Reservoir Quality of Lower Jurassic Muddy Sandstone Reservoirs, Western Sverdrup Basin, Arctic Canada: An SEM Study

A. N. Chowdhury

Clayey sandstones of the Lower Jurassic King Christian Formation, deposited in progradational sequences of shelf and deltaic environments, are the principal gas reservoirs in the deeper areas (about 2,000 m and greater burial depth) of the western Sverdrup basin. The sandstones are dominantly fine-grained and argillaceous. Clay content ranges from 8% to greater than 30%. A scanning electron microscope (SEM) study of these compacted and tight sandstones revealed abundant leached porosity and microporosity in the interstitial detrital clay matrix. Clay diagenesis revealed by SEM includes dissolution of illitic clay matrix and carbonaceous clays, and growth of kaolinite and illite. Clay diagenesis occurred during intermediate to deep burial. The intensity of clay mineral tra sformation correlates well with organic metamorphic facies. Burial leaching of the clay matrix can be attributed to an increase of P_CO2 and a buildup of H⁺ in the pore fluids. Acidic fluids possibly migrated into the reservoir from the underlying and overlying source shales associated with increasing maturation temperatures.

Hydrocarbon production from the deeper reservoirs in the western Sverdrup basin will be primarily from secondary leached porosity in the clay matrix, where late-stage cementation was arrested by earlier hydrocarbon migration. Full reservoir quality and potential of these clayey sandstones can be evaluated only by detailed SEM examination of core materials and well cuttings.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.