Understanding and Managing Risks Posed by Brines Containing Dissolved Carbon DioxideEPA Grant Number: R834383
Title: Understanding and Managing Risks Posed by Brines Containing Dissolved Carbon Dioxide
Investigators: Falta, Ronald W. , Benson, Sally M. , Murdoch, Lawrence C.
Institution: Clemson University , Stanford University
EPA Project Officer: Klieforth, Barbara I
Project Period: November 1, 2009 through October 31, 2012 (Extended to October 31, 2014)
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
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.
Determine the conditions under which dissolved CO2 brines can impact drinking water aquifers and design effective risk reduction strategies. Develop a fundamental understanding of the fate of dissolved and exsolving CO2 at scales ranging from the pore scale to the regional field scale.
Six main activities will be undertaken. 1) Laboratory core experiments will flood cores with CO2 saturated brines at reservoir pressure and temperature. These cores will then be gradually depressurized, and imaged using a medical CT scanner to study the CO2 phase evolution and movement. 2) Pore-scale multiphysics and fine-grid multiphase continuum modeling of these experiments will be used to develop a fundamental understanding of the exsolution and CO2 bubble coalescence phenomena as the CO2 starts to form a mobile phase. 3) Core-scale multiphase continuum modeling will upscale the experimental results with a focus on identifying effective relative permeability functions for use in field scale modeling. 4) Simulations of regional scale behavior using a variable density groundwater flow model will be performed. Several active or potential CO2 storage locations will be simulated during this activity. At least one of these sites will be selected from current supercritical CO2 injection field projects, and at least one will be representative of sites where dissolved CO2 brine injection may be proposed. The simulations will 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) Local field scale (hundreds to thousands of meters) multiphase simulations of the likely failure modes indentified in the regional scale modeling will be performed for each site, using the same hydrogeologic conditions. The regional models will form the boundary conditions for these smaller multiphase models, and the modeling will build on the previous core experiments and modeling. 6) These models will then be used to study remediation strategies and alternative storage methods for each scenario.
This work will develop a scientific understanding of the fate of dissolved CO2 and risks associated with migration of CO2 saturated brine under a variety of realistic conditions. It will lead to improved engineering design of CO2 storage projects and remediation strategies that reduce the risk of CO2 storage. It will develop practical modeling techniques for simulating dissolved and exsolving CO2 phase movement. Perhaps most importantly, it will investigate heretofore unidentified risks to groundwater associated with migration of CO2 saturated brines into drinking water aquifers.