52nd U.S. Rock Mechanics/Geomechanics Symposium,
2018. American Rock Mechanics Association
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ABSTRACT: In geologic formation, the natural fracture as flow conduit is a dominant factor for the subsurface fluid flow. Most of these natural fractures remain open in deep earth mainly through the self-propping by some discrete asperities, the integrity of asperity plays an important role in maintaining the integrity of fractures. The thermo-hydro-mechanical-chemical coupled analysis on asperity integrity is currently prevailing, whereas potential thermos-mechanical failure or damage of asperity is ignored in current analysis. Two potential failure patterns of asperity had been found in our previous research work. This study focuses on the mechanism of one of these two failure patterns: the radial cracking on the top of asperity. An analytical fracture mechanics model is developed to investigate radial cracking. In this paper, the analytical model is firstly compared with previous numerical simulation with comparable results. Then, the effects of two main factors on radial cracking are systematically investigated. Our results show that thermal cooling is the driving force for radial cracking, but overburden pressure could slightly retard this cracking process. Finally, cracking conditions based on combined effects of thermal cooling and overburden loading are provided. The analytical model can assist assessment of asperity failure when subjected to thermal stress.
Fracture as a major factor which greatly affect the fluid flow, heat recovery, colloid transport in environmental remediation, geothermal exploitation, and oil production. These natural and/or man-made fractures are mainly propped by nominal contact of uneven surfaces unless proponents are used. These discrete contacting roughness on fracture surfaces are called asperities. The importance of fractures on hydraulic transmissivity, flow channeling and heat recovery efficiency in fractures has long been acknowledged in areas such as the water flooding for secondary oil recovery (Settari and Warren, 1994; Koutsabelouli and Hope, 1998), the heat extraction in geothermal energy development (Watanabe et al., 2008; Caulk et al., 2016), and the high-level radioactive waste disposal storage (Pyrack-Nolte et al., 1987; Pruess et al., 1990). The integrity of asperity is essentially important in controlling fracture apertures in geological formation.
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