Grantee Research Project Results
2013 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, 2012 through October 31,2013
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:
Geologic disposal of supercritical carbon dioxide 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.
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 are then 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 will then be used to study remediation strategies and alternative storage methods for each CO2 release scenario.
Progress Summary:
During our fourth year on this project, we completed work on Activities 1, 2, 3 and 5. We currently are working to wrap up Activities 4 and 6. So far, we have published three journal papers, four conference papers and two M.S. theses on this project. We have five journal manuscripts that have either been submitted, or that are nearly ready for submission, and the final two students working on this project are nearing graduation (M.S. and Ph.D.). A summary of progress by activity area is provided by task below.
As we near the end of this project we can make 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 compared to CO2 that is injected as a separate phase.
- 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; no runaway instability seen. This is true both in geologic pathways such as permeable faults, as well as in man-made features such as abandoned wells.
- Injection of CO2 as a dissolved phase is likely to have a similar “footprint” to supercritical CO2 injection, but it is much less mobile after injection, and has no inherent tendency to migrate upwards.
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. We conducted additional experiments to evaluate the effect of initial CO2 saturation on the trapped residual saturation during supercritical CO2 flow. This work has been accepted for publication following minor revisions.
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 last year.
Task 3. CO2 Phase Relative Permeability Functions for Multiphase Flow Models
This work was described in detail in previous reports, but we are in the process of submitting a journal paper based on Chris Patterson’s M.S. thesis. That paper describes a new type of hysteretic CO2 phase relative permeability curve that accounts for the variable trapping that occurs as a function of the CO2 phase saturation history at a given location. We were very pleased to find that the results of our CO2 phase trapping experiments performed under Task 1 agree almost perfectly with this new relative permeability model.
Task 4. Regional-Scale Variable Density Groundwater Modeling
Work is continuing in this area. 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, and an M.S. student will be graduating with this topic as her thesis.
Task 5. Multiphase Flow Simulation of Field Scale CO2 Injection
In addition to our earlier work on dissolved CO2 and brine flow up abandoned wells (K. Ellison 2011 M.S. thesis), we also have analyzed dissolved CO2 migration and exsolution in permeable fault zones. This work was published this year.
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 compared 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, in order to be practical, the areal footprint occupied by the dissolved CO2 should be comparable to supercritical CO2 injection. This work will be submitted as a manuscript to the journal Ground Water in the next month or so.
We are working on another study that compares various CO2 injections schemes (dissolved, supercritical, water alternating gas, water/supercritical co-injection) to assess these different methods’ capability for trapping the CO2 (by dissolution or capillary trapping) in a cost- effective manner. We expect this work to lead to another journal paper submission by the end of the summer.
Future Activities:
Task 4. Regional-Scale Variable Density Groundwater Modeling
A journal manuscript on this work will be prepared later this year, and an M.S. student will be graduating with this topic as her thesis.
Task 6. Remediation Designs and Alternative Injection Schemes to Reduce Risk
A manuscript on this work will be submitted to the journal Ground Water in the next month or so.
Work will continue on another study that compares various CO2 injections schemes (dissolved, supercritical, water alternating gas, water/supercritical co-injection) to assess these different methods’ capability for trapping the CO2 (by dissolution or capillary trapping) in a cost- effective manner. We expect this work to lead to another journal paper submission by the end of the summer.
Journal Articles on this Report : 3 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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Ruprecht C, Pini R, Falta R, Benson S, Murdoch L. Hysteretic trapping and relative permeability of CO2 in sandstone at reservoir conditions. International Journal of Greenhouse Gas Control 2014;27:15-27. |
R834383 (2013) R834383 (Final) |
Exit Exit Exit |
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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) |
Exit Exit |
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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.