Regional stratigraphic framework and gas hydrate occurrence offshore eastern India: Core-log-seismic integration of National Gas Hydrate Program Expedition 02 (NGHP-02) Area-B drill sites

摘要

The Indian National Gas Hydrate Program Expedition 02 (NGHP-02) was designed to study the occurrence of gas hydrate along the passive continental margin of the Indian Peninsula in the Bay of Bengal. Twelve holes were logged and measured with logging-while-drilling (LWD) and five holes were cored in Area-B of NGHP-02. The LWD and coring results in Area-B helped to understand the geological significance of sequence stratigraphy in Krishna-Godavari Basin and identified the occurrence of gas hydrate. This study summarized the log- and litho-units in Area-B and establish three integrated units based on the core-log-seismic integration. Most of the downhole log and core inferred gas hydrate occurrences are in the Late Miocene Integrated-Unit B with several sets of reservoir sections exhibiting favorable conditions for hosting gas hydrate. The gas hydrates reservoirs associated with reflectors R1 and R2 were identified and the R1 reservoirs are characterized by fracture- and pore-filling gas hydrate, and the R2 is in sand-rich sediments with pore-filling gas hydrate at high saturations. The thickness variations associated with the R1 and R2 are possibly associated with the development anticlinal structure and are likely related to syn-sedimentary growth of the folding structures. Major gas hydrate zones exist in and around the R1 and R2 near the BSR depth, and mostly have coincident with the fractures and mass-transport deposits. The spatial distribution of gas hydrate in the R1 and R2 reservoirs is highly influenced by the anticlinal structure. This study can be considered a good case for the future gas hydrate studies and explorations in the nearby areas.