Illinois Basin – Decatur Project Research Articles

Mechanisms for Microseismicity Occurrence Due to CO2 Injection at Decatur, Illinois: A Coupled Multiphase Flow and Geomechanics Perspective

ABSTRACT We numerically investigate the mechanisms that resulted in induced seismicity occurrence associated with CO2 injection at the Illinois Basin–Decatur Project (IBDP). We build a geologically consistent model that honors key stratigraphic horizons and 3D fault surfaces interpreted using surface seismic data and microseismicity locations. We populate our model with reservoir and geomechanical properties estimated using well-log and core data. We then performed coupled multiphase flow and geomechanics modeling to investigate the impact of CO2 injection on fault stability using the Coulomb failure criteria. We calibrate our flow model using measured reservoir pressure during the CO2 injection phase. Our model results show that pore-pressure diffusion along faults connecting the injection interval to the basement is essential to explain the destabilization of the regions where microseismicity occurred, and that poroelastic stresses alone would result in stabilization of those regions. Slip tendency analysis indicates that, due to their orientations with respect to the maximum horizontal stress direction, the faults where the microseismicity occurred were very close to failure prior to injection. These model results highlight the importance of accurate subsurface fault characterization for CO2 sequestration operations.

Advancing subsurface analysis: Integrating computer vision and deep learning for the near real-time interpretation of borehole image logs in the Illinois Basin-Decatur Project

The accurate quantification and mapping of subsurface natural fracture systems using borehole imaging logs are critical for the success of CO2 sequestration in geologic formations, optimization of engineered geothermal systems, and hydrocarbon production enhancement. However, traditional interpretation processes suffer from time-consuming procedures and human bias. To address these challenges and expedite fracture analysis, we investigated the application of integrated computer vision and DL workflows to automate image log analysis. Specifically, the design of our workflow was crafted to swiftly detect fractures and baffles by using actual electrical resistivity of borehole wall from microresistivity imaging device alongside their binary representation. This novel approach significantly reduces computational time while providing invaluable insights. By incorporating conventional logging and microseismic data, we present a regional subsurface natural fracture mapping technique. Through the minimization of human bias in image log analysis, our automated workflow achieves reduced fracture interpretation time and costs while ensuring robust and reproducible results. We demonstrated the efficacy of our approach by applying the workflow to the Illinois Basin-Decatur Project site. The automated workflow successfully identified major fractured zones, multiple baffles, and an interbedded layer with a high resolution of 0.01 ft or 0.12 in. (0.3 cm) and can be upscaled to any desired resolution. Validation through microseismic and image log interpretations allows for accurate and near-real-time mapping of fractures and baffles, significantly enhancing CO2 pressure forecasting and postinjection site care. Our approach stands out due to its robustness, consistency, and reduced computational cost compared with alternative feature extraction technologies. It presents exciting possibilities for advancing CO2 sequestration and engineered geothermal efforts by offering comprehensive and efficient fracture mapping solutions. This technology can contribute significantly to the optimization of CO2 sequestration projects, facilitating sustainable environmental practices, and combating climate change.

Quantitative seismic fracture characterization of a sandstone reservoir — Decatur, Illinois Basin

The Illinois Basin Decatur Project, a carbon capture and sequestration task, was undertaken to sequester 1 million tonnes of CO2 into a sandstone reservoir. A 3D seismic survey was conducted to characterize the reservoir. A geomodel was developed from seismic data, inversion results, and well data to geostatistically map the storage potential of the reservoir. However, no fracture model was created or utilized in this exercise. Fractures inherently influence the porosity and permeability of a reservoir. Ignoring them in reservoir characterization is not an optimal reservoir management practice. The image-log interpretation from a few vertical wells drilled in the area shows the bedding plane dips, but no fracture has been identified. However, the lack of fracture crossings in a few vertical wells does not imply that a formation is devoid of fractures altogether. Hence, seismic fracture characterization (leveraging the dense 3D seismic data) is necessary for a reservoir characterization exercise. We utilized the publicly available Decatur 3D seismic data set to run a seismic fracture characterization workflow to delineate potential fracture corridors present in the reservoir. We calculated three edge detection attributes (structural tensor, structure-oriented semblance, and structural dip) in combination to delineate the fracture lineaments. Our workflow extracts several quantitative measures of the seismic lineaments such as dip, azimuth, area, and length, which can be analyzed statistically. The principal focus of this work is to find a way forward to integrate the fractures from seismic data in a geologic model that can be utilized in simulations. Based on our interpretation of seismic fractures, we created a discrete fracture network that can be a building block for creating a finer-resolution fracture model. We also explored the fractal characteristics of seismic-derived fracture lineaments as a way forward for generating discrete fracture networks.

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.

Hydromechanical impact of basement rock on injection-induced seismicity in Illinois Basin

The common explanation of observed injection-induced microseismicity is based on the measured stress state at the injection interval and the assumption that it remains the same in the vicinity. We argue here that representing the stress state in different geologic formations over the injection site with the single Mohr’s circle is insufficient due to local stratigraphic features and contrast in compressibilities of the involved formations. The role of hydromechanical coupling in the microseismic response is also crucial for the proper assessment of the problem. Thoroughly monitored Illinois Basin Decatur Project revealed the majority of CO2 injection-associated microseismic events being originated in the crystalline basement. Even though basement faults can serve as the conduits for fluid flow—the predicted pressure increase seems to be insufficient to trigger seismicity. To address this issue, accurate laboratory measurements of rock properties from the involved formations are conducted. The pre-injection stress state and its evolution are evaluated with the hydromechanically coupled numerical model. It appears that the presence of an offset in a stiff competent layer affects the stress state in its vicinity. Therefore, both the pre-injection stress state and its evolution during the fluid injection should be addressed during the induced seismicity assessment.

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.

Coupled Hydromechanical Modeling of Induced Seismicity From CO2 Injection in the Illinois Basin

AbstractInjection of CO2 for geologic carbon sequestration into deep sedimentary formations involves fluid pressure increases that engage hydromechanical processes that can cause seismicity by activation of existing faults. In this work, we use a coupled multiphase fluid flow and geomechanical simulator to model spatiotemporal fluid pressure and stress changes in order to study the poroelastic effect of CO2 injection on faults in crystalline basement rock below the injection zone. The seismicity rate along features interpreted to be basement faults is modeled using Dieterich's rate‐and‐state earthquake nucleation model. The methodology is applied to microseismicity detected during CO2 injection into the Mount Simon formation during the Illinois Basin—Decatur Project. The modeling accurately captures an observed reduction in seismicity rate when the injection in the second well was into a slightly shallower zone above the base of the Mount Simon formation. Moreover, the modeling shows that it is important to consider poroelastic stress changes, in addition to fluid pressure changes for accurately modeling of the observed seismicity rate.

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.

Analysis of Microseismicity and Reactivated Fault Size to Assess the Potential for Felt Events by CO2 Injection in the Illinois Basin

ABSTRACTThe results of monitoring of carbon dioxide (CO2) injection at the Illinois Basin—Decatur Project (IBDP) and the companion Illinois Industrial Carbon Capture and Sequestration Sources (IL-ICCS) project—have shown that reservoir response to fluid pressure changes can vary significantly at different injection locations within the same reservoir. Predrill reservoir characterization is important to identify potentially seismogenic faults. However, interpretations of newly reprocessed 3D seismic reflection data illustrate the challenges related to their identification in a region dominated by faulting with small vertical offsets. Faults interpreted in the 3D seismic volume range from ∼300 to 1200 m wide and are in the same size range as faults that could have been the source of historical events up to Mw 2.7 in central Illinois. The array of monitoring sensors that was installed for the IBDP continues to collect data, as injection operates in IL-ICCS, the second injection well. CO2 injection rates for the IL-ICCS well are on average 1.7 times the rates injected in the IBDP well, but a significantly reduced rate of induced seismicity is observed. This article presents results of passive seismic monitoring for the duration of the project to date, integrating active and passive seismic data to develop a new interpretation of the subsurface structure at the Decatur site that explicitly identifies pathways for fluid flow into the basement leading to induced seismicity, and provides a geological explanation for the sharp reduction of induced seismicity during injection at higher rates into the second well. The use of seismic moment to estimate the length of seismogenic slip planes in the local subsurface suggests that faults large enough to produce felt seismicity are unlikely to be present at or near the Decatur site.

CO2 induced changes in Mount Simon sandstone: Understanding links to post CO2 injection monitoring, seismicity, and reservoir integrity

The purpose of this study is to quantify geochemical reactions of CO2 and brine with subsurface samples taken from the Mt. Simon sandstone and identify any potential alterations of the geomechanical rock properties that could lead to changes observable in seismic monitoring or result in changes of micro seismicity such as those observed at the Illinois Basin-Decatur Project (IBDP) site. Two Mt. Simon sandstone samples from 6919.3 feet (2109.0 m) and 6926.1 feet (2111.1 m) depth were exposed to supercritical CO2 (scCO2) dissolved in brine at in-situ reservoir conditions for one month. Geochemical, spectral, scanning electron microscopy, and petrophysical methods were used to analyze the samples before and after the one-month exposure. Significant changes were observed. Multiple geomechanical properties were chosen to form the framework against which to interrogate the petrophysical data: Young’s modulus (E), Poisson’s ratio (ν), lambda·rho (λρ), and mu·rho (μρ). In this study we conclude that framework composition, porosity, heterogeneities, effective pressure, and reactive geochemistry are first order controls on trends in the E-μ and λρ-μρ cross plot spaces. Changes in porosity, permeability, dynamic moduli, and brittleness with exposure to these fluids were observed. No change in ultrasonic P-wave attenuation (QP) was observed. Geochemical alteration causes a distinct shift in λρ-μρ in both samples as well as changes in E, ν , and P and S wave seismic velocity values. These observations could provide insight into subsurface monitoring using seismic methods including amplitude variation with offset (AVO) classification.

Integrated Carbon Capture, Utilization, and Storage for the Mid-Continent Region of the United States

Carbon capture, utilization, and storage (CCUS) with CO2 captured from bio-energy projects (BECCS) has been identified as an important technology for reducing CO2 emissions by the Intergovernmental Panel on Climate Change [1]. Capture from ethanol sources is proved at commercial scale (i.e., million tonnes per year scale) for storage at the Illinois Basin-Decatur Project . In states like Nebraska and Kansas where there is a large ethanol production industry in addition to significant electricity generation, CCUS projects can be started immediately with ethanol-based-CO2 as a source and expanded as electricity-generated-CO2 comes on line commercially. A CO2 source corridor was identified from sources in eastern Nebraska westward to sources in Columbus and then southwestward to storage areas in the oilfields in Red Willow and surrounding counties. Between 2.1 and 2.4 million tonnes of CO2 per year could be collected from this source corridor. Stacked storage is an important vehicle for early implementation because revenue from CO2-enhanced oil recovery could be paired with existing tax credits and subsidies to support the construction of capture and transport infrastructure as a commercial enterprise. This study demonstrates the feasibility of the midcontinent hub concept. It shows that the economics and geology are favorable for early implementation of commercial scale CCUS utilizing BECCS to decarbonize biofuels and support local agriculture and oil production.

Mobilization of trace metals from caprock and formation rocks at the Illinois Basin – Decatur Project demonstration site under geological carbon dioxide sequestration conditions

One concern for geologic CO2 sequestration is the potential leakage of CO2 or CO2-saturated brine containing trace metals into overlying aquifers, which poses the risk of adversely affecting underground sources of drinking water. In this work, rock and brine samples collected in the Illinois Basin – Decatur Project (IBDP), a large-scale geological CO2 sequestration demonstration project in Decatur, Illinois, USA, as well as synthetic brine samples were used to understand the mobilization of trace metals as a result of CO2–rock–brine interactions under IBDP-specific conditions (50 °C and 20.6 MPa). Rock sample characterization indicated that, at the IBDP site, trace metal concentrations were greatest in cap rock samples from the Eau Claire Formation, compared with those from formations above and below this Formation. The natural brine samples collected from the Mt. Simon Sandstone reservoir were highly reducing and saline, with trace metal concentrations up to 680 times greater than the U.S. Environmental Protection Agency-prescribed drinking water standards. Batch leaching experiments indicated that both trace metal mobilization from rock and immobilization from the brine occurred when high-pressure CO2 was introduced into the rock-brine system. The amounts of metals mobilized from the rock generally accounted for <5% of the total metals in the rock, but for some metals, including Ni, Pb, and Tl, up to 63% of the metals in the rock were mobilized to the brine. Leaching of trace metals into synthetic brines was different from that into the natural brine. The results of this study provided current information on the trace element sources and will help in risk simulations and experimental design to further evaluate potential impact of leakage on groundwater quality, which is important for future GCS projects to consider for monitoring and containment assurance purposes.

Reactive alteration of a Mt. Simon Sandstone due to CO2-rich brine displacement

We report a series of acidified brine flow-through experiments designed to quantify the coupled alteration of geochemical, structural and fluid transport properties of a Mt. Simon sandstone core recovered at a depth of 2110.5 m as part of the Illinois Basin Decatur Project (IBDP). Flow-through experiments were completed at representative in-situ conditions to isolate the stages of initial CO2 injection: first, a single-phase (CO2–saturated brine, Stage 1) followed by a second multi-phase (CO2–saturated brine and supercritical CO2, Stage 2) experiment. During both stages, effluent major and trace cation concentrations were tracked through time. Two imaging methods were employed to analyze the structural alterations of the rock core induced by the percolation of CO2-saturated brine and supercritical CO2: (1) scanning electron microscopy-petrography before Stage 1 and after Stage 2 and (2) computed tomography (CT) scans before and after Stage 2.The time series of Stage 1 effluent solutes were used to constrain a reactive transport simulation of the system. Modeling results suggest the evolution of the solute composition is a result of coupled dissolution of K-feldspar, calcite, illite and pyrite, and precipitation of montmorillonite, mesolite, alunite, diaspore, goethite and muscovite. The model predicted a net opening of pore space and associated increased permeability at the inlet. However, across the whole core, an overall decrease in permeability of approximately 23% ± 0.01 after Stage 1 was determined experimentally. CT analysis confirmed a corresponding decrease in porosity. A comparable permeability decrease was directly measured during Stage 2, concurrent with a decrease in the volume of macro-pores based on multiple CT-resolution methods. In total, this coupled approach demonstrates that geochemical alterations exert a first order control on the evolution of fluid transport properties through time at the earliest stages of in-situ CO2 injection and suggest that chemical dynamics ultimately influence both the magnitude and timing of alterations to the physical integrity of Mt. Simon reservoir over these timescales.

Carbon sequestration at the Illinois Basin-Decatur Project: experimental results and geochemical simulations of storage

The Midwest Geological Sequestration Consortium is conducting the Illinois Basin-Decatur Project (IBDP), a large-scale demonstration of carbon sequestration that injected the CO2 from an ethanol plant into the Mt. Simon Sandstone. Using site-specific data and samples, batch experiments were conducted at reservoir conditions and the reactive transport code TOUGHREACT was used to model the CO2 migration and interactions in the injection formation. In the model, most of the mineral alteration occurred after the injection was completed and brine displaced the CO2 at the base of the plume. K-feldspar dissolution led to a nearly 10% increase in porosity which is a maximum estimate of alteration because, the model omits mineral transformations and may underestimate clay precipitation and the effects of grain coatings. The batch experiments recreated these conditions and showed a little alteration. In both the model and experiments, the bulk of the mineralogy remained inert. Calcite precipitated within the modeled plume where the transformation of K-feldspar to clays buffered the pH, though this process only produced minor mineral sequestration. Less-permeable layers in the model baffled the ascent of the CO2 plume and caused it to spread laterally. The plume did not reach the upper third of the Mt. Simon Sandstone. Both the model and the batch experiments show that the bulk of the Mt. Simon Sandstone will undergo little change due to CO2 injection, and the batch experiments show the feldspar dissolution in the model is likely limited.

Sensitivity thresholds of groundwater parameters for detecting CO2 leakage at a geologic carbon sequestration site.

Geologic carbon sequestration (GCS) projects in the USA are required to monitor groundwater quality for geochemical changes above the injection area that may be a result of CO2 or brine leakage from the storage reservoir. Should CO2 migrate into the groundwater around the compliance wells monitoring the shallower hydrologic units, each compliance parameter could react differently depending on its sensitivity to CO2. Statistically determined limits (SDLs) for detection of CO2 leakage into groundwater were calculated using background water quality data from the Illinois Basin Decatur Project (IBDP) sequestration site and prediction and tolerance intervals for specific compliance parameters. If the parameter concentrations varied outside of these ranges during the injection and post injection periods of a GCS project, then additional actions would be required to determine the reason for the changes in groundwater concentrations. Geochemical modeling can simulate the amount of CO2 needed to alter water quality parameters a statistically significant amount. This information can then inform GCS operators and regulators as to which compliance parameters are relevant (sensitive) to CO2 leakage for a given setting. For the system studied in here, Fe, Ca, K, Mg, CO2, and pH were sensitive to CO2 addition while Al, Cl, Na, and Si were not.

Petrology, geochronology, and geophysical characterization of Mesoproterozoic rocks in central Illinois, USA

The Precambrian basement rocks of the Eastern Granite-Rhyolite Province (EGRP) in central Illinois (midcontinent region of North America) exhibit a complex history of early volcanism, granite emplacement, and intrusion of mafic rocks. A comprehensive suite of dedicated petrographic analyses, geophysical logs, and drill core from four basement-penetrating wells, two-dimensional and three-dimensional seismic reflection data, and U-Pb age data from the Illinois Basin–Decatur Project (IBDP) and Illinois Carbon Capture Storage (ICCS) Project site provide new constraints for interpreting the Precambrian basement of the Illinois Basin. These new data reveal the basement to be compositionally and structurally complex, having typical EGRP felsic volcanic rocks intruded by the first reported gabbro in the Precambrian basement in Illinois. Zircons (n ​= ​29) from rhyolite give a U-Pb weighted mean average age of 1467 ​± ​9 ​Ma. Zircons (n ​= ​3) from a gabbro dike that intrudes the rhyolite yield a concordia age of 1073 ​± ​12 ​Ma, which corresponds to Grenville-age extension and represents the first Grenville-age rock in Illinois and in the EGRP. A high-resolution three-dimensional seismic reflection volume, coincident with the four wells, provides a context for interpreting the petrological data and implies a high degree of heterogeneity for basement rocks at the IBDP–ICCS site, as also shown by the drill cores. The occurrence of Grenville-age gabbro is related to a prominent bowl-like structure observed on local two-dimensional seismic reflection profiles and the three-dimensional volume that is interpreted as a deep-seated mafic sill complex. Furthermore, heterogeneities such as the brecciated EGRP rhyolite and later gabbro intrusion observed in the basement lithology at the IBDP–ICCS may reflect previously unknown distal elements of the 1.1 ​Ga Midcontinent Rift in the EGRP and more likely Grenville-age extension.

Soil gas monitoring at the Illinois Basin – Decatur Project carbon sequestration site

An extensive monitoring, verification, and accounting (MVA) program was carried out from 2011 to 2016 as part of the Illinois Basin – Decatur Project (IBDP), a large-scale carbon capture and storage (CCS) demonstration project in Decatur, Illinois, USA. As part of the monitoring program, a near-surface monitoring network for soil gas was used to characterize the natural variability of CO2 and identify anomalies that could be associated with CO2 leakage in the vadose zone. In the fall of 2011, 21 permanent soil gas sampling nests were installed on-site and three nests were installed off-site as reference locations. Soil gas was collected from three depth intervals (15–30, 47–61, 107–122 cm) at each nest. Fixed gas (CO2, N2, O2, and light hydrocarbon) concentrations, stable carbon isotopic composition (δ13C), and radiocarbon (14C) content of CO2 in soil gas were monitored during the pre-injection, injection, and post-injection phases from 2011 to 2016. Both CO2 concentrations and carbon isotopic compositions showed large spatial and temporal variations; however, the relationships among CO2, N2, and O2 concentrations in soil gas indicated that these variations should be attributed to natural processes and not CO2 leakage. Soil CO2 concentrations responded to temperature and precipitation variations and increased with increasing soil depth. While 14C cannot be used to determine the occurrence of CO2 leakage at IBDP site due to the indistinctive signature between injected CO2 and soil gas CO2, experiences at IBDP validated that δ13C can serve as an effective natural tracer at this site. Results from this project have value for future industrial CCS projects that plan to use soil gas monitoring techniques for site characterization and leakage detection.

An Operations Perspective on Injectivity and Capacity

Injectivity and capacity are two of the most important criteria of a CO2 storage site’s screening and selection process. A geologic formation can be characterized directly to quantify injectivity and capacity via the permeability-thickness and porosity- thickness products, respectively. After a project starts, the importance of each to the project is slightly different. Maintaining injection rate is one primary challenge during active injection operations, while the long-term storage capacity is one primary challenge to the storage project. For specific projects, the daily injection rate of CO2 and the ultimate storage quantity desired are based on the capture and compression facility, and the CO2 source is the driver to determine the mandatory qualifications of a site. Injectivity is defined as the ratio of the injection rate to the pressure change between the well and the storage zone, which is proportional to the permeability-thickness product. The initial start-up and subsequent start-ups of CO2 injection following short and extended shut-in periods are ideal times for multirate CO2 injection. These injection tests performed periodically can show injectivity behavior over longer periods of time so that the trends of the injection interval response can be analyzed and projected for longer terms when a stimulation or another sub-interval perforation may be required for injection. Because rate and pressure are generally direct measurements, injectivity-time, rate-pressure-time, and rate-pressure relationships can be used to diagnose trends in injection operations that are not apparent from injection rate alone. Capacity is defined as a quantity (mass or volume) of CO2 that can be injected and stored in a specific geologic formation from a specific injection project; it is proportional to porosity-thickness product. While permeability and capillary pressure are not part of the capacity calculation, both properties determine the accessibility of the porosity to injected CO2, hence the part of the pore space that can be used for storage. Furthermore, local geologic heterogeneity and architecture will strongly influence petrophysical flow properties and determine the plume size and shape. Storage efficiency has been used to define the fraction of the pore volume (or bulk volume) in which CO2 can be stored. It includes geologic (e.g. ratio of net to gross thickness), macroscopic (e.g. gravity), and microscopic (e.g. saturation) terms. It is relatively simple to quantify capacity if the location and distribution of CO2 is not required; however, if approximate dimensions of CO2 plume is necessary, it is very difficult to quantify confidently capacity. Prior to CO2 injection, statistical methods, numerical simulation, and a limited number of analytical methods are available. During injection, the most direct measurement is cased hole logging (e.g. neutron capture logs), which only measures very near wellbore CO2 saturation above a threshold saturation (e.g. 5%). Once the CO2 plume area, thickness, and saturation are adequate to make a detectable seismic contrast, a seismic survey may be helpful, but it detects only the thicker and higher CO2 saturation parts of the plume. Real-time analyses of injectivity and capacity during CO2 injection can provide operators with information necessary to plan for contingencies that increase certainty and meet the CO2 project goals. During site screening and selection, project risk can be reduced, but only after actual CO2 injection can these properties be more convincingly estimated. Injection operation results and observations, from the US Department of Energy sponsored Illinois Basin Decatur Project at Decatur, Illinois, USA, are used to demonstrate changes in injectivity and capacity through time and their influence on operations.

Modeling Commercial-Scale CO2 Injection in Mt. Simon Sandstone Near Decatur, IL Storage Sites

Advancing carbon capture and storage (CCS) to commercialization necessitates exploiting CO2 storage resources efficiently, which likely will involve multiple injection sites (or entire projects) accessing the same regional storage complex. This situation is presently occurring in central Illinois, where a series of three U.S. Department of Energy-sponsored storage projects are utilizing the Cambrian Mt. Simon Sandstone storage complex near Decatur, Illinois. From 2011 to 2014, the Illinois Basin – Decatur Project (IBDP) injected CO2 at a rate of 0.33 million tonnes per year (Mt/yr), and in 2017, the Illinois Industrial CCS Project (IL-ICCS) began injecting approximately 1 Mt/yr (planned rate) in a well 1.6 km apart. Recently, the CarbonSAFE Illinois – Macon County Project began investigating whether more than 50 Mt of CO2 can be injected into the Mt. Simon Sandstone over several decades (a target rate of 2 Mt/yr) located at a site about 5 km northwest of the other injection locations. As evaluated for this study, the Macon County well would be within the Forsyth Oil Field and drilled to access the same interval of the Mt. Simon storage complex as used by the other injection projects, namely the lower Mt Simon Sandstone. The intent of this paper is to assess the feasibility of the Forsyth site for commercial CO2 storage to further develop the storage resource by evaluating whether the target rate can be achieved, designing an injector to meet the target rate, and describing the potential contact of subsurface plumes resulting from these separate but proximal central Illinois projects. This entails modelling the behaviour of the injected CO2 and evaluating the well perforated intervals, plume sizes, pressure responses, and contact with existing CO2 plumes at the Decatur sites. To understand the interaction of three subsurface plumes, a static geologic model was generated to encompass the proposed Forsyth site (CarbonSAFE project) and the existing Decatur sites (IBDP and IL-ICCS projects), an area 22.5  22.5 km2 and a vertical section of 664 m. The static model was developed to represent the geological architecture and heterogeneity of the Mt. Simon storage complex at the Forsyth and Decatur sites through regional correlations based on geophysical data from wells at the Decatur sites. A dynamic model with integrated fluid and rock–fluid properties was constructed from the static model. The primary CO2 storage mechanisms modeled were structural and stratigraphic trapping, residual gas trapping, and solubility trapping. Mineral trapping resulting from geochemical reactions among CO2, rock, and formation water were considered negligible because the target formation is quartz sandstone.

On the Path to Commercial CCS: Scaling from Field Demonstration to Regional Hub

Commercial-scale industrial Carbon Capture Utilization and Storage (CCUS) has long been an objective to reduce carbon dioxide (CO2) emissions and increase storage and production potential. As a technology, it is deemed critical for achieving CO2 reductions that can lead to Paris Agreement targets for below 2°C global average temperature increases. Many models to mitigate atmospheric CO2 emissions call for CCUS from bioenergy, also known as BECCS, as a significant contributor to help achieve these climate goals. Facilitating the development of commercial-scale projects from industrial sources of CO2 has been a strategic process across multiple phases leading ultimately to a succession of projects of increasing scale in the Central United States. Four major CCS projects in the Illinois Basin region, USA exemplify the strategic pathway defined more than a decade ago by the U.S. Department of Energy – National Technology Laboratory (US DOE). Starting in 2003, the Midwest Geological Sequestration Consortium (MGSC), one of the US DOE Regional Carbon Sequestration Partnerships, has been working to define regional CCUS potential, conducting small enhanced oil and enhanced coalbed methane projects, and conducting a large-scale deep saline CCS storage project. As a direct outcome of the Illinois Basin – Decatur Project (IBDP), a one million tonne storage demonstration, the Illinois Industrial Sources CCS Project (ICCS) has expanded infrastructure and injection potential to industrial commercial-scale. Advancing CCS even further, the CarbonSAFE Macon County and Wabash feasibility projects seek to conduct physical and social site characterization leading to the development of storage complexes with the potential to receive and store over 50 million tonnes of CO2 from single or multiple sources. These projects combined provide an excellent example of how leveraging research, public-private partnerships, resources, relationships, and experience move CCUS forward regionally resulting in infrastructure to support storage and utilization hubs. This paper provides a brief summary of CCUS projects the Illinois Basin region of the US Midwest, and discusses of areas of overlap between projects, as well as the ways in which resources and collaborations have benefitted and challenged the individual projects. Broader lessons are provided to facilitate scale-up with CCS and CCUS deployment throughout the region.