低渗砂岩酸压增注技术研究与应用

Research and Application of Acid-fracturing for Increasing Injection Rate in Low Permeability Sandstone Reservoirs

辽河油田ZQ区块储层物性差,平均孔隙度为12%,渗透率分布在0~1mD之间,属于典型的中孔-低渗透油藏。长期以来,该区块约有30%的注水井存在注水压力上升快、长期注水高压、注不进等现象,采用常规酸化增注措施后,平均有效期只有61d,注水状况无法彻底改变。借鉴国内类似储层的注水井增注经验,提出了ZQ区块酸压增注措施。通过建立油藏和压裂裂缝的二维渗流模型,对比了酸压增注与常规注水的压力扩散和增注量,证实酸压增注的理论可行性;通过室内岩心柱刻蚀实验,证实砂岩岩面酸蚀后能够形成导流裂缝;同时对酸液进行优化,采用有机酸体系减缓酸岩反应时间,增大酸蚀处理半径。在现场应用了5井次酸压增注施工,措施后平均日注量24.3m^3/d,同时邻近油井平均动液面上升120m。酸压增注为低渗透砂岩油藏改善注水效果提供了一项有效技术手段。

ZQ block in Liaohe Oilfield has poor physical properties,with average porosity of 12% and permeability of 0-1mD,which is a typical medium-porosity and low-permeability reservoir.About 30% water wells in ZQ block had the problems of rapid raise of injection pressure ,high pressure and no injection for a long time.After conventional acidizing,the average duration was only 61 days,and the injection situation was not significantly improved yet.Based on the experience of similar reservoirs in China,acid-fracturing for increasing injection rate was carried out in ZQ block.A two-dimensional percolation model for the reservoirs and fractures was established to compare the pressure diffusion and increased injection rate by the acid-fracturing and conventional water injection,which proved the theoretical feasibility of the acid-fracturing for increasing injection rate.Core etching experiments confirmed that conductive cracks could be formed after the sandstone surface was etched by the acid.Meanwhile,the acid was optimized,and the organic acid system was used to slow down the acid rock reaction time and increase the etching treatment radius.After the acid-fracturing technology was applied for five well-times in the field,the average injection rate reached 24.3m^3/d and average moving liquid level raised 120m in neighboring oil wells.The acid-fracturing for increasing injection rate is effective for improving the effect of water drive in the low permeability sandstone reservoir.