Bombay High is an offshore oilfield 160 kilometres (99 miles) off the coast of Mumbai, India. The oil operations are run by Indias 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 Indias oil requirement and accounted for about 38% of all domestic production as per data available till 2004.
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.
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.
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.
Figure 2: gamma-ray log, well-a1, well-a2, well-a3, repectivelyShale (sand) formations show high (low) gamma-ray intensity. Since we areinterested in identifying reservoir rocks (which are non-shaly), identification ofboundaries between different subsurface formations in well-log data becomesnecessary.
Figure 3: resistivity log, well-b1, b2, b3 respectively.Hydrocarbon-bearing formations are characterized with high resistivity compared tothose of non-hydrocarbon bearing formations which is represented by scalograms of theresistivity 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 depthscorresponding to the decrease in neutron porosity.
Figure 5: velocity logs, well-d1,d2,d3Velocity logs generated from sonic logs measure the interval transit time of soundwaves in the formations. As expected, velocities are usually low for the reservoir rocks(lime stone and sand stone) when compared to shaly formations.
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 .
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
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
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
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 SystemIntroduction 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.
Petroleum System mapRegional structure andselected oil and gasfields.
Total CompositePetroleum SystemImportant elements Source Rockwhich constitutes Panna formation of Palaeocene-EarlyPetroleum System 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.
Total CompositePetroleum SystemImportant elements Reservoir rockwhich constitutes Limestone is the main reservoir. Limestone isPetroleum System 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.
Total CompositePetroleum SystemImportant elementswhich constitutes Cap rockPetroleum System 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.
Total CompositePetroleum SystemImportant elementswhich constitutes SealPetroleum System 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.
Burial history chartGeneralized stratigraphyof Bombay-Cambay-Kutch area:
Total CompositePetroleum SystemImportant processeswhich constitutes Trap formationPetroleum System Anticlinal reversal & fault closures are mainly trap. Structure within anticlinal reverse is mostly developed by drape sandstone. Trend of fault closures are ENE- WSW.
Total CompositePetroleum SystemImportant processeswhich constitutes Generation-Migration-AccumulationPetroleum System 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.
Total CompositePetroleum SystemEvents chart:Generation-Migration-Accumulation
• 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.
• 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.
• 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
• 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.
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.
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
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