Saturation, Acoustic Properties, Growth Habit, and State of Stress of a Gas Hydrate Reservoir from Well Logs

Abstract

Gas hydrates are a class of solid ice-like substances that form when water and natural gas combine at high pressure and low temperature, conditions that are found in and below permafrost, and in the shallow sediments of continental slopes. This paper describes the responses of resistivity, nuclear, sonic, and nuclear magnetic resonance logging tools to gas hydrate-bearing sediments. Gas hydrate saturation is estimated by a combination of density and magnetic resonance porosity logs, and by resistivity measurements. These methods generally agree except where the borehole is washed out. The dipole sonic log is used to estimate the orientation and magnitude of maximum and minimum horizontal stresses. Vertical stress is found by integrating the density log over true vertical depth. Results agree with mechanical measurements made in an offset well. A combination of magnetic resonance and sonic measurements is used to determine the pore scale growth habit of gas hydrate. The growth habit in the marine sediments studied here appears to be different from that found in the Arctic. However, both are consistent with hydrate-bearing sediments that are liquid-water-wet.