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.

9706482 古德温断层可以充当地下水流的管道或屏障，并且由于断层带中的成岩作用和变形，其渗透性会随着时间的推移而变化。 我们建议通过对固结不良沉积物中断层带渗透性的空间分布进行综合地质/水文调查来研究断层对流体流动的影响。 以前所有关于断层带渗透性的研究都集中在岩石上，但美国许多重要的含水层都是由固结不良的沉积物组成的。 我们对沉积含水层断层带水文地质单元的表征将基于对挖掘出的正断层切割松散新生代沉积物的详细研究。 沙山断层暴露得非常好，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。 断层带的特点是相对于邻近沉积物优先胶结，并包括细长定向的胶结带，记录了降水时地下水流的方向。 对断层带结构和胶结物分布的初步研究表明，断层带渗透性特征以可预测的方式变化。 我们构建了一个概念模型，其中断层带的宽度和渗透性结构在横向和纵向上发生变化，具体取决于断层并置的沉积物。 这种变化由两个端元表示：（1）当细粒、低渗透单元如粉砂和粘土与断层并置时，变形区域狭窄且胶结弱。 (2)当断层并置粗砂等较粗粒、初中至高渗透性单元时，变形带较宽，胶结程度为中至强。 对断层带内变形特征、断层带内外胶结模式以及沉积物地层变化的详细地质测绘和岩相研究将用于完善断层带水文地质学的初步概念模型。 作为理解胶结对流体流动影响的起点，我们将考虑非胶结和胶结状态。 被断层切割的非胶结断层带水文地质单元和岩石地层单元的渗透率变化将通过气体微型渗透率计和落水头渗透率测量的组合来确定。 预胶结渗透率将通过溶解水泥并确定重新充填沉积物的渗透率以及应用将颗粒尺寸与渗透率相关的经验公式来估计。 这项研究的一个基本挑战是使用厘米级渗透率值来描述沉积物的更大规模渗透率特征。 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。 较大规模（即十米到百米规模）的水文地质单元可被视为离散结构，并通过地质绘图和单元内米级测量的分布来表征。 然后，概念模型和定量测量将与基于变差函数和交叉变差函数的经典地质统计连续体方法以及离散统计方法一起使用，以表征沙山断层带内水文地质单元和岩石物理性质的空间分布，并将这些联系起来断层并置的岩石地层单元的空间分布和岩石物理性质。 该项目的综合性使得各个阶段的协作势在必行。 统计设计将与数据收集结合起来，初步分析将用于指导后期的测量策略。