裂缝扩展注水技术中的裂缝扩展规律研究

Fracture Propagation in Water Injection above Fracture Propagation Pressure

低渗透油藏开发主要面临注水困难的问题,而裂缝扩展注水技术是提高低渗透油藏注水能力的有效技术。基于微可压缩流体假设和Griffith理论,分析了裂缝扩展注水机理,建立了裂缝扩展注水的扩展周期模型和裂缝半缝长扩展增量模型,讨论了注水量、滤失系数等参数对裂缝扩展规律的影响。结果表明:在裂缝扩展过程中,缝内压力呈不规则的周期性变化,随着注水量的增加,压力上升的速度越来越快;注水量越高,裂缝越容易扩展;随着注水时间增加,初始滤失系数越小裂缝越容易扩展;滤失系数减小越快,裂缝扩展越快,半缝长增量越小。

Injection difficulty is one of the main problems in developing low-permeability reservoirs.The technique of water injection above fracture propagation pressure is feasible to increase water injection capacity of low-permeability reservoirs.On the basis of micro-compressible fluid assumption and Griffith theory,the mechanism of the water injection above fracture propagation pressure is analyzed.In addition,water injection cycle model and half-fracture length increment model are established.The effects of water injection and filtration coefficient are analyzed.It is found that the change of pressure is irregular during fracture propagation.The rate of pressure rise increases with the increase of injection volume.The higher the injection flow rate,the higher the fracture expansion.If the initial filtration coefficient is low,the fracture propagation would be much easier with the increase of injection time.If the filtration coefficient decreases rapidly,the fracture propagation would be fast and the half-fracture length increment would be short.