Shut-in after fracturing is generally adopted for wells in shale oil reservoirs, and imbibition occurring in matrix nanopores has been proven as an effective way to improve recovery. In this research, the molecular dynamics (MD) simulation was used to investigate the effects of wettability and pressure on nanopores imbibition during shut-in for a typical shale reservoir Jimsar. The results indicate that the microscopic advancement mechanism of the imbibition front is the competitive adsorption between “interfacial water molecules” at the imbibition front and “adsorbed oil molecules” on the pore wall. The essence of spontaneous imbibition involves the adsorption and aggregation of water molecules onto the hydroxyl groups on the pore wall. The flow characteristics of shale oil suggest that the overall push of the injected water to the oil phase is the main reason for the displacement of adsorbed oil molecules. Thus, shale oil especially the heavy hydrocarbon component in the adsorbed layer tends to slip on the walls. However, the weak slip ability of heavy components on the wall surface is an important reason that restricts the displacement efficiency of shale oil during spontaneous imbibition. The effectiveness of spontaneous imbibition is strongly dependent on the hydrophilicity of the matrix pore's wall. The better hydrophilicity of the matrix pore's wall facilitates higher levels of adsorption and accumulation of water molecules on the pore wall and requires less time for “interfacial water molecules” to compete with adsorbed oil molecules. During the forced imbibition process, the pressure difference acts on both the bulk oil and the boundary adsorption oil, but mainly on the bulk oil, which leads to the occurrence of wetting hysteresis. Meanwhile, shale oil still existing in the pore always maintains a good stratified adsorption structure. Because of the wetting hysteresis phenomenon, as the pressure difference increases, the imbibition effect gradually increases, but the actual capillary pressure gradually decreases and there is a loss in the imbibition velocity relative to the theoretical value. Simultaneously, the decline in hydrophilicity further weakens the synergistic effect of pressure difference because of the more pronounced wetting hysteresis. Thus, selecting an appropriate well pressure enables cost savings and maximizes the utilization of the formation's natural power for EOR.

A single geological carbon dioxide (CO2) storage within salinity aquifer as a paramount stratagem in the context of forthcoming CO2 sequestration initiatives. Within the expansive tapestry of terrestrial salinity aquifers in China, replete with nuances in mineral composition and structural diversity, a paradigm distinct from the marine sedimentary basins of North America, a labyrinthine stratigraphic environment of elevated complexity unfolds. Consequently, conspicuous lacunae and insufficiencies manifest within the existing knowledge reservoir pertaining to CO2-water-rock (mineral) reaction mechanisms. Notably, a conspicuous dearth of insights prevails concerning the dissolution kinetics inherent to individual minerals embroiled in these reactions. The present investigation undertakes a scrupulous exploration into the dissolution and erosive processes manifest within four emblematic terrestrial minerals in conjunction with CO2. Furthermore, the study meticulously scrutinizes the evolution of ionic composition and pH within the formation water throughout the trajectory of the geochemical reactions. To accomplish this, a simulation apparatus is configured to emulate conditions germane to temperature, pressure, and mineralization characteristics characteristic of a prototypical salinity aquifer reminiscent of the Daqing oilfield in China. The findings that emerge from this scrutiny reveal that the erosive action of CO2 fluid begets varying degrees of dissolution within the four minerals under investigation. Moreover, our meticulous inquiry lays bare that, in the terminal phases of the reaction process, feldspar precipitates secondary minerals, characterized primarily by dawsonite, in response to the aquatic milieu typifying the profound salinity stratum of terrestrial sedimentation. This milieu is notably enriched with Na+ ions and NaHCO3. This phenomenon suggests that feldspar, under these specific conditions, assumes the mantle of a mineral amenable to carbon sequestration, thus enriching the reservoir for CO2 mineralization within the salinity stratum of terrestrial sedimentation.