Spent Shale Formations: Potential Source for CO2 Sequestration

Spent Shale Formations: Potential source for CO₂ Sequestration

Prashanth Mandalaparty, Robert Krumm and Milind Deo

While producing oil from shale in-situ, the shale is retorted in the geological formation without mining to the surface. The objective of the current study is to explore the possibility of using the (spent) shale repository as a potential source for geological sequestration of CO₂. For this research, the shale samples used were retorted at different temperatures in order to address the following problem:  the response of different initial mineral matrices and unreacted organic components to CO₂ injection.  The experimental apparatus consists of isolated, high-pressure reactors operated at varying conditions with pure CO₂ as the feed gas.  Initial XRD analysis of the raw and spent shale samples from Green River formation reveal carbonates, quartz, and feldspars as the principal inorganic components. Calcite and dolomite constitute the carbonate sections in the shale and microcline (K-feldspar) and plagioclase feldspar make up the silicate section. Kaolinite is present in significant portions and silica is mainly present as quartz. Illite forms the clay portion of the shale. SEM analysis of the reacted spent shale sample at 100⁰C reveals precipitation of calcite, magnesite and possibly dolomite. Carbonation of feldspars was also observed, made evident by the precipitation of carbonates with their respective principal ions. These changes in rock mineralogy are complemented by the changes in brine chemistry. Base case kinetic models were developed using Geo-Chemists Work Bench (GWB). The results from these models indicate a rapid pace of sequestration reactions when compared to experiments. Thus this study provides useful laboratory data (with model comparisons) when considering CO₂ sequestration in different spent shale repositories.