Some THMC controls on the evolution of fracture permeability

SOME THMC CONTROLS ON THE EVOLUTION OF FRACTURE PERMEABILITY 

Department of Energy and Geo-Environmental Engineering and The Energy Institute, Pennsylvania State University, University Park, PA 16802, USA 

Importantly, fracture permeabilities may either reduce or increase, in surprising ways, depending on the paths of stress or chemical potential. We illustrate this behaviour through observations during flow-through tests on samples of varied rock types. These include a fractured porous medium (Berea sandstone), and fractures in both silicic (Arkansas novaculite) [Polak et al., 2003 Yasuhara et al., 2004] and carbonate rocks (Bellefonte Limestone) [Polak et al., 2(X)4]. 

These measurements provide unusual constraint on the evolving processes. Importantly, they allow the source of dissolved components to be determined we need to discriminate whether the source is from free-face dissolution of the fracture wall, or from stress-mediated dissolution at contacting asperities. This distinction is crucial since these two mechanisms impart opposite effects in the sense of permeability change, under net dissolution free-face dissolution increases permeability, and pressure solution reduces permeability. 

Permeability remains at this reduced magnitude while the core is at 120°C, and reduces further as the core is cooled, until it finally rises suddenly as it approaches 20°C. This behaviour, together with 

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