Influence of Typical Core Minerals on Tight Oil Recovery during CO2 Flooding Using the Nuclear Magnetic Resonance Technique

CO2 flooding is widely recognized as an efficient way of developing tight reservoirs. Multiple types of minerals in tight rocks may interact with introduced CO2, 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 CO2 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 CO2 flooding and investigate how the minerals contained in these tight cores affect the tight oil recovery during CO2 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, CO2 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 CO2 is injected. However, with regard to the quartz-dominated core, oil residing in both the smaller and larger pores is significantly recovered after CO2 injection. This work may help understand the question of how the minerals residing in core samples affect oil recovery from a pore-scale perspective.