Simon Sandstone Research Articles

The effect of clay and contacts between sand grains on the elastic properties of sandstones

AbstractHigh‐porosity sandstones are important for hydrocarbon production, underground CO2 storage, extraction of geothermal energy and freshwater aquifers. Porosity of sandstones may be estimated using elastic wave velocities, but these depend also on fluid saturation, clay content, pore shape and contacts between sand grains. An understanding of how elastic properties of sandstones depend on these factors is important for characterizing their storage potential and for geomechanical issues, such as sanding, borehole stability, reservoir compaction and fracturing. Ultrasonic velocity measurements in clay‐bearing sandstones indicate that much of the clay in shaly sandstones is non‐load‐bearing. This enables a simple approach for modelling the elastic properties of shaly sandstones that includes the effect of pore concavity and agrees with ultrasonic P‐ and S‐velocities measured in the laboratory. Despite this agreement, some clay may reside within the contacts and may act to inhibit the development of quartz cement, thus reducing porosity loss and helping to preserve storage volume. This appears to be the case for the Lower Mt. Simon Sandstone, a target formation for underground storage of CO2 in the Illinois Basin, for which the bulk moduli agree with the predicted bulk moduli, but the shear moduli are lower than predicted. This appears to result from an increase in a shear compliance of the grain contacts that may enable sliding along the grain contacts and increase the tendency to shear failure.

Geological risk and uncertainty for underground storage of buoyant fluids, lessons learned in Illinois

Abstract This paper describes selected natural gas storage and carbon capture and storage (CCS) case studies from Illinois, USA, their general applicability to subsurface buoyant fluid storage, and summarizes lessons learned. In Illinois, a 70-year history of sustained natural gas storage has provided a foundational understanding of risk associated with using the subsurface for storing buoyant fluids. In addition to natural gas storage, over 3 million tonnes of CO 2 have been injected into the Cambrian Mt Simon Sandstone at the Decatur, IL CCS project site. In Illinois, many of the storage projects are in the Mt Simon Sandstone, a saline (aquifer) reservoir. In gas storage fields the characterization of faulting and seal properties has historically not been adequate. Identification of Precambrian palaeotopography is essential when completing initial site assessment in reservoirs close to the Precambrian contact. The presence of basement palaeotopographical highs increases the risk of not having a storage reservoir and increased chance of induced seismicity. The Cambrian Mt Simon Sandstone of the Illinois Basin has some of the most suitable strata in the midwestern USA for the sequestration of CO 2 and storage of energy in the form of natural gas. The improved understanding gained from natural gas storage and from carbon sequestration is also directly applicable to assessing the potential of emerging energy storage technologies, such as compressed air energy storage (CAES) and geological hydrogen storage.

Dynamic estimates of geologic CO2storage resources in the Illinois Basin constrained by reinjectivity of brine extracted for pressure management

AbstractGeologic carbon storage (GCS) is likely to be an important part of global efforts to decarbonize the energy industry. Widespread deployment of GCS relies on strategies to maximize CO2injection rates while minimizing reservoir pressurization that could induce seismicity and/or fluid leakage into groundwater resources. Brine extraction from CO2storage formations with subsurface reinjection elsewhere could mitigate pressure buildup associated with GCS. Therefore, evaluation of CO2storage resources should consider the injectivity of produced brine in geologic layers above or below the CO2storage formation. For this study, a methodology was developed to estimate brine injectivity from formation depth and thickness using flow modeling and optimization techniques. The methodology was demonstrated in the Illinois Basin, where GCS in the Mt. Simon Sandstone is ongoing. Based on pressure constraints and considering only regions of the shallower units where salinity and sealing conditions were met, maximum brine injection rates were estimated within the Mt. Simon and three overlying hydrostratigraphic layers. Results indicate that a large area exists where CO2injectivity could be optimized by brine extraction and reinjection. © 2022 The Authors.Greenhouse Gases: Science and Technologypublished by Society of Chemical Industry and John Wiley & Sons Ltd.

Illitization in the Mt. Simon Sandstone, Illinois Basin, USA: Implications for carbon dioxide storage

Clay mineral cementation is one of the most important controls on sandstone reservoir properties. In this paper, the diagenetic history of the Mt. Simon reservoir complex is studied to reveal the origin, timing, and controls of illitization. Samples of sandstone and shale from Mt. Simon reservoir complex were acquired from the Illinois Basin–Decatur Project (IBDP), a CO2 storage demonstration project in the central Illinois Basin. Petrographic, SEM, TEM, XRD analyses and K/Ar age dating were completed to identify the major detrital and diagenetic components of the samples and reveal illite to be the major clay component in all samples. Illitic clay coatings in the lower Mt. Simon reservoir are identified as a major control on reservoir properties by inhibiting major precipitation of authigenic quartz during illitization, resulting in highly permeable sandstone, essential for CO2 storage. The coating box-work morphology and mineralogy are indicative of a detrital smectite origin with subsequent illite growth associated with feldspar dissolution and kaolinite alteration. The mineralogy of bulk material and separate grain size fractions (2–0.6 μm; 0.6–0.2 μm; < 0.2 μm) with illite polytypes 2M1, 1M, and 1Md were quantified and age dated via 40K-40Ar methods. The shales or reservoir seals contain the highest proportions of detrital illite with illite in the lower Mt. Simon Sandstone reservoir identified as solely diagenetic. Two major events of illitization are identified throughout the Mt. Simon with more porous reservoir rock exhibiting the older event from approximately 360 to 315 Ma and tighter sandstone units with reservoir properties too low to be considered reservoir exhibiting illite dates from 250 to 220 Ma. This partitioning of illitization is attributed to varied mineralogy controlled by depositional changes and evolution of the greater basin.

High-Resolution Pore Space Imaging, Mineralogical Characterization, and Sealing Capacity Estimates of Confining Units at a Geologic Carbon Storage Demonstration: The Illinois Basin–Decatur Project, USA

At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.

Geochronology of Cambrian Sedimentary and Volcanic Rocks in the Illinois Basin: Defining the Illinois Aulacogen

The Wabash #1 well, drilled for the Wabash CarbonSAFE Project and located in Vigo County, Indiana, USA, was drilled in early 2020 as a stratigraphic test well to characterize and evaluate the basal Cambrian Mt. Simon Sandstone for carbon dioxide storage (TD=8750 ft; 2667 m). The Wabash #1 well is located along the eastern flank of a newly interpreted Cambrian aulacogen that occurs in western Indiana and eastern Illinois. Here we present 938 new detrital zircon U-Pb ages (LA-ICPMS) from early Cambrian sandstones sampled near the base of the well. A basalt lava flow was penetrated at ~8530 ft (2600 m) and has an 40Ar/39Ar age of 525.03 +/- 1.10 Ma, which represents the first known Cambrian crust in the Illinois Basin. The two sandstone samples from beneath the basalt are dominated by zircons derived from the Midcontinent Granite-Rhyolite terrane. The sandstone samples from above the basalt reflect a mixture of these locally derived Mazatzal and Granite-Rhyolite terrane zircons, but also distal Archean, Grenville, and Yavapai zircons. Each sample has small numbers of Cambrian zircons, which is consistent with those in basal Cambrian sandstones in other deep wells to the west. These early Cambrian detrital zircons and early Cambrian age of the basalt, combined with sediment thickness patterns permit the interpretation of the Illinois aulacogen, which formed during the final stage of Rodinian rifting.

Effects of Hydrogeological Heterogeneity on CO2 Migration and Mineral Trapping: 3D Reactive Transport Modeling of Geological CO2 Storage in the Mt. Simon Sandstone, Indiana, USA

We used three-dimensional (3D), high-resolution simulations facilitated by parallel computation to assess the effect of hydrogeological heterogeneity in the Mt. Simon Sandstone on CO2 plume evolution and storage and geochemical reactions in a portion of the Illinois Basin, Indiana. Two scenarios were selected to investigate the effects of the hydrogeological heterogeneity in 3D reactive transport simulations: a heterogeneous case with variable porosity and permeability, and a homogenous case with constant porosity and permeability. The initial pressure, temperature, and mineralogical distributions are consistently applied in both the heterogeneous case and the homogeneous case. Results indicate that including hydrogeological heterogeneity in 3D reservoir simulations for geological CO2 storage significantly impacts modeling results for plume migration patterns, CO2-water-mineral interaction, reservoir quality, and CO2 plume containment. In particular, results indicate that (1) the CO2 plume reached the top of the Mt. Simon Sandstone in the homogeneous case, but was restrained to the lower third of the formation when hydrogeologic heterogeneity was considered; (2) the dominant trapping mechanism in the heterogeneous case was mineral trapping (43%), while it was solubility trapping (47%) in the homogeneous case (at 10,000 years); (3) incorporating reservoir heterogeneity in the model leads to a higher likelihood of long-term containment.

Geomechanical aspects of induced microseismicity during CO2injection in Illinois Basin

Carbon sequestration activities are increasing in a global effort to mitigate the effects of greenhouse gas emissions on the climate. Injection of wastewater and oil-field fluids is known to induce seismic activity. This makes it important to understand how that risk relates to CO2injection. Injection of supercritical CO2into the Cambrian Mt. Simon sandstone in Illinois Basin induced microseismicity that was observed below the reservoir, primarily in the Precambrian crystalline basement. Geomechanical and flow properties of rock samples from the involved formations were measured in the laboratory and compared with geophysical log data and petrographic analysis. The controlling factors for induced microseismicity in the basement seem to be the hydraulic connection between the reservoir and basement rock and reactivation of pre-existing faults or fractures in the basement. Additionally, the presence of a laterally continuous low-permeability layer between reservoir and basement may have prevented downward migration of pore pressure and reactivation of critically stressed planes of weakness in the basement. Results of the geomechanical characterization of this intermediate layer indicate that it may act as an effective barrier for fluid penetration into the basement and that induced microseismicity is likely to be controlled by the pre-existing system of faults. This is because the intact material is not expected to fail under the reservoir stress conditions.

Gouge formation and dilation impacts to flow during fracture shearing

Flow in fractures is of critical importance to fluid flow in low-permeability shales, particularly when they restrict vertical migration from reservoirs. The Mt. Simon Sandstone is a target for geologic CO 2 sequestration and the overlying Eau Claire Formation is the sealing formation capping this reservoir. The lower Eau Claire, a primary barrier to upward migration of CO 2 from the Mt. Simon, is lithologically heterogenous with a mixture of sandstone and shale. We use a series of flow-through experiments on fractured samples from the Eau Claire to document the morphological changes taking place in the fracture and surrounding rock as it is sheared in a stepwise fashion. The samples were imaged using computed tomography after each shearing episode and flow resistance was calculated based on the pressure differential across each core. We found that gouge accumulations in the fracture plane led to specific instances of self-sealing behavior despite the fact that most samples increased in average fracture aperture and transmissivity . Gouge limited the increase or, in some cases, decreased flow through these samples. Fractures adjacent to shale-rich zones and concordant with bedding were more likely to show evidence of self-sealing, while increased sandstone content and fracture orientation perpendicular to bedding planes was more likely to result in fracture dilation and fracture permeability increases. Reactivation and shearing of vertical fractures in lithologically heterogenous caprocks is more likely to pose risks to long term CO 2 storage scenarios. • Computed Tomography illustrates fracture shearing in Eau Claire formation. • Fracture transmissivity and dilation can be limited by gouge during shearing. • Mixed lithologies and diagenetic cements increase likelihood of gouge creation. • Shale-adjacent fractures are more likely to show localized sealing. • Self-sealing behaviors are less likely in fractures perpendicular to bedding.

Identifying geological structures through microseismic cluster and burst analyses complementing active seismic interpretation

At the Decatur carbon capture and storage site (IL, USA) CO2 has been injected from 2011–2014 and from 2017 to present near the base of the Lower Mt. Simon Sandstone saline reservoir, resulting in microseismicity. Microseismicity is mainly located in the basement and distributed in distinct spatial clusters. The lack of significant impedance contrasts within the basement makes the interpretation of active-source seismic reflection data challenging, however, recent reprocessing allowed to resolve faults above and at the top of the basement. These faults generally do not coincide with the location of microseismic events and their continuation to the general depth of the seismic events cannot be assumed. This paper shows how the interpretation of the microseismicity can complement structural interpretations of active-source seismic reflection data. In particular, we analyze clusters and bursts (abrupt increases) of microseismicity, identify unresolved, smaller-scale weaknesses and extract statistical parameters. These parameters allow comparisons with the interpreted faults, and with fracture sets intercepted by boreholes. During injection at the Decatur site, the injection pressure was kept far below fracture pressure, nevertheless, seismic events were induced and spread far beyond the expected extent of the CO2 plume. We argue that local stress transfers related to the CO2 injection reactivated pre-existing fractures within the critically stressed basement. Finally, we conducted a slip tendency analysis for faults interpreted from active seismic, selected cluster, bursts and nodal planes from focal mechanisms to determine if the interpreted structures are optimally oriented with respect to the stress regime. Our results suggest that the orientation of fractures close to the injection well, generally shows slight deviations from the optimal orientation for slip. This might indicate either slight local deviations of the maximum horizontal stress azimuth from the average direction used in the analysis, or the lack of optimally oriented fractures at this location.

Pore-scale simulation of viscous instability for non-Newtonian two-phase flow in porous media

The impact of micro-heterogeneity on non-Newtonian two-phase flow is the focus of the present study. The direct numerical simulation of non-Newtonian fluids (modelled using shear stress-dependent Meter model) displacing oil in 3D Mt. Simon sandstone and 2D heterogeneous porous media were considered over a range of wettabilities (strong imbibition to strong drainage), capillary numbers and viscosity ratios. This study suggests that heterogeneity of the porous medium can potentially lead to an unstable fluid flow front (even after use of polymer). Therefore along with capillary number and viscosity ratio, heterogeneity is the governing factor for controlling viscous and capillary fingering, and it is crucial to account for the microscale heterogeneity of porous media to design polymer solution injection.

Impact of exposure to brine/CO2 on the mechanical and transport properties of the Mt. Simon Sandstone

AbstractWhen sandstone rocks are exposed to CO2‐saturated brine, their transport and mechanical properties can, potentially, change due to chemical reactions as a result of such exposure. This paper investigates changes in the flow‐through characteristics, porosity, and the mechanical properties of Mt. Simon Sandstone samples caused by such exposure to brine/CO2. A core, extracted from the Mt. Simon formation, was first characterized for its porosity and relevant transport properties, and it was then aged for over 500 hr in CO2‐saturated brine at formation‐relevant pressure, temperature, and confining stress conditions. The deformation of the sample was measured in situ during aging via strain gauges attached to the core's surface. Following the aging experiment, the sample's porosity and transport properties were again analyzed. Our experiments show that both the porosity and permeability of the Mt. Simon sandstone sample increase due to exposure to brine/CO2, with the impact on permeability being more significant. The deformation measurements employing strain gauges indicate a weakening of the core material. Analysis of the composition of the brine at the conclusion of the testing reveals changes, specifically, an increase in the concentration of several of the cations. These changes are indicative of mineral/clay dissolution, consistent with the porosity, permeability, and strain gauge measurements. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Upscaling non-Newtonian rheological fluid properties from pore-scale to Darcy’s scale

Continuity and momentum equations govern the pore-scale flow properties of the fluid in the porous media, whereas Darcy’s law governs Darcy scale properties of the fluid transport in porous media. The empirical shift factor relates the steady shear-dependent viscosity of non-Newtonian fluids to the Darcy viscosity in porous media. The reported values of the empirical shift factor cover three orders of magnitude depending on the considered fluid-medium configurations. This creates a challenge to upscale non-Newtonian rheology from pore-scale to Darcy’s scale. We upscale Darcy viscosity based on pore-scale shear viscosity of Meter model fluid and viscoelastic linear Phan-Thien-Tanner fluid. We propose a Bundle-of-Capillaries model modified with pore-correction coefficient and fluid-correction coefficient. We numerically simulate the flow of polyacrylamide fluid, modelled using Meter model and linear Phan-Thien-Tanner model, through 3D symmetric micro-channel, 2D porous medium and 3D Mt Simon sandstone. Pore-scale direct numerical simulation using linear Phan-Thien-Tanner model showed viscoelastic instability in heterogeneous Mt Simon sandstone at low Reynolds number flow. Direct numerical simulations overestimate Darcy viscosity due to the presence of stagnant zones without active flow.

Deep neural networks for improving physical accuracy of 2D and 3D multi-mineral segmentation of rock micro-CT images

Segmentation of 3D micro-Computed Tomographic (μCT) images of rock samples is essential for further Digital Rock Physics (DRP) analysis, however, conventional methods such as thresholding and watershed segmentation are susceptible to user-bias. Deep Convolutional Neural Networks (CNNs) have produced accurate pixelwise semantic (multi-category) segmentation results with natural images and μCT rock images, however, physical accuracy is not well documented. The performance of 4 CNN architectures is tested for 2D and 3D cases in 10 configurations. Manually segmented μCT images of Mt. Simon Sandstone guided by QEMSCANs are treated as ground truth and used as training and validation data, with a high voxelwise accuracy (over 99%) achieved. Downstream analysis is used to validate physical accuracy. The topology of each mineral is measured, the pore space absolute permeability and single/mixed wetting multiphase flow is modelled with direct simulation. These physical measures show high variance, with models that achieve 95%+ in voxelwise accuracy possessing permeabilities and connectivities orders of magnitude off. A network architecture is introduced as a hybrid fusion of U-Net and ResNet, combining short and long skip connections in a Network-in-Network configuration, which overall outperforms U-Net and ResNet variants in some minerals, while outperforming SegNet in all minerals in voxelwise and physical accuracy measures. The network architecture and the dataset volume fractions influence accuracy trade-off since sparsely occurring minerals are over-segmented by lower accuracy networks such as SegNet at the expense of under-segmenting other minerals which can be alleviated with loss weighting. This is an especially important consideration when training a physically accurate model for segmentation.

Advanced Geomechanical Model to Predict the Impact of CO2-Induced Microstructural Alterations on the Cohesive-Frictional Behavior of Mt. Simon Sandstone

We investigated the influence of CO2-induced geochemical reactions on the cohesive-frictional properties of host rock within the context of CO2 storage in a saline aquifer and focused on the Mt. Simon sandstone. The research objective was to model geo-mechanical changes due to host rock exposure to CO2-saturated brine while accounting for heterogeneity, double-scale porosity, and granular structure. We formulated a three-level multi-scale model for host rocks. We conducted scanning electron microscopy analyses to probe the microstructure and grid nanoindentation to measure the mechanical response. We derived new nonlinear strength upscaling solutions to correlate the effective strength characteristics and the macroscopic yield surface to the micro-structure at the nano-, micro-, and meso-scales. Specifically, our theoretical model links CO2-induced microstructural alterations to a reduction in the size of the yield surface, and a drop in the value of the friction coefficient. In turn, regarding the Illinois Basin Decatur Project, the CO2-induced drop in friction coefficient is linked to an increase in the risk of fault slip and a higher probability of induced microseismicity during and after the end of CO2 underground injection operations. The theoretical model presented is essential for the geo-mechanical modeling of CO2 underground injection operations at multiple length-scales.

Interpreting pre-vegetation landscape dynamics: The Cambrian Lower Mount Simon Sandstone, Illinois, U.S.A.

ABSTRACTThe Cambrian Mount Simon Sandstone has been the subject of extensive study and multiple industrial-scale carbon storage demonstrations at Decatur, Illinois, USA. The development of a reliable paleoenvironmental model is critical to successful large-scale carbon dioxide (CO2) storage, but is complicated by the need to interpret pre-vegetation sedimentation processes. The present study presents a paleoenvironmental model of the Lower Mount Simon Sandstone, based on analysis of primary sedimentary structures in two cores and four complete high-resolution resistivity logs (FMI).The Lower Mount Simon Sandstone represents a vertical “drying-up” sequence composed of three associated depositional units: a north–south oriented coastal system at the base, an eastward-directed fluvial unit in the middle, and a westward-directed eolian system at the top that recycled medium- and fine-grained sand in the basin. Quantitative analysis of fluvial cross-strata indicates that the perennial river system was shallow (c. 1 m deep) with relatively narrow channel belts (c. 1 km). Adjacent sandy eolian-floodplain deposits contain abundant thin, crinkly planar laminae that are enriched in fines and are interpreted as cementation surfaces, likely of biological origin. Deflation lags and wind-ripple strata are commonly interbedded with the crinkly strata, suggesting that the recurrence of erosion and deposition that controlled sedimentary preservation on the floodplain were dominated by eolian transport, re-wetting, and (bio-) cementation. Such a prominent role of exposure to the wind, basin-scale sediment recycling, and eolian removal of fine-grained sediment would have ceased to exist for most climates after the development of vegetation on land, yet, may well be key to understanding the environmental context for early life on Earth.

Identifying the Optimal Path and Computing the Threshold Pressure for Flow of Bingham Fluids Through Heterogeneous Porous Media

Understanding flow of non-Newtonian fluids in porous media is critical to successful operation of several important processes, including polymer flooding, filtration, and food processing. In some cases, such as when a non-Newtonian fluid can be represented by the power-law model, simulation of its flow in a porous medium is a straightforward extension of that of Newtonian fluids. In other cases, such as flow of Bingham fluids, there is a minimum external threshold pressure below which there would be no macroscopic flow in the porous medium. Computing the threshold pressure is a difficult problem, however. We present a new algorithm for determining the threshold pressure for flow of a Bingham fluid through a porous medium, modeled by a pore-network (PN) model. The algorithm, the ant colony optimization (ACO), is described in detail and together with the PN model is used to determine the minimum pressure for flow of Bingham fluids in a heterogeneous porous medium, the Mt. Simon sandstone, whose PN and morphological properties were extracted from the sandstone’s image. To assess the accuracy and computational efficiency of the ACO algorithm, we also carry out the same computations with two previous methods, namely invasion percolation with memory (IPM) and the path of minimum pressure (PMP) algorithms. The IPM does not guarantee identification of the optimal flow path with the minimum threshold pressure, while the PMP algorithm provides an approximate, albeit accurate, solution of the problem. We also compare the computational complexity of the three methods. For large PNs, both the IPM and PMP are much less efficient than the ACO algorithm. Finally, we study the effect of the morphology of the pore space on the minimum threshold pressure.

Influence of geochemical reactions on the creep behavior of Mt. Simon sandstone

The capture and subsurface storage of carbon dioxide is a sustainable option that is currently pursued worldwide to mitigate greenhouse gas effect. However, predicting the long-term mechanical integrity of CO2 underground storage systems remains a challenge. To address that question, it is essential to understand the influence of fluid-rock chemo-mechanical interactions on the long-term and on the time-dependent mechanical properties. In turn, the long-term mechanical response and the time-dependent mechanical behavior can be represented by the creep response. We investigate the impact of CO2-induced geochemical reactions on the creep response of Mt. Simon sandstone with a 50–400 μm grain size. We perform static and dynamic flow experiments on Mt. Simon sandstone specimens under geological conditions, at a temperature of T=50–53 °C and for CO2 pressures of P=8.62, 17.2 MPa under both static flow and dynamic flow-through conditions. After aging, we employ creep indentation testing, high-resolution SEM-EDS, computer vision, machine learning, and micromechanics modeling to probe changes on the microstructure and mechanical properties. Following both static and dynamic flow-through experiments, we observe a 10–22% decrease in quartz volume fraction and an increase in both the microporosity (7–28%) and nanoporosity (60–65%). Additional CO2-induced microstructural changes include an enlargement of pore throats and the formation of channels. These observations point to the presence of CO2-induced K-feldspar dissolution and clay dissolution reactions. The macroscopic creep behavior is logarithmic and the macroscopic creep modulus varies depending on the microporosity and the relative quartz and feldspar content. As a result of these geochemical reactions and of the related microstructural changes, a 55–60% decrease in the macroscopic logarithmic creep modulus is predicted.

Estimating the net costs of brine production and disposal to expand pressure-limited dynamic capacity for basin-scale CO2 storage in a saline formation

If carbon capture and storage (CCS) needs to be deployed at basin- or larger-scale, it is likely that multiple sites will be injecting carbon dioxide (CO2) into the same geologic formation. This could lead to excessive pressure buildup, overlapping induced pressure fronts, and pressure interference with neighboring uses of the subsurface. Extracting the in situ brine from the storage formation could be necessary to relieve pressure constraints; control migration of the CO2 plume, displaced brine, and the induced pressure front; and sequester more CO2 while reducing potential risks. Such active pressure management could be very costly, and it could present a formidable economic constraint on the feasible scale of deployment of CCS. Alternatively, there may be high-injectivity zones (“storage sweet spots”) where a significant volume of CO2 could be stored without producing brine. For simulated deployment of CO2 storage sites across the Illinois Basin, the results of this study suggest that brine production could be required to sequester 20 % or more of the regional CO2 emissions of major stationary sources in the Mount Simon Sandstone saline formation. In some cases, brine production could expand pressure-limited CO2 storage capacity enough to more than compensate for the additional costs of pressure management, but only if produced brine could be cheaply reinjected onsite for disposal in an overlying geologic formation. With or without brine production, this study found that the lowest-cost deployment option was to inject CO2 only into a potential storage sweet spot of the Mount Simon Sandstone.

Influence of Clay Wettability Alteration on Relative Permeability

AbstractUnderstanding the wettability of porous materials is important to model fluid flow in the subsurface. One of the critical factors that influences wetting in real reservoirs is the composition of geologic materials. The wetting properties for clay minerals can have a particularly strong impact on flow and transport. In this work, we analyze the chemical composition of a Mt. Simon sandstone core to resolve the microscopic structure of clay regions and assess how alterations to the local wetting properties influence multiphase transport based on core flooding experiments and relative permeability simulations. We show that whichever fluid has greater affinity toward clay minerals will tend to accumulate within these high surface area regions, leading to dramatic shifts in the relative permeability. This work establishes the essential importance of the mineral composition and associated wetting properties in the modeling of flow and transport in reservoir‐scale systems.