USING HIGH PERFORMANCE COMPUTING TO EXAMINE THE EFFECTS OF THERMAL GRADIENTS IN CARBONATE CCUS RESERVOIRS

Geologic Carbon Capture, Utilization, and Storage (CCUS) has the potential to prevent large volumes of the heat-trapping greenhouse gas CO₂­­­­­­ from entering the atmosphere and exacerbating global climate change. In order for CCUS to meaningfully reduce emissions, considerable amounts of CO₂ will need to be injected into globally abundant carbonate reservoirs. Importantly, both CO­_­2 and carbonate solubility decrease with increasing temperature at typical carbonate reservoir conditions. Tutolo et al. (2014) experimentally showed that, when surface-temperature CO₂ is injected into geothermally warm carbonate reservoirs, this temperature-dependent behavior may lead to mass transfer along flow paths leading away from the CO₂ injection well and associated porosity and permeability redistribution. In this study, we utilize the massively parallel reactive transport simulator PFLOTRAN to upscale the Tutolo et al. (2014) experimental results to the reservoir scale. We focus on both calcite and dolomite reservoirs at a range of temperatures (50-200°C) and background hydraulic head gradients (0-0.1 m/m) and make a number of important observations relevant to carbonate-based CCUS operations. Firstly, calcite’s relatively rapid precipitation kinetics cause it to primarily precipitate just outside of the low-temperature zone near the injection well, whereas dolomite tends to precipitate over a greater distance down-gradient from the injection well. The spatial distribution and volume of the precipitated minerals can affect reservoir injectivity, particularly if precipitates concentrate within primary flow pathways. Additionally, CO₂ exsolution, which was the dominant permeability-reducing mechanism noted by Tutolo et al. (2014), appears to have a much less dramatic effect at the reservoir scale. A key conclusion of this study is, thus, that large-scale, three dimensional reactive transport simulations of the type presented here are necessary to evaluate the risks and longevity of proposed CCUS reservoirs.

Ref.: Tutolo et al. (2014) ES&T 48: 2445-2452.