Abstract

The study aims to determine the depositional facies, high resolution sequence stratigraphy and diagenetic processes of Early Oligocene carbonates in N & N-W of Heera, Mumbai Offshore. Foraminiferal assemblage and microfacies from cores of Well A, B, C, D and E are indicative of facies association related to four depositional environments i.e., restricted inner lagoons-tidal flats, shallow open lagoons, high energy carbonate bars-shoal complex and deeper mid-ramps of a westerly dipping homoclinal carbonate ramp. Two high frequency (4th Order) depositional sequences bounded by sequence boundary, DS1 and DS2 displaying hierarchical stacking pattern are identified and correlated across wells. Furthermore, the study highlights the influence of vadose zone diagenesis resulting from short diastems/subaerial exposure. This diagenetic process has led to the development of favorable porosity in the highstand systems tract (HST) carbonates and effecting the underlying transgressive systems tract (TST) sediments in Well D, C, and E. Vadose zone diagenesis effect during short diastem/ subaerial exposure have rendered good porosity due to dissolution in HST carbonates and occasionally effected underlying TST sediments (Well D, C and E). By mapping and correlating the sequences, the study identifies thin carbonate bars that hold potential as reservoirs. These carbonate bars are envisaged to extend along Wells E, D, and C in northwest-southeast trend. Furthermore, a more pronounced development of these carbonate bars, oriented in the same direction, and are anticipated towards the western extent of the study area.