exploration of new zealand’s deepwater frontier gns ... · minerals are planning to acquire a...
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exploration of New Zealand’s deepwater frontier ����
The New Zealand Exclusive Economic Zone (EEZ) is the 4th largest in the world at about 4 million square kilometres or about half the land area of Australia. The Legal Continental Shelf claim presently before the United Nations, may add another 1.7 million square kilometres to New Zealand’s jurisdiction. About 30 percent of the EEZ is underlain by sedimentary basins that may be thick enough to generate and trap petroleum. Although small to medium sized discoveries continue to be made in New Zealand, big oil has so far eluded the exploration companies.
Exploration of the New Zealand EEZ has barely started. Deepwater wells will be drilled in the next few years and encouraging results would kick start the New Zealand deepwater exploration effort. Research efforts have identified a number of other potential petroleum basins around New Zealand, including the Pegasus Sub-basin, basins in the Outer Campbell Plateau, the deepwater Solander Basin, the Bellona Basin between the Challenger Plateau and Lord Howe Rise, the New Caledonia Basin beyond deepwater Taranaki and the Reinga Basin to the northwest of Northland.
The first to be investigated will probably be the Pegasus Sub- basin at the southern end of the East Coast Basin. This region lies east of Cook Strait and north of the Chatham Rise in water depths of 500 to 3000 metres. Its area is at least 40,000 square kilometres, although its ultimate size is unknown. The Pegasus Sub-basin overlies the transition from subduction along the East Coast of North Island to strike-slip motion through South Island. The single deep penetration seismic line that crosses the region shows Cretaceous and Paleogene sequences dipping below Neogene turbidite deposits up to 5 kilometres thick. Crown Minerals are planning to acquire a broad reconnaissance 2D survey across the Pegasus Sub-basin within the next year.
The future for deepwater exploration in New Zealand is exciting but by no means assured. While any one of the above basins could contain the volumes of oil and gas that could transform the New Zealand economy, it is ultimately up to exploration companies to decide whether potential rewards are worth the risk of finding out. At the same time, the New Zealand government has led the charge by acquiring basic data across several basins and has successfully attracted new entrants into the country. What follows should be of great interest to the whole exploration community.
Contact Chris Uruski ([email protected]) or listen to his talks at the upcoming NZPC, APPEA, and EABS conferences for a cook’s tour of the NZ deepwater frontier.
GNS Science at upcoming conferences ����
Meet us at the New Zealand Petroleum Conference in Auckland (Booths 24 and 25), and the APPEA conference in Perth (Booth 7 and 8). The Eastern Australian Basins Symposium in Sydney in September 2008 will be another big event for us. See us at Booth 28.
contact us ����
Please contact us for no-obligation technical advice on how our specialists can help with your exploration.
www.gns.cri.nz/hydrocarbons
+64 4 570 1444
GNS Science 1 Fairway Drive, Avalon P O Box 30 368, Lower Hutt 5040 New Zealand
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introduction ����
This informal newsletter is produced to tell the industry about highlights in petroleum-related research at GNS Science. We want to inform you about research that is going on, and provide useful information for your operations. We welcome your opinions and feedback.
Petroleum research at GNS Science
Our research programme on New Zealand's Petroleum Resources receives $2.4M p.a. of government funding, through the Foundation of Research Science and Technology (FRST), and is one of the largest research programmes in GNS Science. The funding runs from July 2003 to June 2009. The broad scope of the research is outlined on the following link: http://www.gns.cri.nz/research/programmes.html#sufficiency
More detail on the research is contained in additional links on that page.
For a list of research outputs and publications in recent years, contact Peter King at [email protected].
Find out more
To find out more about current petroleum research at GNS Science, check our constantly-changing website, www.gns.cri.nz/hydrocarbons, or contact our scientists directly by sending an e-mail to [email protected]. You can discuss with us about how to get involved in the research, including how to leverage government funds for research topics of particular interest to you.
Get involved in ensuring this research capability
GNS Science undertakes commissioned consultancy work for virtually all petroleum exploration companies in New Zealand. What is perhaps not appreciated, is that the expertise, capacity and databases behind this commercial work is under-pinned by the injection of government funding, which allows our research capability to be maintained. GNS Science will be re-bidding for new research funding later this year, for start-up in July 2009. Given the government’s current energy strategy, and the fact that the allocation of funding is highly competitive, there can be no guarantee that the petroleum research programme will continue. Our research proposals will be strengthened enormously however, if we have backing from industry. There are many ways that you can show support for the research and help to demonstrate its relevance to government funders. We are seeking comment, advocacy and steering from industry on the scope and priorities of required future research. What topics do you see as key areas? Where should we be concentrating our research efforts to help you find New Zealand's petroleum resources? We would particularly welcome direct involvement though co-funding and in-kind contributions (such as provision of data).
Contact Peter King ([email protected]) with comments or for more information.
carbon capture and storage ����
Geological storage of CO2 is one of the hottest topics in geoscience world-wide. GNS Science is contributing to a baseline study on the feasibility of carbon capture and underground storage in New Zealand as a mechanism for reducing our greenhouse gas emissions. We are about halfway through a separate 17-month FRST-funded programme that used the same expertise as required in the petroleum sector. The research will help major CO2 emitters and government to
develop implementation policy and mitigation strategies and will pave the way for pilot-scale projects to capture carbon dioxide and store it in deep geological formations. The project is a collaboration between three organisations, each providing specialist expertise: GNS Science (petroleum geology, reservoir architecture, and geological risk), CRL Energy (coal science and advanced technologies) and the University of Auckland (numerical reservoir modelling).
The programme is assessing the possibilities for subsurface storage of CO2 in the Waikato and onshore Taranaki regions. Potential storage options being evaluated include coal seams, deep aquifers, depleted oil and gas fields, and potential enhanced oil and gas recovery projects. Desktop overview studies for onshore storage are almost complete. We are also investigating a small offshore region west of the Manukau Lowlands as a potential storage region for emissions from the Huntly Power Station and Glenbrook steel mill. Our studies on risk assessment, capture, transport, injection, monitoring and verification are continuing. In the first half of 2008, a panel of international experts will review the work we have completed to date. At the end of the project, we will rank potential storage sites for suitability. A longer-term goal is to develop a proof-of-concept demonstration CO2 storage site in New Zealand.
Contact Rob Funnell ([email protected]) for more information.
digital Taranaki ����
In the mid 1990’s, a series of structural and paleogeographic maps of the Taranaki Basin were constructed from available seismic and well data by GNS Science. This product, called the "Taranaki Atlas", is a benchmark reference for overview assessment of petroleum prospectivity of the basin. We are now undertaking a major, multi-year initiative, called the Seismic Facies Mapping Project, to develop a revised and fully digital atlas of the structure, stratigraphy and paleogeography of the Taranaki Basin. This integrated project will draw upon a wealth of newly-available data, to create up-dated interpretations of seismic sequences, calibrated to lithology, age, and paleo-bathymetry in wells and outcrop. As part of the project, seismic interpretations are being validated by structural restoration of selected regional transects along composite 2D seismic lines. The long term goal of the project is to create a rigorous geological framework for the next generation of 4D petroleum system models of the Taranaki Basin.
To date, we have been focusing offshore, with an initial emphasis on creating a standardised seismic and well database. The offshore data set comprises over 2,500 2D lines, several 3D surveys and 60 wells, compiled using open-file data from Crown Minerals and proprietary data contributed by the New Zealand exploration industry. The project database is designed to be dynamic rather than static so that new exploration data can be easily incorporated into future models of the Taranaki Basin.
The offshore Kupe region was mapped as a pilot study and is nearing completion. Key outcomes to date include: interpretation of nineteen horizons tied to eight wells in the Kupe region, incorporating revised biostratigraphic well data and stratigraphic correlation. A structural restoration of a NW-SE composite section that traverses the central basin from the western platform, through the Maui and Kupe regions, to east of the Taranaki Fault, has been used to validate the new seismic interpretation. The database for the next region, the Central Graben, has been compiled.
Numerous data trades with exploration companies have made the assembly of a comprehensive dataset possible. In return for access to confidential data, participating companies gain early access to the project results.
Contact Malcolm Arnot at [email protected] for more information or to get involved in the project.
Mangahewa project update ����
The Mangahewa Formation is one of the main exploration targets in the Taranaki Basin and has been penetrated in a large number of onshore and offshore wells. Proven reservoir intervals occur in coastal sand bodies and in locally thick, stacked fluvial channel sandstones within the coastal plain environment.
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journal-style papers. Standardised statistical data includes net to gross, bed lengths, thicknesses, texture and aspect ratios. The atlas is not only focused on the sand geometries in the outcrops but also the shale architecture, which is important for understanding baffles and barriers in deepwater reservoirs. There is a uniform presentation format of the various outcrops via photomosaics, lithologic sections, detailed facies and architectural element descriptions. The atlas is one of the largest on a single geologic topic that has been published. Below is an example page from Taranaki.
For more information, please contact Peter King ([email protected]).
new student projects ����
We currently have a number of students doing PhD and MSc studies in conjunction with GNS studies or under part-supervision from GNS staff. Most studies are related in some way to the Digital Taranaki Seismic Facies Mapping project:
� Jan Baur is a joint VUW/GNS Science PhD student looking at seismic facies and seismic attribute analysis over the "Digital Taranaki" areas. Supervisors are Tim Stern, Beate Leitner, Peter King;
� Marc Gibba is a University of Dublin PhD student working with Andy Nicol on structural mapping and normal fault evolution in the northern onshore Taranaki and offshore north Taranaki graben area. Supervisor is John Walsh;
� Chris Mitchell is a Stanford University PhD student working with Rob Funnell, doing a seismic interpretation and basin modelling project on the Western Stable platform. Supervisor is Steve Graham (AAPG Distinguished Educator awardee);
� Katie Maier is a Stanford PhD student working with Peter King and Malcolm Arnot on seismic and outcrop architecture of the Urenui Formation, in northern onshore and offshore Taranaki. Supervisor is Steve Graham;
� Sarah Grain is a joint VUW/GNS Science MSc student looking at distribution and facies of the Moki Sand interval in the southern-central Taranaki basin area. Supervisors are Cliff Atkins and Peter King;
� Brad Hopcroft is a University of Waikato MSc student working with Peter King on Oligocene sequences along the eastern margin of Taranaki. Supervisor is Peter Kamp.
To learn more about these student projects, e-mail [email protected].
� database of published and new grain size data (over 60 wells);
� summary statistics of porosity, permeability and grain size data by well and formation;
� data plots and illustrative figures;
� representative photomicrographs of various Taranaki reservoirs (over 80 wells);
� summary of reservoir quality by formation.
This catalogue of information and interpretations uses both existing open-file data and GNS Science data sources. It has been designed to allow the user to assess the potential for reservoir quality both geographically and stratigraphically, and includes data from most cored Taranaki wells released by January 2007.
This report has been designed as an interactive HTML document on a single DVD, summarising reservoir properties in the Taranaki Basin by formation.
A top navigation bar remains the same on all pages of this report providing immediate reference to the stratigraphy, well maps and summary statistics (porosity, permeability, grain density and grain size by well, formation and burial depth) as well as links to the raw data as Excel spreadsheets.
The left hand navigation panel lists the various formations that are discussed within the report, while additional links accessed directly from the contents of a page in the report allow the user to continue reading the relevant section whilst having access to other data.
Contact [email protected] to take a look at the product.
digital well summary sheets ����
A set of digital completion logs for open file New Zealand wells is available at GNS Science. These well sheets provide the most up-to-date, complete summary of petroleum wells in New Zealand. Sheets are generated from the petroleum report library and GNS Science in-house post-well data, integrating drilling operations, acquisition and post-well study data. The product consists of a hardcopy printed at 1:5,000 or 1:10,000 scale and one digital copy provided in WellCAD and PDF format. Customised outputs at any scale and format depending on end-user requirements are provided. All data on the well sheets are truly digital. They are held in a database format, exchangeable with other computer systems and software. Well sheets will include the following data and information:
� General well data: location, timing, elevation, water depth, target/s, well results and status etc;
� Drilling operations data: casings, well deviation, drilling fluids;
� Acquisition data: wireline logs, original litho- and chronostratigraphy (from wellsite and final well report), side wall cores and conventional cores, shows, cuts, total gas and chromatographs data, pressure data, TWT checkshots, seismic markers (from final well report);
� Well testing: RFT, DST;
� Post-well revised data: litho- and chronostratigraphy, paleobathymetry and -environment, sedimentology, geochemistry.
Examples are available on-line at www.gns.cri.nz or via [email protected].
forthcoming publication ����
The fantastic exposures of the Mount Messenger and Urenui formations along the north Taranaki coast are already world renowned, and are about to receive more publicity. GNS Science has contributed several papers on our research into the various depositional elements of this Late Miocene succession to a new publication from AAPG that is due in February or March 2008. The publication, AAPG Studies 58, Atlas of deep-water outcrops, assembles the first collection of quantitative architectural data on deep-water successions exposed in outcrop from all seven continents, for use as analogue data in reservoir characterisation and modelling, and for comparing and contrasting differing depositional settings. The atlas is in hard copy, but also has a CD ROM with more comprehensive
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An initial (phase 1) study already completed focused on delineating trends in the mid-late Eocene Mangahewa Formation along a NW-SE trending transect through 8 wells across the Taranaki peninsula. This comprehensive and multi-disciplinary study is freely available as a digital, interactive product, complete with database. The second phase of the Mangahewa Project, which adds 27 wells to the dataset, and which extends across the length of the mid-late Eocene fairway (offshore and onshore), is now underway.
The main aim of this study is to correlate the mid-late Eocene deposits across the reservoir fairway by integrating biostratigraphic ages, coal sulphur trends and paleoenvironments from miospores, dinoflagellates and foraminifera with sedimentological interpretations from available cores and wireline logs. The product will also be provided as an interactive, web-based document and illustrative guide to the Mangahewa Formation. All data, core photographs, core and log interpretations, cross-sections and time-slice paleogeography maps will be provided in the report.
Please contact Karen Higgs ([email protected]) for a copy of the Mangahewa Project phase 1 CD or for more information on phase 2 of the study.
TrapTester looks at fault seals in the Kupe field ����
Many petroleum fields are located somewhat paradoxically on or adjacent to heavily faulted active plate boundaries. One such field is Kupe. When such fields are cut by active faults they are commonly thought to be susceptible to dilatation-induced leakage. Relay ramps and associated damage zones can increase permeability around faults, further enhancing migration and increasing risk to sealing within the field. However, the presence of hydrocarbon reservoirs adjacent to some active faults suggests that the faults must locally be sealing at least. In this study we used a quality 3D seismic reflection volume, numerical modelling and fault seal modelling using our new TrapTester tool to investigate the
relationships between active fault geometries and their effect on permeability and leakage within and around the Kupe Field.
Seismic interpretation of the reprocessed Kerry 3D seismic reflection volume has revealed numerous en-echelon arrays of steeply dipping, NE-striking faults sub-parallel to maximum horizontal shortening. Near-seafloor time slices suggest a number of the faults are associated with seismically imaged features very near the seafloor (within about 5 milliseconds TWTT) and may therefore be active. Some of these faults appear to have velocity anomalies associated with them, possibly indicating gas migration, while a fraction also appear to penetrate to reservoir depths. These observations suggest that incipient, plate boundary-related faults may be at risk for leaking in a critical range of orientations in the Kupe area. However, high clay contents in the fault rock may counteract predicted mechanical instability, particularly along relatively large throw faults. Preliminary numerical models suggest that in layered shale-sandstone sequences, there are sharp decreases in fault permeability with increasing fault throw once the clay-rich layers become smeared into the fault.
Contact Brad Ilg at [email protected] to learn more about our new structural geology capabilities.
oil-oil and oil-source rock correlations ����
Oil-oil and oil-source rock correlations are an essential tool for assisting petroleum exploration, particularly in basins with multiple petroleum systems. To evaluate these relationships in several New Zealand basins, a set of 10 oils and gas condensates has been investigated by molecular organic geochemistry to assess oil quality, source and maturity, and to verify interpretations of data sets collected over the last decades. The 10 samples, including five seep oils and ranging from yellow gas condensates to black, waxy oils, are from the Great South, Canterbury, South Westland, Grey River, Murchison, and East Coast basins. Detailed comparison is also made to Taranaki oils and gas condensates.
Four of the seep oils, from the East Coast and South Westland basins, have biomarker distributions consistent with marine oils with minor terrestrial input. The East Coast seep oils are similar to the Kora oils of the Taranaki Basin, but have δ13C isotope signatures consistent with derivation from the Late Cretaceous–Paleocene Whangai Formation. The gas condensates from the Canterbury and Murchison basins are derived from predominantly terrestrial source rocks, but with significant marine influence and relatively high anoxicity during deposition. In contrast, oils from the Grey River and Great South Basins are more terrestrial, with the oils from Petroleum Creek-3 and Kotuku (seep oil), in particular, having negligible marine influence.
Certain biomarker classes can be used to indicate oil families. The Grey River oils and the Galleon-1 gas condensate are derived predominantly from gymnosperm organic matter which groups them with the Late Cretaceous Maui oil family of Taranaki, whereas only the gas condensate from Murchison Basin contains elevated amounts of biomarkers indicative of angiosperm biomass implying a Tertiary age. The remaining oils and condensates show no or only minor correlation to the Taranaki oil families, reflecting the range of source rock age and facies that exists within New Zealand sedimentary basins.
We’re doing much more on understanding the sources of New Zealand petroleum. Contact Klaus Zink on [email protected] for more info.
accolades for New Zealand timescale monograph ����
The New Zealand Geological Timescale, edited by emeritus scientist Roger Cooper (GNS Science monograph 22, 2004), continues to attract wide praise. In the latest issue of the international journal Stratigraphy (vol. 4: 362-364, 2007) the volume is reviewed in some depth by Brian McGowran of the University of Adelaide. In his review, he describes it as a "superb and beautifully produced volume", and he notes that this continues the GNS Science tradition of producing monographs that are simply and clearly written and aim at a wide range of readers. Lead author of the 1995 international timescale, Bill Berggren, has added in other correspondence to Roger: “your volume on NZ chronostratigraphy and time scale is magnificent. Fully comparable to the 2004 time scale of Gradstein and company! Beautifully written and documented”.
The original print run of 3,000 copies of monograph 22 has now sold out and it has just been reprinted (NZ$40 from GNS Science Publications). Also available are a wall chart (NZ$10 from GNS Science, or free at http://www.gns.cri.nz/what/earthhist/dating) and a reference card (free, contact: [email protected]).
faults and fluid flow: the TURI consortium ����
Late Miocene basin floor turbidite fans of the Mount Messenger Formation, superbly exposed in cliff sections on the west coast of the North Island, represent an excellent outcrop analogue for subsurface deep-water turbidite reservoirs. In the
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the cretaceous frontier ����
The Cretaceous is a frontier in Taranaki that may hold great potential. A study of Cretaceous stratigraphy is ongoing as part of our FRST-funded petroleum research programme. The Late Cretaceous Rakopi Formation represents one of the most important petroleum source rock units in the Taranaki Basin, whilst both the Rakopi Formation and younger North Cape Formation are potential reservoir units. However, relatively few well penetrations have drilled into Cretaceous strata and therefore much of the FRST-funded work has been outcrop-based. Work from previous years has focused on the Rakopi Formation, whilst more recently this has been extended up into the overlying North Cape Formation. The study encompasses detailed sedimentological work together with paleontological, coal, geochemical and petrographic studies. Primary aims are to better understand depositional environments of Cretaceous strata, to refine models of hydrocarbon generation and to investigate reservoir quality of the Cretaceous sandstones.
Contact Greg Browne on [email protected] for more info.
reservoir quality in the Taranaki basin ����
Reservoir quality is a primary risk for successful petroleum exploration in Taranaki. This new non-exclusive GNS Science report reviews available reservoir quality data to provide a comprehensive resource for exploration. Reservoir degradation (and local enhancement) through burial, compaction, cementation and secondary porosity generation is discussed in this report and may provide a means to predict reservoir quality in as yet un-drilled parts of the Taranaki Basin. The report can be used as both an illustrative guide and a database, comprising the following main elements:
� general well information with links to key sections of well completion reports;
� summary wireline log profiles by formation (over 100 wells);
� database of conventional core analysis data (over 90 wells);
that punctuated an overall Paleocene–Eocene aggradational to transgressional pattern. The absence of the Tartan Formation from coastal Otago and the proximal offshore wells Rakiura-1, Tara-1 and Takapu-1A is most likely due to sediment bypass and/or erosion. The basal part of the overlying Laing Formation was deposited during a transgression commencing in the latest Paleocene-earliest Eocene.
The idea of the Tartan being a regressive deposit, characterised by disseminated woody particles, is controversial and makes the current upwelling model for the formation redundant (at least in the GSB). However, more and more evidence for this theory shows up from geochemistry (like unusually high C/N ratios compared with normal marine organic-rich mudstone).
Talk to Poul Schioler ([email protected]) to find out more.
opening a new frontier ����
Fifteen years from now, the lower half of the South Island could be enjoying an impressive economic boost if large petroleum accumulations are discovered in the Great South Basin. GNS Science has played a vital role in attracting major oil companies to explore in this 360,000km
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swathe of wild ocean off the south eastern coast of the South Island. New Zealand’s biggest and most prospective sedimentary basin will be a challenge, even for the world’s biggest privately owned oil company ExxonMobil – a partner in one of the three licence holding consortia.
Our involvement with this basin goes back many years. In 1999 we published a definitive basin study, GNS Science Monograph 20, which synthesises three decades of government and industry research. In 2002 we produced a comprehensive review that provides workstation-ready data and analysis needed by the petroleum exploration industry to evaluate prospectivity. Called the Great South Basin Regional Review, it covers all exploration to date, petroleum geology, geochemistry, analysis of the well failures from the 1970s and 1980s, estimated oil and gas volumes, and discussion of the main exploration risk factors. We marketed this product extensively overseas where it has been well received. A number of exploration companies have described it as the most useful and best produced prospectivity product they have seen.
In 2006 we processed and interpreted 3,100km of seismic data acquired by the Ministry of Economic Development. It shows sediments up to 8km thick in the deeper parts of the basin and a number of geological structures capable of holding giant oil and gas fields. Because the region is some distance from the plate boundary and has been seismically quiet for the past 50 million years, there is a good chance that petroleum has remained within the trap structures. So any accumulations have the potential to be larger than the Maui gas field. In the past two years we have run workshops and fieldtrips for companies looking at exploring in this area.
The outcome, in 2007, of a commitment from the licence-holders to invest over $1 billion in exploring for oil and gas will benefit all New Zealanders. It equates to a doubling of the investment in exploration in New Zealand. As well as helping us to reduce our dependence on imported oil, it will generate cash that can be used to research and develop other energy alternatives for New Zealand.
Contact [email protected] for more info on our Great South Basin studies.
1230000
31700
Oil Kitchens (MMbbl)
Lower Hoiho Formation
(105-85 Ma)
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Tongaporutu River area, turbidite sandstones are offset by an array of normal faults of various orientations and throws that are also well exposed along the cliff face. GNS Science is participating in a consortium with CSIRO and Curtin University, funded by major international exploration companies, and with input from our research programme, to investigate the effects of faulting on sandstone reservoir architecture and flow behaviour. The main aims of this study are to characterise the hydraulic connectivity and conductivity in complex faulted thin-bedded to thick-bedded clastic reservoir rocks. This information will be used to develop upscaling strategies that successfully account for the effects of sub-seismic faulting (juxtaposition, membrane sealing) and sedimentary variability on fluid flow in reservoirs of this kind. Data acquisition includes: outcrop mapping, section measuring and 3D photogrammetry of the cliff section, combined with behind-outcrop 3D ground penetrating radar, high-resolution 2D seismic and 3D seismic, coring, logging and pump testing.
The project is in its final year. Most data have been collected, and we are now embarking on the integrated interpretation phase, including construction of a detailed 3D geological framework model, and analysis of fault characteristics.
Malcolm Arnot ([email protected]) is the GNS Science project leader for the TURI consortium.
tight gas reservoirs ����
Taranaki's tight gas resources have been attracting increasing attention in recent years, but reservoir quality and deliverability remain a problem. In 2007 we published a paper in the Journal of Sedimentary Research that documents the use of integrated diagenetic and burial history analysis to better understand reservoir quality of a tight gas reservoir in the Taranaki Basin. A case-study was undertaken on the gas-charged Eocene K3E Kapuni Group reservoir in Cardiff-1, where a failure to produce commercial quantities of gas was inferred by the operator to be due to poor reservoir quality. In our study, K3E sandstone samples were examined to explore reasons for low permeability and to relate diagenetic reactions to the history of burial and temperature and to the timing of oil expulsion from nearby kitchens. Analytical techniques included thin section petrography, scanning electron microscopy, X-ray diffraction, fluid inclusion analysis, K-
Ar dating and stable isotopic analysis. In addition, a detailed burial history was generated for the Cardiff-1 site, providing a basis for predicting the timing of CO2, oil and gas generation and expulsion from both Cretaceous and Paleogene source rocks. This integrated approach demonstrates the tools necessary to understand diagenetic and fluid-flow histories with implications for both exploration and reservoir management of deep gas plays.
For more information and a reprint, contact Karen Higgs on [email protected].
structural modelling using 2D Move ����
Here is another example of how we are undertaking increasing amounts of structural geology research. The 2006 Crown Minerals seismic reflection survey (DUN06) greatly improved imaging of deep sedimentary successions, their bounding faults, and underlying basement configurations in the Great South Basin and provided an opportunity to test our new 2D Move structural restoration software.
Our seismic stratigraphic interpretation illustrates that most early rift-fill successions have wedge-shaped geometries, Indicating deposition contemporaneous with fault growth. Individual growth strata wedges can greatly exceed 100km
2 in
area. Previously identified primary play types (drape-fold and inverted-fault plays) are directly dependent on growth strata wedge geometry and interpreted bounding faults for charge, focusing, migration paths and trap formation. Some interesting amplitude anomalies were noted including, a ~15km wide seismic “wipe-out” zone coinciding with a 2,000m interval of gas and oil shows previously recorded in Toroa-1.
Structural interpretation of line DUN06-13 shows listric (“spoon- shaped”) normal faults, some with interpreted throws exceeding 3,000m and slips approaching 12,000m. The larger faults are assumed to sole into a mid-crustal detachment (“low-angle fault”) for kinematic reasons. This interpretation implies that the crustal extension was asymmetric, and is structurally valid, but needs further testing.
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Our improved understanding of initial basin-forming structural style should aid predictions of the nature and distribution of deeply-buried potential source and (possibly) reservoir rocks, which were previously unrecognised on older seismic data. An asymetric rift model would also have implications for heat flow distribution and, ultimately, generation, expulsion and migration of petroleum from source sequences.
Our results are available on-line from www.crownminerals.govt.nz or contact Brad Ilg, [email protected].
Cretaceous ‘Terrestrial & Transgressive' last well control
Model
‘Early Cretaceous’
‘Early Cretaceous and/or Jurassic’
the Tartan Formation- a Great South Basin source rock ����
A new model for the Tartan Formation suggests that this potential source rock is not necessarily distributed in a narrow band related to Paleocene marine upwelling around New Zealand, as previously thought, but may have a much different origin, with a broader (and thereby deeper!) distribution.
A detailed palynological analysis of sidewall core samples taken from below, within and above the Tartan Formation in the four Great South Basin wells Hoiho-1C, Kawau-1A, Pakaha-1 and Toroa-1 shows that the Tartan Formation is positioned in the Thanetian (Upper Paleocene) NZP5 dinoflagellate zone, corresponding to the international nannofossil zones NP 7–9a, somewhat below the Paleocene-Eocene boundary and at the same stratigraphic level as the Waipawa Formation of the East Coast Basin.
Palynofacies analysis of the sample kerogen from the upper part of the underlying Wickliffe Formation contains a mixed assemblage of marine algae and terrestrially derived plant material, indicating deposition in a proximal, probably shallow-water marine environment. The Tartan Formation itself is characterised by very high percentages of degraded brown phytoclasts and rare marine algae indicating a marginal marine, proximal depositional setting.
The palynofacies changes observed may be best explained as a result of base-level changes in a shallow-water epeiric sea.
The Tartan Formation was deposited in the central and southern parts of the basin during a regression in the Thanetian