低渗透油藏水平井分段压裂半解析产能计算与影响因素研究

摘要

低渗透油藏渗透率极低,往往存在启动压力梯度,其分段压裂水平井的渗流机理复杂,影响产能的因素多.基于双重介质渗流微分方程,采用点源理论和压降叠加原理,同时考虑启动压力梯度和水力裂缝导流能力,建立了低渗透油藏水平井分段压裂半解析产能计算模型,进行了产量求解与数值反演,并结合实例进行了计算与分析.结果表明:启动压力梯度对产能影响较大,启动压力梯度越大,产量越低;水力裂缝与井筒间夹角对产量有一定影响,但不明显,夹角呈90°时产量最高;水力裂缝导流能力对初期产量有明显影响,但后期影响不大;水平井两端的水力裂缝对产量的影响大于中部的水力裂缝,应尽量在水平井两端增加压裂段数和裂缝长度;储容比和窜流系数主要影响中期产能,储容比越大,产量下降越快,窜流系数越大,产量越高.研究结果不仅深化了对低渗透油藏分段压裂水平井渗流规律的认识,而且对水平井分段压裂的优化设计提供了重要指导与建议.%A low permeability reservoirs usually have threshold pressure gradient with extremely low permeability. The seepage mechanism of multi-stage fractured horizontal wells are complex and the productivity are affected by many factors.Based on the du-al-porosity medium seepage differential equation,applying point source theory and superposition principle,a semi-analytical pro-ductivity model for the multi-stage fractured horizontal wells is established, considering the threshold pressure gradient and hy-draulic fracture conductivity.Then the calculation of production and the numerical inversion are conducted,following by the analy-ses of the influence factors combining specific examples.The study results show that the threshold pressure gradient has great ef-fect on productivity.The larger the threshold pressure gradient is,the lower the production will be.The angle between the hydraulic fracture and wellbore has a little influence on production,but not obvious,and the highest production appears when the angle is 90°.The conductivity of the hydraulic fracture has obvious effect on the initial production,but a little influence on that in the later period.The hydraulic fracture at both ends of the horizontal wells affect more than that in the middle,so the fractured horizontal well's stages and the length of the fracture should be increased.The storage ratio and cross flow coefficient mainly affect the medi-um-term productivity.The larger the storage ratio is,the faster the production will decrease.And the larger the cross flow coeffi-cient is,the higher the production will be.The results of this study not only contributes to the deep understanding of the multi-stage fractured horizontal well's seepage laws in the low permeability reservoirs,but also provides some important guidance and ad-vice for the optimization design of the multi-stage fractured horizontal wells.