A new global database to improve predictions of permeability distribution in crystalline rocks at site scale

Abstract

A comprehensive worldwide permeability data set has been compiled consisting of 29,000 in situ permeabilities from 221 publications and reports and delineating the permeability distribution in crystalline rocks into depths of 2000 meters below ground surface (mbgs). We analyze the influence of technical factors (measurement method, scale effects, preferential sampling, and hydraulic anisotropy) and geological factors (lithology, current stress regime, current seismotectonic activity, and long‐term tectonogeological history) on the permeability distribution with depth, by using regression analysis and k‐means clustering. The influence of preferential sampling and hydraulic anisotropy are negligible. A scale dependency is observed based on calculated rock test volumes equaling 0.6 orders of magnitude of permeability change per order of magnitude of rock volume tested. Based on the entire data set, permeability decreases as log(k) = −1.5 × log(z) − 16.3 with permeability k (m2) and positively increasing depth z (km), and depth is the main factor driving the permeability distribution. The permeability variance is about 2 orders of magnitude at all depths, presumably representing permeability variations around brittle fault zones. Permeability and specific yield/storage exhibit similar depth trends. While in the upper 200 mbgs fracture flow varies between confined and unconfined, we observe confined fracture and matrix flow below about 600 mbgs depth. The most important geological factors are current seismotectonic activity (determined by peak ground acceleration) and long‐term tectonogeological history (determined by geological province). The impact of lithology is less important. Based on the regression coefficients derived for all the geological key factors, permeability ranges of crystalline rocks at site scale can be predicted. First tests with independent data sets are promising.

Tracking Fluid Flow in Shallow Crustal Fault Zones: 1. Insights From Single‐Hole Permeability Estimates

“…Similar observations were made on cataclasites from the Alpine Fault, New Zealand (Carpenter et al, ). While such trends are difficult to generalize, hydraulic and geothermal data and global data compilations have shown nevertheless that a decrease in permeability with depth is a basic hydromechanical property of the brittle crust (Achtziger‐Zupancic et al, ; Manning & Ingebritsen, ).…”

Large Earthquake Reshapes the Groundwater Flow System: Insight From the Water‐Level Response to Earth Tides and Atmospheric Pressure in a Deep Well

“…However, the thickness of the aquitard layer ( b ′) is smaller than L con in Wang's leaky model. We can determine that K ′ is equal to 1.58×10 ‐7 m/s before the earthquake and equal to 3.15×10 ‐7 m/s after the earthquake when we set b ′ at 500 m. Based on K con = D con × S s , we can infer the value of K con from the barometric response model when we use a common specific storage S s value for the confining layer (10 ‐8 ; Achtziger‐Zupančič et al, ), so the aquitard hydraulic conductivity will be 6.9×10 ‐9 m/s before the earthquake and 1.4 ×10 ‐8 m/s after the earthquake. This vertical hydraulic conductivity is 1–2 orders of magnitude smaller than the value calculated from the leaky model.…”

Compiling and Mapping Global Permeability of the Unconsolidated and Consolidated Earth: GLobal HYdrogeology MaPS 2.0 (GLHYMPS 2.0)

“…Permeability, the ability of a porous material to transmit fluids, is fundamental in controlling the rate in which fluids flow in the surface of the Earth, which impacts a wide variety of shallow and deep Earth processes and water resource evaluation (Achtziger‐Zupančič et al, ; Fan, ; Fan et al, ; Gleeson & Ingebritsen, ; Ingebritsen & Manning, ). The lack of regional permeability data in the past has hampered integration of groundwater dynamics and interactions into regional to global land surface and hydrology models (Bierkens, ; Fan, ).…”