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Deep Gondwana Sediments of a Part of Krishna-Godavari Basin - A Potential and Prospective Area for Unconventional Gas Deposits

Prasad V. Inupakutika, Negi S. Bharat, Saksena K. Amit, and Singh R. Ram
Geochemistry, KDMIPE-ONGC, Dehradun, India

At present about 15% of the total gas production in USA is from unconventional basin-centered (synclinal) gas resources. Basin Centered Gas Systems (BCGS) are large and wide synclinal accumulations of gas in deep abnormally pressured sequences. The paper presents geoscientific studies performed in Kavitam-Poduru High and surrounding area of Krishna-Godavari basin (India), which reveals several similarities with established BCG accumulations.

The Gondwana sediments comprising coal, carbonaceous shale and sandstone of Kommugudem (Permian) Formation is about 300-400m thick sequence that have undergone deeper burial varying from 2.8km in the flanks to a maximum of around 7km in different lows. It is identified to be an effective source rock for gas and condensate occurrences in Mandapeta as well as Mandapeta-West fields.

The results of 1-D basin modeling performed in the representative lows indicate that the Kommugudem (Permian) source rock has attained 98-99% kerogen transformation with critical moment corresponding to 50% transformation ratio (TR) at 110-80 Ma. The source rock units of Raghavapuram Shale (Early Cretaceous) have also attained kerogen transformation to the extent of 90% at the base with maturity of 1.5%VRo and TR: 12% at the top of the sequence.

The presence of continuous gas shows in a couple of deep wells, which penetrated the Mandapeta (Permo-Traissic) Formation indicate that the deep basinal lows may have conditions favorable for development of tight-gas sands as Basin Centered Gas Accumulations (BCGA) based on the evaluation of pressure data, shale density and sonic logs trends corroborating over-pressured sequences.

The probability of existence of the “sweet spots” in the Kavitam-Poduru high trend is likely because of the inversional features observed and large amounts of hydrocarbons generated from the Kommugudem source rocks .

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery