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Petroleum Systems of the Mumbai Offshore Basin, India

 

Goswami, Basant Giri1, Harvir Singh1, A. K. Bhatnagar1, A. K. Sinha1, Ram Raj Singh1 (1) KDM Institute of Petroleum Exploration, Oil & Natural Gas Corporation Ltd, Dehradun, India

 

Mumbai Offshore Basin, a pericratonic rift basin in the western continental shelf of India covers about 1,48,000 km2 from coast to 200m isobath. The basin is divided into six tectonic blocks and the sedimentary fill ranges from 1100-5000m. Several large oil and gas fields have been discovered in this basin and the presence of hydrocarbons has been established in the multiple pay zones belonging to L-III limestone reservoir of Miocene age (only in Mumbai High), Mukta (Early Oligocene), Bassein (Middle Eocene) and Panna (Paleocene to early Eocene) reservoirs. The work presents the detailed geochemical evaluation on more than 200 rock extracts and 250 oil samples and maturity modeling in key generative depressions of all the tectonic blocks of the basin.

 

Results indicate that only Panna Formation has good to excellent effective source rocks throughout the basinal part of each block in entire basin. Middle of Panna Formation has attained a 0.6% VRo at about 12-20 Ma in various blocks. Panna source rock in the lower layer has predominantly Type III kerogen but contains mixed kerogen in the upper layer. However, Panna source rock in few wells in Mahim graben and DCS area also possess Type I kerogen. Based upon the variations in the organofacies, oils have been placed into two groups. Group-I oils having only terrestrial signatures and correlate with the source rock extracts from the lower layer whereas the group-II oils have mixed input, isotopically heavier than the group-I oils and correlate with the source rock extracts from upper layer of the Panna Formation. Major petroleum systems in the basin are: Panna-L-III, Panna-Mukta, Panna-Bassein and Panna-Panna.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California