Integrated geological, geophysical, and hydrological study of field-scale fault-zone cementation and permeability

现场尺度断层带胶结和渗透性的综合地质、地球物理和水文研究

• 批准号: 1557232
• 负责人: Glenn Spinelli
• 金额: $ 56.76万
• 依托单位: New Mexico Institute of Mining and Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-01 至 2020-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1557232&HistoricalAwards=false
• 关键词: Integrated; geological; geophysical; hydrological; study

Because faults can be barriers to underground fluid flow, they influence groundwater supply, contaminant transport, petroleum production, and underground waste storage. Natural cements commonly precipitate along fault zones; these cements can dramatically inhibit fluid flow across a fault. However, determining the distribution of fault zone cements is difficult. As a result, fault-zone cementation is typically not accounted for in estimates of the impact of faults on fluid flow. This study aims to take advantage of unique electrical properties of natural cements to characterize the three-dimensional spatial distribution of cement for an exceptionally well-exposed fault zone. Then, the hypothesis that the degree and continuity of fault-zone cementation is a key control on fluid flow will be tested by drawing water from wells adjacent to the fault. The results of this project can be applied to better understand contaminant transport in faulted aquifers, the characterization of hydrocarbon reservoirs, and induced seismicity associated with wastewater injection. Undergraduate and graduate students will be involved with all stages of the project, which will enhance education for underrepresented minorities at New Mexico Tech (NMT), a Hispanic-serving institution with a focus on science, technology, engineering, and mathematics (STEM) fields. In addition, the geophysical equipment and groundwater wells used in this project will be long-lasting teaching resources both for NMT and for summer field courses sponsored by other universities.The objectives of this project are to characterize field-scale permeability across a fault and link the hydrogeologic behavior of the fault to spatial variations in the degree of fault-zone cementation. The central hypotheses are: 1) there are more pronounced variations in the degree of cementation down-dip than along the strike of the fault because the up/down-section variations in grain size are larger than those along strike, and 2) extensive cementation does not reduce cross-fault permeability at the field-scale (i.e. the de facto hypothesis for hydrogeologic models that neglect the potential effects of fault-zone cementation). The proposed project comprises: 1) characterizing the degree and extent of cementation along the surface exposure of the fault; 2) collecting resistivity and chargeability data in transects across the fault, deriving empirical relationships between the degree of fault-zone cementation and normalized chargeability for shallow portions of the fault, and using those relationships to map the estimated degree of cementation for deeper portions of the fault; 3) coring the fault at depth to confirm the degree of cementation; and 4) conducting well tests to determine permeability across the fault in both strongly- and weakly-cemented sections. The study will generate geologically based geophysical observations, providing a unique 3D map of cementation patterns from the land surface to ~30 m depth, in transects covering 700 m along the strike of the Loma Blanca fault. Interpreting well tests across the fault in the context provided by the geologic and geophysical observations will allow for the development of a holistic view of fault-zone permeability, improving predictive models of the hydrogeologic impacts of faults.

由于断层可能成为地下流体流动的障碍，因此它们会影响地下水供应、污染物输送、石油生产和地下废物储存。天然胶结物通常沿着断层带沉淀；这些水泥可以极大地抑制流体流过断层。然而，确定断层带胶结物的分布很困难。因此，在估计断层对流体流动的影响时，通常不考虑断层带胶结作用。本研究旨在利用天然水泥独特的电特性来表征异常暴露的断层带的水泥的三维空间分布。然后，将通过从断层附近的井中抽水来检验断层带胶结的程度和连续性是流体流动的关键控制因素的假设。该项目的结果可用于更好地了解断层含水层中的污染物迁移、碳氢化合物储层的特征以及与废水注入相关的诱发地震活动。本科生和研究生将参与该项目的所有阶段，这将加强新墨西哥理工学院 (NMT) 中代表性不足的少数族裔的教育，这是一所为西班牙裔服务的机构，专注于科学、技术、工程和数学 (STEM) 领域。此外，该项目中使用的地球物理设备和地下水井将成为 NMT 和其他大学赞助的夏季实地课程的长期教学资源。该项目的目标是表征跨断层的现场尺度渗透性，并将断层的水文地质行为与断层带胶结程度的空间变化联系起来。中心假设是：1）下倾胶结程度的变化比沿断层走向的胶结程度变化更明显，因为上/下断面的粒度变化大于沿走向的变化；2）广泛的胶结作用不会降低现场尺度的跨断层渗透率（即忽略断层带胶结作用潜在影响的水文地质模型的事实假设）。拟议项目包括：1）表征沿断层表面暴露的胶结程度和范围； 2) 收集断层横断面的电阻率和荷电率数据，得出断层带胶结程度与断层浅部标准化荷电率之间的经验关系，并利用这些关系绘制断层较深部分的估计胶结程度； 3）对断层进行深度取心，确认胶结程度； 4) 进行试井以确定强胶结层和弱胶结层断层的渗透率。该研究将生成基于地质的地球物理观测结果，提供沿 Loma Blanca 断层走向覆盖 700 m 的横断面中从陆地表面到约 30 m 深度的胶结模式的独特 3D 地图。在地质和地球物理观测提供的背景下解释断层上的试井将有助于形成断层带渗透性的整体视图，改进断层水文地质影响的预测模型。