CO 2 flooding is widely recognized as an efficient way of developing tight reservoirs. Multiple types of minerals in tight rocks may interact with introduced CO 2 , resulting in more complex mechanisms of tight reserve recovery from tight reservoirs. It is necessary to reveal the impact of core minerals on tight oil recovery, which is critical in understanding the fundamental mechanisms of CO 2 flooding for enhanced tight reserve recovery. In this work, 18 tight core samples, retrieved from the Changqing oilfield, are characterized to obtain their mineral compositions. Three typical core samples are then selected to conduct CO 2 flooding and investigate how the minerals contained in these tight cores affect the tight oil recovery during CO 2 flooding using the nuclear magnetic resonance technique. On the basis of the characterization results, Changqing tight cores mainly contain three typical minerals, i.e., illite, montmorillonite, and quartz. With regard to illite-dominated cores, CO 2 is not efficient in extracting oil from the smaller pores when the injection pressure is lower than the minimum miscible pressure (MMP); on the contrary, crude oil can be efficiently recovered from both the smaller and larger pores when the injection pressure is beyond the MMP. With regard to the montmorillonite-dominated core, oil saturation in the medium pores increases when CO 2 is injected. However, with regard to the quartz-dominated core, oil residing in both the smaller and larger pores is significantly recovered after CO 2 injection. This work may help understand the question of how the minerals residing in core samples affect oil recovery from a pore-scale perspective.
Comprehensive knowledge of the absolute adsorption of light hydrocarbons and CO 2 is significant for shale reservoir assessment and CO 2 stimulation optimization. In this work, excess adsorption isotherms are first obtained for CH 4 , n-C 4 H 10 , and CO 2 on typical shale. The simplified local density (SLD) theory is then used to obtain the adsorption-phase density for CH 4 , n-C 4 H 10 , and CO 2 in organic pores, which is then employed for absolute adsorption calculation. The absolute adsorption of CH 4 , n-C 4 H 10 , and CO 2 is compared to prove the potential of CO 2 for shale hydrocarbon recovery as well as CO 2 sequestration in shale reservoirs. The results show that CH 4 , n-C 4 H 10 , and CO 2 can form adsorption layers and result in a much higher adsorbed phase density than that at the pore center. Based on the SLD theory, C 4 H 10 shows the highest adsorbed density on the shale surface than CO 2 and CH 4 at all pressure ranges. In addition, absolute adsorption is higher than the excess values in line with the previous molecular simulation methods. Absolute adsorption is calculated in the order of n-C 4 H 10 > CO 2 > CH 4 , indicating the suitability of CO 2 for CH 4 recovery but also that it may not be feasible for recovering heavier hydrocarbons, i.e., n-C 4 H 10 . This study provides insights into the mechanism of shale resources recovery using CO 2 method, which is theoretically crucial for shale resource assessment and production optimization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.