Scientific Drilling into the San Andreas Fault: Rare Gas 'Ages' of Matrix Fluids in Drill Core and Fluid Dynamics

该项目分析在SAFOD第三阶段岩心运行期间收集的基质流体样本，以确定流体流入/流出断裂带的流量，使用由OsenBrueck(1996)开创并由该小组演示的既定惰性气体方法[Stute等人，2005,2007，Ali等人，2007，AGU和EarthScope摘要]。在SAFOD第三阶段取心计划(2007)期间，将对从先前NSF支持下采集的17个基质流体样品进行孔隙流体年龄、年龄梯度和基质流体的3He/4He同位素剖面的评估。这些结果将被解释为表明流入/流出SAFZ的流体的大小和方向。基质流体的~4He和~(40)Ar“年龄”是水岩比、固相产气率和释放到孔隙流体中的产气量的函数。本研究中要测量的一套惰性气体同位素将用于分离非大气(生产和积累的)和大气稀有气体组分。基本上，回收的钻芯的外层在回收岩芯后立即被现场取出，并将来自中心的一小部分样本放入真空容器中。然后将大气气体从容器中移除，并将容器密封。稀有气体和基质流体目前正在从回收的样品中扩散出来。在这个项目的过程中，释放到顶空的惰性气体将通过质谱学确定，基质流体的总体积将根据重量确定。固体中的稀有气体浓度也被用来确定基质孔隙流体中过量稀有气体丰度的源函数和岩石中稀有气体的释放。将使用阶跃加热实验来确定固相扩散损失。基质流体“年龄”和“年龄”梯度的计算将被用来估计断裂带内/附近的流体运移的时间尺度和方向，在运移的时间尺度上(10到100年)。

This project analyzes matrix fluid samples collected during SAFOD Phase III core runs to determine the flow of fluids into/from the fault zone using established noble gas methodologies pioneered by Osenbrueck (1996) and demonstrated by this group [Stute et al.,2005, 2007, Ali et al., 2007, AGU and EarthScope abstracts]. The 17 matrix fluid samples obtained from drillcore collected with previous NSF support during the SAFOD Phase III coring program (2007) will be evaluated with regard to pore fluid ages, age gradients and 3He/4He isotopic profiles of matrix fluids. These results will be interpreted to indicate the magnitude and direction of fluid flow into/from the SAFZ. The 4He and 40Ar "age" of the matrix fluid is a function of the water/rock ratio, production rates in the solid phase and the fraction of produced gases released to the pore fluid. The suite of noble gas isotopes to be measured in this study will be used to separate non-atmospheric (produced and accumulated) and atmospheric noble gas components. Essentially, the outer rind of the recovered drillcore was removed on site immediately after core recovery and a small subsample from the center was placed in a vacuum container. Atmospheric gases were then removed from the container and the container was sealed. Noble gases and matrix fluids are currently diffusing out of the recovered sample. During the course of this project, the noble gases released to the headspace will be determined mass spectrometrically and the total volume of matrix fluid will be determined by weight. Noble gas concentrations in solids are also used to determine the source function for excess noble gas abundances in matrix pore fluids and the release of noble gases from the rock. Step heating experiments will be used to determine the diffusive loss from the solid phase. The calculation of the matrix fluid "age" and "age" gradient will be used to estimate the time scale and direction of fluid transport in/near the fault zone on the time scale of the transport (10s to 100s of years).