Mechanism Of Injection Above Fracture Propagation Pressure In Low Permeability Reservoir

Waterflood development is the most profitable and effective technical measure for enhanced oil recovery in the development of the field since 1940s. It is widespread used all over the world. Injection above fracture propagation pressure (IFPP) is a technology which is used in the regular injection wells. The technology can achieve the purpose of constant displacement injection by enhancing pressure to breakdown pressure cyclically and forming new fracture.In this paper, according to an integrated research, a more detailed mechanism of IFPP is given based on the underground rock damage and the mechanism of fracture initiation. The reason of crack surface contamination in the water injection process is analyzed. The filtration coefficient is introduced to describe the integrated pollution of the crack surface. Regarding injected water as a compressible fluid, pressure history in the crack is derived. Water injection cycle model is derived by conventional mass balance method. On this basis, fracture length model of the crack extension is studied according to Griffith theory.Fracture propagation laws are analyzed according to the actual parameters. The following conclusions are given. During fracture propagation, the change of pressure is irregular. The pressure ascending velocity is more and more quickly with the injection volume increasing. The higher injection flow rate, the more the number of expansion is. The poorer water quality, the faster the crack, the smaller the increment of fracture length is. If the filtration coefficient is much larger, it is not easy to extend the cracks. With the number of crack propagation increasing, the fracture length increment increases.At the same time, according to the improved black oil model, the recovery and oil displacement efficiency under different fracture orientation are studied, which compared with the ideal status. The impact of injection and filtration coefficient under different fracture azimuth to IFPP is investigated. The impact of different well spacing, pattern and different injection time to IFPP is simulated. In short, the degree of recovery can improve by IFPP technology compared with conventional injection. It has wide application prospects.