BOMBAY HIGH

BY HIMADRI SAMAL 27.09.16

1. Bombay High Himadri Samal RN: 16/ESC/AGE005 M.Sc 1 st Sem,First Year. SAMBALPUR UNIVERSITY

2. I ntroduction Bombay High is an offshore oilfield 160 kilometres (99 miles) off the coast of Mumbai, India,in about 75m of water of The Arabian Sea. The oil operations are run by India's Oil and Natural Gas Corporation (ONGC). 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 followed by a detail survey in 1972.

3. Here,the structure is a “North-northwest to South-southeast” trending doubly plunging Anticline with a faulted East Limb,65km long & 23km wide & is the most probable reason to call it “BOMBAY HIGH” It supplied 14% of India's oil requirement and accounted for about 38% of all domestic production as per data available till 2004.

4. GEOPHYSICS 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.

5. 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 solve the geologic problems associated with field development and production . A few wells drilled later on confirmed the seismic predictions . In 1997, acquisition of seismic data in Bombay High offshore through Ocean Bottom Cable (OBC) with dual sensors was the watershed in the use of latest tools in ONGC.

6. 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.

7. 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

8. 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

9. 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.

10. 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.

11. General Geology Bombay High is One of the six sedimentary basins on Western Continental Margin , i.e. Kutch Saurashtra Bombay offshore Konkan Lakshadweep Kerala Bombay offshore basin is the largest with an arial extent of 120,000 km 2 .

12. An intra cratonic basin. It is the 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

13. 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 Litho -stratigraphic sequence

14. Stratigraphy A hiatus is present between the formation of Metamorphosed basement –Deccan trap, Deccan trap ± Jafrabad , Jafrabad - Pipavav , Pipavav ±  Mahuva and Mahuva - Mahim . P art of Mahuva formation of Miocene age. 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

15. Petroleum System Bombay offshore basin accounts for nearly two thirds of the annual petroleum production of India. Regional structure and selected oil and gas fields.

16. 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

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

18. 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. 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.

19. B urial history chart Generalized stratigraphy of Bombay-Cambay-Kutch area:

20. Production AND Exploration History After Discovery Regional geophysical surveys were conducted by seismic vessel in the confirmed reservoir area. 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.

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

22. 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

23. ACCIDENTS A major fire on 27th July, 2005 destroyed the Mumbai High North platform . The raging fire that gutted an ONGC oil-drilling platform in The Bombay High oil field area was caused when an ONGC vessel “MSV Samudra Suraksha ” sent to pick up a sick worker at the giant platform. This mishap resulted in serious oil leakage ,engulfing the platform & vesssel in a major infeno . The damage to “ Samudra Suraksha ” was extensive but not enough to sink it. Rebuilding the platform cost an estimated amount of Rs 1200 crore . Death :10 Missing :14 Rescued:361 Total:385

24. Future prospects 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. 1600 sq km in Mumbai High field 375 sq km in Heera field.

25. 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.

26. SOURCES . 1.ONGC,INDIAN GOVT. 2.THE HINDU 3.THE ECONOMIC TIMES 4.REDIFF.COM 5.WIKIPEDIA 6.SLIDESHARE.NET 7.INTERNET S PECIAL THAN KS TO SWAPNIL PATIL,COAL INDIA EMPLOYEE & PRANAB

27. THANKING YOU