The significance of hydrothermal alteration zones for the mechanical behavior of a geothermal reservoir

Abstract

Background: The occurrence of hydrothermally altered zones is a commonly observed phenomenon in brittle rock. The dissolution and transformation of primary minerals and the precipitation of secondary minerals affect rocks in terms of mechanics, stress conditions, and induced seismicity.

Is There a Link Between Mineralogy, Petrophysics, and the Hydraulic and Seismic Behaviors of the Soultz‐sous‐Forêts Granite During Stimulation? A Review and Reinterpretation of Petro‐Hydromechanical Data Toward a Better Understanding of Induced Seismicity and Fluid Flow

“…A further important aspect with respect to microseismicity is the mechanical properties of the fractures arising from their mineralogical infilling. Meller and Kohl () showed on the basis of induced seismicity during the 2000 stimulation of GPK1 that the large‐magnitude events are induced on fractures showing no significant clay filling resulting from hydrothermal alteration. Besides the evidence that clay‐rich fractures tend to produce smaller seismic events, they also showed a possible relationship between clay filling in fractures and the occurrence of aseismic slip.…”

“…The seismicity is driven by the local stress field but triggered on an existing fracture by the pore pressure increase; (ii) temperature decrease induced by cool fluid interacting with hot rock causing contraction of the fracture surface (thermoelastic strain) and slip within or around the reservoir; (iii) volume change due to fluid injection or withdrawal that causes a perturbation in local stress conditions, which are already close to failure state (see also Cornet, Bérard, & Bourouis, ); and (iv) chemical alteration of fracture walls because of the interaction of nonnative fluids, thus changing the coefficient of friction and/or cohesion on those surfaces. Reduced friction would promote small seismic events (Meller & Kohl, ).…”

Integrated Research as Key to the Development of a Sustainable Geothermal Energy Technology

“…[60] Furthermore,k nowledge of the in situ stress field, its highly debated rotations,a nd mechanicalp roperties of the reservoir obtained from borehole breakout patterns are essentialf or reservoir engineering in terms of the stability of the construction andt he predictability of seismic hazards that result from productionacross the entire reservoir. [61,62] 3.1.7. Insights from the Soultz-sous-Fôrets case study…”

“…The five steps in the curve are attributed to large structures inside the reservoir, which affect the propagation of fluid and seismicity.T hese structures could be either large fracture zones focusing fluid flow and microseismicity,a sp ostulated by Evans, [43] or very clay-richz ones,w hichh amper spreading of the seismic cloud. [62] In Figure 18 b, constant friction coefficientsa nd cohesion are used for the calculation of P c .T he evolutiono fs eismicity illustrated by Figure 18 aa nd bi sv ery different. Whereas the number of seismic events exponentially increasei nF igure 18 a, the uniform friction and cohesion curve of Figure 18 bs hows ar apid increase in the number of sheared fractures with increasing pressure.…”

Experimental investigation of mechanical properties and energy features of granite after heat treatment under different loading paths

“…In geotechnical engineering, surrounding rock may withstand high temperature, which occurs in instances such as a radioactive waste repository [1][2][3], enhanced geothermal system [4][5][6], volcano flank [7], and the reconstruction of tunnels after fire disasters. Changes in the properties of rock after undergoing high temperature may affect stability and even induce engineering accidents.…”