Magnus Soldal

• Crisci, Eleonora; Giger, Silvio B.; Laloui, Lyesse; Ferrari, Alessio; Ewy, Russel T. & Stankovic, Rudy [Vis alle 9 forfattere av denne artikkelen] (2024). Insights from an extensive triaxial testing campaign on a shale for comparative site characterization of a deep geological repository. Geomechanics for Energy and the Environment. ISSN 2352-3808. 38. doi: 10.1016/j.gete.2023.100508.
• Soldal, Magnus (2022). Laboratory Evaluation of the Acoustic Velocity Stress- and Strain Sensitivity of the Draupne Shale, 83rd EAGE Annual Conference & Exhibition 2022. European Association of Geoscientists and Engineers (EAGE). ISSN 978-90-73834-12-5. doi: 10.3997/2214-4609.202210852.
• Park, Joonsang; Griffiths, Luke; Dautriat, Jérémie; Grande, Lars; Vera Rodriguez, Ismael & Iranpour, Kamran [Vis alle 16 forfattere av denne artikkelen] (2022). Induced-seismicity geomechanics for controlled CO<inf>2</inf> storage in the North Sea (IGCCS). International Journal of Greenhouse Gas Control. ISSN 1750-5836. 115. doi: 10.1016/j.ijggc.2022.103614. Fulltekst i vitenarkiv
• Soldal, Magnus; Skurtveit, Elin & Choi, Jung Chan (2021). Poroelastic and Mechanical Anisotropy of the Draupne Caprock, 55th U.S. Rock Mechanics/Geomechanics Symposium. American Rock Mechanics Association (ARMA). ISSN 978-0-9794975-6-8.
• Griffiths, Luke; Soldal, Magnus; Marin-Moreno, Héctor; Park, Joonsang; Victor, R. A. & Ramos, E. R. F. [Vis alle 9 forfattere av denne artikkelen] (2021). Unravelling wave-velocity and electrical resistivity changes during core flooding experiments on Berea sandstone using in situ micro-CT imaging, 55th U.S. Rock Mechanics/Geomechanics Symposium. American Rock Mechanics Association (ARMA). ISSN 978-0-9794975-6-8.
• Skomedal, Eiliv; Park, Joonsang; Soldal, Magnus & Smith, Halvard (2021). Electro-osmosis to Enhance Shale Barrier, 55th U.S. Rock Mechanics/Geomechanics Symposium. American Rock Mechanics Association (ARMA). ISSN 978-0-9794975-6-8.
• Soldal, Magnus & Skurtveit, Elin (2021). Laboratory study on the potential for fault reactivation of the Draupne caprock during CO2 injection. 15th International Conference on Greenhouse Gas Control Technologies, GHGT-15. Social Science Research Network (SSRN). ISSN 1556-5068. doi: 10.2139/ssrn.3815609.
• Soldal, Magnus; Skurtveit, Elin & Choi, Jung Chan (2021). Laboratory evaluation of mechanical properties of draupne shale relevant for CO<inf>2</inf> seal integrity. Geosciences. ISSN 2076-3263. 11(6). doi: 10.3390/geosciences11060244. Fulltekst i vitenarkiv
• Bohloli, Bahman; Soldal, Magnus; Smith, Halvard; Skurtveit, Elin; Choi, Jung Chan & Sauvin, Guillaume (2020). Frictional Properties and Seismogenic Potential of Caprock Shales. Energies. ISSN 1996-1073. 13(23). doi: 10.3390/en13236275. Fulltekst i vitenarkiv Vis sammendrag

  Fractures and faults are critical elements affecting the geomechanical integrity of CO2 storage sites. In particular, the slip of fractures and faults may affect reservoir integrity and increase potential for breach, may be monitored via the resulting seismicity. This paper presents an experimental study on shale samples from Draupne and Rurikfjellet formations from the North Sea and Svalbard, Norway, using a laboratory test procedure simulating the slip of fractures and faults under realistic stress conditions for North Sea CO2 storage sites. The motivation of the study is to investigate whether the slip along the fractures within these shales may cause detectable seismic events, based on a slip stability criterion. Using a direct shear apparatus, frictional properties of the fractures were measured during shearing, as a function of the shear velocity and applied stress normal to the fracture. We calculated the friction coefficient of the fractures during the different stages of the shear tests and analysed its dependency on shear velocity. Information on velocity-dependent friction coefficient and its evolution with increasing slip were then used to assess whether slip was stable (velocity-strengthening) or unstable (velocity-weakening). Results showed that friction coefficient for both Draupne and Rurikfjellet shales increased when the shear velocity was increased from 10 to 50 µm/s, indicating a velocity-strengthening behaviour. Such a behaviour implies that slip on fractures and faults within these formations may be less prone to producing detectable seismicity during a slip event. These results will have implications for the type of techniques to be used for monitoring reservoir and caprock integrity, for instance, for CO2 storage sites

• Minardi, Alberto; Giger, Silvio B.; Ewy, Russel T.; Stancovic, Rudy; Stenebråten, Jørn & Soldal, Magnus [Vis alle 9 forfattere av denne artikkelen] (2020). Benchmark study of undrained triaxial testing of Opalinus Clay shale: Results and implications for robust testing. Geomechanics for Energy and the Environment. ISSN 2352-3808. 25. doi: 10.1016/j.gete.2020.100210. Fulltekst i vitenarkiv Vis sammendrag

  Triaxial testing of argillaceous rocks and shales is significantly more challenging than conventional rock mechanical testing. The challenges are mainly related to the very low permeability of these geomaterials, and their sensitivity to exposure of atmosphere and brines, which induces variations of water content, suction and effective stress. There are currently no international standards to guide service laboratories for robust testing procedures for shales. A benchmark study of undrained triaxial testing was therefore initiated with three leading service laboratories in shale testing, performing 13 tests and using two different methods of establishing sample saturation prior to deformation. Both methods paid particular attention to minimize volume expansion of the specimens during saturation, and the loading rate during the shear phase in all tests was selected based on intrinsic sample properties and drainage configurations to ensure pore fluid pressure equilibration across the specimen. Opalinus Clay shale core material from the Mont Terri underground research laboratory was used for testing specimens, and intervals on cores were pre-selected on the basis of computer tomography to minimize material heterogeneity. A detailed diagnostic analysis of all tests was performed, and a comparison of the testing results is presented. Good reproducibility of the effective stress paths was achieved by the different laboratories for tests at identical or near-identical initial effective stress conditions. In particular, the test results over a larger range of effective stresses indicate very similar evolution of the fluid pressure during testing and a consistent picture for the derivation of global material properties. On the example of Opalinus Clay, the study demonstrates that robust triaxial testing results can be achieved for shales if some key challenges are adequately addressed.

• Bohloli, Bahman; Skurtveit, Elin; Choi, Jung Chan; Grande, Lars; Sauvin, Guillaume & Soldal, Magnus [Vis alle 7 forfattere av denne artikkelen] (2020). Determination of shear properties and evaluation of fracture reactivation for a clay-rich shale: a case study from Svalbard, Arctic Norway. Bulletin of Engineering Geology and the Environment. ISSN 1435-9529. 79, s. 4859–4872. doi: 10.1007/s10064-020-01814-x. Vis sammendrag

  This paper presents results of the direct shear tests on pre-fractured specimens from Rurikfjellet Formation, Svalbard, Arctic Norway. It also evaluates the risk of shear failure along pre-existing fractures due to possible over pressure. Rurikfjellet Formation is composed of clay-rich shale and is part of the cap rock for the proposed CO2 storage pilot at Svalbard. Shear properties of the cap rock system are of great importance for the integrity of the reservoir beneath. Three specimens from Rurikfjellet Formation were subjected to direct shear test. Results of the experiments showed that the peak friction coefficient was slightly higher than the residual coefficient. Shear stiffness of the specimens varied between 19 and 21 MPa/mm determined from secant method and between 26 and 32 MPa/mm determined from tangent method. The specimens showed slight dilation in the very initial phase of shearing but exhibited strong compression with increased displacement (and normal stress). This indicates that a slip along fractures in Rurikfjellet shale may be governed by compression which in turn implies self-sealing of fractures that may occur during a shear displacement. Evaluation of fracture reactivation under stress conditions close to that of the current situation at Svalbard showed that there is a safety margin of about 4 to 5 MPa overpressure before a failure may occur along the critically oriented fractures. Overall, the measured compression behaviour and the estimated safety margin for Rurikfjellet shale suggest that this unit may act as a good seal for the proposed CO2 storage reservoir.

• Skurtveit, Elin; Sundal, Anja; Bjørnarå, Tore Ingvald; Soldal, Magnus; Sauvin, Guillaume & Zuchuat, Valentin [Vis alle 8 forfattere av denne artikkelen] (2020). Experimental investigation of natural fracture stiffness and flow properties in a faulted CO2 bypass system (Utah, USA). Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 125(7). doi: 10.1029/2019JB018917. Fulltekst i vitenarkiv Vis sammendrag

  Fracture stiffness and flow properties have been measured in the laboratory using naturally fractured fault rock samples from the Little Grand Wash fault, Utah, USA. We compare fracture closure and related flow change during isotropic loading of two fractures which have been subject to various amounts of paleo‐reactive flow. The two tested fractures are described as (i) a small‐aperture fracture (0.1 mm) with negligible geochemical alterations of the fracture surface and (ii) a large‐aperture fracture (0.53 mm) where precipitates are observed on the fracture surface. X‐ray imaging is used for quantification of fracture aperture and fracture surface contact distribution. The petrographical characterisation using scanning electron microscopy and x‐ray powder diffraction is performed pre‐test and describes burial and uplift diagenesis as well as pulses of reactive fluid flow within the fault. The stress dependent flow and deformation experiment provides new data on fracture stiffness and flow for naturally developed fractures in siliciclastic rock. Fracture stiffness is found to be highest for the small‐aperture fracture due to its high fracture contact ratio and well‐developed surface mating during closure. For the naturally altered and rougher, large‐aperture fracture, fracture stiffness is lower and a highly stress dependent decay in flow is observed during initial closure. The results illustrate that a natural fracture with high contact ratio and well mated surfaces will close during loading, whereas a fracture associated with high flow rates and affected by previous geochemical alteration maintains a high flow rate compared to the host rock during similar loading.

• Bohloli, Bahman; Choi, Jung Chan & Soldal, Magnus (2019). Fracture Reactivation in Shale: Laboratory Testing and Analytical Modeling, 5th International Conference on Fault and Top Seals 2019, Palermo, Italy 8 - 9 September 2019. European Association of Geoscientists and Engineers (EAGE). ISSN 978-1-5108-9236-1. doi: 10.3997/2214-4609.201902323.
• Giger, S.B.; Minardi, A.; Ferrari, A; Laloui, Lyesse; Ewy, R.T. & Stankovic, R. [Vis alle 10 forfattere av denne artikkelen] (2019). Benchmark Study of Undrained Triaxial Testing of Opalinus Clay: Results and Implications for Robust Testing, 6th EAGE Shale Workshop 2019, Bordequx, France 28 April - 1 May 2019 . European Association of Geoscientists and Engineers (EAGE). ISSN 978-1-5108-8666-7. doi: 10.3997/2214-4609.201900267. Vis sammendrag

  We have performed a comparative study of undrained triaxial testing with five different laboratories, to explore the reproducibility of test results. Opalinus Clay was sourced as testing material from a borehole at the Mont Terri URL. Cores were vacuum-sealed, and resin impregnated immediately after recovery. Systematic determination of basic properties such as water content, grain density and bulk mineralogy of specimens after testing assisted in diagnostic test evaluation. A detailed testing protocol was requested to avoid specimen damage during initial loading («swelling») and to verify specimen saturation. A balanced pore fluid was used for testing, and a consolidation phase was performed to reach specific target effective stress levels prior to the shear phase. One laboratory deviated from these protocols, as it did not use an external pore fluid. Instead, specimens were brought to variable saturation levels in a desiccator prior to assembling them into the rig. For specimens with almost identical basic properties, the test results were indeed found to be in very good agreement, despite the different procedures applied. Differences in test results can be attributed to material heterogeneity. The study provides compelling evidence that robust triaxial testing can be achieved with shales.

• Griffiths, Luke; Dautriat, Jérémie; Vera Rodriguez, Ismael; Iranpour, Kamran; Sauvin, Guillaume & Park, Joonsang [Vis alle 13 forfattere av denne artikkelen] (2019). Inferring microseismic source mechanisms and in situ stresses during triaxial deformation of a North-Sea-analogue sandstone. Advances in Geosciences. ISSN 1680-7340. 49, s. 85–93. doi: 10.5194/adgeo-49-85-2019. Fulltekst i vitenarkiv Vis sammendrag

  Monitoring microseismic activity provides a window through which to observe reservoir deformation during hydrocarbon and geothermal energy production, or CO2 injection and storage. Specifically, microseismic monitoring may help constrain geomechanical models through an improved understanding of the location and geometry of faults, and the stress conditions local to them. Such techniques can be assessed in the laboratory, where fault geometries and stress conditions are well constrained. We carried out a triaxial test on a sample of Red Wildmoor sandstone, an analogue to a weak North Sea reservoir sandstone. The sample was coupled with an array of piezo-transducers, to measure ultrasonic wave velocities and monitor acoustic emissions (AE) – sample-scale microseismic activity associated with micro-cracking. We calculated the rate of AE, localised the AE events, and inferred their moment tensor from P-wave first motion polarities and amplitudes. We applied a biaxial decomposition to the resulting moment tensors of the high signal-to-noise ratio events, to provide nodal planes, slip vectors, and displacement vectors for each event. These attributes were then used to infer local stress directions and their relative magnitudes. Both the AE fracture mechanisms and the inferred stress conditions correspond to the sample-scale fracturing and applied stresses. This workflow, which considers fracture models relevant to the subsurface, can be applied to large-scale geoengineering applications to obtain fracture mechanisms and in-situ stresses from recorded microseismic data.

• Park, Joonsang; Grande, Lars; Sauvin, Guillaume; Bohloli, Bahman & Soldal, Magnus (2018). Laboratory acoustic emission test with a brittle shale cap-rock, Seventh EAGE Workshop on Passive Seismic. Proceedings of a meeting held 26-29 March 2018, Krakow, Poland.. European Association of Geoscientists and Engineers (EAGE). ISSN 978-1-5108-5941-8. doi: 10.3997/2214-4609.201800047. Vis sammendrag

  The integrity of cap-rock is a critical issue for both injection and production operations and we need to make sure that any induced alteration in the subsurface is within acceptable range. For such a purpose, micro-seismic is a useful technique. However, it is not always the case that we can record events, as shown in the current study. Therefore, it is recommended to perform extensive laboratory-based AE tests with different lithology and all possible stress conditions (path, rate, etc.). From such datasets and experiences, we can have better and confident ideas of how to interpret acquired field-scale micro-seismic data by linking to geomechanical behaviors of cap-rock.

• Bohloli, Bahman; Omolo, Lameck; Soldal, Magnus; Wilkinson, Heidi & Morgan, Elin Katrine (2016). Laboratory study of physical, mechanical and flow properties of cement grouts. I Grøv, Eivind; Olsson, Roger & Butler, Saskia (Red.), 8th Nordic Grouting Symposium Oslo, Norway, 26.-27. September 2016. Norwegian Group for Rock Mechanics (NBG). ISSN 978-82-8208-050-7. s. 99–110.
• Bohloli, Bahman; Skurtveit, Elin; Choi, Jung Chan; Grande, Lars; Soldal, Magnus & Wilkinson, Heidi (2015). Shear Strength Parameters of Cretaceous Shales from the Cap-rock of the Longyearbyen CO2 Storage Pilot, Svalbard, 2nd EAGE Workshop on Geomechanics and Energy: The Ground as Energy Source and Storage - Proceedings of a meeting held 13-15 October 2015, Celle, Germany.. Curran Associates, Inc.. ISSN 9781510814202. doi: 10.3997/2214-4609.201414313.
• Park, Joonsang; Sauvin, Guillaume; Soldal, Magnus & Bohloli, Bahman (2015). Feasibility Study on Seismic and CSEM Monitoring of CO2 Injection Based on Laboratory Acoustic and Resistivity Measurement, 3rd Sustainable Earth Sciences Conference and Exhibition - Use of the Sub-surface to Serve the Energy Transition: Proceedings of a meeting held 13-15 October 2015, Celle, Germany. Curran Associates, Inc.. ISSN 978-1-5108-1419-6. doi: 10.3997/2214-4609.201414279. Vis sammendrag

  In this work, we apply a set of acoustic velocity and electrical resistivity measured during CO2 core flooding laboratory test in order to explore the sensitivity of field-scale data through a synthetic 1D model. We demonstrate the feasibility of monitoring CO2 injection into subsurface by geophysical means. So far, seismic and CSEM data were considered into the scope of work. In near future, we may also integrate gravity data.

• Skurtveit, Elin; Choi, Jung Chan; Soldal, Magnus; Grande, Lars; Maurer, R. & Horsrud, Per (2015). Mechanical Anisotropy Characterization of the Draupne Formation, North Sea, 4th International Conference on Fault and Top Seals 2015: Art or Science? Proceedings of a meeting held 20-24 September 2015, Almeria, Spain.. Curran Associates, Inc.. ISSN 9781510814172. doi: 10.3997/2214-4609.201414078. Vis sammendrag

  Anisotropy is an important characteristic for the mechanical characterization of shale. Both strength and elastic parameters vary with orientation of material due to the lithological anisotropy in the material. A triaxial test program on varying plug orientation was designed to investigate the mechanical anisotropy in the Draupne Formation. From the triaxial experiments, clear strength anisotropy is observed especially in certain range of orientation. Post-test CT images shows that the strength anisotropy is mainly related to failure in bedding planes. The observed strength anisotropy implies that orientation dependent failure criteria should be considered for realistic geomechanical modelling of seal integrity.

• Soldal, Magnus; Park, Joonsang; Lameck, Omolo; Tran, Trung; Sauvin, Guillaume & Johnsen, Øistein [Vis alle 7 forfattere av denne artikkelen] (2015). Geophysical monitoring of CO2 flow during sandstone flooding experiments. I van Kraanen, Marjolein (Red.), Proceedings third EAGE workshop on rock physics: from rocks to basin - applying rock physics in prospect evaluation and reservoir characterization. Curran Associates, Inc.. ISSN 978-94-6282-153-8. doi: 10.3997/2214-4609.201414395. Vis sammendrag

  In this study, liquid CO2 is injected into fully brine saturated reservoir core samples in the laboratory, and consequently changes in electrical resistivity, acoustic velocities (ultrasonic frequency) and their anisotropy are measured. To enhance the spatial resolution, a system enabling velocity and resistivity measurements at different points and in different directions along the specimen's axial direction has been developed. Electrical resistivity and acoustic velocity and amplitude are all clearly influenced by pore-scale heterogeneity and fluid flow pattern and it is important to study this interaction. So far, focus has been related to CO2 geological storage, but the outline of the study is believed to also be applicable for CO2 injection for enhanced oil recovery (EOR). The study is still ongoing and some preliminary results are presented here and discussed.

• Aker, Eyvind; Kühn, Daniela; Vavryčuk, Václav; Soldal, Magnus & Oye, Volker (2014). Experimental investigation of acoustic emissions and their moment tensors in rock during failure. International Journal of Rock Mechanics And Mining Sciences. ISSN 1365-1609. 70, s. 286–295. doi: 10.1016/j.ijrmms.2014.05.003.
• Alemu, Binyam Lema; Aker, Eyvind; Soldal, Magnus; Johnsen, Øistein & Aagard, Per (2013). Effect of sub-core scale heterogeneities on acoustic and electrical properties of a reservoir rock: a CO2 flooding experiment of brine saturated sandstone in a computed tomography scanner. Geophysical Prospecting. ISSN 0016-8025. 61(1), s. 235–250. doi: 10.1111/j.1365-2478.2012.01061.x. Vis sammendrag

  The effect of sub-core scale heterogeneity on fluid distribution pattern, and the electrical and acoustic properties of a typical reservoir rock was studied by performing drainage and imbibition flooding tests with CO2 and brine in a laboratory. Moderately layered Rothbach sandstone was used as a test specimen. Two core samples were drilled; one perpendicular and the other parallel to the layering to allow injection of fluids along and normal to the bedding plane. During the test 3D images of fluid distribution and saturation levels were mapped by an industrial X-ray CT-scanner together with simultaneous measurement of electrical resistivity, ultrasonic velocities as well as amplitudes. The results showed how the layering and the flooding direction influenced the fluid distribution pattern and the saturation level of the fluids. For a given fluid saturation level, the measured changes in the acoustic and electrical parameters were affected by both the fluid distribution pattern and the layering orientation relative to the measurement direction. The P-wave amplitude and the electrical resistivity were more sensitive to small changes in the fluid distribution patterns than the P-wave velocity. The change in amplitude was the most affected by the orientation of the layering and the resulting fluid distribution patterns. In some instances the change due to the fluid distribution pattern was higher than the variation caused by the change in CO2 saturation. As a result the Gassmann relation based on ‘uniform' or ‘patchy' saturation pattern was not suitable to predict the P-wave velocity variation. Overall, the results demonstrate the importance of core-imaging to improve our understanding of fluid distribution patterns and the associated effects on measured rock-physics properties.

• Skurtveit, Elin; Aker, Eyvind; Soldal, Magnus; Angeli, Matthieu & Wang, Zhong (2012). Experimental investigation of CO2 breakthrough and flow mechanisms in shale. Petroleum Geoscience. ISSN 1354-0793. 18(1), s. 3–15. doi: 10.1144/1354-079311-016.
• Alemu, Binyam Lema; Aker, Eyvind; Soldal, Magnus; Johnsen, Øistein & Aagaard, Per (2011). Influence of CO2 on rock physics properties in typical reservoir rock: A CO2 flooding experiment of brine saturated sandstone in a CT-scanner. Energy Procedia. ISSN 1876-6102. 4, s. 4379–4386. doi: 10.1016/j.egypro.2011.02.390. Fulltekst i vitenarkiv Vis sammendrag

  Laboratory core flooding experiment was run to investigate the joint use of electrical resistivity, ultrasonic velocities and 3D images of fluid distribution to improve current understanding of CO2 and brine behaviour during drainage and imbibition in reservoir rocks. The test specimen was cylindrical Rothbach sandstone measuring 100 mm in length and 38 mm in diameter, with a porosity of 23% and an average permeability of 400 mD. The brine saturated specimen was drained by injecting CO2 and later imbibed with brine while monitoring changes in resistivity and ultrasonic velocity measurements. Actual fluid saturation level and distribution have been mapped simultaneously using X-ray CT scan. CO2 saturation calculations based on CT values showed a steep saturation gradient at start of drainage and the gradient flattened with more CO2 injected into the sample. The ultrasonic compressional velocity (V p) measurements depicted a continuous decrease with increase in CO2 saturation while the resistivity of the sample increased proportionally with increase in CO2 saturation. A CO2 saturation of 53% was achieved at the end of drainage after injection of 20 pore volume (PV) CO2. This resulted in a decrease of V pby 7.2% while the amplitude decreased by as much as 48%. At the end of drainage, the resistivity of the sample increased to 13.9 Ω-m from full brine saturated value of 3.2 Ω-m. During imbibition, the sample was re-saturated close to 100% after 10 PV brine injection. Change in V p due to CO2 saturation level variation was relatively consistent during drainage and imbibition (no hysteresis) where as the resistivity of the sample was more affected by the flooding history resulting in hysteretic variation in resistivity. Resistivity index (RI) values did not show a consistent pattern and a single Archie’s saturation exponent (n) could not be assigned.

• Angeli, Matthieu; Soldal, Magnus; Skurtveit, Elin & Aker, Eyvind (2009). Experimental percolation of supercritical CO2 through a caprock. Energy Procedia. ISSN 1876-6102. s. 3351–3358. doi: 10.1016/j.egypro.2009.02.123. Fulltekst i vitenarkiv Vis sammendrag

  Leakage of CO2 into the atmosphere is the most crucial concern for geological storage of anthropogenic CO2. Leakage routes could develop through existing wells and pipelines, but also by natural migration of CO2 rich pore-fluid through the caprock and in fault zones. Therefore, a thorough geological characterization of the prospective formation identifying seal capacity, integrity and possible migration pathways must be performed prior to injection of CO2. A caprock is a low permeable confining layer trapping CO2 stored in a reservoir rock. Although the caprock acts as a seal, its lower boundary will be in contact with CO2 saturated pore water or even pure CO2. Chemical interaction between the pore fluid and the caprock may change its material properties. The aim of this study is to increase our understanding of the interaction between CO2 and caprock, focusing on the microstructural properties of the rock. A flow through cell is used to flood a shale core (40 mm long and 38 mm diameter) with supercritical CO2 at a temperature of 35 ∘C and at pressures above 7.5 MPa. A pressure gradient is applied across the sample to obtain a breakthrough of CO2 in the core. During flooding both axial and radial strain of the core are measured together with the acoustic velocities in the axial direction. The measurements are performed both for the brine saturated core and at various stages during flooding with CO2. The experimental results suggest flow of CO2 along defined pathways within the shale. These pathways are likely to be controlled by the increasing pore pressure at the bottom of the sample which allows reopening of the cracks in the lower part of the sample, allowing CO2 to enter the shale. Flow of CO2 into the cracks in the lower part of the sample is followed by percolation of CO2 in the upper part of the sample where the effective pressure is higher and crack reopening is less likely to occur.

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• Choi, Jung Chan; Skurtveit, Elin; Soldal, Magnus & Grande, Lars (2023). Effect of undrained creep on the long-term mechanical stability of North Sea mudstones and shales.
• Soldal, Magnus & Skurtveit, Elin (2023). Measurements of capillary breakthrough pressures and permeabilities in traditional seals and application for CO2 storage.
• Braathen, Alvar; Skurtveit, Elin; Mulrooney, Mark Joseph; Haines, Emma Michie; Faleide, Thea Sveva & Osmond, Johnathon [Vis alle 10 forfattere av denne artikkelen] (2022). Understanding faults and their influence on fluid flow.
• Choi, Jung Chan; Skurtveit, Elin; Soldal, Magnus & Grande, Lars (2022). Can the creep stabilize a fault? : Undrained stress path of the shale creep.
• Soldal, Magnus (2022). Undrained pore pressure response of the Draupne shale.
• Silva, Diana Carolina Alves da; Skurtveit, Elin; Soldal, Magnus & Suzuki, Yusuke (2021). Mechanical parameters of synthetic Draupne gouge using Direct Shear Testing.
• Soldal, Magnus; Skurtveit, Elin & Bohloli, Bahman (2021). The potential for seismicity during slip of fractured Draupne shale .
• Park, Joonsang; Griffiths, Luke; Dautriat, Jérémie; Grande, Lars; Vera Rodriguez, Ismael & Iranpour, Kamran [Vis alle 16 forfattere av denne artikkelen] (2021). Induced-seismicity geomechanics for controlled CO2 storage in the North Sea (IGCCS). SSRN Electronic Journal. doi: 10.2139/ssrn.3819665.
• Griffiths, Luke; Dautriat, Jérémie; Park, Joonsang; Vera Rodriguez, Ismael; Iranpour, Kamran & Sauvin, Guillaume [Vis alle 13 forfattere av denne artikkelen] (2021). The Influence of Super-critical CO2 Saturation on the Mechanical and Failure Properties of a North Sea Reservoir Sandstone Analogue. SSRN Electronic Journal. doi: 10.2139/ssrn.3818808.
• Grande, Lars; Park, Joonsang; Griffiths, Luke; Bjørnarå, Tore Ingvald; Sauvin, Guillaume & Soldal, Magnus [Vis alle 8 forfattere av denne artikkelen] (2020). Geomechanical and geophysical evaluations for safe CO2 storage in the North Sea.
• Griffiths, Luke; Park, Joonsang; Soldal, Magnus; Sauvin, Guillaume; Grande, Lars & Choi, Jung Chan [Vis alle 13 forfattere av denne artikkelen] (2020). Assessing the potential of microseismic monitoring of North Sea geological CO2 storage sites through laboratory testing.
• Skurtveit, Elin; Bjørnarå, Tore Ingvald; Bohloli, Bahman; Soldal, Magnus; Eidsvig, Unni & Gasda, Sarah [Vis alle 9 forfattere av denne artikkelen] (2020). Dynamic changes in fault permeability – How can experimental work provide support for fault seal integrity?
• Skurtveit, Elin; Bjørnarå, Tore Ingvald; Bohloli, Bahman; Soldal, Magnus; Eidsvig, Unni & Gasda, Sarah [Vis alle 10 forfattere av denne artikkelen] (2020). Dynamic changes in fault permeability How can experimental work provide support for fault seal integrity?
• Griffiths, Luke; Dautriat, Jérémie; Vera Rodriguez, Ismael; Iranpour, Kamran; Sauvin, Guillaume & Park, Joonsang [Vis alle 12 forfattere av denne artikkelen] (2019). Characterization of insitu stress from laboratory-scale microseismic data, relevant to North Sea reservoirs. Vis sammendrag

  Microseismic monitoring at sites such as hydrocarbon reservoirs, mines, and geological CO2 storage reservoirs, can inform on rock integrity, fault locations and geometries, and localised stress changes. For example, at CO2 injection sites, pressure changes may cause slip on pre-existing fractures, resulting in detectable induced seismicity, indicating the progression of the CO2 plume and the pressure front preceding it, and providing a means for assessing the risk of leakage. Moment tensors are commonly inferred from microseismic data and, if fault planes are known, stress and fault orientations may also be inferred. However, it is difficult to verify the results of these methods at the reservoir scale, where measurements of in-situ stresses are unavailable, and faults can be too small to be observed by seismic surveys. Here, we apply the above methods to laboratory scale microseismic events—Acoustic Emissions (AE), where the situations are well controlled. Namely, we know: how the stress is changing, and where and when the failure plane is developing. For this, we acquired and analysed AE data during the deformation of a sandstone sample (a material relevant to North Sea reservoirs) until formation of a through-going fracture, which we then reactivated.

• Griffiths, Luke; Dautriat, Jérémie; Vera Rodriguez, Ismael; Iranpour, Kamran; Sauvin, Guillaume & Park, Joonsang [Vis alle 13 forfattere av denne artikkelen] (2019). Inferring microseismic source mechanisms and in situ stresses during triaxial deformation of a North-Sea-analogue sandstone. Advances in Geosciences. ISSN 1680-7340. doi: 10.5194/adgeo-49-85-2019.
• Park, Joonsang; Blomberg, Ann Elisabeth Albright; Waarum, Ivar-Kristian; Totland, Christian; Yakushev, Evgeniy & Pedersen, Geir [Vis alle 13 forfattere av denne artikkelen] (2019). Integrated Monitoring Approach for Offshore Geological CO2 Storage, Proceedings Offshore Technology Conference (OTC 2019) 6-9 May 2019, Houston, Texas, USA.. Curran Associates, Inc.. ISSN 978-1-5108-8710-7. doi: 10.4043/29324-MS. Vis sammendrag

  Measurement, monitoring and verification (MMV) are vital to ensure the conformance and containment of geological carbon storage (GCS). This requires cost-efficient and multidisciplinary approaches. To investigate this challenge in an offshore environment, we have studied and tested different monitoring approaches, covering seismic, electromagnetic, micro-seismic, active and passive sonar, and chemical sensing methods. The studies in the manuscript are based on laboratory- and field-scale tests. The data of our current interest are various as mentioned above, and for both deep- and shallow-focused monitoring. We measured laboratory geophysical data in the scenario of CO2 flowing through a fracture in a sandstone core sample (De Geerdalen Formation, Svalbard, Norway) to see the possibility of detecting leakage. The field-scale feasibility was also demonstrated through a synthetic modeling study. Laboratory acoustic emission tests were performed with North-Sea relevant rock samples to evaluate the micro-seismic applicability to offshore GCS monitoring. Acoustic and chemical sensor technologies are considered essential for marine monitoring of the seabed and water column, but knowledge and documentation on how to optimally use and combine these technologies is scarce. During a recent controlled CO2 release experiment, we have investigated the performance of different acoustic and chemical technologies for application to GCS monitoring. By quantifying the capabilities and limitations of different acoustic and chemical technologies, we aim to provide operators with the knowledge needed to maximize monitoring performance while minimizing the number of sensors and costly operations. First, it was learned through a laboratory rock physical test that electromagnetic signal is relatively sensitive to CO2 flow through fracture (and potentially faults as well) compared to seismic. The acoustic emission tests showed that reservoir sandstone core samples are subjected to induced seismicity, whereas the cap-rock or shale are rather quiet during these tests. To be conclusive, more tests and data analysis are required. Nevertheless, the up to date result indicates that detection of leakage in shale only via micro-seismic might be challenging. Initial results from the cotrolled experiments releasing CO2 to the water column indicate that a small amount of CO2 in gas phase may be detected from a large distance (100s of meters) using a broadband echo sounder. Passive acoustic detection of a small leak (1.15 l/min) was feasible from a distance of 10m. A plume of dissolved CO2 was detectable using chemical CO2 and pH sensors placed 4-10 m from the origin of the leak, when releasing CO2 at a rate of 5-6 l/min. Finally, we have investigated how to integrate the deep-focused geophysical and shallow-focused seafloor monitoring techniques. In our study, we have used a set of leakage scenarios (leakage path, rate, etc.) available in the literature. In addition, we have included into our discussion additional datasets e.g. surface/seafloor heaving and gravity not directly acquired in the current study but available through literature. We conclude that integrating different datasets and different disciplines are necessary to maximize the extracted information and eventually to save cost as well. In addition, relevant future R&D task candidates have been identified.

• Soldal, Magnus; Skurtveit, Elin; Bohloli, Bahman; Wilkinson, Heidi; Choi, Jung Chan & Griffiths, Luke [Vis alle 7 forfattere av denne artikkelen] (2019). Experimental and analytical assessment of Draupne shale seal integrity for CO2 storage sites . Fulltekst i vitenarkiv Vis sammendrag

  Carbon dioxide (CO2) capture and storage is one of the most important measures to reduce the atmospheric concentration of CO2. To ensure safe storage, operations must be conducted in way that respects operational limitations. Furthermore, the operational limitations should be based on models appropriately accounting for relevant material properties and in-situ stress conditions. In this study, we combine various experimental approaches on the Draupne shale to get a more complete picture of the properties of intact and naturally fractured samples and to evaluate the feasibility of using passive seismic to monitor this North Sea caprock. The measured properties combined with in-situ stresses are used to calculate stresses acting on arbitrarily oriented fractures and associated stabilities using an in-house developed software.

• Park, Joonsang; Blomberg, Ann Elisabeth Albright; Waarum, Ivar-Kristian; Totland, Christian; Yakushev, Evgeniy & Pedersen, Geir [Vis alle 12 forfattere av denne artikkelen] (2019). Integrated Monitoring Approach for Offshore Geological CO2 Storage.
• Griffiths, Luke; Park, Joonsang; Sauvin, Guillaume; Soldal, Magnus; Grande, Lars & Mondol, Nazmul Haque [Vis alle 13 forfattere av denne artikkelen] (2019). Microseismic monitoring of reservoir rock and cap rock integrity at North Sea geological CO2 storage sites: insights from acoustic emission testing. Geophysical Research Abstracts. ISSN 1029-7006.
• Nooraiepour, Mohammad; Soldal, Magnus; Park, Joonsang; Mondol, Nazmul Haque; Hellevang, Helge & Bohloli, Bahman (2018). Geophysical Monitoring of Gaseous and Supercritical CO2 Fracture Flow Through a Brine-Saturated Shale Caprock. Vis sammendrag

  Pre-existing and induced fractures and faults can play a role as bypass conduits and fast leaking channels in CO2 storage sites. They should therefore be well characterized during site selection, and monitored thoroughly during operation to track the movement and fate of the CO2 plume. Despite to date extensive research on the geophysical properties of brine- and CO2-saturated porous reservoir rocks, changes in acoustic velocity and electrical resistivity during a sole fracture fluid displacement are, however, rather little investigated. Hence, we herein present a laboratory study of core-scale geophysical monitoring during drainage-imbibition cycles of the brine-CO2 system through a shale caprock core sample with a vertical fracture. The experiments were conducted using both gaseous and scCO2 with 4 and 9 MPa pore pressures, respectively, at 12 MPa confining pressure. The tests were performed at 40°C during the loading and unloading stages in order to look into the hysteresis effect. We used a fractured core sample from the Upper Jurassic organic-rich shales of the Draupne Formation, which is the primary caprock for the Smeaheia CO2 storage site – a full-scale CCS project in Norway. The primary objective of the experiment was to compare the geophysical measurements using gaseous and scCO2 drainage-imbibition cycles during the tests in a core-scale experiment. Moreover, we were interested to see how sensitive acoustic velocity and electrical resistance techniques are to the fracture fluid displacement using different CO2 phase states. The outcomes of our high-pressure high-temperature experiment of simultaneous measurements of fracture flow and geophysical properties indicate that potential leakage of injected CO2 through the fractured-shale caprock can be detected in the core-scale laboratory experiments. The performed drainage-imbibition cycles using gaseous and scCO2 resulted in different behaviors in P-wave velocity (Vp) and electrical resistance in axial and radial directions for these two phase states. The measured Vp during the displacement of fracture fluid, CO2-brine subsequent cycles, showed a limited sensitivity in terms of magnitude and relative change. The electrical resistance, on the other hand, shows higher sensitivity and larger variation during fluid displacement along the fracture. It was also observed that the crossplot of Vp versus electrical resistance could detect and even differentiate the different phases during the loading and unloading stages.

• Skurtveit, Elin; Sundal, Anja; Soldal, Magnus; Sauvin, Guillaume & Bjørnarå, Tore Ingvald (2018). CO2 flow, alteration and geomechanical response in confining units – An experimental approach. Fulltekst i vitenarkiv
• Soldal, Magnus; Sauvin, Guillaume; Park, Joonsang; Mannseth, Trond; Tveit, Svenn & Agersborg, Remy [Vis alle 8 forfattere av denne artikkelen] (2017). Geophysical monitoring for offshore CO2 storage combined with rock physics lab data(based on SUCCESS WP3 final report Geophysics).
• Grande, Lars; Bohloli, Bahman; Skurtveit, Elin; Park, Joonsang; Soldal, Magnus & Sauvin, Guillaume (2017). Geomechanical testing of shale for micro-seismic potential at CO2 storage pilot on Svalbard, Norway.
• Skurtveit, Elin; Sundal, Anja; Sauvin, Guillaume; Soldal, Magnus; Zuchuat, Valentin & Braathen, Alvar (2017). Fracture flow experiments addressing CO2 migration in fault zone.
• Park, Joonsang; Soldal, Magnus; Sauvin, Guillaume; Nooraiepour, Mohammad; Mondol, Nazmul Haque & Bohloli, Bahman (2017). On wave propagation in a CO2/Brine-saturated fractured core.
• Bohloli, Bahman; Park, Joonsang; Sauvin, Guillaume; Grande, Lars; Soldal, Magnus & Nooraiepour, Mohammad [Vis alle 8 forfattere av denne artikkelen] (2017). Triaxial testing and geophysical monitoring of reservoir and cap rock samples from UNIS CO2 LAB pilot, Longyearbyen Svalbard, Norway.
• Grande, Lars; Soldal, Magnus & Mondol, Nazmul Haque (2015). Dynamic to static relationships of shear modulus for sand and sandstones, 3rd International Workshop on Rock Physics, 13-17 April 2015, Perth, Australia.
• Tran, Trung; Omolo, Lameck; Soldal, Magnus; Mondol, Nazmul Haque; Park, Joonsang & Johnsen, Øistein (2015). Tracking Co2 Front Development with Electrical Resistivity Measurements - An Experimental Study.
• Omolo, Lameck; Tran, Trung; Soldal, Magnus; Mondol, Nazmul Haque; Grande, Lars & Park, Joonsang [Vis alle 7 forfattere av denne artikkelen] (2015). Multidirectional acoustic velocity measurement during CO2 flooding in sandstones.
• Soldal, Magnus; Omolo, Lameck; Tran, Trung; Johnsen, Øistein; Mondol, Nazmul Haque & Sauvin, Guillaume [Vis alle 9 forfattere av denne artikkelen] (2015). CO2 flooding experiment of reservoir sandstones-monitoring changes in acoustic and electric properties. Vis sammendrag

  We present an advanced laboratory work to measure electrical resistivity, acoustic velocity (ultrasonic frequency) and anisotropy during injection of liquid CO2 into initially brine saturated reservoir core samples. A novel measurement system has been developed, where velocity and resistivity are measured at different points along the specimen axial direction. The changes in velocity and resistivity observed during the CO2 injection will be a critical element in interpreting geophysical field data to understand reservoir behaviour.

• Johnsen, Øistein & Soldal, Magnus (2014). Combined rock mechanics, rock physics and CT image quantification of physical processes.
• Johnsen, Øistein; Soldal, Magnus; Park, Joonsang; Mondol, Nazmul Haque & Alemu, Binyam Lema (2014). C02 - Resistivity and Ultrasonic Velocity Measurements During CO2-brine Drainage and Imbibition.
• Johnsen, Øistein; Soldal, Magnus; Park, Joonsang; Mondol, Nazmul Haque & Alemu, Binyam Lema (2014). Resistivity and Ultrasonic Velocity Measurements During CO2-brine Drainage and Imbibition. EarthDoc.
• Johnsen, Øistein; Alemu, Binyam Lema; Aker, Eyvind & Soldal, Magnus (2012). Rock Physical Properties and CT Imaging of CO2-brine Displacement in Reservoir Sandstone. Vis sammendrag

  Recent CO2-brine drainage and imbibition experiments in natural sandstone reservoir analogue (23% porosity cylindrical Rothbach cored perpendicular to bedding, average permeability of 400 mD) demonstrate the implications of sub-core scale heterogeneity on fluid distribution of the involved phases and the associated geophysical response. The initially brine saturated specimen was drained by stepwise injecting liquid CO2, and changes in resistivity and ultrasonic velocity was monitored while simultaneously imaging the fluid distribution by an industrial CT-scanner. A similar procedure was subsequently used for re-imbibition with brine. The results indicate a close link between the response of the measured physical and the tomographically mapped minute saturation levels and provides a deeper understanding of the implications of the flooding and imbibition processes.

• Grande, Lars; Mondol, Nazmul Haque; Berre, Toralv; Soldal, Magnus & Madshus, Christian (2011). Stress induced velocity anisotropy in loose sands. 1st Internation Rock Physics Workshop.

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