1,721,040 research outputs found
Experimental rig to improve the geophysical and geomechanical understanding of CO2 reservoirs
Full text linkWe intend to perform experiments that simulate real Carbon Capture and Storage (CCS) conditions in the laboratory, and hence provide the necessary knowledge to interpret field seismic surveys. Primarily, our research is focused on determining seismic rock properties (i.e., wave velocities and attenuation) of real and artificial 50 mm diameter brine-CO2-bearing sandstone and sand samples that are representative host rocks of real CCS scenarios. Accordingly, we have integrated into a new triaxial cell system both an ultrasonic pulse-echo method for accurate velocity (± 0.3%) and attenuation (± 0.1 dB cm-1) measurements, and an electrical resistivity tomography (ERT) method to monitor homogeneity of pore fluid distribution within the samples. The use of ERT provides calibration data for field scale techniques (such as marine controlled source electromagnetic surveying) but also allows measurements of bulk resistivity, fluid diffusion monitoring, flow pathway characterization, and determination of the relative permeability for different brine/brine-CO2 ratios. By simultaneously measuring ultrasonic P- and S-wave velocities and electrical resistivity, we also provide data for joint inversion of seismic and electric field data. Furthermore, the stress-strain behaviour of the sample is continuously monitored with the aid of electrical gauges, so that we deal consistently and simultaneously with the geophysical and geomechanical response of the reservoir when submitted to CO2 injections
(Table 1) Description of IODP rock samples from the Atlantis Massif, near the Mid-Atlantic Ridge
No full textIn supplement to: Falcon-Suarez, Ismael Himar; Bayrakci, Gaye; Minshull, Tim A; North, Laurence J; Best, Angus; Rouméjon, Stéphane; Expedition 357 Scientists (2017): Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge. Geophysical Journal International, 211, 686-699, https://doi.org/10.1093/gji/ggx34
(Table 2) Physical properties of IODP rock samples measured under various confining pressures
No full textIn supplement to: Falcon-Suarez, Ismael Himar; Bayrakci, Gaye; Minshull, Tim A; North, Laurence J; Best, Angus; Rouméjon, Stéphane; Expedition 357 Scientists (2017): Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge. Geophysical Journal International, 211, 686-699, https://doi.org/10.1093/gji/ggx34
Integrated geophysical and hydromechanical assessment for CO2 storage: shallow low permeable reservoir sandstones
Full text linkGeological reservoirs can be structurally complex and can respond to CO2 injection both geochemically and geomechanically. Hence, predicting reservoir formation behaviour in response to CO2 injection and assessing the resulting hazards are important prerequisites for safe geological CO2 storage. This requires a detailed study of thermal-hydro-mechanical-chemical coupled phenomena that can be triggered in the reservoir formation, most readily achieved through laboratory simulations of CO2 injection into typical reservoir formations. Here, we present the first results from a new experimental apparatus of a steady-state drainage flooding test conducted through a synthetic sandstone sample, simulating real CO2 storage reservoir conditions in a shallow (?1 km), low permeability ?1mD, 26% porosity sandstone formation. The injected pore fluid comprised brine with CO2 saturation increasing in steps of 20% brine/CO2 partial flow rates up to 100% CO2 flow. At each pore fluid stage, an unload/loading cycle of effective pressure was imposed to study the response of the rock under different geomechanical scenarios. The monitoring included axial strains and relative permeability in a continuous mode (hydromechanical assessment), and related geophysical signatures (ultrasonic P-wave and S-wave velocities Vp and Vs, and attenuations Qp?1 and Qs?1, respectively, and electrical resistivity). On average, the results showed Vp and Vs dropped ?7% and ?4% respectively during the test, whereas Qp?1 increased ?55% and Qs?1 decreased by ?25%. From the electrical resistivity data, we estimated a maximum CO2 saturation of ?0.5, whereas relative permeability curves were adjusted for both fluids. Comparing the experimental results to theoretical predictions, we found that Gassmann's equations explain Vp at high and very low CO2 saturations, whereas bulk modulus yields results consistent with White and Dutta–Odé model predictions. This is interpreted as a heterogeneous distribution of the two pore fluid phases, corroborated by electrical resistivity tomography images. The integration of laboratory geophysical and hydromechanical observations on representative shallow low-permeable sandstone reservoir allowed us to distinguish between pure geomechanical responses and those associated with the pore fluid distribution. This is a key aspect in understanding CO2 injection effects in deep geological reservoirs associated with carbon capture and storage practices
Assessing the carbon sequestration potential of basalt using X-ray micro-CT and rock mechanics
No full textMineral carbonation in basaltic rock provides a permanent storage solution for the mitigation of anthropogenic CO2 emissions in the atmosphere. 3D X-ray micro-CT (XCT) image analysis is applied to a core sample from the main basaltic reservoir of the CarbFix site in Iceland, which obtained a connected porosity of 2.05–8.76%, a reactive surface area of 0.10–0.33mm−1 and a larger vertical permeability (2.07×10−10m2) compared to horizontal permeability (5.10×10−11m2). The calculations suggest a CO2 storage capacity of 0.33 Gigatonnes at the CarbFix pilot site. The XCT results were compared to those obtained from a hydromechanical test applied to the same sample, during which permeability, electrical resistivity and volumetric deformation were measured under realistic reservoir pressure conditions. It was found that permeability is highly stress sensitive, dropping by two orders of magnitude for a −0.02% volumetric deformation change, equivalent to a mean pore diameter reduction of 5μm. This pore contraction was insufficient to explain such a permeability reduction according to the XCT analysis, unless combined with the effects of clay swelling and secondary mineral pore clogging. The findings provide important benchmark data for the future upscaling and optimisation of CO2 storage in basalt formations
Geophysical early warning of salt precipitation during geological carbon sequestration
Full text linkSequestration of industrial carbon dioxide (CO2) in deep geological saline aquifers is needed to mitigate global greenhouse gas emissions; monitoring the mechanical integrity of reservoir formations is essential for effective and safe operations. Clogging of fluid transport pathways in rocks from CO2-induced salt precipitation reduces injectivity and potentially compromises the reservoir storage integrity through pore fluid pressure build-up. Here, we show that early warning of salt precipitation can be achieved through geophysical remote sensing. From elastic P- and S-wave velocity and electrical resistivity monitoring during controlled laboratory CO2 injection experiments into brine-saturated quartz-sandstone of high porosity (29%) and permeability (1660 mD), and X-ray CT imaging of pore-scale salt precipitation, we were able to observe, for the first time, how CO2-induced salt precipitation leads to detectable geophysical signatures. We inferred salt-induced rock changes from (i) strain changes, (ii) a permanent ~ 1.5% decrease in wave velocities, linking the geophysical signatures to salt volume fraction through geophysical models, and (iii) increases of porosity (by ~ 6%) and permeability (~ 7%). Despite over 10% salt saturation, no clogging effects were observed, which suggests salt precipitation could extend to large sub-surface regions without loss of CO2 injectivity into high porosity and permeability saline sandstone aquifers
Pressure-varying CO 2 distribution affects the ultrasonic velocities of synthetic sandstones
Full text linkWe performed a novel experiment in which three synthetic sandstones – manufactured using a common method but having different porosities – were saturated with brine and progressively flooded with CO2 under constant confining pressure. The fluid pressure was varied around the critical pressure of CO2 and repeated measurements were made of resistivity, in order to assess the saturation, and elastic wave velocity during the flood. The measured saturated bulk moduli were higher than those predicted by the Gassmann–Wood theory, but were consistent with behaviour described by a recently derived poroelastic model which combines “patch” and “squirt” effects. Measurements on two of the samples followed a patch-based model while those on the highest porosity sample showed evidence of squirt-flow behaviour. Our analysis suggests that the appropriate fluid mixing law is pressure dependent, which is consistent with the notion that the effective patch size decreases as fluid pressure is increased. We derive simple empirical models for the patch dependence from fluid pressure which may be used in seismic modelling and interpretation exercises relevant to monitoring of CO2 injection
Bayrakci, Gaye; Falcon Suarez, Ismael; Minshull, Tim; North, Laurence; Best, Angus. (Table 1) Description of IODP rock samples from the Atlantis Massif, near the Mid-Atlantic Ridge. PANGAEA 2017, 10.1594/PANGAEA.873533 [Output (Electronic)]
No full textIn supplement to: Falcon-Suarez, Ismael Himar; Bayrakci, Gaye; Minshull, Tim A; North, Laurence J; Best, Angus; Rouméjon, Stéphane; Expedition 357 Scientists (2017): Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge. Geophysical Journal International, 211, 686-699, https://doi.org/10.1093/gji/ggx34
Bayrakci, Gaye; Falcon Suarez, Ismael; Minshull, Tim; North, Laurence; Best, Angus. (Table 1) Description of IODP rock samples from the Atlantis Massif, near the Mid-Atlantic Ridge. PANGAEA 2017, 10.1594/PANGAEA.873533 [Output (Electronic)]
No full textIn supplement to: Falcon-Suarez, Ismael Himar; Bayrakci, Gaye; Minshull, Tim A; North, Laurence J; Best, Angus; Rouméjon, Stéphane; Expedition 357 Scientists (2017): Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge. Geophysical Journal International, 211, 686-699, https://doi.org/10.1093/gji/ggx34
Experimental assessment of the stress-sensitivity of combined elastic and electrical anisotropy in shallow reservoir sandstones
Full text linkSeismic and electromagnetic properties are generally anisotropic, depending on the microscale rock fabric and the macroscale stress field. We have assessed the stress-dependent anisotropy of poorly consolidated (porosity of approximately 0.35) sandstones (broadly representative of shallow reservoirs) experimentally, combining ultrasonic (0.6 MHz P-wave velocity, VP, and attenuation 1/QP) and electrical resistivity measurements. We used three cores from an outcrop sandstone sample extracted at 0°, 45°, and 90° angles with respect to the visible geologic bedding plane and subjected them to unloading/loading cycles with variations of the confining (20–35 MPa) and pore (2–17 MPa) pressures. Our results indicate that stress field orientation, loading history, rock fabric, and the measurement scale, all affect the elastic and electrical anisotropies. Strong linear correlations (R2 > 0.9) between VP, 1/QP, and resistivity in the three considered directions suggest that the stress orientation similarly affects the elastic and electrical properties of poorly consolidated, high-porosity (shallow) sandstone reservoirs. However, resistivity is more sensitive to pore pressure changes (effective stress coefficients n > 1), whereas P-wave properties provide simultaneous information about the confining (from VP, with n slightly less than 1) and pore pressure (from 1/QP, with n slightly greater than 1) variations. We found n is also anisotropic for the three measured properties because a more intense and rapid grain rearrangement occurs when the stress field changes result from oblique stress orientations with respect to rock layering. Altogether, our results highlighted the potential of joint elastic-electrical stress-dependent anisotropy assessments to enhance the geomechanical interpretation of reservoirs during production or injection activities
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