Experimental Investigation on the Countercurrent Imbibition Distance and Factors Influencing the Imbibition Recovery of Carbonated Fracturing Fluid

Summary The integration of fracturing, energy enhancement, and imbibition (IFEI) has proven successful in shale oil development, with one of the keys to enhancing development efficiency lying in improving imbibition effectiveness during the well shut-in phase. Carbonated water (CW) imbibition effectively combines the advantages of CO2 and water for enhanced oil recovery. Nevertheless, research on its performance in shale oil reservoirs remains scarce, and its application in fracturing has not been investigated. This study, for the first time, proposes using CW as a dispersion medium in the formulation of carbonated fracturing fluid to enhance IFEI development in shale oil. Computed tomography (CT) online scanning experiments were specifically designed to investigate the countercurrent imbibition distance (CID) and recovery (CIR) across various fluids, including formation water, nanovariable viscosity slickwater (NVS) fracturing fluids, and the newly formulated carbonated fracturing fluid. Additionally, separate imbibition experiments were carried out to assess the overall imbibition recovery of these fluids, focusing on exploring various factors influencing the imbibition of carbonated fracturing fluid. CT scans reveal that carbonated fracturing fluid significantly enhances imbibition performance, achieving a CID of 1.75 cm and a CIR of 6.95%. Compared with formation water and NVS fracturing fluids, it exhibits increases in CID by 0.75 and 0.25 cm, and improvements in CIR by 4.77 and 1.90%, respectively. Further insights from the imbibition experiments demonstrate that carbonated fracturing fluid achieved the highest recovery at 29.28%, surpassing NVS fracturing fluids (25.17%) and formation water (10.21%). Enhanced imbibition recovery was facilitated by elevated CO2 content, higher temperatures, and increased matrix permeability. Correlation analysis reveals that among the parameters selected, CO2 content exerts the most significant influence, followed by permeability, with temperature having the least impact. This study offers novel insights into the efficient development of shale oil through IFEI and the use of CW.