Permeability reduction in granite under hydrothermal conditions

Abstract

Abstract. The formation of impermeable fault seals between earthquake events is a feature of many models of earthquake generation, suggesting that earthquake recurrence may depend in part on the rate of permeability reduction of fault zone materials under hydrothermal conditions. In this study, permeability measurements were conducted on intact, fractured, and gouge-bearing In contrast, prefractured samples showed higher rates of permeability decrease at a given temperature. The surfaces of the fractured samples showed evidence of dissolution and mineral growth that increased in abundance with both temperature and time. The experimentally grown mineral assemblages varied with temperature and were consistent with a rock-dominated hydrothermal system. As such mineral deposits progressively seal the fractured samples, their rates of permeability decrease approach the rates for intact rocks at the same temperature. These results place constraints on models of precipitation sealing and suggest that fault rocks may seal at a rate consistent with earthquake recurrence intervals of typical fault zones.

A numerical model simulating reactive transport and evolution of fracture permeability

“…Dissolution-driven sealing, likely resulting from dissolution beneath propping asperities in contact, is reported for natural and artificial fractures at elevated temperatures ð> 3008CÞ in sandstone [1,2], in granite [3], and in quartz [4], and at modest temperatures (50-1508CÞ in tuff [5] and in novaculite [6]. These are supplemented by results at both high confining stress ð> 150 MPaÞ in granite [7] and at low stress (0.2 MPa) in marble where an acidic permeant is circulated [8].…”

Evolution of fracture normal stiffness due to pressure dissolution and precipitation

“…Their combined effect leads to a redistribution of material, driven by spatial gradients in chemical potential, from the mechanically stressed grain contacts to the mechanically open pore space (Weyl, 1959;Rutter, 1976;Gratz, 1991;Lehner and Leroy, 2004). Although the hydraulic response to such compaction processes on fractures have been extensively studied (Moore et al, 1994;Durham et al, 2001;Morrow et al, 2001;Polak et al, 2003;Yasuhara et al, 2006), quantitative studies of the mechanical effects are sparse, and they remain experimentally challenging.…”

Extreme hydrothermal conditions at an active plate-bounding fault

“…1). Borehole injection experiments, earthquake aftershock studies, and laboratory experiments on fault zone materials reveal that the earthquake process perturbs the fault zone, which then heals during the post-seismic period [22][23][24][25][26] .…”