ABSTRACT: The effective source rocks of Cambay Basin, India

Banerjee, Atanu, Sukumar Pahari, Mamta Jha, Adarsh Kumar Sinha, A. K. Jain, N. Kumar, N. J. Thomas, K. N. Misra, Kuldeep Chandra , ONGC Ltd, Dehradun, India (2) ONGC Ltd

We identified the effective source rocks (SR) and determined their maturation histories to derive exploration leads and inputs for petroleum system study. SR screening of 15000 samples reveals six laterally extending potential sources (PS) with kerogen II/III in middle Eocene (Kalol formation) to lower Paleocene (Olpad formation). The PS's are SR4 (base of Kalol), SR5 and SR6 (top of Cambay Shale) and SR7 and SR8/9 and SR11/12 (top and base of Olpad formations respectively). Kinetics derived 'hydrocarbon expelled' values are 0 to 0.4, 4 to 16, and 16 to 32 MT/m2 for Kalol, Cambay Shale, and Olpad. Values are high in the south for Kalol and Cambay Shale and in the north for Olpad. In the north, SR11/12, SR8/9, and SR7 attained peak oil generation (vitrinite reflectance, VRo, ~0.75 %) at 45, 5, and 1 mybp respectively. SR6 and SR5 attained generation threshold (0.5% VRo) recently. In the south, SR11/12, SR8/9, SR7, and SR6 attained 0.75% VRo at 50, 8, 7, and 3 mybp and SR5 and SR4 attained 0.5% VRo at 7 and 6 mybp respectively. Chromatographic and isotope data of 108 oils and 42 PS samples show that SR7-SR8/9 vertically filled the Paleocene to mid Eocene reservoirs across the basin. Subsequently, SR6-SR5 in central Cambay and SR6-SR5-SR4 in the south charged the overlying reservoirs. Conventional and basin centered accumulations in the strata between SR7 and SR8/9 that contains free hydrocarbons under pressure is likely. Hydrocarbons generated in SR11/12, possibly lost in axial areas, may exist at margins.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia