This paper provides a review of hydromechanical (HM) couplings in fractured rock, with special emphasis on HM interactions as a result of, or directly connected with human activities. In the early 1960s, the coupling between hydraulic and mechanical processes in fractured rock started to receive wide attention. A series of events including dam failures, landslides, and injection-induced earthquakes were believed to result from HM interaction. Moreover, the advent of the computer technology in the 1970s made possible the integration of nonlinear processes such as stress–permeability coupling and rock mass failure into coupled HM analysis. Coupled HM analysis is currently being applied to many geological engineering practices. One key parameter in such analyses is a good estimate of the relationship between stress and permeability. Based on available laboratory and field data, it was found that the permeability of fractured rock masses tends to be most sensitive to stress changes at shallow depth (low stress) and in areas of low in-situ permeability. In highly permeable, fractured rock sections, fluid flow may take place in clusters of connected fractures which are locked open as a result of previous shear dislocation or partial cementation of hard mineral filling. Such locked-open fractures tend to be relatively insensitive to stress and may therefore be conductive at great depths. Because of the great variability of HM properties in fractured rock, and the difficulties in using laboratory data for deriving in-situ material properties, the HM properties of fractured rock masses are best characterized in situ.

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The role of hydromechanical coupling in fractured rock engineering

Zoback and Gorelick [(2012) Proc Natl Acad Sci USA 109(26):10164–10168] have claimed that geologic carbon storage in deep saline formations is very likely to trigger large induced seismicity, which may damage the caprock and ruin the objective of keeping CO2 stored deep underground. We argue that felt induced earthquakes due to geologic CO2 storage are unlikely because (i) sedimentary formations, which are softer than the crystalline basement, are rarely critically stressed; (ii) the least stable situation occurs at the beginning of injection, which makes it easy to control; (iii) CO2 dissolution into brine may help in reducing overpressure; and (iv) CO2 will not flow across the caprock because of capillarity, but brine will, which will reduce overpressure further. The latter two mechanisms ensure that overpressures caused by CO2 injection will dissipate in a moderate time after injection stops, hindering the occurrence of postinjection induced seismicity. Furthermore, even if microseismicity were induced, CO2 leakage through fault reactivation would be unlikely because the high clay content of caprocks ensures a reduced permeability and increased entry pressure along the localized deformation zone. For these reasons, we contend that properly sited and managed geologic carbon storage in deep saline formations remains a safe option to mitigate anthropogenic climate change.

/pdf/geologic-carbon-storage-is-unlikely-to-trigger-large-ypw47vtust.pdf

Geologic carbon storage is unlikely to trigger large earthquakes and reactivate faults through which CO2 could leak

Over the last few decades, it has become clear that various human activities have the potential to generate seismic activity. Examples include subsurface waste injection, reservoir impoundment in the vicinity of large dams, and development of mining, geothermal or hydrocarbon resources. Recently, induced seismicity has also become a concern in connection with geologic carbon sequestration projects. This study focuses on seismicity induced by hydrocarbon production by summarizing the published case studies and describing current theoretical approaches to model these. It is important to understand the conditions under which hydrocarbon production may lead to seismic activity in order to ensure that they are performed safely. Our knowledge of induced seismicity in hydrocarbon fields has progressed substantially over the last few years owing to more intensive high-quality instrumentation of oil fields and a continuous effort to understand the phenomenon theoretically. However, much of the available literature is dispersed over a variety of journals and specialized reports. This review aims at providing a first step toward making the current knowledge about induced seismicity in hydrocarbon fields more accessible to a broad audience of scientists.

Induced Seismicity in Hydrocarbon Fields

https://www.taqainnederland.nl/wp-content/uploads/2015/06/pdf/KNMI%20rapport.pdf

J.P.A. Roest

Papers

Investigating fault slip in a model of an underground gas storage facility