Understanding the coupled transport of water and ions in gas shales for interpreting hydraulic fracture flowback data

在北美，通过钻井和完成多分支/多裂缝水平井利用致密碳氢化合物资源生产石油和天然气正成为一种普遍做法。然而，要高效、负责任和可持续地开发这种资源，就需要对所涉及的大规模水力压裂作业进行仔细的评估。主要问题包括1)压裂水回收效率低，2)采出水中各种盐类浓度较高，3)缺乏可靠的模型来利用排液过程中测得的压力、速率和浓度数据来描述诱发裂缝网络。为了验证这一假设，将对从钻入不列颠哥伦比亚东北部霍恩河盆地不同页岩成员的岩心中挑选的页岩样本进行广泛的流动实验。据估计，该盆地的天然气储量高达500 TCF，是北美第三大天然气聚集地。这项实验研究旨在了解裂缝水渗入页岩基质和离子从页岩扩散到裂缝水的基本机制。此外，将对实验数据进行模拟，以获得模拟现场规模过程所需的参数，包括1)关井期间裂缝中的自发渗漏和盐分聚集，以及2)排液作业中的水和盐的传输。拟议中的研究将由两名博士和两名硕士学生进行，将帮助该行业了解水和页岩之间的复杂相互作用，以评估压裂作业和优化未来的开发计划。

Oil and gas production from tight hydrocarbon resources by drilling and completion of multilateral/multifractured horizontal wells is becoming a common practice in the North America. However, efficient, responsible, and sustainable development of such resources requires careful evaluation of massive hydraulic fracturing operations involved. The main concerns include 1) inefficient recovery of fracturing water, 2) high concentration of various salts in the produced water, and 3) lack of reliable models for characterizing the induced fracture network using the pressure, rate and concentration data measured during flowback operations.This research hypothesizes that a large fraction of non recovered water is imbibed into the shale matrix during the shut-in period. To test this hypothesis, extensive flow experiments will be conducted on shale samples selected from cores drilled into different shale members of the Horn River Basin, located in northeastern British Colombia. It is estimated that up to 500 TCF of natural gas is stored in this basin, making it the third largest North American natural gas accumulation. This experimental study is aimed at understanding the fundamental mechanisms controlling the imbibition of fracture water into the shale matrix and diffusion of ions from shale into fracture water. Furthermore, the experimental data will be modeled to obtain the parameters required for modelling field scale processes including 1) spontaneous water leak off and salt concentration build up in fractures during the well shut in period, and 2) transport of water and salt during flowback operations.The proposed research, that will be conducted by two PhD and two MSc students, will help the industry to understand the complex interaction between water and shale for evaluating fracturing operations and optimizing future development plans.