Optimization of fracture network parameters of the wide zone SRV by old well in ultra low-permeability oil reservoirs

Ultra low-permeability oil reservoirs are characterized by tight reservoirs and developed natural fractures, so the effective injection-production displacement system can be hardly established. And in order to increase the single-well production rate, the conventional refracturing technology is usually adopted, but the conventional refracturing can only increase the fracture length to improve the flow conductivity of fractures, but cannot increase the fracture zone width effectively to enlarge the lateral swept range of fractures. In this paper, the concept of wide zone SRV (stimulated reservoir volume) was put forward. That is to increase the fracture zone width by inducing secondary fractures or communicating natural fractures in the lateral direction of primary hydraulic fractures. Then, the rational fracture zone width of the wide zone SRV was optimized and the method for calculating the rational fracture zone width was developed. Finally, the fracture network parameters (e.g. flow conductivity of primary and secondary fractures and half fracture length) were optimally designed by means of orthogonal experiment method. It is shown by taking one certain well group in the ultra low-permeability oil reservoir as the example that the rational fracture zone width of refracturing is in the range of 13−46 m. And the scheme on the optimal fracture network parameter of Well G127-160 includes the flow conductivity of the primary fracture of 0.15 μm² · cm, half fracture length of 140 m, fracture zone width of 50 m and flow conductivity of secondary fracture of 0.04 μm² · cm. The refracturing simulated according to the scheme can control the water cut rising speed and increase the stimulated cumulative oil production greatly. The research results provide the technical idea for the potential tapping of the remaining oil in the lateral direction of the fractures of old wells in ultra low-permeability oil reservoirs.