Abstract
AbstractSeismic monitoring of injected CO2 plumes in fractured storage reservoirs relies on accurate knowledge of the physical mechanisms governing elastic wave propagation, as described by appropriate, validated rock physics models. We measured laboratory ultrasonic velocity and attenuation of P and S waves, and electrical resistivity, of a synthetic fractured sandstone with obliquely aligned (penny‐shaped) fractures, undergoing a brine‐CO2 flow‐through test at simulated reservoir pressure and temperature. Our results show systematic differences in the dependence of velocity and attenuation on fluid saturation between imbibition and drainage episodes, which we attribute to uniform and patchy fluid distributions, respectively, and the relative permeability of CO2 and brine in the rock. This behavior is consistent with predictions from a multifluid rock physics model, facilitating the identification of the dispersive mechanisms associated with wave‐induced fluid flow in fractured systems at seismic scales.
Highlights
From the microscopic scale to large faulting systems, cracks are present in almost every rock formation found in the Earth's crust
This behavior is consistent with predictions from a multifluid rock physics model, facilitating the identification of the dispersive mechanisms associated with wave‐induced fluid flow in fractured systems at seismic scales
These factors include the distinction between pore pressure and pore fluid distribution effects (Falcon‐Suarez et al, 2016, 2017, 2018), the frequency dependence of elastic wave properties and the methodology to upscale information collected in laboratory (Lei & Xue, 2009; Mikhaltsevitch et al, 2014; Nakagawa et al, 2013), or the effect of mineralogical changes in the elastic and transport properties of the rock (Canal et al, 2013; Hangx et al, 2010, 2015; Vialle et al, 2014; Vialle & Vanorio, 2011)
Summary
From the microscopic scale to large faulting systems, cracks are present in almost every rock formation found in the Earth's crust. Previous studies have analyzed a number of factors affecting the brine‐CO2 saturation dependence in saline sandstone reservoirs—the most suitable geological context for GCS (Michael et al, 2010) These factors include the distinction between pore pressure and pore fluid distribution effects (Falcon‐Suarez et al, 2016, 2017, 2018), the frequency dependence of elastic wave properties and the methodology to upscale information collected in laboratory (Lei & Xue, 2009; Mikhaltsevitch et al, 2014; Nakagawa et al, 2013), or the effect of mineralogical changes in the elastic and transport properties of the rock (Canal et al, 2013; Hangx et al, 2010, 2015; Vialle et al, 2014; Vialle & Vanorio, 2011). Most of these studies are restricted to nonfractured rocks (Nooraiepour et al, 2018), the nucleation and reactivation of fractures endanger safe GCS (Rutqvist, 2012; Velcin et al, 2020)
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