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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Recent seismicity at Ceboruco Volcano (Mexico)

Magma and related hydrothermal fluid movement, and their interaction with solid rock, in active volcanic regions, generate a wide variety of seismic waves whose characterization can mitigate the risk of a potential eruption. Located in the western region of the Trans-Mexican Volcanic Belt, Ceboruco Volcano, whose last eruptive period was 1870–1875, is considered to be one of the most hazardous volcanoes in Mexico. We have conducted a detailed study of the seismicity in the surroundings of Ceboruco's volcanic edifice to assess the current state of this volcano. A dense temporary seismic network with 25 seismic stations in an area of 16 km × 16 km was deployed between November 2016 and July 2017, as part of the P-24 project of the CeMIEGeo consortium; this effort has allowed the detection of 81 earthquakes concentrated beneath the crater with depths between 4 and 8 km. In this study, we observe that the recorded seismicity occurs in swarms, and we specifically identify four sequences that we characterize in detail via the first focal mechanisms available for this volcano. Our results suggest a change in the local seismicity distribution compared to earlier observations, which reported seismic activity near the volcano edifice associated with fluid migration along zones of weakness related to the extensional stresses of the Tepic-Zacoalco rift. The changes in seismic patterns and obtained focal mechanisms are consistent with observed fluid effects at many geothermal sites worldwide, but also could suggest resumption of activity at this currently dormant volcano.

58 GEOSCIENCES↗
DOE OSTI2024

Risk Considerations of Transitioning CO2-EOR Field to CO2 storage Field: Case Study

In the United States (U.S.), carbon dioxide (CO2) injection wells at EOR sites are currently regulated as Class II wells under the U.S. Environmental Protection Agency’s (EPA) Underground Injection Control (UIC) program while dedicated geological CO2 storage (GCS) wells are considered Class VI wells. A CO2-EOR facility considering a transitioning from tertiary oil recovery to injecting CO2 for the primary purpose of long-term storage is required to obtain a Class VI permit where this transition poses an increased risk to underground sources of drinking water. This study considers how transitioning operations from CO2-EOR to storage can impact reservoir plume and pressure transient in the storage envelope, and how these changes could impact area of review and potential unwanted fluid migration. We developed a case study to assess subsurface response and leakage risks associated with a representative, hypothetical operation in a carbonate reservoir. This reservoir transitions from tertiary hydrocarbon recovery to dedicated GCS. Reservoir simulations were run for a set of credible CO2-EOR scenarios to estimate distributions of fluids phases and pressures throughout the model domain after CO2 flooding as well as forecasting the behavior of the reservoir after the transition to a dedicated storage phase. The evolutions from all simulated scenarios were used as the basis for leakage risk quantification using the National Risk Assessment Partnership’s Open-Source Integrated Assessment Model (NRAP-Open-IAM) with a novel reduced-order model to estimate time-dependent leakage of CO2, brine, and hydrocarbon fluids through potentially leaky wells. Results include a description of reservoir response, an estimate of the areal extent that could potentially be impacted by leakage to underground sources of drinking water, and estimates of the magnitude of potential leakage. Considerations for dedicated storage injection well selection, injectivity, and injection scheme performance and potential leakage risk are presented, with implications for risk assessment of well transition discussed. This study presents a risk-based workflow for the Class II to Class VI well transition. Integrating credible numerical simulation of viable CO2-EOR to dedicated CO2 storage with quantitative risk assessment tools, such as the NRAP-Open-IAM, will provide a valuable means to devise operational scenarios and inform decision-making related to storage benefit, leakage risk, and liability. Presented at the SPE/AAPG/SEG Carbon Capture Utilization and Storage Conference in Houston, TX, March 11-13, 2024.

Liu, Guoxiang↗
DOE OSTI2013

NEAR-SURFACE GEOPHYSICAL CHARACTERIZATION OF A HOLOCENE FAULT CONDUCIVE TO GEOTHERMAL FLOW NEAR PYRAMID LAKE, NEVADA

Linear deposits of calcium carbonate tufa columns mark recent faults that cut 11 ka Lake Lahontan sediments at Astor Pass, north of Pyramid Lake, Nevada. Throughout the Great Basin, faults appear to control the location of geothermal resources by providing pathways for fluid migration. Reservoir-depth (greater than 1 km) seismic imaging at Astor Pass reveals a fault that projects to one of the lines of tufa columns at the surface. The presence of the tufa deposits suggests this fault carried warm geothermal waters through the lakebed clay sediments in recent time. The warm fluids deposited the tufa when they hit cold Lake Lahontan water at the lakebed. Lake Lahontan covered this location 11 ka to a depth of at least 60 m. In collaboration with the Pyramid Lake Paiute Tribe, an Applied Geophysics class at UNR investigated the near-surface geophysical characteristics of this fault. The survey at and near the tufa columns comprises near-surface Pwave seismic reflection and refraction, electrical resistivity tomography, nearsurface refraction microtremor arrays, nine near-surface direct-current resistivity soundings, magnetic surveys, and gravity surveys. The refraction microtremor results show shear velocities near tufa and faults to be marginally lower, compared to Vs away from the faults. Overall, the 30-m depth-averaged shear velocities are low, less than 300 m/s, consistent with the lakebed clay deposits. These results indicate that no seismically fast (> 500 m/s) tufa deposits are present below the surface at or near the tufa columns. Vs30 averages were for example 274 ± 13 m/s on the fault, 287 ± 2 m/s at 150 m east of the fault, and 290 ± 15 m/s at 150 m west of the fault. The P-velocity refraction optimization results similarly indicate a lack of high-velocity tufa buried below the surface in the Lahontan sediments, reinforcing the idea that all tufa was deposited above the lakebed surface. The seismic results provide a negative test of the hypothesis that deposition of the lakebeds in the Quaternary buried and preserved older tufa columns within the section. Near-surface Wenner arrays with a-spacings up to 30 m show a higher resistivity near the faults, and tufa, than away from the faults. Resistivity averages within a few meters of the surface were 33 ± 17 ohm-m on the fault, 13 ± 3 ohm-m east of the fault, and 9 ± 3 ohm-m west of the fault. It is possible that the geothermal waters are fresher, and more resistive, than waters held in the lakebed clays. Water samples from more than 1 km depth in exploration wells have a TDS of 2500 p.p.m., nearly drinking-water quality. The relatively resistive water, perhaps localized by greater permeability along the fault, could explain the higher resistivity measured near the fault. The results show that there is no high-velocity, high-resistivity tufa along the faults below the surface, so we are unable to use buried tufa to locate the faults that may promote geothermal upwelling in this area. We further hypothesize that as sedimentation buried the tufa during the Quaternary, warm geothermal waters re-dissolved it, and re-precipitated it in the cold lake-bottom water.

15 GEOTHERMAL ENERGY↗
DOE OSTI2017

Interpretation of Ground Temperature Anomalies in Hydrothermal Discharge Areas

Abstract Researchers have long noted the potential for shallow hydrothermal fluids to perturb near‐surface temperatures. Several investigators have made qualitative or semiquantitative use of elevated surface temperatures; for example, in snowfall calorimetry, or for tracing subsurface flow paths. However, a quantitative framework connecting surface temperature observations with conditions in the subsurface is currently lacking. Here, we model an area of shallow subsurface flow at Burgdorf Hot Springs, a rustic commercial resort in the Payette National Forest, north of McCall, ID, USA. We calibrate the model using shallow (0.2 m depth) ground temperature measurements and overburden thickness estimates from seismic refraction studies. The calibrated model predicts negligible loss of heat energy from the laterally migrating fluids at the Burgdorf site, in spite of the fact that thermal anomalies are observed in the unconsolidated near‐surface alluvium. Although elevated near‐surface ground temperatures are commonly assumed to result from locally high heat flux, this conflicts with the small apparent heat loss during lateral flow inferred at the Burgdorf site. We hypothesize an alternative explanation for near‐surface temperature anomalies that is only weakly dependent on heat flux, and more strongly controlled by the Biot number, a dimensionless parameter that compares the rate at which convection carries heat away from the land surface to the rate at which it is supplied by conduction to the interface.

Price, Adam N.↗
DOE OSTI2019

Analysis of land-based CSEM data for CO2 monitoring at Bell Creek, MT

Monitoring subsurface fluid migration is critical to any CO2 injection operation like enhanced oil recovery or carbon storage. The controlled-source electromagnetic (CSEM) method provides a promising low-cost, non-invasive alternative to conventional monitoring methods. To investigate the use of CSEM for monitoring CO2 injection, we are conducting a time-lapse charged well casing CSEM survey at the Bell Creek oil field. There, CO2 is injected into the reservoir for enhanced oil recovery, which also results in incidental carbon storage. From October 2017 to October 2018 we completed three field campaigns, and we plan to complete one more in July 2019. We have analyzed the signal strength and variance of the time-lapse CSEM data. Difference data signal strength well exceeds the standard deviation of the data, and it agrees with estimates of expected signal strength derived from numerical modeling. This analysis indicates that our survey can detect the change in conductivity within the reservoir due to fluid movement.

time-lapse, land CSEM, monitoring, processing↗
DOE OSTI2015

Probabilistic geomechanical analysis of compartmentalization at the Snøhvit CO 2 sequestration project

Abstract Pressure buildup caused by large‐scale CO 2 injection is a key concern during a carbon sequestration project. Large overpressures can compromise seal integrity, reactivate faults, and induce seismicity. Furthermore, pressure buildup is directly related with storage capacity. In this work we study the geomechanical response to CO 2 injection at Snøhvit, to understand the potential for fault reactivation, leakage, and contamination of the producing interval through bounding faults. Furthermore, we evaluate the potential contribution of a structural component to reservoir compartmentalization. We combine simplified analytical models, based on critically stressed fracture theory and a Mohr‐Coulomb failure criterion, with a rigorous sensitivity analysis. Large stress uncertainties are present and reflected in the modeling results. It was found that under the most likely stress state the faults are fairly stable and caprock hydrofracturing would be expected before fault reactivation. In most of the analyzed cases, the critical pressure perturbation needed for reactivation is above 13 MPa, which was the limiting pressure increase before reaching the fracture pressure. Faults were found to be ~ 20% less stable when considering variations in S Hmax orientation. In those cases, fault reactivation could be expected before caprock failure if injection continued. However, if the pressure increase did reach the critical values for seal failure estimated under the worst case (and least likely) stress state, no indication of such failure can be observed in the measured pressure response. Finally, the potential role of a structural component in the compartmentalization and fluid migration is difficult to assess due to the stress state uncertainty.

Chiaramonte, Laura↗
DOE OSTI2020

Emerging technologies and radical collaboration to advance predictive understanding of watershed hydrobiogeochemistry

Increasing population and resource-intensive lifestyles are driving enhanced demands for clean water, food, and energy. In parallel, land-use change, climate change, and perturbations—including drought, floods, fires, and early snowmelt—are significantly reshaping interactions within watersheds throughout the world. While watersheds are the Earth's key functional unit for assessing and managing water resources, hydrological processes in watersheds also mediate biogeochemical interactions that support terrestrial life on Earth (Kaushal, Gold, Bernal, & Tank, 2018; National Research Council, 2012). Although society is dependent upon clean water availability, tractable prediction of watershed hydrobiogeochemical behavior, including watershed response to perturbations, remains a challenge. Central to the challenge are complex, multiscale interactions between plants, microorganisms, organic matter, minerals, dissolved constituents, and migrating fluids, which occur within and across bedrock-to-canopy compartments and along extensive lateral gradients of a watershed. Several recent community reports have synthesized formidable challenges associated with watershed science and technology (AGU, 2018; Blöschl et al., 2019). Here, we discuss emerging technologies and collaboration modes that are critical for developing generalizable insights about and predictive understanding of complex watershed hydrobiogeochemical behavior, which are important for underpinning optimized natural resource management.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Impact of wettability alteration on 3D nonwetting phase trapping and transport

We investigate capillary trapping and fluid migration via x-ray computed microtomography (x-ray CMT) of nonwetting phase (air) and wetting phase (brine) in Bentheimer sandstone cores which have been treated to exhibit different degrees of uniform wettability. x-Ray CMT scans were acquired at multiple steps during drainage and imbibition processes, as well as at the endpoints; allowing for assessment of the impact of wettability on nonwetting phase saturation and cluster size distribution, connectivity, topology and efficiency of trapping. Compared with untreated (water-wet) Bentheimer sandstone, cores treated with tetramethoxylsilane (TMS) were rendered weakly water-wet, and cores treated with octadecyltrichlorosilane (OTS) demonstrate intermediate-wet characteristics. As apparent contact angle increases, drainage flow patterns deviate from those derived for water-wet systems, total residual trapping and trapping efficiency decrease, and buoyancy plays a larger role during nonwetting phase mobilization; this has significant implications for CO 2 migration and trapping during CO 2 sequestration operations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

A 2.5D Reactive Transport Model for Fracture Alteration Simulation

Understanding fracture alteration resulting from geochemical reactions is critical in predicting fluid migration in the subsurface and is relevant to multiple environmental challenges. Here in this paper, we present a novel 2.5D continuum reactive transport model that captures and predicts the spatial pattern of fracture aperture change and the development of an altered layer in the near-fracture region. The model considers permeability heterogeneity in the fracture plane and updates fracture apertures and flow fields based on local reactions. It tracks the reaction front of each mineral phase and calculates the thickness of the altered layer. Given this treatment, the model is able to account for the diffusion limitation on reaction rates associated with the altered layer. The model results are in good agreement with an experimental study in which a CO 2 -acidified brine was injected into a fracture in the Duperow Dolomite, causing dissolution of calcite and dolomite that result in the formation of a preferential flow channel and an altered layer. Finally, with an effective diffusion coefficient consistent with the experimentally observed porosity of the altered layer, the model captures the progressive decrease in the dissolution rate of the fast-reacting mineral in the altered layer.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Pore-Scale Analysis of Calcium Carbonate Precipitation and Dissolution Kinetics in a Microfluidic Device

In this work, we have characterized the calcium carbonate (CaCO 3 ) precipitates over time caused by reaction-driven precipitation and dissolution in a micromodel. Reactive solutions were continuously injected through two separate inlets, resulting in transverse-mixing induced precipitation during the precipitation phase. Subsequently, a dissolution phase was conducted by injecting clean water (pH = 4). The evolution of precipitates was imaged in two and three dimensions (2-, 3-D) at selected times using optical and confocal microscopy. With estimated reactive surface area, effective precipitation and dissolution rates can be quantitatively compared to results in the previous works. Our comparison indicates that we can evaluate the spatial and temporal variations of effective reactive areas more mechanistically in the microfluidic system only with the knowledge of local hydrodynamics, polymorphs, and comprehensive image analysis. Here, our analysis clearly highlights the feedback mechanisms between reactions and hydrodynamics. Pore-scale modeling results during the dissolution phase were used to account for experimental observations of dissolved CaCO 3 plumes with dissolution of the unstable phase of CaCO 3 . Mineral precipitation and dissolution induce complex dynamic pore structures, thereby impacting pore-scale fluid dynamics. Pore-scale analysis of the evolution of precipitates can reveal the significance of chemical and pore structural controls on reaction and fluid migration.

58 GEOSCIENCES↗
DOE OSTI2017

Hydrophobic Solvation of Gases (CO 2 , CH 4 , H 2 , Noble Gases) in Clay Interlayer Nanopores

In the past few years, experimental studies have shown that CO 2 is roughly 5 times more soluble in water-saturated clay interlayer water than in bulk liquid water. The fundamental basis of this selectivity remains unknown, as does its relevance to other gases. Here, we use molecular dynamics (MD) simulations and gravimetric adsorption experiments to determine the solubilities of CO 2 , CH 4 , H 2 , and noble gases in clay interlayer water. Our results confirm that clay minerals, despite their well-known hygroscopic nature, have a significant hydrophobic character at the atomistic scale. The affinity of dissolved gases for the clay surface shows significant variations related to the size and shape of the adsorbing molecules and the structuring of interfacial water by clay surfaces. Our results indicate that dissolved gases likely do not behave as inert tracers in fine-grained sedimentary rocks such as shale and mudstone, as routinely assumed in groundwater hydrology studies. Lastly, our results have implications for the fundamental science of hydrophobic adsorption, for the use of dissolved gases as tracers of fluid migration in the subsurface, and for low-carbon energy technologies that rely on fine-grained sedimentary rocks, such as carbon capture and storage, nuclear energy, and the transition from coal to natural gas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

DeFault: DEep‐Learning‐Based FAULT Delineation Using the IBDP Passive Seismic Data at the Decatur CO2 Storage Site

Abstract The carbon capture, utilization, and storage (CCUS) framework is an essential component in reducing greenhouse gas emissions, with its success hinging on the comprehensive knowledge of subsurface geology and geomechanics. Passive seismic event relocation and fault detection offer vital insights into subsurface structures and the ability to monitor fluid migration pathways. Accurate identification and localization of seismic events, however, face significant challenges, including the necessity for high‐quality seismic data and advanced computational methods. To address these challenges, we introduce a novel deep learning method, , specifically designed for passive seismic source relocation and fault delineating for passive seismic monitoring projects. By leveraging data domain‐adaptation, allows us to train a neural network with labeled synthetic data and apply it directly to field data. Using , the passive seismic sources are automatically clustered based on their recording time and spatial locations, and subsequently, faults and fractures are delineated accordingly. We demonstrate the efficacy of on a field case study involving injection related microseismic data from Decatur, Illinois area. Our approach accurately and efficiently relocated passive seismic events, identified faults and could aid in potential damage induced by seismicity. Our results highlight the potential of as a valuable tool for passive seismic monitoring, emphasizing its role in ensuring CCUS project safety. This research bolsters the understanding of subsurface characterization in CCUS, illustrating machine learning’s capacity to refine these methods. Ultimately, our work has significant implications for CCUS technology deployment, an essential strategy in combating climate change. Plain Language Summary In our quest to tackle climate change, we use a strategy known as carbon capture, utilization, and storage (CCUS) to keep greenhouse gases out of the atmosphere. This strategy relies heavily on our ability to understand what's happening deep under the earth's surface. To make sure we store super critical safely, we need to accurately map out the geological structure, especially faults, but this is tough without high‐quality data and complex computer programs. We've developed a new tool called “DeFault,” which uses advanced machine learning to improve how we find and map these underground features. “DeFault” is smart enough to learn from numerically simulated data and then apply what it’s learned to real‐world situations. It groups together seismic activity—tiny tremors and shifts in the earth—based on when and where they happen, which helps us spot where there might be cracks or faults. We tested “DeFault” in Illinois, where CO 2 is injected underground, and it successfully pinpointed where these tremors occurred and mapped out the faults, helping to prevent accidents accurately in the future. Our study shows that “DeFault” will be a powerful ally in making CCUS safer and more effective, especially for the Illinois Basin Decatur Project. Key Points Faults and fractures introduced by carbon storage can be monitored by passive seismicity DeFault algorithm enables an automatic process for accurate and efficient passive seismic event locating and clustering

58 GEOSCIENCES↗
DOE OSTI2017

Numerical Modeling of CO 2 and Brine Leakage through Open Fracture in a Fault Zone: Open Channel Flow or Darcy Flow

Understanding fluids migration and leakage risk along the fault zone is necessary to guarantee the safety of CO 2 geological storage. The validity of Darcy’s law gets challenged in dealing with the flow in open fractures since the occurring of turbulence flow. In this study, we develop a 2D model with usage of T2Well, an integrated wellbore-reservoir simulator, to investigate the leakage problem along open fractures which are embedded in a fault zone from the deep injection reservoir to shallow aquifers. The results record a positive feedback of gas expansion and pressure response in fracture, which causes a quick downward propagation of highly gas saturated zone from the top of fracture and an easy gas breakthrough in the shallower aquifers. The decreasing of aperture size of fracture significantly enhances the leakage rates in fracture, but with less influences as aperture increases. In comparison, the Equivalent Porous Media models show a good approximation with the momentum model of large apertures but poor for the small one. Nevertheless, the differences are small in terms of final CO 2 distribution among various aquifers, suggesting that Darcy’s law may be still “effective” in solving flow problem along fractures in a constant injection system at a large time scale.

58 GEOSCIENCES↗
DOE OSTI2014

Parallel Infrastructure Modeling and Inversion Module for E4D

Electrical resistivity tomography ERT is a method of imaging the electrical conductivity of the subsurface. Electrical conductivity is a useful metric for understanding the subsurface because it is governed by geomechanical and geochemical properties that drive subsurface systems. ERT works by injecting current into the subsurface across a pair of electrodes, and measuring the corresponding electrical potential response across another pair of electrodes. Many such measurements are strategically taken across an array of electrodes to produce an ERT data set. These data are then processed through a computationally demanding process known as inversion to produce an image of the subsurface conductivity structure that gave rise to the measurements. Data can be inverted to provide 2D images, 3D images, or in the case of time-lapse 3D imaging, 4D images. ERT is generally not well suited for environments with buried electrically conductive infrastructure such as pipes, tanks, or well casings, because these features tend to dominate and degrade ERT images. This reduces or eliminates the utility of ERT imaging where it would otherwise be highly useful for, for example, imaging fluid migration from leaking pipes, imaging soil contamination beneath leaking subsurface tanks, and monitoring contaminant migration in locations with dense network of metal cased monitoring wells. The location and dimension of buried metallic infrastructure is often known. If so, then the effects of the infrastructure can be explicitly modeled within the ERT imaging algorithm, and thereby removed from the corresponding ERT image. However, there are a number of obstacles limiting this application. 1) Metallic infrastructure cannot be accurately modeled with standard codes because of the large contrast in conductivity between the metal and host material. 2) Modeling infrastructure in true dimension requires the computational mesh to be highly refined near the metal inclusions, which increases computational demands. 3) The ERT imaging algorithm requires specialized modifications to accommodate high conductivity inclusions within the computational mesh. The solution to each of these challenges was implemented within E4D (formerly FERM3D), which is a parallel ERT imaging code developed at PNNL (IPID #30249). The infrastructure modeling module implement in E4D uses a method of decoupling the model at the metallic interface(s) boundaries, into several well posed sub-problems (one for each distinct metallic inclusion) that are subsequently solved and recombined to form the global solution. The approach is based on the immersed interface method, with has been applied for similar problems in other fields (e.g. semiconductor industry). Comparisons to analytic solutions have shown the results to be very accurate, addressing item 1 above. The solution is implemented about an unstructured mesh, which enables arbitrary shapes to be efficiently modelled, thereby addressing item 2 above. In addition, the algorithm is written in parallel and shows excellent scalability, which also addresses equation 2 above. Finally, because only the boundaries of metallic inclusions are modeled, there are no high conductivity cells within the modeling mesh, and the problem described by item 3 above is no longer applicable.

Johnson, TimC.↗
DOE OSTI2024

Tracking Seismic Velocity Perturbations at Ridgecrest Using Ballistic Correlation Functions

Abstract We present results based on data of a dense nodal array composed of 147 stations, deployed in 2022 near the epicenter of the 2019 Mw 7.1 Ridgecrest earthquake to investigate characteristics of the seismic wavefields. Through array analyses, we identified two primary components. First, we observed far-field P waves dominating the 0.5–1.2 Hz frequency range, which are likely primarily generated by wind-driven oceanic swell activity. Second, we detected near-field body waves resulting from anthropogenic activities in the frequency range 2–8 Hz. We examined noise correlation functions derived from data of the dense deployment and regional stations to explore fault-zone seismic velocity changes using ballistic arrivals, with a focus on velocity perturbation shortly before and after the Ridgecrest earthquake sequence. Our findings exhibit distinct behavior compared to results obtained through standard coda-wave interferometry. Particularly, we observed a decrease in P-wave travel time on certain station pairs prior to the 2019 earthquake sequence. Supported by detailed investigation of the local seismic wavefields, we interpret the decreasing P-wave travel time as likely caused by a velocity increase away from the fault, possibly related to fluid migration. However, additional information is necessary to verify this hypothesis.

Geochemistry & Geophysics↗
DOE OSTI2014

Characterization of Pliocene and Miocene Formations in the Wilmington Graben, Offshore Los Angeles, for Large-Scale Geologic Storage of CO₂

Geomechanics Technologies has completed a detailed characterization study of the Wilmington Graben offshore Southern California area for large-scale CO₂ storage. This effort has included: an evaluation of existing wells in both State and Federal waters, field acquisition of about 175 km (109 mi) of new seismic data, new well drilling, development of integrated 3D geologic, geomechanics, and fluid flow models for the area. The geologic analysis indicates that more than 796 MMt of storage capacity is available within the Pliocene and Miocene formations in the Graben for midrange geologic estimates (P50). Geomechanical analyses indicate that injection can be conducted without significant risk for surface deformation, induced stresses or fault activation. Numerical analysis of fluid migration indicates that injection into the Pliocene Formation at depths of 1525 m (5000 ft) would lead to undesirable vertical migration of the CO₂ plume. Recent well drilling however, indicates that deeper sand is present at depths exceeding 2135 m (7000 ft), which could be viable for large volume storage. For vertical containment, injection would need to be limited to about 250,000 metric tons per year per well, would need to be placed at depths greater than 7000ft, and would need to be placed in new wells located at least 1 mile from any existing offset wells. As a practical matter, this would likely limit storage operations in the Wilmington Graben to about 1 million tons per year or less. A quantitative risk analysis for the Wilmington Graben indicate that such large scale CO₂ storage in the area would represent higher risk than other similar size projects in the US and overseas.

54 ENVIRONMENTAL SCIENCES↗