Effect of brine-CO₂ fracture flow on velocity and electrical resistivity of naturally fractured tight sandstones

Abstract

Fracture networks inside geological CO 2 storage reservoirs can serve as primary fluid flow conduit, particularly in low-permeability formations. While some experiments focused on the geophysical properties of brine-and CO 2 -saturated rocks during matrix flow, geophysical monitoring of fracture flow when CO 2 displaces brine inside the fracture seems to be overlooked.We have conducted laboratory geophysical monitoring of fluid flow in a naturally fractured tight sandstone during brine and liquid CO 2 injection. For the experiment, the low-porosity, lowpermeability naturally fractured core sample from the Triassic De Geerdalen Formation was acquired from the Longyearbyen CO 2 storage pilot at Svalbard, Norway. Stress-dependence, hysteresis and the influence of fluid-rock interactions on fracture permeability were investigated.The results suggest that in addition to stress level and pore pressure, mobility and fluid type can affect fracture permeability during loading and unloading cycles. Moreover, the fluid-rock interaction may impact volumetric strain and consequently fracture permeability through swelling and dry out during water and CO 2 injection, respectively. Acoustic velocity and electrical resistivity were measured continuously in the axial direction and three radial levels.Geophysical monitoring of fracture flow revealed that the axial P-wave velocity and axial electrical resistivity are more sensitive to saturation change than the axial S-wave, radial P-wave, and radial resistivity measurements when CO 2 was displacing brine, and the matrix flow was negligible. The marginal decreases of acoustic velocity (maximum 1.6% for axial V p ) compared to 11% increase in axial electrical resistivity suggest that in the case of dominant fracture flow within the fractured tight reservoirs, the use of electrical resistivity methods have a clear advantage compared to seismic methods to monitor CO 2 plume. The knowledge learned from

Experimental mechanical compaction of reconstituted shale and mudstone aggregates: Investigation of petrophysical and acoustic properties of SW Barents Sea cap rock sequences

“…Ensuring a safe and secure fullscale geologic CO 2 sequestration requires comprehensive analyses of coupled hydrologic-geomechanical-geochemical processes that control fate of the CO 2 plume in subsurface (Rutqvist, 2012). Among other considerations, implementing various monitoring techniques is a necessity for establishing a reliable long-term operation (Wurdemann et al, 2010;Nooraiepour et al, 2018a).…”

CO2‐Brine Substitution Effects on Ultrasonic Wave Propagation Through Sandstone With Oblique Fractures

“…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). However, most of these studies are restricted to nonfractured rocks (Nooraiepour et al, 2018), although the nucleation and reactivation of fractures endanger safe GCS (Rutqvist, 2012; Velcin et al, 2020).…”

Experimental assessment of the stress-sensitivity of combined elastic and electrical anisotropy in shallow reservoir sandstones

“…In this regard, we find experimental approaches based on multidirectional array measurement using a single core plug (e.g., Wang, 2002;Kovalyshen et al, 2018), and several cores extracted at different angles (with respect to the formation bedding) from the same rock (e.g., Louis et al, 2004;Best et al, 2007;Martínez and Schmitt, 2013;Falcon-Suarez et al, 2017a). For resistivity anisotropy determinations, we also find the single-core (Guo et al, 2011;North et al, 2013;North and Best, 2014;Falcon-Suarez et al, 2017cBayrakci et al, 2018;Nooraiepour et al, 2018) and multi-coring (e.g., Wang et al, 2009;Falcon-Suarez et al, 2017a) experimental strategies. The use of several plugs implies relying the uniformity of adjacent plugs is preserved (i.e., absolute homogeneity of precursor specimen), which in practice is impossible to guarantee (Best et al, 2007); but, unlike the single-core, this method is easily implemented using conventional equipment.…”

“…A number of works have addressed the integration of elastic waves and resistivity properties of rock samples under reservoir conditions, at the laboratory (centimetric) scale. They include general characterizations of common (sandstones and carbonates) reservoir formations (Louis et al, 2003(Louis et al, , 2004Wang et al, 2009;Wang and Gelius, 2010;Han et al, 2011aHan et al, , b, 2018Falcon-Suarez et al, 2019), pore fluid distribution monitoring during CO2 geosequestration (Alemu et al, 2013;Falcon-Suarez et al, 2016, 2017bNooraiepour et al, 2018), methane hydrate formation (Sahoo et al, 2018;Attias et al, 2020) and the assessment of secondary (alteration) mineralization (e.g., the degree of serpentinization of mafic/ultramafic rocks (Falcon-Suarez et al, 2017c;Bayrakci et al, 2018)). Commonly, these studies assess the stress dependency of both parameters under defined states of stress and pore fluid conditions.…”