Field Analysis of Effective Reservoir Permeabilities in Gas-Hydrate-Bearing Sediments

Timothy Collett¹, Scott Dallimore², and Steve Hancock^3
1 U.S. Geological Survey, Denver, CO
² Geological Survey of Canada, Sidney
³ APA Petroleum Engineering Inc, Calgary, AB

The Mallik 5L-38 Gas Hydrate Research Well, drilled in the Mackenzie River Delta of northern Canada, was an integral part of a field experiment to test the physical response of a gas hydrate deposit to various advanced production methods. Pressure drawdown tests were conducted on gas-hydrate-bearing sedimentary sections in the Mallik 5L-38 well using Schlumberger's Modular Dynamic Tester (MDT) tool. Conventional pressure transient analysis techniques were used to evaluate the MDT test data, yielding effective permeabilities ranging from 0.0011 to 0.13 mD. Downhole nuclear magnetic resonance (NMR) well logging also revealed high effective permeabilities within the gas-hydrate-bearing reservoirs of the Mallik 5L-38 well, with NMR derived effective permeabilities ranging from about 0.001 to 0.1 mD. Further analysis of the NMR log data from the Mallik 5L-38 well also revealed the presence of a “movable” free-water phase within gas-hydrate-bearing sandstone reservoirs. The NMR inferred free-water phase likely represents the compressive porous media fluid phase along which flow was established and measured during the MDT gas hydrate tests. The presence of an interconnected porous media fluid phase and relatively high effective permeabilities, suggests that simple reservoir depressurization techniques may be a more efficient gas hydrate production scenario than previously considered.