Quanlin Zhou

Modeling Basin- and Plume-Scale Processes of CO2 Storage for Full-Scale Deployment

Integrated modeling of basin- and plume-scale processes induced by full-scale deployment of CO(2) storage was applied to the Mt. Simon Aquifer in the Illinois Basin. A three-dimensional mesh was generated with local refinement around 20 injection sites, with approximately 30 km spacing. A total annual injection rate of 100 Mt CO(2) over 50 years was used. The CO(2)-brine flow at the plume scale and the single-phase flow at the basin scale were simulated. Simulation results show the overall shape of a CO(2) plume consisting of a typical gravity-override subplume in the bottom injection zone of high injectivity and a pyramid-shaped subplume in the overlying multilayered Mt. Simon, indicating the important role of a secondary seal with relatively low-permeability and high-entry capillary pressure. The secondary-seal effect is manifested by retarded upward CO(2) migration as a result of multiple secondary seals, coupled with lateral preferential CO(2) viscous fingering through high-permeability layers. The plume width varies from 9.0 to 13.5 km at 200 years, indicating the slow CO(2) migration and no plume interference between storage sites. On the basin scale, pressure perturbations propagate quickly away from injection centers, interfere after less than 1 year, and eventually reach basin margins. The simulated pressure buildup of 35 bar in the injection area is not expected to affect caprock geomechanical integrity. Moderate pressure buildup is observed in Mt. Simon in northern Illinois. However, its impact on groundwater resources is less than the hydraulic drawdown induced by long-term extensive pumping from overlying freshwater aquifers.

Pressure Buildup and Brine Migration During CO2 Storage in Multilayered Aquifers

Carbon dioxide injection into deep saline formations may induce large-scale pressure increases and migration of native fluid. Local high-conductivity features, such as improperly abandoned wells or conductive faults, could act as conduits for focused leakage of brine into shallow groundwater resources. Pressurized brine can also be pushed into overlying/underlying formations because of diffuse leakage through low-permeability aquitards, which occur over large areas and may allow for effective pressure bleed-off in the storage reservoirs. This study presents the application of a recently developed analytical solution for pressure buildup and leakage rates in a multilayered aquifer-aquitard system with focused and diffuse brine leakage. The accuracy of this single-phase analytical solution for estimating far-field flow processes is verified by comparison with a numerical simulation study that considers the details of two-phase flow. We then present several example applications for a hypothetical CO2 injection scenario (without consideration of two-phase flow) to demonstrate that the new solution is an efficient tool for analyzing regional pressure buildup in a multilayered system, as well as for gaining insights into the leakage processes of flow through aquitards, leaky wells, and/or leaky faults. This solution may be particularly useful when a large number of calculations needs to be performed, that is, for uncertainty quantification, for parameter estimation, or for the optimization of pressure-management schemes.

Flow and transport in unsaturated fractured rock: effects of multiscale heterogeneity of hydrogeologic properties

The heterogeneity of hydrogeologic properties at different scales may have different effects on flow and transport processes in a subsurface system. A model for the unsaturated zone of Yucca Mountain, Nevada, is developed to represent complex heterogeneity at two different scales: (1) layer scale corresponding to geologic layering and (2) local scale. The layer-scale hydrogeologic properties are obtained using inverse modeling, based on the available measurements collected from the Yucca Mountain site. Calibration results show a significant lateral and vertical variability in matrix and fracture properties. Hydrogeologic property distributions in a two-dimensional, vertical cross-section of the site are generated by combining the average layer-scale matrix and fracture properties with local-scale perturbations generated using a stochastic simulation method. The unsaturated water flow and conservative (nonsorbing) tracer transport through the cross-section are simulated for different sets of matrix and fracture property fields. Comparison of simulation results indicates that the local-scale heterogeneity of matrix and fracture properties has a considerable effect on unsaturated flow processes, leading to fast flow paths in fractures and the matrix. These paths shorten the travel time of a conservative tracer from the source (repository) horizon in the unsaturated zone to the water table for small fractions of total released tracer mass. As a result, the local-scale heterogeneity also has a noticeable effect on global tracer transport processes, characterized by an average breakthrough curve at the water table, especially at the early arrival time of tracer mass. However, the effect is not significant at the later time after 20% tracer mass reaches the water table. The simulation results also verify that matrix diffusion plays an important role in overall solute transport processes in the unsaturated zone at Yucca Mountain.

Experimental study on effects of geologic heterogeneity in enhancing dissolution trapping of supercritical CO2

Dissolution trapping is one of the primary mechanisms that enhance the storage security of supercritical carbon dioxide (scCO2) in saline geologic formations. When scCO2 dissolves in formation brine produces an aqueous solution that is denser than formation brine, which leads to convective mixing driven by gravitational instabilities. Convective mixing can enhance the dissolution of CO2 and thus it can contribute to stable trapping of dissolved CO2. However, in the presence of geologic heterogeneities, diffusive mixing may also contribute to dissolution trapping. The effects of heterogeneity on mixing and its contribution to stable trapping are not well understood. The goal of this experimental study is to investigate the effects of geologic heterogeneity on mixing and stable trapping of dissolved CO2. Homogeneous and heterogeneous media experiments were conducted in a two-dimensional test tank with various packing configurations using surrogates for scCO2 (water) and brine (propylene glycol) under ambient pressure and temperature conditions. The results show that the density-driven flow in heterogeneous formations may not always cause significant convective mixing especially in layered systems containing low-permeability zones. In homogeneous formations, density-driven fingering enhances both storage in the deeper parts of the formation and contact between the host rock and dissolved CO2 for the potential mineralization. On the other hand, for layered systems, dissolved CO2 becomes immobilized in low-permeability zones with low-diffusion rates, which reduces the risk of leakage through any fault or fracture. Both cases contribute to the permanence of the dissolved plume in the formation.

Experimental analysis of spatial correlation effects on capillary trapping of supercritical CO2 at the intermediate laboratory scale in heterogeneous porous media

Author(s): Trevisan, L; Pini, R; Cihan, A; Birkholzer, JT; Zhou, Q; Illangasekare, TH | Abstract:

Effects of diffusive property heterogeneity on effective matrix diffusion coefficient for fractured rock

Heterogeneities of diffusion properties are likely to influence the effective matrix diffusion coefficient determined from tracer breakthrough curves. The objectives of this study are (1) to examine if it is appropriate to use a single, effective matrix diffusion coefficient to predict breakthrough curves in a fractured formation, (2) to examine if a postulated scale dependence of the effective matrix diffusion coefficient is caused by heterogeneity in diffusion properties, and (3) to examine whether multirate diffusion results in the previously observed time dependence of the effective matrix diffusion coefficient. The results show that the use of a single effective matrix diffusion coefficient is appropriate only if the interchannel and intrachannel variability of diffusion properties is small. The scale dependence of the effective matrix diffusion coefficient is not caused by the studied types of heterogeneity. Finally, the multirate diffusion process does not result in the time dependence of the effective matrix diffusion coefficient. oefficient is appropriate only if the inter- and intrachannel variability of diffusion properties is small. The scale dependence of the effective matrix diffusion coefficient is not caused by either type of the studied heterogeneity. Finally, the multi-rate diffusion process does not result in the time dependence of the effective matrix diffusion coefficient.

Basin-Scale Hydrologic Impacts of CO2 Storage: Regulatory and Capacity Implications

Basin-Scale Hydrologic Impacts of CO 2 Storage: Regulatory and Capacity Implications Jens T. Birkholzer*, Quanlin Zhou Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 *Corresponding author: jtbirkholzer@lbl.gov, ph. 510 486-7134 Abstract Industrial-scale injection of CO 2 into saline sedimentary basins will cause large-scale fluid pressurization and migration of native brines, which may affect valuable groundwater resources overlying the deep sequestration reservoirs. In this paper, we discuss how such basin-scale hydrologic impacts can (1) affect regulation of CO 2 storage projects and (2) may reduce current storage capacity estimates. Our assessment arises from a hypothetical future carbon sequestration scenario in the Illinois Basin, which involves twenty individual CO 2 storage projects in a core injection area suitable for long- term storage. Each project is assumed to inject five million tonnes of CO 2 per year for 50 years. A regional-scale three-dimensional simulation model was developed for the Illinois Basin that captures both the local-scale CO 2 -brine flow processes and the large- scale groundwater flow patterns in response to CO 2 storage. The far-field pressure buildup predicted for this selected sequestration scenario suggests that (1) the area that needs to be characterized in a permitting process may comprise a very large region within the basin if reservoir pressurization is considered, and (2) permits cannot be granted on a single-site basis alone because the near- and far-field hydrologic response may be affected by interference between individual sites. Our results also support recent studies in that environmental concerns related to near-field and far-field pressure buildup may be a limiting factor on CO 2 storage capacity. In other words, estimates of storage capacity, if solely based on the effective pore volume available for safe trapping of CO 2 , may have to be revised based on assessments of pressure perturbations and their potential impact on caprock integrity and groundwater resources, respectively. We finally discuss some of the challenges in making reliable predictions of large-scale hydrologic impacts related to CO 2 sequestration projects.

Imaging and quantification of spreading and trapping of carbon dioxide in saline aquifers using meter‐scale laboratory experiments

The role of capillary forces during buoyant migration of CO2 is critical toward plume immobilization within the postinjection phase of a geological carbon sequestration operation. However, the inherent heterogeneity of the subsurface makes it very challenging to evaluate the effects of capillary forces on the storage capacity of these formations and to assess in situ plume evolution. To overcome the lack of accurate and continuous observations at the field scale and to mimic vertical migration and entrapment of realistic CO2 plumes in the presence of a background hydraulic gradient, we conducted two unique long-term experiments in a 2.44 m × 0.5 m tank. X-ray attenuation allowed measuring the evolution of a CO2-surrogate fluid saturation, thus providing direct insight into capillarity-dominated and buoyancy-dominated flow processes occurring under successive drainage and imbibition conditions. The comparison of saturation distributions between two experimental campaigns suggests that layered-type heterogeneity plays an important role on nonwetting phase (NWP) migration and trapping, because it leads to (i) longer displacement times (3.6 months versus 24 days) to reach stable trapping conditions, (ii) limited vertical migration of the plume (with center of mass at 39% versus 55% of aquifer thickness), and (iii) immobilization of a larger fraction of injected NWP mass (67.2% versus 51.5% of injected volume) as compared to the homogenous scenario. While these observations confirm once more the role of geological heterogeneity in controlling buoyant flows in the subsurface, they also highlight the importance of characterizing it at scales that are below seismic resolution (1–10 m).

Research project on CO2 geological storage and groundwaterresources: Large-scale hydrological evaluation and modeling of impact ongroundwater systems

If carbon dioxide capture and storage (CCS) technologies areimplemented on a large scale, the amounts of CO2 injected and sequesteredunderground could be extremely large. The stored CO2 then replaces largevolumes of native brine, which can cause considerable pressureperturbation and brine migration in the deep saline formations. Ifhydraulically communicating, either directly via updipping formations orthrough interlayer pathways such as faults or imperfect seals, theseperturbations may impact shallow groundwater or even surface waterresources used for domestic or commercial water supply. Possibleenvironmental concerns include changes in pressure and water table,changes in discharge and recharge zones, as well as changes in waterquality. In compartmentalized formations, issues related to large-scalepressure buildup and brine displacement may also cause storage capacityproblems, because significant pressure buildup can be produced. Toaddress these issues, a three-year research project was initiated inOctober 2006, the first part of which is summarized in this annualreport.

Modeling Three-Dimensional Groundwater Flow and Advective Contaminant Transport at a Heterogeneous Mountainous Site in Support of Remediation

Modeling Three-Dimensional Groundwater Flow and Advective Contaminant Transport at a Heterogeneous Mountainous Site in Support of Remediation Strategy Quanlin Zhou, Jens T. Birkholzer, Iraj Javandel, and Preston D. Jordan Ernest Orlando Lawrence Berkeley National Laboratory Earth Sciences Division 1 Cyclotron Road, MS 90-1116, Berkeley CA 94720 USA Abstract A calibrated groundwater flow model for a contaminated site can provide substantial information for assessing and improving hydraulic measures implemented for remediation. A three-dimensional transient groundwater flow model was developed for a contaminated mountainous site, at which interim corrective measures were initiated to limit further spreading of contaminants. This flow model accounts for complex geologic units that vary considerably in thickness, slope, and hydrogeologic properties, as well as large seasonal fluctuations of the groundwater table and flow rates. Other significant factors are local recharge from leaking underground storm drains and recharge from steep uphill areas. The zonation method was employed to account for the clustering of high and low hydraulic conductivities measured in a geologic unit. A composite model was used to represent the bulk effect of thin layers of relatively high hydraulic conductivity found within bedrock of otherwise low conductivity. The inverse simulator ITOUGH2 was used to calibrate the model for the distribution of rock properties. The model was initially calibrated using data collected between 1994 and 1996. To check the validity of the model, it was subsequently applied to predicting groundwater level fluctuation and groundwater flux between 1996 and 1998. Comparison of simulated and measured data demonstrated that the model is capable of predicting the complex flow reasonably well. Advective transport was approximated using pathways of particles originating from source areas of the plumes. The advective transport approximation was in good agreement with the trend of contaminant plumes observed over the years. The validated model was then refined to focus on a subsection of the large system. The refined model was subsequently used to assess the efficiency of hydraulic measures implemented for remediation.