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Collaborating Authors
Results
Exploring the Link between Permeability and Strength Evolution during Fracture Shearing
Ishibashi, T. (Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology) | Asanuma, H. (Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology) | Fang, Y. (The Pennsylvania State University) | Wang, C. (The Pennsylvania State University) | Elsworth, D. (The Pennsylvania State University)
Abstract: The evolution of fracture permeability during shearing is crucial in defining the impact of hydraulic stimulation in geothermal and hydrocarbon reservoirs and in describing earthquake mechanisms in induced seismicity. In exploring this phenomenon we link permeability evolution to strength evolution during fracture shearing. In particular, permeability is expected to be incremented by shear-induced dilation for velocity-weakening (i.e., seismic slip) rock fractures and decremented by shear-induced compaction or neutral deformation for velocity-strengthening (i.e., aseismic slip) failure. To confirm our assumptions, a series of experiments are conducted in a triaxial pressure vessel, where confining pressure, pore pressure, and shearing velocity are applied independently, and the evolution of fracture permeability is concurrently monitored. We explore rock rheology through these experiments for both velocity-weakening (e.g., Westerly granite) and velocity-strengthening (e.g., Green River shale) states. The results of comparison study are different from what we expected, but are useful to link between permeability and strength evolution during fracture shearing. This concept will be, furthermore, probed by linking permeability evolution to concepts of dilation and wear recovered from rate-state characterizations of frictional behavior (see Fang et al., 2016 for detail). Introduction Fluid injection into geothermal and hydrocarbon reservoirs (i.e., hydraulic stimulation) is recognized as one of the most general processes to improve or maintain the ability of reservoirs. However, at the same moment, fluid injections into underground can cause earthquakes (Ellsworth, 2013; Majer et al., 2007), and the construction of modeling frameworks for such induced-seismicity are desirable to determine the best scenario of fluid injection (Fang et al., 2015b; Norbeck et al., 2015). To adequately model such induced-seismicity during fluid injection or define the impact of hydraulic stimulation, mechanical property (i.e., strength/friction) and hydraulic property (i.e., permeability) of rock fracture during shearing are necessary to be clarified. Though there are significant number of previous studies for the mechanical property (Fang et al., 2015a; Kohli and Zoback, 2013; Marone, 1998), previous studies which note on the hydraulic property are limited. Although the hydraulic properties of fracture has been explored through laboratory experiments (Esaki et al., 1999), numerical models (Ishibashi et al., 2016) or field experiments (Guglielmi et al., 2015a, 2015b), it is difficult to explain these results uniformly. Specifically, in the former two studies, the effects of shearing velocity on hydraulic properties are ignored. Furthermore, no discussion on the link between strength and permeability during shearing are presented.
- North America > United States > Texas (0.28)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.32)
Abstract: There is wide concern that pressurized CO2 fluid has a potential to induce seismicity in the impermeable caprocks that overlie CO2 injection formations. However, the possible impact of induced seismicity on sustainable CO2 containment from geological CO2 sequestration remains unclear because the earthquakes play a significant but mysterious role in influencing the integrity of the caprocks by hypothesized interrelated friction-permeability interaction processes: (1) the earthquakes may occur seismically (i.e., frictionally unstable), enhancing the permeability of faults instantly and leading to potential breaching and loss of inventory; or (2) the earthquakes may occur aseismically (i.e., frictionally stable), closing the aperture of faults and reducing permeability through creep. In this study, we explore these processes through experiments in which we measure the frictional parameters and hydraulic properties using Green River shale sample as an analogue caprock candidate. We observe that fracture permeability declines during shearing while the increased sliding velocity reduces the rate of decline. The physics of these observed behaviors are explored via parametric study and surface measurement of fractures, showing that both permeability and frictional strength are correlated to the fracture asperity evolution that is controlled by the sliding velocity and fracture material. Through the velocity step, the velocity strengthening behavior is observed for Green River shale, suggesting that for Green River shale, only aseismic slip would occur at a low sliding velocity during which the permeability would decrease. Introduction Geological storage of carbon dioxide (CO2) is considered a viable method to significantly reduce CO2 emissions from energy production and to reduce global impacts on climate (Falkowski et al., 2000). Injection of CO2 into deep saline aquifers or depleted oil and gas reservoirs has the potential to sequester significant mass of CO2 in a sustainable manner (Holt et al., 1995; Bachu and Adams, 2003; Orr, 2009; Szulczewski et al., 2012). One key to the success of long-term CO2 storage is the integrity of the resulting seal of impermeable caprocks that contain the charge to deep saline aquifers and prevents leakage into the atmosphere or potable aquifers (Shukla et al., 2010). However, the presence of preexisting faults and fractures distributed throughout the upper crust may influence the longevity of this storage (Anderson and Zoback, 1982; Curtis, 2002). Fluid injection activities (e.g., hydraulic fracturing, deep disposal of wastewater, enhanced geothermal stimulation, etc.) can reactivate pre-existing faults and induce seismicity (Healy et al., 1968; Raleigh et al., 1976; Kanamori and Hauksson, 1992; McGarr et al., 2002; Shapiro et al., 2006; Majer et al., 2007; Suckale, 2009; Ellsworth, 2013; Walsh and Zoback, 2015; Guglielmi et al., 2015; Im et al., 2016). Likewise, large-scale injection of CO2 that generates overpressures and decreases effective normal stresses may reactivate preexisting faults in caprocks (Fig. 1). As a result, CO2-injection induced seismicity may raise the potential that the rupture of caprocks could jeopardize the seal integrity and ultimately result in loss of charge of CO2 (Chiaramonte et al., 2008; Rutqvist, 2012; Zoback and Gorelick, 2012). Hence, it is of particular interest to understand the evolution of permeability of caprocks as a result of seismic and aseismic deformation in caprocks.
- North America > United States > Colorado (0.29)
- North America > United States > Texas (0.28)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Petroleum Play Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.76)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.46)