Mechanism and Influencing Factor Analysis of Near-Well Stimulation for Hot Dry Rock Reservoirs by Liquid CO2 Phase Transition Blasting: Applied to Matouying Uplift

To improve the heat transfer efficiency of the hot dry rock (HDR) well group, a near-well stimulation method of liquid CO₂ phase transition blasting (LCO₂-PB) is put forward, the fracturing characteristics and mechanism of samples induced by impact dynamic load are analyzed, the effects of hydraulic fracturing cracks, buried depth, shock wave amplitude, and blasting frequency on the reservoir stimulation are clarified, and feasible suggestions have been proposed for its on-site application. Results show that the dynamic load applied by LCO₂-PB can effectively increase the number and connectivity of cracks and enhance the complexity of damaged cracks. The existence of hydraulic fracturing cracks has a promoting effect on the generation and distribution because blasting stress wave can reflect and refract in the hydraulic fracturing cracks and torn apart the surrounding area. The buried depth has a suppressive effect on the impact range of blasting because its increases the difficulty of reservoir crack initiation. The shock wave amplitude of LCO₂-PB is beneficial for the fracturing effect of the reservoir while it also increases the risk of wellbore damage. There is a linear positive correlation between the blasting frequency and the crack zone area, and there is an optimal blasting frequency to form a connected crack network and avoid serious damage to the wellbore. For HDR reservoirs with large buried depth, prefracturing, increasing the shock wave amplitude, and selecting the appropriate blasting frequency can significantly improve the near-well stimulation effect and promote the exploitation of HDR resources.