Hydrological and geochemical characterization of shallow aquifer water following a nearby deep CO₂ injection in Wellington, Kansas

Abstract

Domestic and irrigation well water quality in south-central Kansas is threatened by multiple sources of contamination including CO₂-EOR activities, evaporite dissolution and oilfield brine release. This research identifies potential groundwater flow paths for contaminant migration in a concentrated area mixed with oil, injection, irrigation and domestic wells. Groundwater (GW) sampling took place before and after CO₂ injections into the Mississippian in to assess temporal changes in water quality in a ~2 mile radius around injection well KGS 2-32. Samples were analyzed for stable isotopes, rare earth elements (REE), major and trace ions, dissolved organic carbon (DOC) with a select few analyzed for dissolved CO₂ and hydrocarbons. Results of major ion chemistry reveal an evaporite control on geochemistry in wells screened within the paleoterrace as opposed to the incised valley. Bedrock channeling due to erosional scouring of the paleovalley is speculated to have led to secondary porosity thereby increasing GW flow. Similar stable isotopic and Br/Cl mass ratios between SW-3, Shepherd and Zehr indicate water is similarly sourced; lower total dissolved solids within incised valley could result from dilution from infiltration through overburden sediments. Br/Cl, SO₄/Cl, Na/Cl and (Ca+Mg)/Na ratios indicate Shepherd, Zehr and SW-3 are possibly impacted by a recent salt plume movement through this portion of the shallow aquifer. An increase in total dissolved solids and Mg/Ca ratios with temperatures less than 25°C over a 25 to 200 ft. depth interval into the Permian Shale of the uplands could have resulted from increasing calcitization and reduction in effective porosity. Dissolved REEs showed most domestic and surface waters contain similar signatures, indicating similarly sourced water. Additionally, there was no CO₂ leakage found within the sampling timeframe and a future leaked plume may be impeded by decreasing porosity from current secondary mineralization processes taking place in the Permian Shale.