future discoveries of oil are forecast at 1,005 billion barrels. World estimated ultimate recoverable conventional crude resources are the sum of cumulative production (720 billion barrels of oil), reserves (1,111 billion), and future discoveries and field growth (1,005 billion), totaling 2,836 billion barrels of oil.

World natural gas reserves are estimated to be 90 billion barrels, and estimated undiscovered natural gas liquids are estimated at 102 billion barrels (Masters, Root, & Attanasi, 1994). Gas is converted to oil equivalent using 6,000 ft3 per barrel. World Oil (1997) estimated world proven natural gas reserves at 5,177,178.9 billion ft3.

The goal of Table 1 is to give a basic overview where the energy resources are located in the Central Asian republics. It was compiled from different studies of the amount of gas and oil found in these nations. The majority of the data comes from Wood MacKenzie, a private consulting firm based in Scotland, while other sources are U. S. government studies and International Energy Agency reports. Each country is divided into either areas or geological basins (both indicated in bold type) or major fields. The estimated proven columns denote the remaining reserves that have been discovered, while the estimated possible columns show the amount of potential resources, including both the proven and the

undiscovered. The total range of estimates for each country coming from different sources is listed in Table 2. As these ranges demonstrate, it is difficult to get an exact number for the amount of oil and gas reserves in Central Asia, but one can see the scale of resources that are available. Kazakhstan and Azerbaijan have the potential to become world suppliers of both oil and gas, and Turkmenistan has extensive gas resources .

The daily production figures of the Central Asia countries in 1995 are given in the Table 3. Azerbaijan had the largest production (183,000 barrels a day), and Uzbekistan was in the second place with 162,000 barrels a day. Kazakhstan was producing 128,000 barrels a day in 1995. Turkmenistan’s daily production in 1995 equaled 79,000 barrels a day. Georgia, Kyrgystan, and Tajikistan were producing very small amounts of oil (less than 4,000 barrels a day). Combined daily production of the Central Asia region in 1995 was 560,000 barrels a day. Wood MacKenzie (1998) estimated combined current oil and condensate production in the region at 800,000 barrels a day. They also predict a fourfold increase in production to 3.1 million b/d by 2020. The forecast assumes the discovery of three Tengiz-size oil fields off the shore of Kazakhstan between 2000 and 2010 and one large offshore discovery in Turkmenistan.

Table 4 contains data on the proven oil and gas reserves by country reported by World Oil (1997) and data on the reserves of Azerbaijan, Kazakhstan, Turkmenistan, and Uzbekistan from this report. We took the highest estimates from the range of the proven resources for each country and compared them to the reserves of other counties with the proven oil and gas reserves exceeding 1 billion barrels of oil. The first two column represents ranking of countries in the descending order based on the amount of oil reserves. It is clear that Kazakhstan and Azerbaijan contain significantly larger amounts of oil than Turkmenistan and Uzbekistan, whose reserves do not exceed 1 billion barrels of oil. Out of the four Central Asia countries, Kazakhstan has the oil reserves (22 billion barrels) that come closest to those of such countries as Norway (about 27 billion barrels), Libya (23.5 billion barrels), the United States (22 billion barrels), and Nigeria (about 21 billion barrels). It is interesting that even if we take the lowest estimate of the reserves (10 billion), Kazakhstan will still retain its place in the table, yielding only to Algeria with approximately 13 billion barrels of oil. Azerbaijan’s oil reserves (6.5 billion barrels ) put it in between Brazil (about 7 billion barrels) and Canada (5.5 billion barrels). Azerbaijan’s oil reserves are also close to the estimated proven oil reserves of Malaysia (5.1 billion barrels), India (5 billion barrels), and the U.K. (5 billion barrels). The lower end estimate of Azerbaijan’s proven oil is 3.6 billion barrels of oil. In this case, Azerbaijan’s reserves are compatible with those of Egypt (3.7 billion), Australia (3.7 billion), Oman (3.6 billion), and Colombia (3.5 billion). It could be also compared to the reserves of Angola, but the reported reserves of Angola (3.6 billion barrels) do not reflect the string of billion-barrel discoveries offshore in 1997 that make Angola’s reserves significantly larger.

The third and fourth columns of Table 4 show the ranking of the countries in descending order based upon the proven gas reserves. Turkmenistan has the largest amount of gas reserves out of the four Central Asia counties evaluated in this study. Turkmenistan’s gas reserves are estimated at 93 to 155 trillion ft3 of gas, which places Turkmenistan in between the U.S. (167 trillion) and Venezuela (142 trillion). Uzbekistan also contains significant gas reserves (70 to 106 trillion ft3). This number puts Uzbekistan in between Nigeria (110 trillion ft3) and Australia (83.5 trillion). Kazakhstan’s highest estimated value of proven gas reserves is 83 trillion ft3, which puts Kazakhstan close to Australia (83.5 trillion) and Malaysia (79 trillion). Azerbaijan (16.5 trillion ft3) has significantly lower gas reserves. Azerbaijan’s gas reserves are close to those of Yemen (17 trillion) and Brunei (13.5 trillion).

Table 5 summarizes the world distribution of hydrocarbons by region. The regions are ranked in the descending order, and the highest estimated values of proven reserves were used for Central Asia. The total proven oil and condensate reserves of Central Asia estimated in this study varies from 15 to 31 billion barrels, and the highest value is close to the total amount of reserves of Western Europe (34 billion). However, Central Asian oil reserves are one twentieth of those of Middle Eastern countries and one fifth of the oil reserves of Eastern Europe ( which includes Russia). Central Asian gas reserves are in third place if we use the highest estimates for Central Asia (360 trillion ft3 of gas). This number is close to the reserves of Africa (344 trillion ft3 of gas). Gas reserves of Central Asia approximately equal one fifth of the gas reserves of Eastern Europe (which includes Russia) or the Middle East, and represent almost 7% of the world’s total.

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Conclusions

The Central Asian region includes a number of petroleum basins that are different in their geological development, reservoir types, hydrocarbon types, and quantity of resources. The South Caspian, North Caspian (Pricaspian), North Usturt, Mangyshlak, and Amu-Darya geological basins contain hydrocarbon reservoirs. The territory of Azerbaijan includes part of the South Caspian basin. Kazakhstan’s territory contains a part of the South Caspian and almost all of the North Caspian, Mangyshlak, and North Usturt basins. Turkmenistan’s territory includes a part of the South Caspian basin and Amu-Darya. Uzbekistan’s territory contains a large part of the Amu-Darya basin.

The South Caspian is a mature exploration basin with over 150 years of development. However, large known oil and gas fields are in the Caspian offshore (Guneshli, Chirag, Kyapaz) awaiting development. Detailed seismic surveying of the deeper parts of the Caspian offshore may reveal new untested structures that contain commercial quantities of hydrocarbons. At the moment, most of the Turkmenistan Caspian shelf, with more than 40 untested structures, remains relatively undrilled. Turkmenistan is also disputing the Kyapaz field, which was discovered by Azerbaijan. A number of exploration blocks were offered for bidding in September 1997. Turkmenistan postulates undiscovered reserves on its Caspian shelf at 3 billion metric tons (22 billion bbl) of oil and 4.8 trillion cubic meters (168 tcf) of gas.

The northern Caspian and northwestern Kazakhstan are also areas with large amounts of proven reserves and high potential for new discoveries. Almost three quarters of all the Kazakhstan reserves are in two supergiant fields—the Tengiz (oil) and Karachaganak (gas). The recoverable reserves of Tengiz have been recently updated to 12 billion barrels of oil with an estimated 25 billion barrels of oil in place. Most of the fields in the northern part of the basin, such as Karachaganak, contain mostly gas with a small amount of oil.

The North Usturt and Amu-Darya basins have some potential in oil and gas exploration. Seismic surveys and extensive exploration programs are expected to reveal potential drilling targets. The Amu-Darya Basin contains mainly gas reserves with a minor amount of oil.

Kazakhstan is a leader among the Central Asian countries in the amount of proven reserves and the potential for new findings. It has 10 to 22 billion barrels of proven crude reserves and 53 to 83 trillion ft3 of gas. Kazakhstan’s territory is the largest among the Central Asia countries and contains four different geological basins. Those basins remain largely unexplored even though current exploration activity is high.

Azerbaijan has the second largest reserves among the Central Asian countries. It is a mature oil and gas country and will remain an important producer for decades. The new large discoveries, if made, would be confined to the deep water in the Caspian offshore.

Turkmenistan has large gas reserves (95 to 155 trillion ft3 of gas). A large territory of Turkmenistan remains unexplored. It is quite possible that important discoveries will made onshore and offshore in the part of the South Caspian basin that belongs to Turkmenistan.

Uzbekistan does not have a significant amount of oil but contains large amounts of gas (70 to 105 trillion ft3). It also has a large territory that has not been well explored for oil and gas.

The total proven oil reserves of the Central Asian countries were estimated in this study as ranging from 15 to 31 billion barrels, and proven gas reserves estimates vary from 230 to 360 trillion ft3 of gas (Table 2). Central Asian reserves represent approximately 2.7% of the world total proven oil reserves and 7% of the world gas reserves.

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References

Abrams, M. A., & Narimanov, A. A. (1997). Geochemical evaluation of hydrocarbons and their potential sources in the western South Caspian depression, Republic of Azerbaijan. Marine and Petroleum Geology, 14(4), 451-468.

Alikhanov, E. N. (1978). Geokhimiya Kaspiiskigo morya [Geochemistry of the Caspian Sea]. Baku: Elm Publishing House.

Bagrintseva, K. I., & Belozerova, G. Ye. (1990). Types and properties of reservoirs in sub-salt sediments of the North Caspian depression. Petroleum Geology, 24(7-8), 230-232.

Clarke, J. W. (1993). Observations on the geology of Azerbaijan. International Geology Review, 35, 1089-1092.

Clarke, J. W. (1994). Petroleum potential of the Amu-Dar’ya province, western Uzbekistan, and eastern Turkmenistan. International Geology Review, 36, 407-415.

Cook, H. E., Zempolich, W. G., Zhemchuzhnikov, V. G, & Corboy, J. J. (1997, November). Inside Kazakstan: Cooperative oil and gas research. Geotimes, 16-20.

Edwards, J. D. (1997). Crude oil and alternate energy production forecasts for the twenty-first century: the end of the hydrocarbon era. American Association of Petroleum Geologists Bulletin, 81(8), 1292-1305.

Energy Information Administration. (1995). Annual Energy Review (DOE/EIA Publication No. 0384 [95]). Washington, DC: United States Department of Energy.

Gabrielyants, G. A. (1994). North Ustyurt independent gas-oil region. Petroleum Geology, 28(7-8), 278-280.

Golov, A. A., Komissarova, I. N., & Nemtsov, N. I. (1990). Zones of oil-gas accumulation in Paleozoic carbonates of the North Caspian depression and its frame. Petroleum Geology, 24(7-8), 247-249.

Ivanhoe (1995).

Klosterman, M. J., Abrams, M. A., Aleskerov, E., Abdullayev, E., Guseinov, A. N., & Narimanov, A. A. Hydrocarbon systems of the Evlak-Agdzhabedi depression, Azerbaijan. Azerbaijan Society of Petroleum Geologists Bulletin, 1, 89-118.

Marbo, R. (1996). The world’s oil supply, 1930-2050, a review article. The Journal of Energy Literature, 2(1), 25-34.

Masters, C. D., Root, D. H., & Attanasi, E. D. (1994). World petroleum assessment and analysis. Proceedings of the Fourteenth World Petroleum Congress, 529-541.

Murzagaliyev, D. M. (1996). Riftogenesis and oil-gas potential of Mangyshlak. Geologiya Nefti i Gaza, 5, 36-39.

Narimanov, A. A., & Palaz, I. (1995, May 22). Oil history, potential converge in Azerbaijan. Oil and Gas Journal, pp. 32-39.

O’Connor, R. B., Jr., & Sonnenberg, S. (1991, June 3). Amu Darya liquids potential indicated. Oil and Gas Journal, pp. 104-109.

Popkov, V. I., Rabinovich, A. A., & Timurziyev, A. I. (1992). New directions for oil and gas exploration in Mangyshlak. Geologiya Nefti i Gaza, 6, 14-15.

Reynolds, A. D., Simmons, M. D., Bowman, M. B., Henton, J., Brayshaw, A. C., Ali-Zade, A. A., Guliyev, I. S., Suleymanova, S. F., Ateava, E. Z., Mamedova, D. N., & Koshkarly, R. O. (1998). Implications of outcrop geology for reservoirs in the Neogene Productive Series: Apsheron Peninsula, Azerbaijan. American Association of Petroleum Geologists Bulletin, 82(1), 25-49.

Ruehlman, J. F., Abrams, M. A., & Narimanov, A. A. (1995). The petroleum systems of the West South Caspian Basin. American Association of Petroleum Geologists Convention Abstracts, Houston, TX.

Zonenshain, L. P, & Le Pichon, X. (1986). Deep basins of the Black Sea and Caspian Sea as remnants of Mesozoic back-arc basins. Tectonophysics, 123, 181-211.

Ulmishek, G. F., & Masters, C. D. (1993). Petroleum resources in the former Soviet Union (U.S. Geological Survey Open-File Rep. No. 93-316).

Wood MacKenzie (1998, March 9). Oil and Gas Journal.

World Oil (1997, August).

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Author Note

Manik Talwani, Schulmberger Professor of Geophysics, Department of Geology and Geophysics; Andrei Belopolsky, Graduate Student in the Department of Geology and Geophysics; Dianne L. Berry, Graduate

© 1998 by the Baker Institute at Rice University. Questions or Comments

about the Caspian Energy Study? Email the Study Coordinator, Amy

Myers Jaffe.

"Balanced Filled Lakes Worldwide: Insights for Optimum Source

Character and Distribution In Brazilian Continental Margin Basins"

Authors: BOHACS, KEVIN M. & NEAL, JACK E., Exxon Production Research

Company, Houston, Texas, USA

Abstract:

Exxon has developed the concept of lake-basin type, which is useful for sorting out the complexities of lacustrine deposition to derive a predictive framework. Balanced-filled lakes are one of three lake-basin types recognized from recurring lithofacies associations and stratal stacking patterns. Balanced-Filled lake systems contain the most prolific lacustrine source rocks and beneficent facies juxtapositions for hydrocarbon accumulation, based on observations of lacustrine strata of many different ages and basins (e.g.: East Africa Quaternary, USA Tertiary, China & Africa Cretaceous).

Balanced-Filled lakes can be shallow or deep with thick or thin sequences but they share similar geochemical and sequence-stratigraphic attributes. Parasequences and sequences are meters to tens of meters thick, distinctly expressed in seismic, logs, and geochemistry, and formed by a combination of progradation and desiccation. Lake-water chemistry varies systematically from fresh to saline/alkaline. Most organic-rich rocks are deposited in the profundal zone, with subordinate amounts in the lake plain behind mixed biogenic-clastic shorelines. Organic matter is dominantly algal Type I, typically with TOC £ 30% and HI £ 650 mgHC/g C. Organic facies are relatively constant laterally, changing only relatively close to shore. Sequence boundaries are formed by a mix of erosion and desiccation— erosion may be best developed during transgression.

Comparison of geochemical, geological, and geophysical data from Balanced-Filled lakes worldwide with Brazilian basins provides a greater understanding of source rocks in the lacustrine systems responsible for most of the giant oil accumulations in offshore Brazil and suggests strategies for successful exploration and exploitation.

Speaker Biography:

Kevin M. Bohacs is a sedimentologist and stratigrapher with the Petroleum Geochemistry section of Exxon Production Research Company. He received his B.Sc.(Honors) in geology from the University of Connecticut in 1976 and his Sc.D. in experimental sedimentology from M.I.T. in 1981. At EPR, he leads the application of sequence stratigraphy and sedimentology to organic-rich rocks from deep sea to swamps and lakes, in basins around the world. As a Research Associate, his primary focus is to keep the geo- in geochemistry. He has written numerous papers on the stratigraphy and sedimentology of hydrocarbon source rocks. He was co-recipient of the AAPG Jules Braunstein Memorial Award for best poster session paper in 1995 for work on coal sequence stratigraphy and of the AAPG Best International Paper in 1998 for work on lakes.

HGS Environmental / Engineering Section Dinner Meeting

Title of talk

Author:

Date: Apr. 14, 1999

Place: Jalapeno's - 2702 Kirby (at Westheimer)

Time: 6:00 - 7:00 PM - Dinner; 7:00 - 8:30 PM Lecture, Career Opportunities, and

Networking

Cost: $16.00 per person for a full dinner including tip. Dinner is optional.

Abstract:

International Dinner Meeting

The paleo-Volga delta and lacustrine sequence stratigraphy of the South

Caspian basin

Author: Dag Nummedal

Abstract:

The Productive Series of the South Caspian basin consists primarily of Pliocene delta deposits of the Volga River. GCA reservoirs at the Apsheron Sill and numerous old fields in the transition and onshore areas of Azerbaijan contain Productive Series beds. Outcrops on the Apsheron Peninsula north of Baku, extensive seismic data, and cores in the GCA field provide the data base to determine age, depositional systems, stratigraphic architecture, and reservoir properties of the Productive Series.

SOCAR (State Oil Company of Azerbaijan) invited five companies (Agip, BP Amoco, Conoco, Tpao, Unocal) to undertake a joint study of the sedimentology and stratigraphy of much of the Productive Series. The 13 investigators involved in the study (see Project Team) emphasized the highly productive Pereriva and Balakhany suites and outcrops of the Kirmaku, Nkp, and Nkg suites. Related projects by other Unocal personnel added valuable insights into the sedimentology, with some being presented as posters in conjunction with this talk.

Age of the Productive Series was determined by a combination of Ar39/Ar40 dates of ash deposits bracketing the Productive Series, graphic correlation of micropaleontological data and event beds, and adjustments based on the global oxygen isotope curve for the Pliocene and latest Miocene. The Miocene-Pliocene boundary (5.3 Ma) lies at or near the base of the Pereriva Sandstone, and the top of the Productive Series (top Surakhany) is about 3.0 Ma.

Lake levels in the Caspian repeatedly rose and fell during deposition of the Productive Series. Climatic cycles responsible for the changes in lake level dramatically affected the sediment yield from the Volga drainage basin. At lowstands of lake level, the climate was hot, evaporation from the lake was high, and there was little to no flow of water or sediment into the lake. Extensive lake-margin exposure surfaces characterize the lowstands.

As cooler and wetter climate replaced the hot and dry periods, lake levels rose. During early, slow rises in lake level, major sandstone packages of braided fluvial deposits grading lakeward into thin mid-channel bars and braid-delta fronts accumulated.

During late transgressions and highstands, the deltas were well north of the Apsheron region and only distal prodelta mudstones accumulated in the study area. With no sandstones deposited between the transgressive and highstand muds and the next overlying exposure surface, the Volga delta apparently did not prograde back south during the subsequent fall in lake level. Return to a hot, dry climate probably left the river dried out as lake level fell. This is very different from marine systems where major delta complexes generally prograde as sea level falls.

Changes in lake level occurred on time scales ranging from about 106 to 104 years, with some or all perhaps driven by Milankovitch cycles. Longer cycles may include a tectonic component unrelated to cmatic variations. Because of the strong climatic influence on lake level change and stratigraphic architecture, there is more "order" (predictive cyclicity) in the paleo-Volga deposits than in any documented marine deltaic succession.

Understanding how climate/lake level cycles control the timing of sand delivery into the Caspian basin has clear exploration significance. At the development scale, the systematic vertical change in depositional systems within nested sequences of different thicknesses exerts the dominant control on heterogeneity and connectivity of reservoirs and seals.

Project Team

1 Project team: V. Abreu (Unocal), Z. Bati (Tpao), H. E. Clifton (Conoco), ), T. D. Demchuk (Conoco), M. Fornaciari (Agip), A. A. Narimanov (Socar), D. Nummedal (Unocal), G. W. Riley (BP Amoco), A. Sayilli (Tpao), J. A. Stein (BP Amoco), V. E. Williams (Unocal), R. J. Witmer (Unocal), D. S. Van Nieuwenhiuse (Amoco).

Biographical Sketch

Dag Nummedal is manager of geology in the exploration and production technology division of the Unocal Corporation, Sugar Land, Texas. He was a professor in the Department of Geology and Geophysics at Louisiana State University in Baton Rouge from 1978 to 1996. His Ph.D. is from the University of Illinois and his M.S. and B.S. degrees are from the University of Oslo, Norway.

Nummedal's research and teaching have covered stratigraphy, petroleum geology, coastal and shallow marine sedimentation, coastal engineering, and planetary geology. Current research is focused on sedimentation and sequence stratigraphy of the Pliocene paleo-Volga delta in the Caspian basin, Azerbaijan, sequence stratigraphy of Cretaceous shallow marine deposits of the U.S. western interior, and rift basin tectonics and stratigraphy in basins along the SE Asian margin and the Gulf of Suez. Of increasing interest is the practice and theory of management of industrial R&D organizations.

Nummedal has published 80 refereed papers and numerous technical reports, taught short courses and seminars on sequence stratigraphy and related subjects worldwide. He is the current Councilor of Research at SEPM (Society of Sedimentary Geology).

International Explorationists Poster Session

All presenters are with Unocal Corporation, 14141 SW Freeway, Sugar Land, TX 77478

Productive Series and other Neogene Units of the South Caspian Basin: Cronostratigraphy, Paleoclimatology, and Paleogeographyby Roger J. Witmer, V. Eileen Williams, and Vitor S. Abreu

Pliocene/Quaternary Sequence Stratigraphy of the Caspian Sea Region: Interplay of Deltaic Systems and Climatic Control on Nonmarine Depositional Sequencesby Vitor S. Abreu, Dag Nummedal, Paul Ware, Dan Self, Roger Witmer, Art Trevena, Eileen Williams, and Jerzy Trybek

Direct Hydrocarbon Misidentification in the South Caspianby Paul Ware

Tectonics and Structural Geology of the South Caspian Basinby Robert G. Hickman, Dan Self, Marek Kaminski, Vitor Abreu, and Guy Pavey

GLAUCONITE

The occurrence of glauconite in the Schilfsandstein: A key to resolve controversies of the facies analysis?

According to petrographic investigations on samples from shallow-depth boreholes near Eppingen (Kraichgau, SW-Germany) the sandfacies of the Schilfsandstein (Triassic, Middle Keuper, km2) is very likely to have been deposited as a greensand, because the sand contained abundant glauconite-bearing green pellets at the time of deposition. Investigations of Recent greensands have prooved that glauconite can form only in a weakly reducing environment and at low sedimentation rates. Such conditions are prevailing in shallow marine basins. Therefore, the glauconitic green pellets found in the Schilfsandstein are considered to have formed in shallow sea water near-shore of the Keuper Basin.

Further off-shore the silt facies of the Schilfsandstein member was deposited. These conditions remained stable for a rather long period of time.

After the silt-facies period the basin became even shallower probably due to an epirogenic regression. Channels were cut into the previously sedimented silt deposits by the rivers from the continent surrounding the basin in the North and East. Soon after erosin the channels were filled by sand leaving broad strings of sand (Sandstränge).

Mixed with the sand the glaucony of the near-shore basin ranges was redeposited downstream along with the channel-fill. As soon as in contact with the aerated fluvial water the glauconite became instable and lost its potassium content which gave rise to an extensive potassium feldspar authigenesis. The iron content also liberated by the oxidation of the glauconite was precipitated as Fe-hydroxidic pore cement.

By the above suggested two-phase formation of the Schilfsandstein member both its marine and terrestrial features can be combined. The contradiction of the spatial coexistence of the marine silt-facies and the fluvial sandstone-facies is resolved by assuming a temporal succession of both facies.

This model is supported by the potassium feldspar authigenesis, displaying an example of how early diagenetic processes can help unravel the environmental conditions forming a sandstone.

Altered from detrital biotite by marine diagenesis in shallow water under reducing conditions; especially in sandstone.