Diagenesis, Magnetism and Geomechanics of the Mallik 5L-38 Gas Hydrate Reservoir, Mackenzie Delta, Canada

Nicholas S. F. Wilson¹, Randolph J. Enkin², Patrick J. McLellan³, Carmel Lowe², Chris G. Podetz³, Scott R. Dallimore², Mostafa Fayek⁴, and Bruce Taylor^5
1 Geological Survey of Canada Calgary, Calgary, AB
² Geological Survey of Canada - Pacific, Sidney, BC
³ Advanced Geotechnology Inc, Calgary, AB
⁴ University of Tennessee, Knoxville, TN
⁵ Geological Survey of Canada, Ottawa, ON

The roles of diagenesis and geomechanics in the permafrost gas hydrate setting were examined by three independent studies on the Mallik 5L-38 Gas Hydrate Production Well, NE Mackenzie Delta, Canada.

Gas hydrate bearing sands are locally well-cemented by dolomite-calcite cements. Previous research suggested a genetic link between gas hydrate emplacement, dolomite cementation, and pyrite formation in relation to expulsion of saline and reduced fluids from gas hydrate zones. To constrain the diagenetic and geochemical evolution of carbonate and pyrite cement formation and their relationship to gas hydrate emplacement, petrographic and paragenetic studies were integrated with major/trace element geochemistry, and stable isotopic analyses.

Magnetic study of the Mallik core demonstrated that the hydrate-bearing strata differ significantly from other strata. Magnetite, apparent in silt horizons that are too tight to contain hydrate deposits, is reduced to iron sulfide in the gas-hydrate-bearing sand horizons. Magnetic properties from both permafrost and marine settings are investigated in the effort to develop a magnetic remote sensing method for gas hydrate exploration.

Vertical stress magnitudes in the Mallik area were investigated by analyzing bulk density log and core data. Minimum horizontal in-situ stress magnitudes were estimated from leak-off test data and a profile of micro-fracture stress tests. The principal horizontal in-situ stress orientations have been determined from local structural geology, borehole breakouts, deformed-hole-ellipticity and shear velocity anisotropy. FMI image logdata revealed a total of 47 fractures over the logged interval, of which 34 are natural. Natural fracture development varies with depth and is influenced by lithology.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005