Grantee Research Project Results
2012 Progress Report: Understanding and Managing Risks Posed by Brines Containing Dissolved Carbon Dioxide
EPA Grant Number: R834383Title: Understanding and Managing Risks Posed by Brines Containing Dissolved Carbon Dioxide
Investigators: Falta, Ronald W. , Murdoch, Lawrence C. , Benson, Sally M.
Institution: Clemson University , Stanford University
EPA Project Officer: Aja, Hayley
Project Period: November 1, 2009 through October 31, 2012 (Extended to October 31, 2014)
Project Period Covered by this Report: November 1, 2011 through October 31,2012
Project Amount: $891,342
RFA: Integrated Design, Modeling, and Monitoring of Geologic Sequestration of Anthropogenic Carbon Dioxide to Safeguard Sources of Drinking Water (2009) RFA Text | Recipients Lists
Research Category: Targeted Research , Water
Objective:
Background:
Geologic disposal of supercritical carbon dioxide (CO2) in saline aquifers and depleted oil and gas fields will cause large volumes of brine to become saturated with dissolved CO2 at concentrations of 50 g/l or more. As CO2 dissolves in brine, the brine density increases slightly. This property favors the long-term storage security of the CO2 because the denser brine is less likely to move upwards towards shallower depths. In fact, one proposed strategy for reducing risk from CO2 injection activities involves pre-dissolving the CO2 into brine at the surface, and injecting this brine into the disposal formation. While dissolved phase CO2 poses less of a threat to the security of shallower drinking water supplies, the risk is not zero. There are plausible mechanisms by which the CO2 laden brine could be transported to a shallower depth, where the CO2 would come out of solution (exsolve), forming a mobile CO2 gas phase. This significant mechanism for drinking water contamination has received little attention, and there are basic science and reservoir engineering questions that need to be addressed in order to reduce risks to underground drinking water supplies.
Research Approach: Six main activities were identified in the research proposal:
1) Laboratory Experiments. Laboratory core experiments that flood cores with CO2 saturated brines at reservoir pressure and temperature. These cores then are gradually depressurized, and imaged using a medical CT scanner to study the CO2 phase evolution and movement.
2) Pore-Scale and Core-Scale Modeling. Pore-scale multiphysics and multiphase continuum modeling of these experiments are used to develop a fundamental understanding of the exsolution and CO2 bubble coalescence phenomena as the CO2 starts to form a mobile phase.
3) CO2 Phase Relative Permeability Functions for Multiphase Flow Models. Core-scale multiphase continuum modeling to upscale the experimental results with a focus on developing effective relative permeability functions for use in field-scale modeling.
4) Regional-Scale Variable Density Groundwater Modeling. Simulations of regional scale behavior using a variable density groundwater flow model. The simulations are designed to evaluate the effects of upward hydraulic gradients, upward pressure driven brine flow (for CO2 brine injection projects) and most importantly, the effects of groundwater pumping from shallower aquifers.
5) Multiphase Flow Simulations of Field Scale CO2 Injection. Local field-scale (hundreds to thousands of meters) multiphase simulations of the likely failure modes using realistic hydrogeologic and geologic conditions that are representative of CO2 storage locations.
6) Remediation Designs. These models then will be used to study remediation strategies and alternative storage methods for each CO2 release scenario.
Progress Summary:
During our third year on this project, we completed work on Activities 1, 2, and 3. We currently are working to wrap up activities 4, 5, and 6. So far, we have published two journal papers, two conference papers and three MS theses on this project. We have four journal manuscripts that have either been submitted or are nearly ready for submission. A summary of progress by activity area is presented below.
Key Observations from This Research Project
As we near the end of this project, we can draw a number of conclusions:
- Brine containing dissolved CO2 can be mobilized upward by modest hydraulic gradients. As the carbonated brine is depressurized, the CO2 comes out of solution (exsolves) throughout the pore space.
- The exsolved CO2 phase has a very low relative permeability, even at high phase saturations. This means that exsolved CO2 will have a low mobility.
- Hysteric relative permeability can be represented by updating residual saturation in standard models. This relatively simple approach fits data well. Our experiments suggest a linear relationship between maximum CO2 saturation and residual CO2 saturation during supercritical CO2 flow.
- Upward flow of brines containing dissolved CO2 stops when the external driving force is removed, and no runaway instability is seen.
- Injection of CO2 as a dissolved phase is likely to have a similar 'footprint' to supercritical CO2 injection, but is much less mobile after injection.
Task 1. Laboratory Experiments
This work is complete, and we already have published a journal paper on the experiments that involved CO2 exsolution from sandstone cores. This paper was published in the January 2012 issue of the journal Transport in Porous Media [Zuo L, Krevor S, Falta RW, Benson SM. An experimental study of CO2 exsolution and relative permeability measurements during CO2 saturated water depressurization. Transport in Porous Media 2012; 91(2):459-478 ]. Because that work was presented in last year's report, it will not be repeated here.This past summer, we conducted some additional experiments to evaluate the effect of initial CO2 saturation on the trapped residual saturation during supercritical CO2 flow. This work will be submitted as a journal manuscript shortly.
Task 2. Pore-Scale and Core-Scale Modeling
We completed studies of CO2 exsolution in small micromodels. These models include individual pore structures, and by using a microscope, we were able to visualize the exsolution process as water saturated with CO2 is depressurized. This work was published very recently in the journal Advances in Water Resources [Zuo L, Zhang C, Falta RW, Benson SM. Micromodel investigations of CO2 exsolution from carbonated water in sedimentary rocks. Advances in Water Resources 2013;53:188-197].
Task 3. CO2 Phase Relative Permeability Functions for Multiphase Flow Models
This work was described in detail in last year's report, which included the relevant parts of the MS thesis on this work. This year, we published a conference paper on the new relative permeability models, and we have submitted a journal manuscript on the work. The experimental work performed this summer, and described under Task 1, confirmed that the new functions are realistic. There also was a conference paper from this effort.
Task 4. Regional-Scale Variable Density Groundwater Modeling
Work is continuing on this task. During the last year, we performed an analysis of the discharge of saline water to fresh surface water bodies due to CO2 injection processes. We anticipate developing a journal manuscript on this subject later this year.
Task 5. Multiphase Flow Simulation of Field Scale CO2 Injection
Last year, we reported on our work on CO2/brine transport from storage formations to drinking water formations through open abandoned wells, and we included relevant parts of the MS thesis on that topic. We have submitted a journal manuscript from this task. During the past year, we have performed some analyses of CO2 laden brine transport up an open fault in response to pumping from a confined drinking water aquifer. This work was published in a conference paper, and currently is being developed into a journal manuscript.
Task 6. Remediation Designs and Alternative Injection Schemes to Reduce Risk
Our work so far in this area has focused on a comparison of dissolved CO2 injection to the more conventional supercritical CO2 injection. Dissolved CO2 poses a lower escape risk compared to supercritical CO2 because it is not upwardly buoyant. However, to be practical, the areal footprint occupied by the dissolved CO2 should be comparable to supercritical CO2 injection. This work was described in last year's report, and we currently are preparing a journal manuscript. Work this year will continue to focus on CO2 injection strategies that minimize risk of releases.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 16 publications | 5 publications in selected types | All 5 journal articles |
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Type | Citation | ||
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Zuo L, Krevor S, Falta RW, Benson SM. An experimental study of CO2 exsolution and relative permeability measurements during CO2 saturated water depressurization. Transport in Porous Media 2012;91(2):459-478. |
R834383 (2011) R834383 (2012) R834383 (2013) R834383 (Final) |
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Zuo L, Zhang C, Falta RW, Benson SM. Micromodel investigations of CO2 exsolution from carbonated water in sedimentary rocks. Advances in Water Resources 2013;53:188-197. |
R834383 (2012) R834383 (2013) R834383 (Final) |
Exit Exit Exit |
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.