Synthesis of deep multichannel seismic and high resolution sparker data: Implications for the geological environment of the Krishna–Godavari offshore, Eastern Continental Margin of India

Abstract

Proven hydrocarbon occurrence in the Krishna Godavari (KG) basin, a part of the Eastern Continental Margin of India initiated intense exploration activities to discern the potential hydrocarbon bearing structures/payoff zones. Recent discovery of gas hydrates in its offshore triggered detailed exploration measures adopting advanced seismic data acquisition techniques supported by deep drilling to understand its genesis. Interpretation of Multichannel Seismic (MCS) sections highlighted several distinct horizons from Lower Cretaceous to Recent in the sediment overburden, and the nature and configuration of the underlying crust. The sections also depicted the presence of growth faults, shale bulging, toe thrust faulting, delta progradation, active sliding/slumping, buried channels, pinchout structures and reflection free zones, indicating the different types of sedimentary processes, varied geological environments and neotectonic activity in the KG offshore. High resolution sparker (HRS) data revealed subsidence, gas/fluid expulsion pathways, occasional diapiric intrusions and growth faulting in the upper slope, and toe thrust faulting, upthrust and diapiric intrusions in the lower slope. The mid slope is characteried by a well stratified E–W trending basin bounded by upthrust and diapirism. The entire region is associated with gas escape features (blanking zones, columnar type gas vents, fault controlled mud/shale diapirs, large dimension gas saturated zones and pockmarks). The growth faults, shale bulging and toe thrusting seen in the MCS data since Oligocene time could be linked to shale diapirism, upthrust, gas/fluid expulsion, subsidence and mini-basin formation observed on the shallow HRS records. Synthesis of these datasets suggests that the distribution of gas hydrate in the shallow sediments may be controlled by the deeper structural and tectonic configuration. Therefore, knowledge about shallow sedimentary column and its connectivity with deeper strata through faults/fractures and other structural features, and the geological architecture are significantly important to evaluate the genesis of gas hydrates.