Residual Gas Saturation Investigation of Carbonate Reservoir from Western Canada

ABSTRACT

The value of residual gas saturation to water influx is a key factor for estimating recoverable reserves in gas reservoirs overlaying active aquifers or natural gas storage reservoirs. Most of our previous work investigated the determination of residual gas saturation for sandstone reservoirs with high values of porosity and permeability. However, vast gas resources are trapped in low porosity and permeability carbonate reservoirs. A number of cores from a Western Canada carbonate reservoir were tested as part of an experimental program to determine the residual gas saturation at ambient conditions. Primary and secondary spontaneous imbibition tests were performed on each core plug. Different initial water saturation conditions were used and the obtained results were compared. The centrifuge technique was used to set the initial water saturation. The initial imbibition rate was found to be the key for residual gas saturation. The effects of core plug properties were addressed. Our work also addressed the prediction of field scale recovery by application of simple scale-up laws. Different simple predictive models, which were used to fit sandstone reservoirs successfully, were tested as part of this work. The laboratory experimental results were also compared with log data to predict gas production and gas recovery of reservoir under different matrix block sizes.

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