Although technical advances in hydraulically fracturing and drilling enable commercial production from tight reservoirs, oil/gas recovery remains at a low level. Due to the technical and economic limitations of well-testing operations in tight reservoirs, rate-transient analysis (RTA) has become a more attractive option. However, current RTA models hardly consider the effect of the non-uniform production on rate decline behaviors. In fact, PLT results demonstrate that production profile is non-uniform. To fill this gap, this paper presents an improved RTA model of multi-fractured horizontal wells (MFHWs) to investigate the effects of non-uniform properties of hydraulic fractures (production of fractures, fracture half-length, number of fractures, fracture conductivity, and vertical permeability) on rate transient behaviors through the diagnostic type curves. Results indicate obvious differences on the rate decline curves among the type curves of uniform properties of fractures (UPF) and non-uniform properties of fractures (NPF). The use of dimensionless production integral derivative curve magnifies the differences so that we can diagnose the phenomenon of non-uniform production. Therefore, it’s significant to incorporate the effects of NPF into the RDA models of MFHWs, and the model proposed in this paper enables us to better evaluate well performance based on long-term production data.

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.