压裂液向上迁移对浅层地下水环境的影响分析  

Effect of Upward Migration of Hydraulic Fracturing Fluid on Shallow Groundwater

作　　者：王礼恒[1] 董艳辉[1,2] 张倩 段瑞琪[1,2] WANG Liheng;DONG Yanhui;ZHANG Qian;DUAN Ruiqi(Key Laboratory of Shale Gas and Geoengineering,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地质与地球物理研究所中国科学院页岩气与地质工程重点实验室,北京100029 [2]中国科学院大学地球与行星科学学院,北京100049

出　　处：《安全与环境工程》2021年第3期198-205,共8页Safety and Environmental Engineering

基　　金：国家油气重大专项项目(2017ZX05008003-021);国家自然科学基金项目(41702273)。

摘　　要：深部流体迁移过程机理不清造成在水力压裂开发页岩气过程中,对于压裂液或深部地层卤水是否会从深部迁移至浅层而污染地下淡水资源这一问题仍存争议。深部压裂液向上迁移至浅层含水层,必须在自下而上的驱动力作用下经由渗透性能较好的通道才会在短时间内(<10 a)发生。结合我国油气沉积盆地地质与水文地质背景,从地下流体渗流机理出发,分析了页岩气沉积盆地地层渗透率的特征及形成机理,建立了压裂液向上迁移的概念模型。结果表明:地形驱动力和超高压驱动力是携带流体向上迁移的固有驱动力,具有持久性但极限水力梯度为1;而页岩储层上覆地层的渗透率一般小于1×10-16 m2,此时压裂液向上迁移速率小于1 cm/a;水力压裂过程不会改变天然状态下页岩储层上覆地层的渗透率与向上的水力梯度,但新生裂隙若贯通压裂区和导水断层或压裂液进入废弃油气井时,其会对浅层含水层造成污染;利用所建立的压裂液向上迁移的概念模型,对我国典型油气沉积盆地压裂液向上迁移的可能性进行分析发现,在水力压裂前后压裂液很难向上迁移并对浅层地下水造成污染。Because the mechanism of deep hydraulic fracturing fluids upward migration under-ground is still unclear,it is a largely unexamined and uncertain issue,which is the potential for contamination of shallow groundwater due to hydraulic fracturing migration at depth via some preferential flow paths,such as fractures or faults.Upward head gradient and the permeable pathways must be present at the same time if the aquifer is contaminated by fracturing fluid in a short time,e.g.less than 10 years.Combined with the geo-logy and hydrogeology background of petroliferous basins in China,from the theory of fluid seepage in the subsurface,this paper analyzes the characteristics and formation mechanism of permeability of the shale gas reservoir in sedimentary basin and illustrates the mechanism of upward migration of fracturing fluid.The results show that topographic gradients and overpressure are widespread in the oil and gas basin and inherently associated with low permeability rocks(<1×10-16 m2),but the maximum upward head gradient is limited approximately to 1.The flow rate of fracturing fluid upward migration from the deep shale reservoir is on the order of cm year-1 or lower.Hydraulic fracturing operation will not change the permeability of the overlying shale reservoir and upward hydraulic gradient in the natural state because it is ephemeral.However,the vertical fracture growth is extended to the permeable fault,or the fracturing fluid enters the abandoned oil and gas well.It is very likely that the shallow aquifers will be contaminated by fracturing fluid aquifers.Finally,based on the conceptual model,some typical oil and gas basins in China are analyzed and the results show that it is difficult for fracturing fluids to contaminate shallow aquifers.

关 键 词：页岩气开发 压裂液 概念模型 浅层地下水 环境风险 

分 类 号：X741[环境科学与工程—环境工程] X820.3