Gas hydrate saturation and reservoir characterization at sites NGHP-02-17 and NGHP-02-19, Krishna Godavari Basin, eastern margin of India

Abstract

We have characterized the gas hydrate reservoir at Sites NGHP-02-17 and NGHP-02-19 based on isotropic and anisotropic velocity modeling by utilizing both the wireline (WL) and logging-while-drilling (LWD) data independently. The isotropic study is carried out using the simplified three phase Biot equation (STPBE) with density derived porosity and calculated bulk density of sediments as inputs. The anisotropic study uses the transverse isotropic theory for laminated media by considering a layered reservoir model composed of two components: (i) fractures filled with 100% gas hydrates and (ii) isotropic medium composed of water-saturated sediments. In the anisotropic velocity modeling, the reservoir is modeled by incorporating fractures with varying dip angles from 0° to 90°. We estimated gas hydrate saturations using isotropic and anisotropic velocity analysis at both Sites NGHP-02-17 and NGHP-02-19. In both the cases the LWD data derived isotropic model yielded, what appears to be the most accurate values, an average saturation of 45.8% in the high velocity interval between 269 and 285.5 mbsf at Site NGHP-02-17 and 33.8% in the high velocity interval between 306 and 312 mbsf in NGHP-02-19.