Pesca Pubblicazione scientifica Residual gas saturation investigation of a carbonate reservoir from Western Canada FILONE TECNOLOGICO TEMA produzione e cattura RIASSUNTO AbstractThe 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.IntroductionGas reservoirs with naturally occurring underlying aquifers and aquifer gas storage projects both offer possibilities for large volumes of gas to be trapped. A typical carbonate gas reservoir was studied to define the magnitude of trapped gas saturation from both laboratory experiments and well logging investigation. The experimental research followed the research work presented in Ding and Kantzas1, while the residual gas saturation of several gas reservoirs including both sandstone reservoirs and carbonate reservoirs were also investigated (Kantzas et al.2).Most of the research related to imbibition in heterogeneous formations deals with the problem of oil recovery from fractured reservoirs. Not much information was found in the literature regarding recovery from gas reservoirs. Even less information is available on the subject of residual gas saturation from imbibition in carbonate reservoirs. The common conception is that many of the principles that cover oil and gas reservoirs should be the same.Literature data with experiments on residual gas saturation can be found in Geffen et al3. and in Keelan and Pugh4. Geffen et al3. observed a small apparent effect of rate on the value of the residual gas saturation. They also concluded that trapped gas bubbles tend to leave the pore system by diffusion in order to establish thermodynamic equilibrium. They claimed that such diffusion effects should be of little importance in the recovery of gas from reservoirs. When they performed primary and spontaneous imbibition tests (on dry cores) they found that completely submerging the core in water had the disadvantage of mechanically trapping gas in the central portion of the core as water invaded from all directions thus complicating interpretation of the data. They observed that the residual gas saturation values measured on dry cores by water imbibition are essentially the same as those values measured by flow tests starting with connate water in the core. DATA Data di pubblicazione: 04/04/2013 AUTORI DING MINGHUA KANTZAS APOSTOLOS ENTE DI AFFERENZA UNIV CALGARY & TIPM LAB RIVISTA SPE Gas Technology Symposium, 30 April-2 May, Calgary, Alberta, Canada