Multiphase fracturing of deformable media

水力压裂，俗称“水力压裂”，近年来改变了美国能源行业的面貌，英国即将大规模开发一种重要的陆上页岩气资源。水力压裂包括注入加压压裂液，克服储集层岩石的围压和抗张强度，打破在原本不透水的页岩中充当传导通道的裂隙。水基压裂液与主体流体可混溶，注入速度必须快于其在页岩中的消散速度。拟议的项目解决了另一种压裂机理：多相压裂，即气相穿透饱和水的多孔介质。与传统的水力压裂(单相压裂)不同，作用于气/液/粒界面的毛细管力有望在裂缝生长动力学中发挥重要作用。本项目将专注于详细了解控制多相裂缝生长的基本物理机制。利用自制的流动实验台，研究了向含水饱和、可变形的多孔介质中注入加压气体后的裂缝生长动力学和裂缝网络演化规律。我们试图回答的问题包括：表面张力、润湿特性和颗粒尺寸如何影响断裂尖端的生长活动？能否利用毛细管力、可压缩性和注入速度等实验参数来控制不断演变的裂缝模式的形成(进而控制裂缝带的渗透率)？第二个目标是开展CO2压裂的第一个基础研究，重点是压裂过程与随后的CO2在孔隙空间主体流体中的吸收和扩散传输之间的复杂相互作用。使用CO2作为非常规压裂液，有可能实现高渗透裂缝带，由于CO2优先结合到颗粒表面，从而提高甲烷采收率，以及页岩气开采和大规模CO2地质封存相结合的过程。

Hydraulic fracturing, colloquially known as "fracking", has transformed the US energy sector in recent years, and the UK is now on the brink of a potential large scale development of a significant onshore shale gas resource. Fracking involves the injection of pressurized fracturing fluid that overcomes the confining pressure and tensile strength of the reservoir rock, breaking open fissures that act as conductive pathways in the otherwise impermeable shale. The water-based fracturing fluid is miscible with the host fluid, and must be injected at a faster rate than it dissipates within the shale play.The proposed project addresses an alternative fracturing mechanism: multiphase fracturing, where a gaseous phase penetrates a water saturated porous media. Unlike traditional fracking (a single phase process), the capillary forces acting at the gas/liquid/grain interface is expected to play a significant role in the fracture growth dynamics.This project will focus on developing a detailed understanding of the fundamental physical mechanisms that govern multiphase fracture growth. A custom made experimental flow rig will be used to study the fracture growth dynamics and the evolving fracture network pattern upon injection of a pressurized gas into a water-saturated, deformable porous media. Questions we seek to answer include: How does surface tension, wetting properties and grain size influence growth activity at the fracture tips? Can the evolving fracture pattern formation (and by extension the permeability of the fracture zone) be controlled using experimental parameters such as capillary forces, compressibility and injection rate?A second objective is to undertake a first fundamental study of CO2 fracturing, focusing on the complex interplay between the fracturing process, and the subsequent absorption and diffusive transport of CO2 within the pore space host fluid. Using CO2 as an unconventional fracturing fluid has potential for achieving high permeability fracture zones, increased methane recovery as CO2 binds preferentially to grain surfaces, and a combined process of shale gas recovery and large scale CO2 geo-sequestration.