断层对压裂液运移影响的数值模拟研究

Numerical simulation of the fault impact on fracturing fluid migration

水力压裂必然会带来相关环境问题,压裂液对浅层含水层的影响不容忽视。为了查明压裂液潜在的向上运移通道及不同地质条件下压裂液的运移情况,对压裂液潜在的运移通道进行了分类,基于变密度数值模拟软件SEAWAT,考虑不同渗漏点与断层底部距离、不同断层倾角对压裂液运移的影响,设计了6种情景开展了数值模拟。结果表明:压裂液潜在向上运移通道主要有对流传输、裂隙传输以及井管泄露。密度差异产生的浮力是压裂液上升的主要动力。压裂液渗漏点距离断层底部越近,影响范围越大,监测点水位和浓度均最先降低。在存在微弱水力梯度条件下,断层倾角α为20°时,断层对局部水流水位及浓度影响较大;α为90°时,对压裂液运移产生影响较小;α为70°时,断层对压裂液运移影响最大,压裂液会扩散至较大范围。

Hydraulic fracturing,as a new shale gas production method, inevitably raised environmental problems. Fracturing fluid may influence the shallow aquifer,which cannot be ignored. The objective of this study is to identify the potential pathways of fracturing fluid upward migration and show the different migration plume in various geological scenarios. We classified the potential upward migration pathways of fracturing fluid. Based on SEAWAT（ a variable density simulation software）,we considered the distance between the nearest leakage point and the fault,the inclination of the fault,and designed six simulation scenarios. The results show that the fracturing fluid potential migration pathways are convective transport,fracture transport and well pipe leakage. Buoyant caused by density differences is the main driving force of migration. The migration plume is greater if the distance between the leakage point and the fault is closer. The monitoring well also shows an earlier drop in water level and concentration. When there exists week hydraulic gradient,scenario（ dip angle is 20°） shows a greater impact on the local water level and concentration. If the dip angle is 90°,the fracturing fluid transport is less affected,and if the dip angle is 70°,the fault raises the greatest impact on the migration of fracturing fluid,and the fracturing fluid can spread to a wider range.