EVALUATION OF THE DIAGENETIC AND STRUCTURAL INFLUENCES ON HYDROCARBONENTRAPMENT IN THE CARDIUM FORMATION, DEEP BASIN, WESTERN ALBERTA

In the Deep Basin of Alberta, a northwest-trending boundary separates hydrocarbon prone rocks in the west (downdip) from water-bearing rocks in the east (updip). This boundary represents a discontinuity or inte rruption in reservoir character. Otherwise, the updip water would exch ange positions with the downdip hydrocarbons. Possible mechanisms incl ude facies change, diagenetic effect or faulting. An analysis of the C ardium main sand based on thin section, capillary pressure data and st ructural information was performed in an effort to determine the contr olling factors on the location of the oil/water boundary. In the area of study the Cardium main sand forms a quasi-continuous sand unit acro ss the oil/water boundary, minimizing facies change as a trapping mech anism. Capillary pressure information and analysis of thin sections ha s shown that the sandstones on the downdip (oil side) of the boundary are more cemented than those updip resulting in distinctly smaller por e throat sizes downdip. This pattern of capillarity is the reverse req uired for using a diagenetic change to explain the present fluid confi guration, indicating that a diagenetic change is not the trapping mech anism. Structural analysis involving trend surface residuals has shown that the location of the hydrocarbon/water boundary coincides with a change in structural style. A structural interpretation should therefo re be considered as a viable explanation of the hydrocarbon/water boun dary of the Deep Basin.