Evaluation of Gas Saturation During Water Imbibition Experiments

Abstract

Knowledge of gas saturation history is very important in determining gas recovery from gas reservoirs with water influx. Water imbibition is known to control gas recovery. Spontaneous imbibition experiments have been traditionally employed to determine gas saturation. On-line NMR relaxometry is introduced as a method for monitoring co-current imbibition. A group of plugs from a Western Canadian sandstone reservoir were selected and a series of imbibition tests were run. NMR was used to measure the amount of water imbibed in the cores and the gas saturation during each experiment was, in turn, measured. The values of final residual gas saturation and the production profiles were compared to the results from corresponding counter-current imbibition tests. The correlations of residual gas saturation with initial imbibition rate and other operating parameters were investigated. Through interpretation of the NMR spectra, bound water T 2cutoff values were obtained. Water distribution in different pore sizes during the experiments was also calculated. The initial imbibition rate in different pore sizes was measured. Empirical equations from the literature, which were used to describe the behaviour of co-current imbibition tests, were applied to the experimental data. The proposed methodology can be used to evaluate the mechanisms of water imbibition in gas reservoirs.