RUI: Coupled Fold-fracture Evolution in the Stillwell Anticline, West Texas

RUI：西德克萨斯州斯蒂尔韦尔背斜的耦合褶皱-断裂演化

• 批准号: 1220235
• 负责人: Benjamin Surpless
• 金额: $ 12.72万
• 依托单位: Trinity University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220235&HistoricalAwards=false
• 关键词: RUI; Coupled; Fold; fracture; Evolution

The linked formation and evolution of faults, folds, and fracture systems continue to be an important area of research because of the inherent importance of these features to the movement of fluids in the subsurface. A reconnaissance investigation of the well-exposed Stillwell anticline in west Texas has revealed along strike variation in fold geometry tied to different stages of fold evolution; the fold?s geometry supports formation controlled by propagation of an underlying basement fault system. Past research has revealed a range of factors that play important roles in the development of fracture systems in this context, including the influence of initial and transitional fold geometries, the influence of pre-existing fractures, the presence or absence of interlayer slip, and the effects of the underlying fault systems that are responsible for fold development. However, few studies have integrated a quantitative description of fracture strain and width or explored how fracture cement textures can be used to unravel the timing of fracture opening or relict porosities associated with fracture networks. The goal of this project is to integrate an array of evidence in an attempt to answer four primary research questions including: 1) Can structural position within an anticline system be used as a predictor of fracture intensity?; 2) Can mechanical stratigraphy be correlated with fracture stratigraphy?; 3) How to do the distributions, intensities, orientations, and cements of fractures sets vary before, during, and after fold formation?; and 4) What other (non-fracture-related) modes of deformation accommodate strain at different positions within a fold system?The excellent exposure of the anticline provides the opportunity to directly observe fractures, faults, and deformation bands within the folded layers, which can be used to help constrain the kinematic evolution of the fold. In addition, detailed mapping of cross-sectional fracture networks in concert with Schmidt hammer testing of these lithologies, to provide meter-scale semi-quantitative information about the rigidity of deformed beds, will generate a detailed mechanical stratigraphy that can be evaluated in the context of fold and fracture formation. Closely linked with analysis of mechanical behavior, the research team will apply fracture intensity analysis based on both layer thicknesses and structural position within the fold system, taking the wide spectrum of fracture sizes into account. This approach permits evaluation of the scale-dependence of fracture intensity, which can be a serious problem in the evaluation of permeability in subsurface core-based studies. In addition, standard microscopic petrographic analysis and scanning-electron-microscope-based cathodoluminescence imaging will help document growth textures in opening-mode fracture cements to determine synkinematic changes in permeability. Finally, computer kinematic modeling of fault-related fold formation will be used to constrain the predicted distribution of strain across the fold system in order to relate the timing of fracture formation to stages of fold evolution. The results of the proposed research will provide a new view of how permeability evolves during fold formation. Important decisions regarding subsurface water and petroleum exploration are commonly made with incomplete data. If the proposed research can answer the questions posed above, then this coupled fold-fracture investigation of the Stillwell anticline system will provide a model that should reduce uncertainty in permeability evaluation in less well-constrained systems worldwide. In addition to the scientific objectives of the research, the project is integrating undergraduate field instruction with field research, ensuring that undergraduate researchers gain a thorough overall understanding of fundamental geological processes in the context of their own work. In addition, Trinity University undergraduate students will have the opportunity to travel to research labs to perform analyses with faculty at larger research institutions; will disseminate results of their research through independent research papers, senior theses, and presentations at both regional and national meetings; and all project research results and subsequent products will be made accessible to all Trinity students and to the general public through a collaborative project with the Trinity University library.

断层、褶皱和断裂系统的形成和演化仍然是一个重要的研究领域，因为这些特征对地下流体的运动具有固有的重要性。 对德克萨斯州西部暴露良好的斯蒂尔韦尔背斜进行的一项勘察调查显示，褶皱几何形状的沿着走向变化与褶皱演化的不同阶段有关;的几何形状支持由下伏基底断裂系统的传播控制的形成。 过去的研究已经揭示了一系列在这种背景下裂缝系统的发展中发挥重要作用的因素，包括初始和过渡褶皱几何形状的影响，预先存在的裂缝的影响，层间滑动的存在或不存在，以及负责褶皱发展的潜在断层系统的影响。 然而，很少有研究整合了定量描述的裂缝应变和宽度或探讨如何骨折水泥纹理可以用来解开裂缝开口或残余孔隙与裂缝网络的时间。该项目的目标是整合一系列证据，试图回答四个主要的研究问题，包括：1）构造位置在一个背斜系统可以被用来作为断裂强度的预测？2)力学地层学能与断裂地层学相联系吗？3)在褶皱形成之前、之中和之后，裂缝组的分布、强度、方向和胶结物是如何变化的？以及4）在褶皱系统内的不同位置处，还有哪些其他（与断裂无关的）变形模式适应应变？背斜的良好暴露提供了直接观察褶皱层内断裂、断层和变形带的机会，这些可用于帮助限制褶皱的运动学演化。此外，详细绘制横截面裂缝网络，并结合对这些岩性进行施密特锤测试，以提供有关变形地层刚度的米级半定量信息，将生成详细的力学地层学，可以在褶皱和断裂的背景下进行评估形成。与力学行为分析密切相关，研究团队将根据褶皱系统内的层厚度和结构位置进行断裂强度分析，同时考虑到断裂尺寸的广泛性。这种方法允许评价裂缝强度的尺度依赖性，这在基于地下岩心的研究中的渗透率评价中可能是一个严重的问题。此外，标准的显微岩相分析和扫描电子显微镜为基础的阴极发光成像将有助于文件的增长纹理在开放式骨折水泥，以确定同运动的渗透率变化。最后，断层相关褶皱形成的计算机运动学建模将用于约束预测的褶皱系统中的应变分布，以便将断裂形成的时间与褶皱演化的阶段联系起来。拟议的研究结果将提供一个新的观点如何渗透率在褶皱形成过程中的演变。关于地下水和石油勘探的重要决策通常是在数据不完整的情况下做出的。如果拟议的研究可以回答上述问题，那么斯蒂尔韦尔背斜系统的耦合褶皱-断裂调查将提供一个模型，可以减少全球井约束较少的系统中渗透率评估的不确定性。除了研究的科学目标外，该项目还将本科生实地教学与实地研究相结合，确保本科生研究人员在自己的工作背景下对基本地质过程有全面的了解。 此外，Trinity大学的本科生将有机会前往研究实验室，与较大的研究机构的教师进行分析;将通过独立的研究论文，高级论文和在区域和国家会议上的演讲来传播他们的研究成果;和所有项目的研究成果和后续产品将提供给所有Trinity学生和公众通过一个合作项目，Trinity大学图书馆