Bombay High

Siddharth K. Smruti S.R. Sudhanshu G. Swapnil Pal Tarun K. Yash V.

Introduction

Bombay High is an offshore oilfield 160 kilometres (99 miles) off the coast of Mumbai, India. The oil operations are run by India's Oil and Natural Gas Corporation (ONGC).

Bombay Bombay High field was discovered by a Russian and Indian oil exploration team during mapping of the Gulf of Khambhat (earlier Cambay) in 1964-67.

It supplied 14% of India's oil requirement and accounted for about 38% of all domestic production as per data available till 2004.

GEOPHYSICS

Introduction

A Russian and Indian oil exploration team that was mapping the Gulf of Cambay in 1965 in a seismic exploration vessel called "Academic Arkhangelsky" discovered the Bombay High oilfield.

ONGC geophysicist M Krishnamurthy headed the Indian team which was attached with the Russian Offshore seismic expedition.

ONGC had a contract with "Technoexport" of the then-USSR for seismic support.

Data Processing & Interpretation

The first ever momentous application of velocity analysis was on Bombay high. In 1971-72, interval velocity studies indicated presence of limestone reservoir in the structure.

In 1982, a small group of geophysicists was asked to work for the first time in the Development Geology group (Bombay Offshore) to help solve the geologic problems associated with field development and production.

A few wells drilled later on confirmed the seismic predictions of the synergist group and this resulted in significant upward estimate of in-place reserves and in suitable modification of the injection wells locations.

In 1997, acquisition of seismic data in Bombay offshore through Ocean Bottom Cable (OBC) with dual sensors was the watershed in the use of latest tools in ONGC.

Well Logs

Here, gamma-ray, resistivity, neutron porosity, and velocity (Vp) well-log data sets from three vertical wells, viz. Well-A, Well-B, and Well-C are shown in the figures. The wells, located in the Bombay High oilfield in the western offshore basin (Fig. 1) are separated by a distance of approximately 10 km.

Logs of all three wells represent subsurface sections of approximately 500 m below the sea floor. Velocity log data (in units of m/s) were generated from the sonic log.

Data were sampled at 0.15 m and a total of 3280 data points in each log of all three wells were obtained.

Shale (sand) formations show high (low) gamma-ray intensity. Since we are interested in identifying reservoir rocks (which are non-shaly), identification of boundaries between different subsurface formations in well-log data becomes necessary.

Figure 2: gamma-ray log, well-a1, well-a2, well-a3, repectively

Figure 3: resistivity log, well-b1, b2, b3 respectively.

Hydrocarbon-bearing formations are characterized with high resistivity compared to those of non-hydrocarbon bearing formations which is represented by scalograms of the resistivity logs

Figure 4: neutron porosity logs. well-c1, c2, c3 respectively.

Study of the scalograms of the neutron porosity logs of Well-A (Fig. 4c1), Well-B (Fig. 4c2) and Well-C (Fig. 4c3) show high positive coefficients at different depths corresponding to the decrease in neutron porosity.

Figure 5: velocity logs, well-d1,d2,d3

Velocity logs generated from sonic logs measure the interval transit time of sound waves in the formations. As expected, velocities are usually low for the reservoir rocks (lime stone and sand stone) when compared to shaly formations.

General Geology

Bombay High is One of the six sedimentary basins on Western Continental Margin , i.e.

I. KutchII. SaurashtraIII. Bombay offshoreIV. KonkanV. LakshadweepVI. Kerala

Bombay offshore basin is the largest with an arial extent of 120,000 km2 .

General Geology

An intra cratonic basin. southern extension of Cambay basin and encompasses the

Gulf of Cambay and adjacent shelf part of the Arabian sea. result of faulting in the Deccan trap basement during Upper

Cretaceous. This basin is divided into several tectonic units such as - -

Cambay Gulf Shelf to the north - Dahanu depression to the south - Bombay Ratnagiri shelf occupying

central and southern part of

General Geology developed on divergent passive continental margin Three-structural units of carbonate dominant stratigraphy with three

contiguous major depressions. clastic domain follows from Mumbai coast towards Arabian Sea:

Shelfal horst-graben structure

Kon-comoria depression

  kon comaria ridge

  Lakshmi ± Laccadive depression

  Lakshmi ± Laccadive ridge

  Arabian sea

Litho-Stratigraphic sequence

Thickness (meter) Formation Age

1700 Chinchini Miocene

377 Tapti (S1 silt sandstone)

Miocene

500 Mahim (Bombay high)

Miocene

370 Daman Oligocene

314 Mahuva (Heera, Mukta)

Oligocene

300 Pipavav (Diu, Bassein)

Eocene

618 Jafrabad (Panna, Devgarh)

Plaeocene

Deccan trap Cretaceous

Metamorphosed basement rocks

Precambrian

Stratigraphy

A hiatus is present between the formation of Metamorphosed basement –Deccan trap, Deccan trap ± Jafrabad, Jafrabad- Pipavav, Pipavav ± Mahuva and Mahuva- Mahim.

part of Mahuva formation of Miocene age. consists of few meters thick limestone formations separating

from each other by thin layers of shale formations. NNW-SSE trending doubly plunging anticline with a faulted

eastern limb having a throw of about 100 Meters.

Mumbai high is divided into two blocks. 1.Mumbai High North (MHN) 2.Mumbai High South (MHS) The low permeability zone divides the Mumbai high north

and south. There is a 15 meters wide fault between north and south The estimated initial oil-in-place (OIIP) in Mumbai high north

and south is 1659 MMt

ggh

The L-III limestone is the major reservoir in the field, which contains 94% of the proved reserves

Other hydrocarbon producing reservoirs are L-I, L-II and S1. Oil and gas accumulation is found in Basal Clastics and fractured Basement also.

Petroleum System

Bombay offshore basin accounts for nearly two thirds of the annual petroleum production of India. The mature source rocks are present in the lower Eocene Paleocene Panna formation. Further, marginally mature potential source rocks are within the Oligocene in Tapti- Daman and within Neogene in Deep Continental shelf and deeper part of the basin also exist. Hydrocarbons have been discovered in multiple reservoirs in this basin, ranging from fractured basement to middle Miocene.

Introduction

Petroleum System map

Regional structure and selected oil and gas fields.

Total Composite Petroleum System

Source Rock Panna formation of Palaeocene-Early

Eocene is main source rock of crude oil formation. Panna formation spread over the entire Mumbai offshore basin. Besides Panna formation, coral reefs are the source rocks as well as reservoirs.

Panna formation Total Organic Carbons (TOC): 0.5- 20.4 %

Thermal gradient is 3 degree per 100 feet. The source rocks contain mixed type-II and

type-III kerogens.

Important elements which constitutes Petroleum System

Total Composite Petroleum System

Reservoir rock Limestone is the main reservoir. Limestone is

basically Micrite, Biomicrite and chalky type. They posses mainly primary and secondary porosity.

Average Porosity range: 15- 35% Average Permeability: 10 mD to 1 Darcy In the Bombay-High area, oil and gas is produced

from fractured basement through middle Miocene reservoirs, with the most prolific being the platform carbonates such as the lower Miocene L-III limestone.

Other rocks are of Mukta, Baseein, Daman, Panna and Mahuva formation in Tapti Daman block.

Important elements which constitutes Petroleum System

Total Composite Petroleum System

Cap rock Shale is mainly cap rock in Mumbai high.

But somewhere carbonates are also present as cap rocks wherever tight limestone is formed. E.g.: Bassein Reservoir.

Important elements which constitutes Petroleum System

Total Composite Petroleum System

Seal In the Bombay offshore and Kutch areas,

the most likely seals are an extensive series of thick middle to upper Miocene shales. In the Cambay Graben, interbedded Paleocene through middle Miocene shales provides seals for the various reservoirs.

Important elements which constitutes Petroleum System

Burial history chart

Generalized stratigraphy of Bombay-Cambay-Kutch area:

Total Composite Petroleum System

Trap formation Anticlinal reversal & fault closures are

mainly trap. Structure within anticlinal reverse is mostly developed by drape sandstone. Trend of fault closures are ENE-WSW.

Important processes which constitutes Petroleum System

Total Composite Petroleum System

Generation-Migration-Accumulation Generation and expulsion adjacent to the

Bombay-High area may have occurred as early as middle Miocene and continued, or began again, in the Pliocene.

Burial-history data indicate peak generation most likely occurred during the late Miocene and early Pliocene.

Important processes which constitutes Petroleum System

Total Composite Petroleum System

Events chart: Generation-Migration-Accumulation

Production AND Exploration History

• Discovery

• In early 1960’s, a Russian seismic ship Academic Arkhangelsky started exploration in the Mumbai offshore basin.

• Regional geophysical surveys were conducted by this seismic vessel in the area.

• The oil field of Bombay High was thus discovered during the mapping of Gulf of Khambat in 1964-67.

• ONGC first started drilling in Bombay High with the drillship Sagar Samrat in 1973.

• First offshore well was sunk in Feburary 1974.

• The field was put on production in May 1976.

• Production from this field was responsible for rapid growth of the country’s total crude oil production in 1970’s and 1980’s.

Production

• Cumulative production from the Bombay High field has exceeded 2 billion barrels of Oil (BBO) and 3 trillion cubic feet of Gas (TCFG).

• Estimated Initial oil-in-place (OIIP) in Mumbai High North and South is 1659 MMT.

• Up till 2004, Oil field of Bombay High accounted for about 38% of the entire domestic production and supplied 14% of the oil requirement.

• A major fire on 27th July, 2005 destroyed the Mumbai High North platform.

• The north platform used to produce 110,000 barrels of oil every day ( a seventh of the country’s oil).

• Rebuilding the platform cost an estimated amount of Rs 1200 crore.

• The Bombay High oil field reached its peak production level in 1998 with 20 MMT an year.

• The quantity of oil produced at Bombay High has been on the decline since 1990’s due to field GOR and water cut.

• 1.6 billion $ programme is planned by ONGC to improve the oil recovery from the field.

Exploration

• Intense exploration and development activities in the basin have resulted in significant discoveries of several oil and gas fields:

Heera Panna Bassein Neelam Mukta Ratna

Future prospects

• ONGC envisages a total crude oil production of 202.42 MMT by 2030.

• It aims to improve the recovery rate by 40% by 2040.

• ONGC has floated a tender for the acquisition, processing and interpretation of 1975 sq km or 4C-3D seismic data in the Mumbai High area.

1. 1600 sq km in Mumbai High field2. 375 sq km in Heera field.

Conclusion

The study of Geology gives an idea about the formation, stratigraphic sequence and present condition of the Bombay High oilfield.

Study of petroleum system also provides information about generation and expulsion adjacent to the Bombay-High area which may have occurred as early as middle Miocene and continued, or began again, in the Pliocene.

Burial-history data indicate peak generation most likely occurred during the late Miocene and early Pliocene.

Conclusion(contd.)

During the years, with the development of geophysics, ONGC has used modern methodologies like synergists approach and acquisition through ocean bottom cables resulting in a clearer subsurface image and better estimate of in-place reserve

References

CHANDRASEKHAR, E. AND RAO, E.V., 2012, Wavelet Analysis of Geophysical Well-log Data of Bombay Offshore Basin, India, Mathematical Geosciences, Springer-Verlag

NANDA, N.C., 2002, Petroleum Geophysics in ONGC, India - A memoir, Geohorizon, SPG India

Directorate General of Hydrocarbons - Mumbai Offshore Basin (http://www.dghindia.org)

Wikipedia – Bombay High (http://en.wikipedia.org/wiki/Bombay_High)

www.onepetro.org www.offshore-technology.com/projects/mumbai-high http://www.ongcindia.com/specrep1.asp?

fold=special&file=special1.txt http://www.upstreamonline.com/hardcopy/news/article1263483.ece

Questions?

Thank you