MINERALOGICAL CHARACTERIZATION OF THE ARBUCKLE AQUIFER: IMPLICATIONS FOR CO2 SEQUESTRATION

The mineralogy of the saline Arbuckle aquifer in south-central and western Kansas has recently been the subject for assessing regional CO₂sequestration potential. Two wells in south-central Kansas, Wellington KGS 1-32 and 1-28, and one well in southwestern Kansas, Cutter KGS 1, were drilled and examined for relevant parameters. Cores and thin sections were taken from depths ranging from 3681.9’ to 5176.9’ (Wellington) and 5564.3’ to 7540.2’ (Cutter). Dominant mineralogy is dolomite with varying forms of silica and scattered sulfide/clay minerals usually occurring in vugs and/or microfractures.

Three zones of interest were studied at Wellington: the Mississippian pay zone (3670’-3700’), a potential baffle zone in the upper Arbuckle (4400’-4550’), and the proposed CO₂ injection zone (4900’-5050’). The Mississippian oil reservoir is a fine-grained cherty dolomite with subhedral to euhedral dolomite rhombs. High porosity and small grain size could lead to quicker reactions with CO₂ and compete with the miscibility of CO₂ and oil, releasing some of the oil that has been trapped in pore spaces. Baffle zone rocks are characterized by a low porosity dolomitic mudstone to packstone with increasing chert, clay, and sulfide minerals towards the base. Low permeability of the baffle zone could also trap CO₂ and allow its reaction with rock in this interval.

The injection zone shows dolomite with siliceous nodules dispersed throughout with an increase in silica nearing the base. The injection pores are complexly connected with fractures along carbonate-chert boundaries providing ample pore space for lateral flow of CO₂. High porosity and permeability create an ideal setting for initial reaction of CO₂.

Arbuckle thin sections from Cutter KGS 1 exhibit a fine to coarse-grained dolomite mosaic with crystalline and vuggy porosity. Argillaceous materials occur in porous zones with few opaque (sulfide/oxide) minerals. Carbonate mineralogy of both wells provide alkali earth metals to buffer the pH and increase CO₂ solubility. Dissolved cations from clays and other materials create an environment suitable for mineralization trapping CO₂ mechanisms. Characterizing the mineralogy of these wells is vital to predicting the behavior of CO₂ in order to prevent groundwater acidification and control atmospheric CO₂ accumulation.