Petrophysical Evaluation of Gas-Hydrate Formations in National Gas Hydrates Programme Expedition 02 in India

Abstract

Gas hydrates are naturally-occurring crystalline inclusion compounds. They comprise compressed molecules of gas (usually methane) that are ‘lodged’ within a solid lattice of water molecules. For this reason, the gas molecules are called ‘guests’ and the water molecules are called ‘hosts’. Gas hydrates form where there are sources of water and methane under favorable thermodynamic conditions of relatively high pressure and low temperature. Objective of the study is to evaluate Petrophysical Properties from drilled well of NGHP expedition 2 for Gas Hydrate. To identify different hydrate formation and estimation of hydrate saturation. The Work flow to estimate Petrophysical properties is guided by the high resistivity, low transit time and low density. It includes evaluation of different overlays and cross plots of wells like picket plot to firm up different parameters. Porosity is measured by density log, water saturation using Archie's equation; gas hydrate saturation using DMR method and its validation for the results obtained from Pressure core. Electrical resistivity and acoustic travel time mainly used to identify potential Gas Hydrate zones with overlay technique from density porosity and acoustic travel time and other density porosity with total NMR porosity, along with resistivity log are used for identifying potential Gas Hydrate zones in this study. Porosity estimated from density log is used for calculation Hydrate saturation. Gas Hydrate saturation is estimated using standard Archie's equation and Density Magnetic Resonance (DMR) method. Wherever NMR log data is good, saturation estimated from both are in good agreement. Log derived Gas Hydrate saturation are compared and validated with Gas Hydrate saturation obtained from pressure cores. Very good Gas Hydrate saturated zones are observed above BSR in 21 wells in the range of 40-90%. Out of these 21 wells, 16 wells are also having Gas Hydrate saturation in the range of 30-50%. Good Gas Hydrate saturation wells are mainly in area B and C in KG deep water Basin. This study will be very useful in preparation of Geological model for estimation of Gas Hydrate reservesaccurately. This study will also help in NGHP-3 for identifying suitable sites to carry out pilot production testing of Gas Hydrates.