Mechanism of Hydraulic Fracture Propagation in Deep Fracture-Cavity Carbonate Reservoirs

In order to understand the law of hydraulic fracture propagation in deep fracture-cavity carbonate reservoirs during the fracturing process, a mathematical model of hydraulic fracture propagation suitable for fracture-cavity reservoirs was established based on elastic mechanics, fracture mechanics, and fluid-solid coupling theory. On the basis of the model, a numerical simulation was carried out to analyze the interaction law between hydraulic fractures and fracture-cavity reservoirs during propagation, and the technical applicability of “cave connection by natural fractures” was discussed thoroughly. The numerical simulation results show that the locally induced stress field around the fracture-cavity reservoir will be affected when natural fractures develop around the cave, which makes it easier for hydraulic fractures to connect with the fracture-cavity reservoir. The injection of low-viscosity fracturing fluid at large displacement or high-viscosity fracturing fluid at medium and small displacement can only connect to caves that have a small angle with the initial hydraulic fracture propagation direction, while for caves with large angles, forced steering technology should be considered for connection. The results show that according to the distribution relationship between wellbore and fracture-cavity reservoirs, three fracture-cavity reservoir connection modes including direct connection, directional connection, and seam connection can be achieved by using the technique of “cave connection by natural fractures”, which significantly improves the production range of reserves.