Effect of Initial Water Saturation on Spontaneous Water Imbibition

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe effect of initial water saturation on gas recovery by cocurrent spontaneous water imbibition and imbibition rate was investigated both theoretically and experimentally. Equations correlating initial water saturation, gas recovery, imbibition rate, rock/fluid properties, and imbibition time were derived and used to conduct the theoretical analysis. These equations foresee that gas recovery and imbibition rate could increase, remain unchanged, or decrease with increase in initial water saturation, depending on rock properties, the quantity of residual gas saturation, the range of initial water saturation, and the units used in the definitions of gas recovery and imbibition rate. The theoretical predictions were verified experimentally by conducting spontaneous water imbibition at five different initial water saturations, ranging from 0 to about 50%. Water phase relative permeabilities and capillary pressures were calculated using the experimental data of spontaneous imbibition. The effects of initial water saturation on residual gas saturation, water phase relative permeability, and capillary pressure were also studied experimentally. The results in different rocks were compared. It was found that the residual gas saturation by spontaneous imbibition in a fired Berea sandstone sample (clay was removed by firing) was lower than in a natural Berea sandstone sample (clay was not removed). This demonstrates significant wettability alteration caused by firing. In other words, there may be significant wettability differences among different gas-liquid-rock systems.

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“…Li et al (2002) did water-gas COCSI tests on Berea sandstone at different initial water saturations. The final gas recovery decreased with increase in the initial water saturations.…”

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“…They also tested the effect of initial water saturation on the performance and observed that the existence of initial water saturation causes higher ultimate recovery from the surfactant solution imbibition. The existence (Weisbord et al, 2002;Babadagli, 2003c) and amount (Li et al, 2002) of initial water saturation are critical on the recovery and there would be considerable amount of water left from primary and secondary recovery applications in the matrix. These observations showed that additional recovery with surfactant solutions is a possibility after completed imbibition recovery with brine.…”

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“…Several researchers [19][20][21] have observed that recovery for fixed volumes of water increases in a manner that is proportional to t . In capillary-driven processes, recovery is due to imbibition.…”