Hydrogeologic Characterization of the Sand Hill Fault Zone, Albuquerque Basin, New Mexico

新墨西哥州阿尔伯克基盆地沙山断裂带的水文地质特征

• 批准号: 9706482
• 负责人: Laurel Goodwin
• 金额: $ 5.5万
• 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: 1998
• 资助国家: 美国
• 起止时间: 1998-01-01 至 2002-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9706482&HistoricalAwards=false
• 关键词: Hydrogeologic; Characterization; Sand; Hill; Fault

9706482 Goodwin Faults can act as either conduits or barriers to groundwater flow, and their permeability can change over time as a result of diagenesis and deformation in the fault zone. We propose to investigate the influence of faults on fluid flow by conducting an integrated geologic/hydrologic investigation of the spatial distribution of fault-zone permeability in poorly consolidated sediments. all previous studies of fault-zone permeability have focused on rocks, yet many important aquifers in the United States consist of poorly consolidated sediments. Our characterization of hydrogeologic units in fault zones in sedimentary aquifers will be based on detailed study of an exhumed normal fault cutting poorly consolidated Cenozoic sediments. The Sand Hill fault is exceptionally well exposed, providing extensive vertical and lateral sections for study of the geometry and continuity of structures and diagenetic features within the fault zone. The fault zone is distinguished by preferential cementation with respect to adjacent sediments, and includes elongate oriented zones of cement that record the orientation of groundwater flow at the time of precipitation. Preliminary studies of fault-zone structures and cement distribution indicate that fault-zone permeability characteristics vary in a predictable manner. We have constructed a conceptual model in which the width and permeability structure of the fault zone vary both laterally and vertically depending on the sediments juxtaposed by the fault. This variation is represented by two end members: (1) Where fine-grained, low permeability units such as silts and clays are juxtaposed by the fault, the zone of deformation is narrow and weakly cemented. (2) Where relatively coarse-grained, initially moderate to high permeability units such as coarse sands are juxtaposed by the fault, the zone of deformation is wide and moderately to strongly cemented. Detailed geologic mapping and petrographic studies of deformation features within the fault zone, cementation patterns both within and outside the fault zone, and stratigraphic variability of sediments will be used to refine this preliminary conceptual model of fault-zone hydrogeology. As a beginning point for understanding the influence of cementation on fluid flow, we will consider both uncemented and cemented states. The permeability variations of uncemented fault-zone hydrogeologic units and lithostratigraphic units cut by the fault will be determined using a combination of gas minipermeameters and falling head permeability measurements. The pre-cementation permeability will be estimated by dissolving cements and determining the permeability of repacked sediments as well as applying empirical formulae correlating grain size with permeability. One fundamental challenge in this study is to use the centimeter-scale permeability values to describe larger scale permeability characteristic of the sediments. Our approach to this problem will be to used the permeability data to characterize meter-scale hydrogelogic units. The larger-scale (i.e., deca to hectometer scale) hydrogeologic units can be considered as discrete structures and characterized by geological mapping and distribution of meter-scale measurements within the units. The conceptural model and quantitative measurements will then be used with classical geostatistical continuum methods based on variograms and cross-variograms as well as discrete statistical approaches to characterize the spatial distribution of hydrogeologic units and petrophysical properties within the Sand Hill fault zone, and to relate these to the spatial distribution and petrophysical properties of lithostratigraphic units juxtaposed by the fault. The comprehensive nature of this project makes it imperative that collaboration occur at all stages. Statistical design will be incorporated with data collection and initial analyses will be used to guide measurement strategies at the later stages.

小行星9706482 断层既可以作为地下水流的通道，也可以作为地下水流的屏障，由于断层带的成岩作用和变形，断层带的渗透性会随着时间的推移而变化。 我们建议调查断层对流体流动的影响进行综合地质/水文调查的空间分布的断层带渗透性差固结沉积物。 以前对断层带渗透性的所有研究都集中在岩石上，然而美国许多重要的含水层是由不牢固的沉积物组成的。 我们对沉积含水层中断层带水文地质单元的描述将基于对一个切割松散新生代沉积物的正断层的详细研究。 沙山断层非常好地暴露，为研究断层带内结构的几何形状和连续性以及成岩特征提供了广泛的垂直和横向剖面。 断裂带的特点是优先胶结相对于邻近的沉积物，并包括细长的水泥定向带，记录在降水时的地下水流的方向。 对断裂带结构和水泥分布的初步研究表明，断裂带渗透率特征以可预测的方式变化。 我们已经建立了一个概念模型，其中断裂带的宽度和渗透性结构在横向和纵向上都是变化的，这取决于断层并置的沉积物。 这种变化表现在两个端部：（1）在细粒、低渗透性单元（如粉砂和粘土）与断层并置的地方，变形带狭窄且胶结较弱。 (2)当相对粗粒的、最初中等至高渗透性的单元（如粗砂）与断层并列时，变形区较宽，且中等至强胶结。 详细的地质测绘和断层带内的变形特征的岩相学研究，胶结模式内外的断层带，和沉积物的地层变异将被用来完善这个初步的概念模型的断层带水文地质。 作为理解胶结作用对流体流动影响的起点，我们将考虑非胶结状态和胶结状态。 未胶结的断层带水文地质单元和断层切割的岩石地层单元的渗透率变化将使用气体微渗透仪和降水头渗透率测量的组合来确定。 将通过溶解胶结物和确定重新充填沉积物的渗透率以及应用将粒度与渗透率相关联的经验公式来估计胶结前的渗透率。 在这项研究中的一个基本挑战是使用厘米尺度的渗透率值来描述更大尺度的渗透性特征的沉积物。 我们解决这个问题的方法是使用渗透率数据来表征米级水文地质单元。 更大的规模（即，十至百米尺度）的水文地质单元可被视为离散结构，其特征在于地质测绘和单元内米尺度测量的分布。 概念模型和定量测量，然后将使用经典的地质统计连续方法的基础上变异函数和交叉变异函数，以及离散的统计方法来表征沙丘断裂带内的水文地质单位和岩石物理性质的空间分布，并将这些空间分布和岩石物理性质的岩石地层单位并列的故障。 该项目的综合性质使得在所有阶段都必须进行协作。 统计设计将与数据收集相结合，初步分析将用于指导后期阶段的衡量战略。