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.

0454514 Stute科学钻探进入圣安德烈亚斯断层：流体输运分析--岩芯中基质孔隙流体的稀有气体“年龄”Martin Stute，Peter Schlosser，Gisela Winckler首席研究员摘要目前对圣安德烈亚斯断层带（SAFZ）沿着低摩擦滑动的有利解释是在非常高的压力下存在流体。由于流体输运在时间和空间上都有很大的变化，断层带钻孔中的压力梯度和渗透率的现场测量将建立当前条件，但几乎不能提供断层加压周期（数十年）时间间隔内的压力/输运模式的指示。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深处获得的岩心中回收的孔隙流体中稀有气体浓度的分布来确定流入/流出断层带的流体。岩石中的铀、钍衰变系元素和钾产生~ 4 He和~（40）Ar以及成核（~（21）Ne）和裂变（~（132）Ne）稀有气体。由稀有气体浓度导出的流体年龄取决于产出速率和释放到孔隙流体中的速率。 这些气体在孔隙流体中的垂直和水平剖面可以被建模以确定流体流动速度和方向。这些分析所需的样品是通过对在EARTHSCOPE/SAFOD项目框架内从SAFZ不同深度采集的新鲜岩芯进行二次取样而获得的。由于稀有气体从岩石中的损失发生在数小时到数天的时间尺度上，因此对岩心进行二次取样以去除外壳（已经损失了稀有气体），然后将内部部分放置在现场的高真空容器中。 在数周至数月的时间内释放到顶部空间的稀有气体通过质谱法测定，并且总孔隙流体按重量计。惰性气体同位素的全套测量（3，4 He，20，21，22 Ne，36，38，40 Ar，84，86 Kr和129，131，132，134，136 Kr）用于分离非大气（产生于岩石中并积累在孔隙流体中）和大气惰性气体组分。研究还调查了岩石中稀有气体的浓度和产生它们的元素，以确定基质孔隙流体中过量稀有气体丰度的源函数。上文所述的一些方法在研究浅层含水层和少数深层钻探中得到了大量应用，但在深层科学钻探中从未完全使用过。这项研究将建立的方法提供的来源，方向和规模的流体流动的基础假设，超流体静力学流体压力是负责低摩擦滑动沿着SAFZ的几十年的时间尺度上的关键信息。这对理解SAFZ和地震预测具有广泛的影响，影响了加州数百万人。 这项研究的更广泛影响包括培训一名研究生，以及将这项研究的结果纳入哥伦比亚大学的地球科学课程。这项工作也纳入了哥伦比亚灾害和风险研究中心的研究和教育活动，该中心的使命是促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。