Organofacies and source evaluation of Cambay Shale Formation to assess unconventional hydrocarbon potential in Jambusar–Broach area, Cambay Basin, India

The Cambay Basin, on the western continental margin of India, is infilled with transgressive Paleocene to early Eocene Cambay Shale Formation. Cores, electrolog data and correlations, and geochemical data allow organofacies characterization of the formation in the Jambusar–Broach area. Eleven transgressive–regressive sequences have been identified within the formation based on electrolog characteristics. Sedimentological analysis indicates that the bottom fining-upward part of these sequences is rich in organic matter. Geochemical data of these sequences of the formation is evaluated in terms of total organic carbon (TOC), source potential (S1 and S2) and thermal maturity index (Tmax). This clearly shows that the formation is a potential source rock for oil/gas generation, mostly with type III and minor contribution of type II organic matter. Vitrinite reflectance (VRo) data suggest that the formation is in the early to late oil generation window. However, an extrapolated trend of VRo vs. depth shows that the formation is falling within a gas window in the deeper part. The geochemical model based on the computed parameters (TOC, HI, source thickness and kinetics) is integrated with the available geological model of the study area. Then, 3D petroleum system modeling is carried out for evaluation of the source potential of the Cambay Shale Formation. Finally, play chance mapping (PCM) is attempted to identify sweet spots. Thus, the overall approach assists in the exploration of unconventional plays in the area.