PNNL

Abstract

The determination of microscopic residual gas distribution is bene?cial for exploiting reservoirs to their maximum potential. In this work, both forced and spontaneous imbibition (water?ooding) experiments were performed on a high-pressure displacement experimental setup, which was integrated with nuclear magnetic resonance (NMR) to reveal the impacts of capillary number (Ca) and initial water saturation (Swi) on the residual gas distribution over four magnitudes ofinjectionrates(Q = 0.001,0.01,0.1and1mL/min),expressedasCa(logCa =-8.68,-7.68,-6.68and -5.68), and three di?erent Swi (Swi = 0%, 39.34% and 62.98%). The NMR amplitude is dependent on pore volumes while the NMR transverse relaxation time (T2) spectrum re?ects the characteristics of pore size distribution, which is determined based on a mercury injection (MI) experiment. Using this method, the residual gas distribution was quanti?ed by comparing the T2 spectrum of the sample measured after imbibition with the sample fully saturated by brine before imbibition. The results showed that capillary trapping e?ciency increased with increasing Swi, and above 90% of residual gas existed in pores larger than 1 µm in the spontaneous imbibition experiments. The residual gas was trapped in pores by di?erent capillary trapping mechanisms under di?erent Ca, leading to the di?erence of residual gas distribution. The ?ow channels were mainly composed of micropores (pore radius, r 10 µm) at logCa =-5.68. At both Swi= 0% and 39.34%, residual gas distribution in macropores signi?cantly decreased while that in micropores slightly increased with logCa increasing to-6.68 and-5.68, respectively.