The biases and trends in fault zone hydrogeology conceptual models: global compilation and categorical data analysis

Abstract

To investigate the biases and trends in observations of the permeability structures of fault zones in various geoscience disciplines, we review and compile a database of published studies and reports containing more than 900 references. The global data are categorized, mapped, and described statistically. We use the chi‐square test for the dependency of categorical variables to show that the simplified fault permeability structure (barrier, conduit, barrier–conduit) depends on the observation method, geoscience discipline, and lithology. In the crystalline rocks, the in situ test methods (boreholes or tunnels) favor the detection of permeable fault conduits, in contrast to the outcrop‐based measurements that favor a combined barrier–conduit conceptual models. These differences also occur, to a lesser extent, in sedimentary rocks. We provide an estimate of the occurrence of fault conduits and barriers in the brittle crust. Faults behave as conduits at 70% of sites, regardless of their barrier behavior that may also occur. Faults behave as barriers at at least 50% of the sites, in addition to often being conduits. Our review of published data from long tunnels suggests that in crystalline rocks, 40–80% (median about 60%) of faults are highly permeable conduits, and 30–70% in sedimentary rocks. The trends with depth are not clear, but there are less fault conduits counted in tunnels at the shallowest depths. The barrier hydraulic behavior of faults is more uncertain and difficult to observe than the conduit.

Field characterization of elastic properties across a fault zone reactivated by fluid injection

“…For these reasons faults play a major role in various crustal processes and the characterization of their properties and their potential activation is a major issue in seismic risk assessment [Yi et al, 2004] and during reservoir development [Jeanne et al, 2014b], production [Knipe et al, 1998], and management [Fossen et al, 2005]. Many studies have been done to characterize and estimate the structural and hydraulic properties of fault zone [Bense et al, 2013;Scibek et al, 2016], but relatively few have focused on their elastic properties. The reason is that fault zones are very difficult to sample for laboratory testing because they contain highly contrasted types of materials from low cohesive materials to multiscale fractures.…”

Fault zone hydrogeology: introduction to the special issue

“…One final paper attempts to raise awareness of trends and biases in how fault zone hydrogeological properties are characterized by different disciplines (Scibek et al . ).…”

“…Scibek et al . () attempted to identify whether observational bias exists, by bringing together as many data sets as possible from various published sources ranging from hydrogeological investigations, mining studies, structural geology and hydrocarbon reservoir research. These authors then set out to establish whether any particular approach, and/or background of the research team, led to a bias in how fault zones are viewed (i.e.…”

“…Papers in the special issue are organized into the following themes: laboratory characterization of the impact of tectonic deformation on the evolution of hydraulic properties (Giwelli et al 2016), field characterization of fault zone hydrogeology (Achtziger-Zupan ci c et al 2016;Mundy et al 2016), the impacts of faults on hydrothermal convection (Stober et al, 2016;Li et al 2016) and relevance of fault zones for the leakage of CO 2 from deep reservoirs (Bu et al 2016;Raduha et al 2016). One final paper attempts to raise awareness of trends and biases in how fault zone hydrogeological properties are characterized by different disciplines (Scibek et al 2016).…”

“…The reported hydrologic behaviour of fault zones can vary depending on the geologic setting and conditions as well as the underlying goals of the research community undertaking the investigation (Bense et al 2013). Scibek et al (2016) attempted to identify whether observational bias exists, by bringing together as many data sets as possible from various published sources ranging from hydrogeological investigations, mining studies, structural geology and hydrocarbon reservoir research. These authors then set out to establish whether any particular approach, and/or background of the research team, led to a bias in how fault zones are viewed (i.e.…”