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VINOPAL, ROBERT J., and LOUIS TAYLOR, Standard Geological Services Inc., EngleAood, CO; and JOEL MARKS, Texaco Inc., Denver, CO

Abstract: Revisiting the Rocks - Upper Almond Formation: Table Rock Field, Sweehwater County, Wyoming, USA

The Upper AJmond Formation at Table Rock Field is a cyclic sequence of marsh, mudflat, lagoon, tidal channel, barrier bar and shoreface deposits. Approximate total production is 202 BCFG and 4.7 MMBO. Matrix porosity in Upper Almond sublithic and feldspathic sandstones consists of interganular porosity, microporosity and dissolution porosity. Principal diagenetic parameters affecting porosity in Almond sandstones include degree of silica cementation, ductile grain compaction, clay cementation, and grain dissolution. Faces related porosity parameters are grain size, sorting and sandstone composition. Dissolution porosity, formedd through leaching of rock fragments and feldspar grains, is fairly well connected to the intergranular pore system. Three authigenic clay cements are present in the sandstones: illite, mixed-layer illite smectite, and kaolinite. The high surface area of authigenic clays effects water saturation calculations. Potential completion problems associated with clays are fines-migration and clay expansion. Kaolinite platelets and illite fibers are both common and can break loose and migrate and potentially lodge in pore throats. IlIite and illite-smectite clays partially block pore throats and are the principal cause of permeability reduction. Extensive acid treatment of Upper Almond Sandstones should be avoided. The lack of natural fractures is conspicuous in the cores studied. Except for coal beds, natural natural fractures are absent. The scarcity of open natural fractures in the sandstones indicates that horizontal wellbores will not encounter conduits of higher vertical permeability.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana