Modeling strain and pore pressure associated with fluid extraction: The Pathfinder Ranch experiment
Modeling strain and pore pressure associated with fluid extraction: The Pathfinder Ranch experiment
复制标题
DOI：
10.1002/2014jb011169
复制
发表时间：
2014-06
期刊：
影响因子：
--
通讯作者：
A. Barbour;F. Wyatt
中科院分区：
文献类型：
--
作者：
A. Barbour;F. Wyatt
应变计可能受到附近水井抽水的水文影响，这取决于当地岩石的状态。与水文相关的应变信号通常不被使用，并且被认为是麻烦的，因为它们比大多数构造信号（例如，卡斯卡迪亚的潮汐或慢滑事件）大得多，但在这里，我们表明流体提取导致可检测的应变和孔隙压力信号，我们使用这些信号来约束有价值的岩石材料特性，即水力扩散率和弹性剪切模量。我们收集了南加州一对板块边界天文台钻孔应变仪附近的两个活动水井多年来的泵活动。这些数据清楚地证明了流体抽提与变形之间的联系：瞬态应变和孔隙压力的开始与流体抽提的开始密切相关，瞬态信号的大小与累积抽提量密切相关。这些数据还表明，这些仪器可能是远程监测液体注射和提取的工具。基于孔隙弹性模型，我们发现水力扩散系数（0.061 m2s−1至0.126 m2s−1）与断裂火成岩的数据一致，剪切模量（39.7 MPa至101 MPa）与浅花岗闪长岩的数据相当——预计由于风化和其他来源的破坏（如断裂）而变弱。我们推断，该地区的地壳岩石在浅层深处被普遍存在的水力传导裂缝排干：由于施加应力的变化，流体将发生流动，而不是孔隙流体压力的持续变化。
Strainmeters can be subject to hydrologic effects from pumping of nearby water wells, depending on the state of the local rock. Strain signals associated with hydrology are generally not used and regarded as troublesome because they are much larger than most tectonic signals (e.g., tides or slow slip episodes in Cascadia), but here we show that fluid extraction leads to detectable strain and pore pressure signals, which we use to constrain valuable material properties of the rock, namely the hydraulic diffusivity and elastic shear modulus. We collected multiple years of pump activity at two active water wells near a pair of Plate Boundary Observatory borehole strainmeters in southern California. These data demonstrate clearly the connection between fluid extraction and deformation: the onset of transient strains and pore pressures is strongly correlated with both the onset of fluid extraction, and the sizes of the transient signals are strongly correlated with cumulative extraction volumes. These data also suggest that the instruments are a possible tool for remote monitoring of fluid injection and withdrawal. Based on poroelastic modeling, we find estimates of hydraulic diffusivity (0.061 m2s−1 to 0.126 m2s−1) which are consistent with data for fractured igneous rock, and estimates of shear modulus (39.7 MPa to 101 MPa) which are comparable to data for shallow granodiorite—expected to be weak from weathering, and other sources of damage (e.g., faulting). We infer that crustal rock in this region is drained at shallow depths by pervasive, hydraulically conductive fractures: as a result of changes in applied stress, fluid flow will occur rather than a sustained change in pore fluid pressure.