Experimental Investigation on the Spontaneous Imbibition Characteristics of Shale under the Combined Action of CO₂ and Water

Spontaneous imbibition can impact the fluid distribution and saturation within the shale reservoirs, which, in turn, has an impact on the production and storage of shale oil and gas. The spontaneous imbibition characteristics of shale reservoirs under the CO2-brine-rock system will change. In order to understand the spontaneous imbibition characteristics of shale (before and after treatment with different pressures in CO2-brine), we researched the rock samples of shale from Chang 7 3 submember of Ordos Basin accordingly to conduct CO2-brine immersion treatment under different pressure tests, spontaneous imbibition tests (AFO), NMR T 2 tests, contact angle tests, and XRD tests. The results show that the final imbibition mass of/the initial imbibition rate of/the imbibition volume of brine and dodecane for the shale increase with the treatment pressure (CO2-brine immersion stage) increasing on the shale. It is the result of the combination of porosity, wettability, and mineral composition. Although the water wettability of the shale decreases and the relative content of water-wet (oil-wet) minerals decreases (increases), the porosity of the shale increases, so that the final imbibition mass of both brine and dodecane increases. Therefore, porosity has a greater influence on SI. CO2-water treatment at different pressures improves the spontaneous imbibition capacity of shale into water and oil, which will be beneficial to the flowback of fracturing fluid and the recovery of crude oil in the process of shale oil production.