Assessment Of Heat Flow And Gas-hydrate In Krishna Godavari Basin , Constrained From 2 D / 3 D Seismic And Well Log Data

Abstract

Bottom simulating reflector (BSR), representing the base of the gas hydrate stability zone (BGHSZ), is observed over a closely spaced 2D/3D seismic profiles on the continental slope in the Krishna Godavari (KG) basin, eastern continental margin of India. The data reveal that gas hydrate occurs in the KG basin at places where water depths exceed ~850 m. The thickness of the gas hydrate stability field inferred from the BSR on seismic section ranges up to ~250 m. A conductive model was used to calculate the heat flow from the depth of BSR. A regional trend is observed, in which heat flow decreased landward across the basin from an average of ~63 mW/m to ~23 mW/m. A series of Logging-while-Drilling (LWD) and conventional wire-line logs were acquired during the India National Gas Hydrate Program (NGHP) Expedition 01 at several sites across the (KG) Basin. Several approaches exist, each making specific assumptions with respect to how gas hydrate forms in sediment pore space. The preferred methods are effective porosity reduction, using a no-hydrate reference velocity (an empirical approach), and effective medium modeling using a gas hydrate in-frame rock physics model. For both methods, the mode by which gas hydrate forms in sediment pore space represents a significant uncertainty. Here, we utilized electrical resistivity log data from the KG basin to estimate gas hydrate saturation. Since, gas hydrate bearing sediment has higher electrical resistivities than that of the host sediment, we estimate two levels of gas hydrates saturations up to 25% in the depth interval between 70 to 82, and less than 20% in the depth interval between 90 to 104 meter below the seafloor using the resistivity log data at site 15 of NGHP-01.