低渗透油藏多分支裂缝压力动态分析

Dynamic Pressure Analysis of Multi-branch Fractures in Low Permeability Reservoirs

复合应用水力压裂和高能气压裂等多种压裂改造技术开采低渗透油藏,在近井地带形成不受地应力控制的多分支裂缝。基于渗流理论和叠加原理,分析了未穿透储层的多分支裂缝的渗流规律,再利用Green函数和Newman乘积法求得其地层压力解析解,这是一种新的计算多裂缝地层压力的方法,可避免复杂的推导过程。研究表明:未穿透储层的多分支裂缝的井底压力随渗透率、孔隙度的增大而减小,但减小的幅度逐渐减小,且地层渗透率对井底压力的影响更明显;裂缝长度越长,相邻裂缝长度差距越小,裂缝分布越不均匀,裂缝间相互干扰作用越严重。所以在一定经济范围内,裂缝长度存在最优值,裂缝分布越均匀改造效果越好。该研究成果对油气藏的压裂改造设计具有实际指导意义。

Using composited volume fracturing technologies such as hydraulic fracturing and high energy gas fracturing in low permeability reservoirs, multi-branch fractures are generated beyond the control of stress near wellbore zone. Based on the fluid flow theory and the superposition principle, the fluid flow was studied in a reservoir with multi-branch fractures whose height is less than the reservoir＇ s thickness. Using the Green＇ s function and the Newman multiplication method, the analytical solution of formation pressure was obtained, which is a new formula and can be able to understand and avoid the complexity of derivation. The results show that the larger the porosity or the permeability is, the bigger the bottom pressure, but the increase gradually decreases. The effect of the per- meability is more significance in low permeability reservoirs. The bigger the length of fractures, the smaller the difference of adjacent fractures and the more uneven the distribute condition of fractures, the strong interferences between adjacent fractures was. There is an optimal value of the above fracture parameters in a economic scale. The results obtained have important significance to provide a fracture optimization design for exploiting this reservoir efficiently.