The development of shale reservoirs relies on hydraulic fractures. The development process often faces the shortcomings of fast decreasing production rate and insufficient formation energy. The high permeability of gas makes gas injection into shale reservoirs an effective development strategy. In complex fractured reservoirs, reasonable timing of gas injection will significantly improve the development of the reservoir and effectively prevent the risk of gas intrusion. Currently, the shale reservoirs in Changqing Oilfield in the Ordos Basin of China face problems such as low reservoir pressure coefficients, poor physical properties, and obvious non-Darcy flow, which lead to low initial development production of the reservoirs. In this paper, we propose a new development strategy named advanced gas injection, where gas is injected in advance before the production of the production wells to improve the initial formation pressure and fluid physical properties and to realize the improvement of the fluid flow capacity. The advantages of the advanced gas injection strategy in shale reservoirs are analyzed using a shale numerical simulator, the model adopts the embedded discrete fracture model (EDFM) method to realize the fracture modeling, and the components adopt the results of the analysis of the actual extracted fluid components in the field. The simulation results show that advanced gas injection can significantly increase the oil production rate in the early stage of development, and the average oil production rate in the initial stage (three months) is increased by 10-35% compared with the lagging injection. However, the decline rate of production is faster, and this yield difference will be reduced in the subsequent production; further design of the follow-up development strategy is necessary.
Keywords fractured shale reservoir, advanced gas injection, timing of gas injection