Central Indian Basin

The Central Indian Basin is a vast offshore sedimentary trough in the Indian Ocean, extending south‑west of the Indian subcontinent over roughly 1.5 million km² and plunging to water depths exceeding 5,000 m. Its geological continuity, thick Mesozoic‑Cenozoic sediment pile, and prolific hydrocarbon accumulations—most notably the Mumbai High complex—make it one of the world’s most significant offshore oil‑and‑gas provinces.

Geological Origin and Tectonic Evolution

The basin originated during the Late Jurassic breakup of Gondwana, when the Indian plate began rifting away from Madagascar and Antarctica. Seafloor spreading along the Central Indian Ridge, initiated around 150 Ma, created a passive margin that subsequently entered a prolonged thermal‑subsidence phase lasting into the early Cenozoic.

Sedimentation accelerated during the Cretaceous, depositing up to 12 km of clastic and carbonate sequences derived from the eroding Deccan Plateau and the Himalaya‑ward hinterland. The basin’s structural framework is dominated by gentle, west‑to‑southwest‑trending fault blocks that were later overprinted by minor compressional reactivations during the Indo‑Asian collision after 55 Ma.

Sedimentary Architecture and Hydrocarbon Potential

Source rocks are chiefly the Upper Jurassic–Lower Cretaceous marine shales of the Kachchh and Barmer formations, which exhibit total organic carbon values of 2–4 wt % and vitrinite reflectance between 0.8 and 1.2 %Ro, indicating mature to over‑mature hydrocarbon generation. Reservoirs are hosted in the Paleocene–Eocene sandstones of the Mumbai and Bassein formations, where porosities of 12–18 % and permeabilities of 50–200 mD have been recorded in multiple wells.

Structural traps include anticlinal closures and fault‑related rollover hinges, while stratigraphic traps are formed by pinch‑outs of the sand bodies against shale barriers. The India‑Geological Survey (IGS) and the Oil and Natural Gas Corporation (ONGC) have jointly estimated the basin’s undiscovered, technically recoverable resources at 30–40 billion barrels of oil equivalent (BOE), with a gas‑to‑oil ratio of roughly 1.5 : 1.

Exploration and Production History

Commercial exploration commenced in 1974 when ONGC’s Mumbai High field was discovered at a water depth of 1,200 m, followed by first oil production in 1976. By the end of 2023, cumulative output from Mumbai High and its satellite fields—Mumbai High A, B, C, and D—exceeded 1.5 billion barrels of oil and 2.2 trillion cubic feet of gas.

The basin has attracted participation from Reliance Industries, which operates the Bassein‑South block, and from international partners such as TotalEnergies, which drilled the 2020‑2021 deep‑water well in the 3,200 m water‑depth zone of the Central Indian Basin. To date, more than 150 exploration wells have been spudded, yielding a success rate of approximately 30 % for oil and 45 % for gas.

Current Status and Future Outlook

In 2022 ONGC announced the successful drilling of a 4,800 m water‑depth well—CB‑03—targeting the Lower Cretaceous source interval, marking the deepest offshore well ever attempted in the basin. The well encountered a 45 m oil‑bearing sandstone with an average API gravity of 32°, suggesting the presence of a new high‑quality reservoir.

The Indian Ministry of Petroleum and Natural Gas has earmarked ₹12 billion (≈ US$160 million) for a 2024‑2028 deep‑water exploration program, emphasizing the basin’s potential for unconventional gas and for extending the productive life of existing fields through enhanced oil recovery (EOR) techniques such as CO₂ injection.

Significance

Hydrocarbon production from the Central Indian Basin accounts for roughly 15 % of India’s total offshore oil output and 10 % of its offshore gas output, underpinning energy security for a nation consuming over 800 million tonnes of oil equivalent annually. The basin’s strategic location, far from geopolitical flashpoints, also provides a domestic supply buffer against global price volatility.

Beyond energy, the basin’s sedimentary record offers a continuous archive of Indian monsoon evolution, with paleoclimatic proxies preserved in the Cretaceous–Eocene strata. Consequently, the Central Indian Basin remains a focal point for both commercial exploitation and scientific research, embodying a unique convergence of economic, geological, and environmental importance.