Geology of cambay basin

Geology of Cambay Basin explained in a detailed way

1. Submitted by : Ananya Mittal GEOLOGY OF CAMBAY BASIN

2. INTRODUCTION Indian sedimentary basins cover an aerial extent of about 1.79 million sq. Km, both on land and offshore up to 200m isobaths. The sedimentary area in deep water beyond the 200m isobaths has been estimated to be about 1.35 million sq. km. This makes the total sedimentary basinal area as 3.14 million sq. Km. At present, India has 26 sedimentary basins which based on the occurrence of hydrocarbon; exploration and the status of knowledge have been divided into 4 categories.

3. Category of the basin :Proved Area :The total area of the basin is about 53,500 sq. km Structure : => Intra-cratonic rift graben -- in form of long, narrow depression (N-S) Basin setting => similar to Divergent Continental Margin basin

4. CATEGORIZATION OF BASINS Source: petroleum.nic.in

5. Sedimentary basins of India

6. Crude oil & natural gas production in the country is from 7 basins under category-I and deepwater areas. In category-II basins, hydrocarbon discoveries have been made but commercial production is yet to commence. The distribution of total Indian sedimentary area of 3.14 million square kilometer under different categories and deep water is presented as under: Source : Ministry of Petroleum and Natural Gas

7. BASIN INTRODUCTION Location of the Cambay basin and its oil and gas fields (after www.spgindia.org/paper/sopt_2313/tmp_2313)

8. Geological map of Western India ( source: after Biswal SK,1987)

9. Geographic Location of the basin Located in NW margin of Indian Peninsula, one of the best explored sedimentary basin Ankaleshwar Oilfield => first major oilfield of Cambay basin The Cambay rift Basin, a rich Petroleum Province of India, is a narrow, elongated rift graben, extending from Surat in the south to Sanchor in the north. In the north, the basin narrows, but tectonically continues beyond Sanchor to pass into the Barmer Basin of Rajasthan. On the southern side, the basin merges with the Bombay Offshore Basin in the Arabian Sea. The basin is roughly limited by latitudes 21˚ 00' and 25˚ 00' N and longitudes 71˚ 30' and 73˚ 30' E.

10. Cambay Basin: Blocks and Distribution (Source: Kumar et.al, 2017)

11. TECTONIC HISTORY Type of Basin : Intracratonic rift graben. Different Tectonic Zones with in the Basin The Cambay rift valley is bounded by well demarcated basin margin step faults. Based on the cross trends the basin has been divided into five tectonic blocks. From north to south, the blocks are: Sanchor – Tharad Mehsana – Ahmedabad Cambay – Tarapur Jambusar – Broach and Narmada Block

12. Location map for the Cambay basin, India, showing major structural elements. (Source: Banerjee et. al ,2002) The Cambay basin, a rift sag Tertiary basin in the western onshore part of India, includes six tectonic blocks, the Patan, Mehsana, Ahmedabad, Tarapur, Broach, and Narmada, separated by faults aligned transverse to the general north-south axis of the rift

13. Age of the Basin & Sediment-thickness The evolution of the Cambay basin began following the extensive outpour of Deccan Basalts (Deccan Trap) during late cretaceous covering large tracts of western and central India. It’s a narrow half graben trending roughly NNW-SSE filled with Tertiary sediments with rifting due to extensional tectonics. Seismic and drilled well data indicate a thickness of about 8 km of Tertiary sediments resting over the Deccan volcanics.

14. BASIN EVOLUTION The Early Tertiary sediments ranging in age from Paleocene to Early Eocene represent syn-rift stage of deposition controlled by faults and basement highs in an expanding rift system. Sediments are characterised by poorly-sorted, high energy trap derived materials. Early eocene : -Transgression during subsidence stage of the basin resulted in the accumulation of a thick sequence of euxinic black shales (marine sediments) with subordinate coarser clastics. Middle Eocene - witnessed a regressive phase with oscillating conditions of deposition and development of deltaic and lagoonal sequences in the entire basin. Late Eocene - regional southward tilt of the entire rift basin,marked by a regional extensive marine transgression extending far to the north upto Sanchor basin. Oligocene – Lower Miocene : marks another phase of tectonic activity with extensive deposition of coarser clastic sediments in the central and southern blocks.

15. Tectonic framework of western India (modified from Eremenko et al.. 1969)

16. Cambay tertiary basin is a graben b/w Kathiawar(Saurashtra) uplift and aravalli range Geological Section across the Cambay basin along line BB’ (previous fig) (Source : Biswal S.K.,1987)

17. GENERALISED STRATIGRAPHY Stratigraphy of Cambay Basin. Surface and subsurface equivalents of western margin and eastern margin have also been depicted ( Source : Padhy et. al., 2016)

18. The formation began following the extensive outpour of Deccan basalts (Deccan Trap) during late Cretaceous covering large tracts of western and central India. The NW-SE Dharwarian tectonic trends got rejuvenated creating a narrow rift graben extending from the Arabian sea south of Hazira to beyond Tharad in the north. Gradually, the rift valley expanded with time. Paleocene: the basin continued to remain as a shallow depression, receiving deposition of fanglomerate, trap conglomerate, trapwacke and claystone facies, under a fluvio–swampy regime. The end of deposition of the Olpad Formation is marked by a prominent unconformity.

19. Early Eocene: Widespread transgression - deposition of a thick, dark grey, fissile pyritiferous shale sequence, known as the Cambay Shale . Shale sequence divided into Older and Younger Cambay Shale with an unconformity in between. In the following period, relative subsidence of the basin continued leading to the accumulation of the Younger Cambay Shale. The end of Cambay Shale deposition again marked by the development of unconformity- present throughout the basin. Subsequently, there was a strong tectonic activity that resulted in the development of the Mehsana Horst and other structural highs associated with basement faults. Middle Eocene: marked by a regressive phase in the basin leading to the development of the Kalol/ Vaso delta system in the north and the Hazad delta system in the south. Hazad and Kalol/ Vaso deltaic sands are holding large accumulations of oil.

20. Late Eocene-Early Oligocene: Major transgression responsible for the deposition of the Tarapur Shale in North Cambay Basin. The end of this sequence marked by a regressive phase leading to deposition of claystone, sandstone, and shale alternations and a limestone unit of the Dadhar Formation. Paleogene The end witnessed major tectonic activity in the basin resulting in the development of a widespread unconformity. Miocene The depocenters continued to subside resulting in the deposition of enormous thickness of Miocene sediments as the Babaguru, Kand and Jhagadia formations. Pliocene Period of both low and high strands of the sea level, allowing the deposition of sand and shale. Pleistocene to Recent sedimentation mainly of fluvial type ,characteristic deposits of coarse sands, gravel, clays and kankar followed by finer sands and clays, comprising Gujarat Alluvium.

21. PETROLEUM SYSTEM Source rock: Thick Cambay Shale In the northern part of the Ahmedabad-Mehsana Block, coal, well developed within the deltaic sequence in Kalol, Sobhasan and Mehsana fields, also important hydrocarbon source rock. The total organic carbon and maturation studies suggest -shales of the Ankleshwar/Kalol formations also organically rich, thermally mature and have generated oil and gas in commercial quantities. Tarapur Shale. Reservoir: Trapwacke sequence of the Olpad Formation. Consist of sand size basalt fragments Localized sandstone reservoirs within the Cambay Shale as in the Unawa, Linch, Mandhali, Mehsana, Sobhasan, fields, etc are also present.

22. Trap rock: Transgressive shale within deltaic sequence The most significant factor that controlled the accumulation of hydrocarbons in the Olpad Formation is the favorable lithological change with structural support and short distance migration. The lithological heterogeneity gave rise to permeability barriers, which facilitated entrapment of hydrocarbons. The associated unconformity also helped in the development of secondary porosity. Timing of migration & Trap formation: The peak of oil generation and migration is understood to have taken place during Early to Middle Miocene.

23. PETROLEUM PLAYS Paleocene – Early Eocene Play : Formations : Olpad Formation/ Lower Cambay Shale. Reservoir Rocks : Sand size basalt fragments & localized sandstone. Unconformities within the Cambay Shale and between the Olpad Formation and the Cambay Shale - generation of secondary porosities. The Olpad Formation is characterised by the development of piedmont deposits against fault scarps and fan delta complexes. Middle Eocene Play : Formations : Upper Tharad Formation Reservoir Rocks : In Southern part, Hazad delta sands of Mid to Late Eocene & in the Northern part the deltaic sequence is made up of alternations of sandstone and shale associated with coal.

24. Late Eocene – Oligocene Play : Formations : Tarapur Shale, Dadhar Formation. Reservoir Rocks : This sequence is observed to possess good reservoir facies in the entire Gulf of Cambay. North of the Mahi river, a thick deltaic sequence, developed during Oligo– Miocene, has prograded upto south Tapti area. Miocene Play : Formations : Deodar : Formation (LR. Miocene), Dhima Formation (Mid Miocene), Antrol Formation (UP. Miocene) The Mahi River delta sequence extends further westward to Cambay area where Miocene rocks are hydrocarbon bearing

25. REFERENCES SINGH D.N ,Oil and Natural Gas Corporation Ltd., Keshava Deva Malaviya Institute of Petroleum Exploration BISWAS S.K., Regional tectonic framework, structure and evolution of the western marginal basins of India, Tectonophysics . 135 (1987) 307-327 ,Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands BANERJEE A., PAHARI S.,JHA M.,SINHA A.K.,JAIN A.K., KUMAR N.,THOMAS N.J., MISHRA K.N.,CHANDRA K. The Effective Source Rocks in the Cambay Basin, India , March 2002 AAPG Bulletin 86(3) PADHY P K,KUMAR ARUN , CHANDRA Y RAMESH, DAS SHISHIR KUMAR , JHA S K and ADVANI D R, Shale Oil Exploration from Paleocene -early Eocene Sequence in Cambay Rift Basin, India. July 2016 ,Proceedings of the Indian National Science Academy 82(3) Template reference: https://www.free-power-point-templates.com

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