Rutter Ernest, Hackston Abigail
Rock Deformation Laboratory, School of Earth and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK
Rock Deformation Laboratory, School of Earth and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK.
Philos Trans A Math Phys Eng Sci. 2017 Sep 28;375(2103). doi: 10.1098/rsta.2016.0001.
Fluid injection into rocks is increasingly used for energy extraction and for fluid wastes disposal, and can trigger/induce small- to medium-scale seismicity. Fluctuations in pore fluid pressure may also be associated with natural seismicity. The energy release in anthropogenically induced seismicity is sensitive to amount and pressure of fluid injected, through the way that seismic moment release is related to slipped area, and is strongly affected by the hydraulic conductance of the faulted rock mass. Bearing in mind the scaling issues that apply, fluid injection-driven fault motion can be studied on laboratory-sized samples. Here, we investigate both stable and unstable induced fault slip on pre-cut planar surfaces in Darley Dale and Pennant sandstones, with or without granular gouge. They display contrasting permeabilities, differing by a factor of 10, but mineralogies are broadly comparable. In permeable Darley Dale sandstone, fluid can access the fault plane through the rock matrix and the effective stress law is followed closely. Pore pressure change shifts the whole Mohr circle laterally. In tight Pennant sandstone, fluid only injects into the fault plane itself; stress state in the rock matrix is unaffected. Sudden access by overpressured fluid to the fault plane via hydrofracture causes seismogenic fault slips.This article is part of the themed issue 'Faulting, friction and weakening: from slow to fast motion'.
向岩石中注入流体越来越多地用于能量提取和流体废物处置，并且可能引发中小规模的地震活动。孔隙流体压力的波动也可能与天然地震活动有关。人为诱发地震活动中的能量释放对注入流体的量和压力很敏感，这是通过地震矩释放与滑动面积的关系实现的，并且受到断裂岩体水力传导率的强烈影响。考虑到适用的尺度问题，可以在实验室规模的样本上研究流体注入驱动的断层运动。在这里，我们研究了在达利戴尔砂岩和彭南特砂岩中预切割平面上有或没有颗粒状断层泥时的稳定和不稳定诱发断层滑动。它们表现出截然不同的渗透率，相差一个数量级，但矿物学大致相当。在渗透性好的达利戴尔砂岩中，流体可以通过岩石基质进入断层面，并且严格遵循有效应力定律。孔隙压力变化使整个莫尔圆横向移动。在致密的彭南特砂岩中，流体仅注入断层面本身；岩石基质中的应力状态不受影响。超压流体通过水力压裂突然进入断层面会导致发震断层滑动。本文是主题为“断层作用、摩擦与弱化：从慢速到快速运动”的特刊的一部分。
