Performance of free gases during the recovery enhancement of shale gas by CO2 injection: a case study on the depleted Wufeng–Longmaxi shale in northeastern Sichuan Basin, China
Jun Liu, Lingzhi Xie, Bo He, Peng Zhao, Huai-Yu Ding
Abstract
Abstract In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO 2 injection well (IW) and CH 4 production well (PW) are established, aiming to explore the behavior of free gases after CO 2 is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH 4 or CO 2 content in the shale fractures/matrix is invariably heterogeneous. The CO 2 involvement facilitates the ratio of free CH 4 /CO 2 in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH 4 to the free CO 2 , in the ratio of the free CH 4 /CO 2 in the matrix to that in the fractures, in the content of the recovered free CH 4 , and in the content of the trapped free CO 2 . Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO 2 in the free phase to be trapped; furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH 4 in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO 2 injection technique.