Indian Geology/ Basins and Categories
Basins and Categories
Sedimentary Basins of India
There are 26 sedimentary basins in India, covering a total area of 3.4 million square kilometer. The area is spread across onland, shallow water up to 400 meter water depth and deepwater farther up to Exclusive Economic Zone (EEZ). Of the total sedimentary area, 49% of total area is located onland, 12% in shallow water and 39% in the deepwater area. There are 16 onland basins, 7 located both onland and offshore and 3 completely offshore. Tectonically, these basins are classified into 3 groups, based on origin from rifting (intra-cratonic and peri-cratonic), plate collision and crustal sag.
These basins are divided into three categories based on maturity of hydrocarbon resources as under:
• Category-I: Basins, which have reserves and already producing.
• Category-II: Basins, which have contingent resources pending commercial production
• Category-III Basins, which have prospective resources awaiting discovery
Based on conventional resource potential, 7 basins are grouped under Category-I covering 30% of total basinal area and holding 85% of the total unrisked conventional hydrocarbon in-place of 41.8 billion ton oil and oil-equivalent gas. These 7 basins are namely Krishna-Godavari (KG), Mumbai Offshore, Assam Shelf, Rajasthan, Cauvery, Assam-Arakan Fold Belt and Cambay. These basins are fairly appraised to the extent of 47% of country’s total appraised area (1.6 million square kilometer) with 65% of country’s total active operational area (0.3 million square kilometer).
Similarly, Category-II basins cover 23% of total basinal area, holding 9% of the total hydrocarbon in-place. Five basins fall in this category and those are namely Saurashtra, Kutch, Vindhyan, Mahanadi and Andaman. These basins are moderately appraised to the extent of 22% of country’s total appraised area with 26% of country’s total active operational area.
Further, Category-III basins cover 47% of total basinal area, holding 6% of the total hydrocarbon in-place. Fourteen basins fall in this category and those are namely Kerala-Konkan, Bengal-Purnea, Ganga-Punjab, Pranhita-Godavari(PG), Satpura-South Rewa-Damodar, Himalyan Foreland, Chattisgarh, Narmada, Spiti-Zanskar, Deccan Syneclise, Cuddapah, Karewa, Bhima-Kaladgi, and Bastar. These basins are appraised to the extent of 31% of country’s total appraised area with 9% of country’s total active operational area.
The grouping of the basins under the category is dynamic, a Category III basin can be upgraded to II in case there is a discovery (recent instance of Bengal-Purnea basin) or Category II to I, if discoveries are developed for commercial production (Kutch/ Saurashtra basin could be the next as few FDPs already approved). For unconventional resources, the above category will have completely different basin grouping. For example, CBM gas is currently produced from Damodar sub-basin of Satpura-South Rewa-Damodar basin, which is a Category III basin for conventional resources, however by virtue of commercial gas production, the basin will be deemed Category I for unconventional resources.
Under redrafted Revenue Sharing Contract for Hydrocarbon Exploration Licensing Policy, Contractors, operating in Category II and Category III basins for respective conventional and unconventional resources are now exempt of revenue sharing with the government.
CATEGORIZATION OF INDIAN SEDIMENTARY BASINS BASED ON MATURITY OF CONVENTIONAL RESOURCES