Scientific Drilling into the San Andreas Fault: Fluid Transport Analysis - Rare Gas "Ages" of Matrix Porosity Fluids in Drill Core

圣安德烈亚斯断层科学钻探：流体输送分析 - 钻芯中基质孔隙流体的稀有气体“年龄”

• 批准号: 0454514
• 负责人: Martin Stute
• 金额: --
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-03-15 至 2007-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0454514&HistoricalAwards=false
• 关键词: Scientific; Drilling; into; San; Andreas

0454514StuteScientific Drilling into the San Andreas Fault: Fluid Transport Analysis - Rare Gas "Ages" of Matrix Porosity Fluids in Drill CoreMartin Stute, Peter Schlosser, Gisela Winckler Principal InvestigatorsAbstractThe currently favored explanation for the low friction slip along the San Andreas Fault Zone (SAFZ) is the presence of fluids under very high pressure. Since fluid transport is subject to wide variation in both time and space, the in situ measurement of pressure gradients and permeability in a fault zone drill hole will establish the current conditions but provide little indication of pressure/transport patterns over the time interval for pressurization cycles of the fault (decades). This study conducted by researchers from the Lamont-Doherty Earth Observatory of Columbia University tests a methodology to determine the flow of fluids into/from the fault zone using the distribution of rare gas concentrations in pore fluids recovered from cores obtained at depth in the SAFZ. Uranium and Thorium decay-series-elements, and Potassium in rocks produce 4He and 40Ar as well as nucleogenic (21,22Ne) and fissiogenic (132,134,136Xe) rare gases. Fluid 'ages' derived from rare gas concentrations depend on the production rates and the release rates into the pore fluids. Vertical and horizontal profiles of these gases in pore fluids can be modeled to determine fluid flow velocities and directions. Samples for these analyses are being obtained by sub-sampling fresh drill core recovered in the framework of the EARTHSCOPE/SAFOD project from various depths in the SAFZ. Because rare gas loss from the rock occurs over a timescales of hours to days, drill core is sub-sampled to remove the outer rind (which has already lost rare gases) and the internal sections are then placed in high vacuum containers in the field. The rare gases released to the headspace over a period of weeks to months are determined by mass spectrometry and the total pore fluid by weight. The entire suite of measured noble gas isotopes (3,4He, 20, 21, 22Ne, 36, 38, 40Ar, 84,86Kr, and 129,131, 132, 134, 136Xe) is used to separate the non-atmospheric (produced in the rocks and accumulated in pore fluids) from the atmospheric noble gas components. The study also investigates the concentrations of rare gases in the rocks and of the elements producing them to determine the source function for excess rare gas abundances in matrix pore fluids. Some of the approaches described above have seen numerous applications in studies of shallow aquifers and in a few cases of deep drilling, but it has never been used in its entirety in the context of deep scientific drilling. This study will establish the methodology providing key information for the source, direction and magnitude of fluid flow that underlie the hypothesis that superhydrostatic fluid pressures are responsible for low friction slip along the SAFZ on timescales of decades. This has wide ranging implications for the understanding the SAFZ and earth quake prediction, affecting millions of people in California. Broader impacts of the study include the training of a graduate student, and the integration of results of this study in the Earth Science curriculum at Columbia University. This work is also integrated in the research and educational activities of Columbia's Center for Hazards and Risk Research (CHRR) whose mission it is to advance the predictive science of natural and environmental hazards and the integration of science with hazard risk assessment and management.

0454514Stute 对圣安德烈亚斯断层进行科学钻探：流体输运分析 - 钻芯中基质孔隙流体的稀有气体“年龄”Martin Stute、Peter Schlosser、Gisela Winckler 首席研究员摘要当前流行的对沿圣安地列斯断层带 (SAFZ) 低摩擦滑移的解释是在非常高的压力下存在流体。由于流体输送在时间和空间上都会发生很大的变化，因此对断层带钻孔中的压力梯度和渗透率进行现场测量将建立当前条件，但几乎无法提供加压循环时间间隔内的压力/输送模式的指示故障的发生时间（几十年）。这项研究由哥伦比亚大学拉蒙特-多尔蒂地球观测站的研究人员进行，测试了一种方法，利用从 SAFZ 深处获得的岩心回收的孔隙流体中稀有气体浓度的分布来确定流体流入/流出断层带的方法。铀和钍衰变系列元素以及岩石中的钾产生 4He 和 40Ar 以及成核 (21,22Ne) 和裂变 (132,134,136Xe) 稀有气体。由稀有气体浓度得出的流体“年龄”取决于生成速率和向孔隙流体中的释放速率。 可以对孔隙流体中这些气体的垂直和水平剖面进行建模，以确定流体流速和方向。这些分析的样本是通过对在 EARTHSCOPE/SAFOD 项目框架内从 SAFZ 不同深度回收的新鲜钻芯进行二次取样而获得的。由于稀有气体从岩石中的流失发生在数小时至数天的时间范围内，因此对钻芯进行二次取样以去除外皮（已经流失了稀有气体），然后将内部部分放置在现场的高真空容器中。 通过质谱法测定数周至数月期间释放到顶部空间的稀有气体，并按重量测定总孔隙流体。整套测量的稀有气体同位素（3,4He、20、21、22Ne、36、38、40Ar、84,86Kr 和 129,131、132、134、136Xe）用于分离非大气（在岩石和孔隙流体中积累的）来自大气中的稀有气体成分。该研究还调查了岩石中稀有气体的浓度以及产生稀有气体的元素，以确定基质孔隙流体中过量稀有气体丰度的源函数。上述一些方法在浅层含水层研究和一些深钻探案例中得到了广泛应用，但从未在深层科学钻探中得到完整应用。这项研究将建立一种方法，为流体流动的来源、方向和大小提供关键信息，该方法是超静压流体压力导致数十年时间尺度上沿 SAFZ 的低摩擦滑动的假设的基础。这对于理解 SAFZ 和地震预测具有广泛的影响，影响着加利福尼亚州数百万人。 这项研究的更广泛影响包括研究生的培训，以及将这项研究的结果整合到哥伦比亚大学的地球科学课程中。这项工作也被纳入哥伦比亚灾害与风险研究中心 (CHRR) 的研究和教育活动中，该中心的使命是推进自然和环境灾害的预测科学以及科学与灾害风险评估和管理的结合。