Bureau of Economic Geology

"Potential Impacts of Unintended CO2 Release from a Gulf Coast CCUS Sites on Groundwater Chemistry; Creating Geochemical Models to Predict Groundwater Geochemical Changes"

October 5, 2018 9:00 AM
Dr. Pat Mickler

Dr. Patrick J. Mickler,  Bureau of Economic Geology

The capture and storage of CO2 in deep saline reservoirs has been proposed as a way of mitigating anthropogenic forced climate change by reducing the amount of CO2 released to the atmosphere.  Injecting CO2 (sc) into deep formation may cause concern to those near CCUS sites because of the potential impact on overlying groundwater resources.  CO2 may negatively impact potable groundwater chemistry in several ways: 1. The CO2 may migrate upwards along discreet pathways and force carbonate, silicate, sulfide, oxy-hydroxides and sulfate dissolution, absorption/adsorption/desorption reactions, mineral precipitation reactions and may hypothetically mobilize elements such as As and Pb  to concentrations above drinking water standards.  2. Migrating CO2 may mobilize dissolved hydrocarbon gasses into overlying groundwater.  3.  Increases in formation pressure from injected CO2 may displace formation brines into overlying groundwater.

Chemical and physical monitoring of zones above the injection formation, groundwater, soil gas and atmospheric gas have been proposed as ways to identify unintended CO2 release from a CCUS site.  Continuous monitoring designed to identify any unintended CO2 release is prohibitively expensive and likely impossible.  In commercial projects we rely on leakage signals, especially pressure changes, in deeper zones nearer the injection zone. In this context, the role of groundwater monitoring is preparation for an incident or an allegation. This process involves geochemically characterizing the groundwater, soil gas and atmospheric gas systems at the CCUS site to determine ambient spatial and temporal variability. These results can then be used to create models that predict geochemical changes that would result from unintended CO2 releases and determine risk to water resource should release occur. Models may also distinguish between leakage signals and other sources of variability, natural or otherwise.  In this study, we characterize existing groundwater geochemistry of a gulf coast CCUS site and present models that predict geochemical changes to groundwater chemistry that would result from an unintended CO2 release.