Research and Field Test on Energy Storage Fracturing Mechanism of Horizontal Wells in Ultra-Low Permeability Reservoirs

After the production of some horizontal wells in ultra-low permeability reservoirs for a period of time, the production capacity from those wells start to decrease. A research and test on energy storage fracturing mechanism of horizontal wells in ultra-low permeability reservoir have been carried out. According to the failure mechanism of the rock, the laboratory simulated energy storage fracturing experiment was performed, in which the failure of the rock sample within the specimen was detected by acoustic emission. In addition, the stresses change near a wellbore was calculated through finite element method. Experimental and numerical simulation results showed that natural fracture surface has obvious dislocation traces, and a large number of microfractures are produced in the specimen during building up of high pore pressure. During well soaking process after fracturing, in-situ stress field is disturbed for a period of time. The research results showed that the injection of appropriate amount of oil displacement fracturing fluid before fracturing treatment and the imbibition and diffusion by well soaking after fracturing could effectively provide supplement energy in the formation. At the same time, the treated volume and complexity of fractures could be further increased when combined with the optimized volume refracturing. This technology has a good effect in increasing the production of low production horizontal wells due to energy deficit and fracture closure, and it has some reference value for the same ultra-low permeability reservoirs.