The Effect of Partial Molar Volume on Water-shielded Oil Recovery Time by Miscible Gas Injection

Tertiary miscible gas injection is widely used after waterflooding in order to recover the remaining oil in the reservoir. In water-wet media, the thin water film present on the surface of the reservoir rock coalesces into a water layer in some narrower throats, impeding direct contact between the oil behind and the injected gas on the other side. However, the injected gas manages to reach the oil ganglion through dissolving in water and diffusing into oil, causing it to swell gradually and break the water barrier if given enough time. This phenomenon is generally referred to as “water shielding”.

Several models have been previously proposed to estimate the required time for water-shielded oil to break the water barrier, all of which suffer from either requiring measurement of experimental parameters such as partition coefficient or neglecting the gas volume change due to non-ideal mixing. In this study, a new model has been developed which takes into account the partial molar volumes of oil and gas components, and also depends solely on temperature, pressure and fluid compositions as input parameters. The model has been used to investigate the effect of volume change caused by non-ideal mixing on the recovery time of water-shielded oil.