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 CO2 injection well (IW) and CH4 production well (PW) are established, aiming to explore the behavior of free gases after CO2 is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO2 involvement facilitates the ratio of free CH4/CO2 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 CH4 to the free CO2, in the ratio of the free CH4/CO2 in the matrix to that in the fractures, in the content of the recovered free CH4, and in the content of the trapped free CO2. Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped; furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH4 in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO2 injection technique.
Highlights
Current knowledge strongly supports CO2 sequestration in geological formations as a promising approach to respond to the issue of excessive anthropogenic CO2 emissions into the atmosphere, which is treated as carbon-negative technology and has been receiving growing attention (Abidoye et al 2015; Zhang et al 2015; Wan and Liu 2018; Liu et al 2020; Rani et al 2020; Řimnáčová et al 2020)
This work separately studies the performance of free CH4 or free CO2, and the dynamic interaction between free C H4 and free C O2 during the recovery enhancement of shale gas by C O2 injection into the depleted Wufeng–Longmaxi shale, under variable injection well (IW)–production well (PW) locations
This heterogeneous tendency is similar to the vertical variation of the fracture/matrix porosity of the Wufeng–Longmaxi shale shown in Fig. 1, owing to the free gas content being directly determined by the free space under the depleted reservoir pressure
Summary
Current knowledge strongly supports CO2 sequestration in geological formations (e.g., shale and coalbed) as a promising approach to respond to the issue of excessive anthropogenic CO2 emissions into the atmosphere, which is treated as carbon-negative technology and has been receiving growing attention (Abidoye et al 2015; Zhang et al 2015; Wan and Liu 2018; Liu et al 2020; Rani et al 2020; Řimnáčová et al 2020). It was found that a single experimental methodology was usually performed at a restricted scale, and could hardly recognize the free CO2 and free C H4 from the C O2–CH4 mixture at the same time during the dynamic CO2–CH4 interaction in shales Given this situation, physics-based numerical simulations can be employed to address concerns about the free gases during the shale-based CS-EGR process, in which multi-factors can be investigated in a clear and transparent manner. There are two examples; one is that numerical work advocated that the portion of free gas is always less than that of adsorbed gas in the process of C O2–CH4 interplay in shales, under variable reservoir permeability and temperature/pressure (Mohagheghian et al 2019) Another modeling study has suggested that an increase in the ratio of the free C H4 to adsorbed C H4 would decrease the CO2 sequestration potential of the Utica shale formation (Tao et al 2014). Such field data provide a basis for the model development in this numerical work, ensuring this model is as close to the real formation conditions as possible
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
