Characterization of Hydrologically Active Sheet Fractures

[0001146]默多克片状裂隙是控制地下水的重要因素，但人们对其产状、特征和形成过程的了解甚少。该项目的目的是将来自南卡罗来纳西部附近几个研究充分的地点的信息与新的钻孔测试结果相结合，以提高表征薄片裂缝的能力。新的测试将使用一个跨式封隔器，该封隔器配备了精密井眼伸缩仪，类似于地质力学调查中用于测量岩石变形的设备。该装置将以骨折为中心，然后用于进行注射或恢复测试。所得数据将提供裂缝孔径或井眼轴向位移，作为压力和注入（或回收）流体体积的函数。注入顶替测试期间的瞬态孔径变化将提供常规封隔器测试所无法测量的额外描述性记录。初步的理论分析已经得到，进一步的分析将发展，以预测瞬态孔径、体积和驱动压力，作为裂缝长度、间距、连通性和其他变量的函数。这些解决方案将用于评估片状裂缝的特征，如裂缝长度和连通性，这些都是常规封隔器测试无法解决的问题。使用常规封隔器测试可以测量的特性，如裂缝储存性，也将使用新方法进行评估。分析结果将与地面暴露的现场测绘结果、岩心描述、井眼流量计测井、温度测井、井眼雷达、常规封隔器测试和其他方法进行比较。本研究还将研究由于地球潮汐、气压波动或其他影响而引起的孔隙流体压力和裂缝孔径的自然变化。这些载荷可能有助于板状裂缝的增长，并为板状裂缝形成的概念模型提供见解。此外，裂缝孔径对自然应力的响应可以在不进行泵送试验的情况下估计水力导电性、储存性和弹性模量等性能。这项研究的主要贡献是开发一种新的方法来确定结晶岩石中缓倾斜裂缝的力学和水文特征。这将提高定位生产井的能力，通过水力压裂提高油井产能，并评估与污染物迁移相关的风险。

0001146MurdochSheet fractures in crystalline rock are an important control of ground water whose occurrence, characteristics, and processes of formation are poorly understood. The objective of this project is to combine information from several well-studied sites in the vicinity of western South Carolina with results from a new borehole test to improve the ability to characterize sheet fractures. The new test will use a straddle packer fitted with a precision borehole extensiometer, similar to devices used to measure rock deformation during geothechnical investigations. The device will be centered on a fracture and then used to conduct either injection or recovery tests. The resulting data will provide fracture aperture, or axial displacement of the borehole, as functions of pressure and the volume of injected (or recovered) fluid. The transient aperture change during an injection-displacement test will provide an additional descriptive record that goes beyond what can be measured during conventional packer tests. Preliminary theoretical analyses have been derived, and additional analyses will be developed, to predict transient aperture, volume and driving pressure, as functions of fracture length, spacing, connectivity and other variables. Those solutions will be invested to estimate characteristics of sheet fractures, such as fracture length and connectivity, which are beyond the resolution of conventional packer tests. Characteristics that can be measured using conventional packer test, such as fracture storativity, will also be evaluated using the new method. The results of the analyses will be compared to findings from field mapping of surface exposures, as well as core descriptions, borehole flowmeter logs, temperature logs, borehole radar, concentional packer tests, and other methods. This study will also investigate natural variations in pore-fluid pressure and fracture aperture due to Earth tides, barometric pressure fluctuations or other effects. Those loadings may contribute to the growth of sheet fractures, and provide insights into conceptual models of sheet fracture formation. In addition, the response of fracture aperture to natural stresses holds the potential for estimating properties, such as hydraulic conductivity, storativity and elastic modulus, without pumping tests. The primary contribution of this research is expected to be the development of a new method for determining mechanical and hydrologic characteristics of gently dipping fractures in crystalline rock. This will advance the ability to site productive wells, stimulate well productivity by hydraulic fracturing, and evaluate risks associated with contaminant migration.