Heterogeneity characterization from sequence stratigraphic analysis of Paleocene-Early Eocene Cambay Shale formation in Jambusar-Broach area, Cambay Basin, India

The heterogeneity of shale is significant for the evaluation and prediction of shale gas reservoir. In terms of core observations, electrolog data and correlations, the macroscopic and microscopic heterogeneity of Cambay Shale Formation, Cambay Basin, India is characterized and discussed at different scales. The formation is deposited through Paleocene to early Eocene due to marine transgression in the basin. Upper contact of the formation is represented by the Early/Middle Eocene hiatus or ?Y? marker, a 2nd order sequence boundary. The formation is subdivided as Older Cambay Shale (OCS) member and Younger Cambay Shale (YCS) member by Paleocene top or ?Neck? marker, a 1st order sequence boundary. Cambay Shale is the primary source rock of hydrocarbon in the basin and is considered to be homogenous. Log motif and core analysis suggest that the Cambay Shale is not homogeneous ?shale?. Based on sequence stratigraphic analysis, a total of eleven lower order high frequency (3rd order) transgressive-regressive (T-R) sequences have been identified, seven within YCS member (Early Eocene, i. e. between ?Y? and ?N? Marker) and remaining four in OCS member (Paleocene, i.e. below ?N? Marker). These T-R sequences are thick in southern or central part of the basin while thinning towards the basin margin. The Cambay Shale Formation is divisible into three types of facies based on core studies. The top part of each T-R sequence is attributed with coarsening upward HST while the bottom part is fining upward TST, separated by marine flooding events. Quartz and carbonate mineral fractions are dominant in HST as compared to TST of each sequence. This approach of heterogeneity characterization from sequence stratigraphic analysis helps in identification of different sequences (T-R sequences) and provides clues in identifying broader distribution of brittleductile couplets within each T-R sequence in the heterogenous Cambay Shale Formation. This gives an impetus to identify suitable prospective locales to explore unconventional hydrocarbon potential in the study area.

Automated summary

The heterogeneity of Cambay Shale Formation in Cambay Basin, India has been characterized and discussed at different scales through core observations, electrolog data, and correlations. Sequence stratigraphic analysis identified eleven T-R sequences with different facies distribution within the formation, providing clues for exploring unconventional hydrocarbon potential in the study area.