Estimation of Residual Gas Saturation from Different Reservoirs

ABSTRACT

Residual gas saturation is a crucial number to estimate the gas recovery in gas reservoirs with active aquifers. Water influx in gas reservoirs has long been recognized as an important cause of gas trapping in water-wet reservoirs. In this study, the residual gas saturation to water influx was investigated in 47 core plugs, including 29 sandstone plugs from different areas, 2 Berea sandstone plugs and 16 carbonate plugs. Over 100 different experiments were performed, including spontaneous water imbibition and forced water imbibition tests, primary imbibition and secondary imbibition tests, counter current and co-current imbibition tests. Measurements indicated that the value of residual gas saturation depends on many factors, including reservoir properties, the capillary number, experimental procedures, fluid properties and also very strongly depends on the gas solubility and compressibility. The residual gas saturation value from primary and secondary imbibition tests was also used to compare against literature models. Modified models were developed in order to fit the experimental data better.

The residual gas saturation results show that gas recovery should be high under spontaneous imbibition and extremely high under the forced imbibition. However, trapped gas in reservoirs with active aquifers remains as high as 90%. Hopefully this paper can provide some insight for enhance gas recovery in gas reservoirs with active aquifers.

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