Microscopic CO₂ Injection in Tight Rocks: Implications for Enhanced Oil Recovery and Carbon Geo-Storage

Abstract

Carbon dioxide (CO2) injection has been widely used in conventional reservoirs for enhanced oil recovery and CO2 sequestration. Nevertheless, the effectiveness of CO2 injection in tight reservoirs is limited due to diagenetic processes that impact displacement efficiency. This research work assesses the performance of CO2 injection in tight reservoirs and evaluates oil mobilization and fluid distribution within the rock pore systems. A set of experiments, including routine core analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury injection capillary pressure (MICP), was performed on Scioto sandstone. Three core-flooding runs were conducted to evaluate oil recovery of different injection schemes, including tertiary miscible CO2 injection, secondary immiscible CO2 injection, and secondary miscible CO2 injection. A nuclear magnetic resonance (NMR) spectrometer was utilized to evaluate the fluid distribution in pre- and postflooding schemes. Results show that secondary miscible CO2 injection provided the highest displacement efficiency (E d) of 88%, with oil mobilized from both micro- and macropore systems, leading to the highest oil recovery of 93% original oil in place (OOIP). Tertiary miscible CO2 injection had E d of 67%, providing an ultimate oil recovery of 79% OOIP mostly from the macropore system. Limited contribution of micropores during the tertiary miscible CO2 injection is attributed to the increased water content as a result of previously conducted secondary water flooding. Secondary immiscible CO2 injection showed the least oil recovery among the injection schemes of 68% OOIP, which is attributed to the unstable displacement, as indicated by E d of 52%. The efficiency of pore fluid displacement was determined through NMR analyses, and the findings are in line with the displacement efficiency values obtained from core-flood experiments, with a strong positive correlation. This finding is a promising strategy for determining a suitable CO2 injection scheme in tight rocks for oil recovery and CO2 storage.

Perspectives of CO2 Injection Strategies for Enhanced Oil Recovery and Storage in Indian Oilfields

“…Even Wang et al 37 investigated the CO 2 injection in tight gas and found the same; i.e., high pressure helps gas flow more easily, and more water hinders gas flow. AlKharraa et al 38 investigated the effect of CO 2 injection in tight rocks. Tight rocks hold a lot of oil, but getting it out is tricky as a result of the ultralow permeability.…”