Collaborative Research: Using Pore Fluid Pressure Gradients to Test the Relative Importance of Hydrologic Versus Mechanical Heterogeneity in Fracture Formation

合作研究：利用孔隙流体压力梯度测试裂缝形成中水文与力学非均质性的相对重要性

• 批准号: 0635965
• 负责人: Laurel Goodwin
• 金额: $ 8.7万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0635965&HistoricalAwards=false
• 关键词: Collaborative; Research; Using; Pore; Fluid

Extension fractures are common elements of a wide range of geologic settings. They are generally inferred to form in response to high pore fluid pressure and to nucleate on mechanical heterogeneities. Such fractures are of particular societal interest where they provide pathways for fluid flow or contaminant transport in reservoirs or aquifers, yet we still lack the capability to predict where they are likely to form, and in what density. This project examines the hypothesis that spatial variations in hydrologic properties are as important as spatial variations in mechanical properties in controlling where and when fractures form. Thus, a rock's mechanical behavior is a function not only of its heterogeneous mechanical properties, but also its heterogeneous ability to transmit and maintain elevated pore fluid pressures. The relative importance of hydrologic and mechanical heterogeneities in controlling the formation of extension fractures in sandstone, a common natural rock reservoir/aquifer is being investigated in this project. To accomplish this goal, laboratory experiments in that initiate hydraulic fractures while producing a pore fluid pressure gradient within a test sample are being carried out. A drop in both stress and fluid pressure at the boundary creates transient conditions conducive to the generation of extension fractures in finely laminated, well cemented, fine-grained, low diffusivity sandstone samples. By integrating pore fluid pressure gradient experiments with extensive bulk and grain-scale characterization of mechanical and hydrologic heterogeneity, fracture formation can be related to the petrophysical characteristics of a rock - an important step toward predictability. Pre-test analyses include the measurement of hydraulic diffusivity, tracer break-through curves (a proxy for degree of homogeneity), and poroelastic properties in different orientations relative to bedding, the most common physical heterogeneity in sedimentary rocks. Measurement of these bulk responses is complemented by detailed, grain-scale study of both the rock's solid framework and the pore network, and mm-cm scale variations in permeability.Fractures provide important pathways for fluids (such as water or oil) to move underground. Current understanding of how fractures form and grow under geologic conditions is extremely limited. This study attempts to better understand the role of subsurface fluids on the genesis of fractures in rock by studying their growth in a newly developed laboratory-based testing method. Through the combination of detailed analyses of the rock prior to and post fracturing the important variables that that control the timing, location, and intensity of fracturing can be evaluated. Incorporation of this information into models of the subsurface will allow scientists and engineers to more effectively produce or store fluids in the sub-surface of the Earth.

伸展裂缝是广泛的地质背景的常见元素。它们通常被推断为响应于高孔隙流体压力而形成，并在机械非均质性上成核。这种裂缝具有特殊的社会意义，因为它们为储层或含水层中的流体流动或污染物运输提供了途径，但我们仍然缺乏预测它们可能形成的位置和密度的能力。该项目研究的假设是，在控制裂缝何时何地形成时，水文特性的空间变化与力学特性的空间变化一样重要。因此，岩石的力学行为不仅是其非均匀力学性质的函数，而且是其传递和维持升高的孔隙流体压力的非均匀能力的函数。本项目正在研究水文和力学非均匀性在控制砂岩（一种常见的天然岩石储层/含水层）中伸展裂缝形成方面的相对重要性。为了实现这一目标，正在进行启动水力压裂同时在测试样本内产生孔隙流体压力梯度的实验室实验。在边界处的应力和流体压力的下降产生了瞬态条件，有利于在精细层压、胶结良好、细粒、低扩散性砂岩样品中产生延伸裂缝。通过将孔隙流体压力梯度实验与机械和水文异质性的大量和颗粒尺度表征相结合，裂缝形成可以与岩石的岩石物理特性相关-这是迈向可预测性的重要一步。试验前分析包括测量水力扩散率、示踪剂穿透曲线（均匀度的代表）和相对于沉积岩中最常见的物理非均匀性层理的不同方向的孔隙弹性性质。对这些整体响应的测量还需要对岩石的固体骨架和孔隙网络以及渗透率的毫米-厘米尺度变化进行详细的粒度级研究。裂缝为流体（如水或油）在地下移动提供了重要的通道。目前对裂缝在地质条件下如何形成和生长的理解非常有限。本研究试图更好地了解地下流体在岩石裂缝成因中的作用，通过研究它们在一个新开发的实验室为基础的测试方法的增长。通过对压裂前后岩石的详细分析，可以评估控制压裂时间、位置和强度的重要变量。将这些信息纳入地下模型将使科学家和工程师能够更有效地在地球的地下生产或储存流体。