Experimental and Theoretical Investigation of the Growth of a Fluid-Driven Fracture near a Free-Surface

摘要：CMS-0600058这项研究是关于水力裂缝在岩体自由面附近的扩展。这一问题在工业和科学方面有许多应用：工业应用包括最近利用水力压裂在矿坑附近诱发坍塌，并改进浅层环境废物或溢出场的修复工作，而科学应用涉及涉及水力压裂的一些近地表地质过程，例如碟形岩浆底床侵入。与这一问题相关的基本问题涉及地应力和重力对裂缝形状的影响(包括突破半径、到裂缝露头的液源的距离)、裂缝形状和大小的演化、内部流体压力随时间的变化以及过程对岩石和流体性质的依赖。这项研究是明尼苏达大学(UMN)和澳大利亚CSIRO石油公司开展的一项国际合作的联合理论和实验研究。建模工作是UMN活动的重点，涉及开发能够模拟碗形骨折生长的计算模型，并在参数空间中列出解的表格，以确保获得的数值解最具一般性。这项实验室工作在CSIRO石油公司进行，包括在受限和非受限条件下在聚甲基丙烯酸甲酯(PMMA)和二氧化硅玻璃中进行近地表水力压裂实验。将严格解的开发和这些解的实验验证相结合的工作有望产生在各种条件下分析和预测自由表面附近水力压裂扩展的定量手段。无量纲控制参数的引入允许将无数的具体情况折叠到参数空间的一个点中，并打开了计算解的经济制表的可能性。实验研究还将为深部水力压裂的理论解决方案提供有价值的数据，尽管油气藏水力压裂增产具有巨大的经济价值，但深层水力压裂的理论解实际上是不存在的。最后，该实验装置提供了一个观察和量化拉伸(I型)断裂的弯曲轨迹的不同寻常的机会。

Abstract: CMS-0600058 This study is concerned with the propagation of a hydraulic fracture propagating near the free surface of a rock mass. This problem has a number of industrial and scientific applications: the industrial applications include the recent utilization of hydraulic fracturing to induce caving near mine openings and to improve the performance of remediation work at shallow environmental waste or spill sites, while the scientific applications deal with a number of near-surface geological processes involving hydraulic fracturing, such as the saucer-shaped magmatic sill intrusions. Fundamental questions that arise in connection to this problem are related to the influence of the in-situ stresses and gravity on the shape of the fracture (including the breakthrough radius, the distance from the fluid source at which the fracture daylights), the evolution of the fracture shape and size, the variation of internal fluid pressure with time and the dependence of the process on the rock and fluid properties.This research is a joint theoretical and experimental investigation involving an international cooperation between the University of Minnesota (UMN) and CSIRO Petroleum in Australia. The modeling effort, the focus of the activity at the UMN, deals with the development of computational models capable of simulating the growth of a bowl-shaped fracture, and with the tabulation of solutions in a parametric space to ensure most generality of the obtained numerical solutions. The laboratory work, which is carried out at CSIRO Petroleum, involve near-surface hydraulic fracturing experiments in Polymethylmethacrylate (PMMA) and in silica glass, under confined and unconfined conditions. The work combining development of rigorous solutions and experimental validation of these solutions is expected to yield quantitative means to analyze and predict the propagation of a hydraulic fracture near a free-surface, under a variety of conditions. The introduction of dimensionless control parameters allows collapsing countless specific cases into a single point of the parametric space, and opens the possibility of an economical tabulation of the computed solutions. The experimental research will also yield valuable data for benchmarking theoretical solutions of deep hydraulic fractures, which are virtually nonexistent despite the substantial economic value of hydraulic fracturing stimulations of oil and gas reservoirs. Finally, the experimental setup provides an unusual opportunity to observe and quantify the curved trajectory of a tensile (mode I) fracture.