## 1 Introduction
### Shale Interactions (Multi-Mineral)  
A series of three studies have recently been published by the same group investigating dry-CO\({}_{2}\) interactions with Utica shale and evaluating the role water plays in these reactions [13; 25; 50]. In general terms, the minerology of the inorganic Utica shale is around 50% calcite, 20% clays (illite/mica/small amounts of kaolinite), 15% quartz, and 15% other (plagioclase/dolomite/pyrite) [51]. [PERSON] et al. [50] and [PERSON] et al. [13] identified and quantified chemical and physical alterations at the molecular scale and microscale. They also examined the surface interactions of two primary constituents of the shale: clays (illite-smectite, illite, chlorite, and kaolinite) and kerogen. Investigative tools used before and after exposure included FTIR, SEM, and N\({}_{2}\), and CO\({}_{2}\) adsorption. FTIR scans were conducted at 40 \({}^{\circ}\)C and at a series of CO\({}_{2}\) pressures from 0.25 to 8.2 MPa. Scans were periodically conducted until the IR spectra stabilised. This took between 7 and 15 days. All other post-exposure experiments were performed on samples held at 40 \({}^{\circ}\)C and 10.3 MPa for 14 days. The FTIR results showed that carbonate bands increased in intensity after CO\({}_{2}\) exposure. This happened rapidly within the first 15 min, and the magnitude of the observed change was proportional to CO\({}_{2}\) pressure. [PERSON] et al. [50] suggested that carbonate precipitation and dissolution (mostly calcite) occurred until equilibrium was established. Etching and pitting in the calcite matrix, with minor calcite precipitation, were also observed using FE-SEM. This appeared to increase macro-porosity. Quartz and pyrite grains were unaffected. Using adsorption isotherm data for Utica shales, [PERSON] et al. [50] found that the standard BET (total) surface area measured for isotherm data from the so-called BET region (see below) remained relatively stable. However, quenched solid density functional theory (QSDFT) analysis, based on slit/cylindrical pores, performed on the same nitrogen isotherms, showed that the surface area and volume were largely just in the micropores, but that a substantial decrease in these parameters occurred after exposure to CO\({}_{2}\). QSDFT-based analysis was additionally used to measure mesopore volume, and no significant change was seen in this range. Non-local density functional theory (NLDFT) was used to analyse CO\({}_{2}\) absorption data to determine the volume and size distribution of ultra-micropores. Again, only very small changes were recorded in this range. DFT-calculated isotherms fitted the experimental data very well, with a maximum of 1% error. However, the apparently conflictual findings obtained by the different analysis methods for the adsorption data suggested the need for more accurate void space descriptors, which was addressed in subsequent work, as described below. Interestingly, CO\({}_{2}\) adsorption on individual clay constituents demonstrated higher uptakes than those seen for the Utica shale sample itself (see Figure 3). This finding indicated that the constituents in the shale were inaccessible to CO\({}_{2}\) even when the shale was ground to a fine powder. [PERSON] et al. [50] concluded that, although research into the interactions of dry-CO\({}_{2}\) with rocks is very limited, their experiments showed that reactions did occur with the kerogen and clay components of shale. Etching on the Utica shale surfaces showed cycling between carbonate dissolution and precipitation. These authors suggested that this is likely enabled by water retained in the interstitial pore space and matrix. Finally, they stated that, although adsorption takes place in mesopores and micropores, the mesopores may only be accessible through the narrow micropores. Similar suggestions have been made concerning an 'hourglass-type' geometry for the void space of Bowland shale based upon a comparison of mass transfer rates from mass uptake and adsorption calorimetry methods, which are discussed in more detail below.