An experimental study of the temporary plugging mechanisms of rough fractures in hot dry rocks under a high temperature

The temporary plugging and diverting fracturing (TPDF) technique is important for improving the production capacity of hot dry rock (HDR) reservoirs. The key to this technique is to form effective plugged layers in existing fractures. However, HDR reservoirs have a high temperature, high pressure, and tight rocks. Accordingly, temporary plugging agents (TPAs) deliver different plugging performances for HDR fractures and conventional tight reservoirs. To investigate the plugging mechanisms of TPAs for rough fractures in HDRs, this study first reconstructed the physical models of rough fractures in HDRs using the computed tomography (CT) and 3D printing techniques. Second, it proposed a computational method of fracture surface roughness based on the joint roughness coefficient (JRC) theory. Using this method, the surface roughness of the physical models was calculated and then compared with the rock roughness spectra recommended by the International Society for Rock Mechanics and Rock Engineering (ISRM). Third, with the aid of the temporary plugging characteristic experimental system, this study designed and conducted temporary plugging characteristic experiments on rough fractures in HDRs under a high temperature. Last, this study analyzed the influences of different factors, including fracture surface roughness and the particle concentration and type of TPAs, on the fracture plugging efficiency under a high temperature. The results of this study are as follows: Under the same conditions, the temporary plugging efficiency for fractures in HDRs increased by 67.6% when the fracture surface roughness increased by 10.44; the amount of the required TPA mixture increased by 82.5% when the temperature doubled in value, and the optimal particle concentration of TPAs was 1.5% in this experiment. These results can be used as a reference for the hydraulic fracturing of HDRs.