Prediction of pore pressure and fracture pressure from well log data in a gas hydrate reservoir of the Krishna-Godavari basin

Pore pressure is the pressure exerted by the fluids within pore space of a reservoir formation while, fracture pressure is the pressure in the wellbore at which formation wall of a wellbore will crack. The detection of over pressure zone is necessary to manage the risks and uncertainties associated with drilling. Pore pressure as well as the fracture pressure affects the well design, such as mud weight profile and casing depth. These parameters in gas hydrate bearing sediments are estimated from sonic logs in two wells (NGHP-01-10A and NGHP-01-03) located in Krishna Godavari (K-G) basin, eastern continental margin of India (ECMI), using various methods such as Eaton's, Bower's and Miller's. After analysing pore pressure estimated from various methods in two wells, pore pressure estimation from Eaton's sonic shows close correspondence to the available pressure core measurements in the selected depth intervals in well NGHP-01-10A. The estimated pore pressure and fracture pressure ranges from 10.05 to 15.21 and 16.61 to 19.29 MPa for well site NGHP-0110A in the depth range from 1062.05 to 1225.88 m and 12.11 to 14.75 MPa and 16.68 to 20.21 MPa for well site NGHP-01-03 in the depth range from 1140.38 to 1363.80 m. The vertical stress varies from 17.74 to 20.39 MPa in well NGHP-01-10A and 17.94 to 20.91 MPa in well NGHP-01-03 for the whole depth of the logs. The normal pore pressure has been observed in gas hydrate bearing sediments in both the wells. The magnitude of pore pressure slightly increases below bottom simulating reflector (BSR), which may indicate presence of free gas in the study area.