Experimental Examination of Fluid Flow in Fractured Carbon Storage Sealing Formations

Abstract

This report describes a series of experiments where CO 2-saturated-brine flow through fractured seal rocks from three sites within the continental United States that are being considered, or are actively being used, for CCUS pilot studies were examined. The experiments were performed over multiple weeks by injecting CO 2 saturated brine through fractured samples, and were scanned with a computed tomography scanner at regular intervals over the course of the experiment while kept at representative reservoir pressures. The goal was to evaluate the change in the fracture flow that would result from a CO 2 leakage event so that accurate relationships can be implemented in numerical models to assess risk. Of the three different formations studied in this series of fractured seal formation CO 2-saturated-brine flow through experiments, only one formation had a reaction that was greater than the noise in the system. Reactions within the Tuscaloosa claystone sample appeared to reduce the transmissivity of the fracture slightly over the 39 day experiment. The change in the geometry of the fracture was not great enough to view with the medical CT images that were captured during the experiment. All other tests showed a minimal amount of change in the fracture and fracture flow properties.

Alterations of Fractures in Carbonate Rocks by CO2-Acidified Brines

“…One of the challenges we addressed is the rotational scanning of the specimen while maintaining both the high pore pressure and the confining pressure of the core holder. Similar systems in prior experiments used medical scanners for periodic real-time imaging. ,− The resulting images, with a resolution on the order of 100 μm, provided valuable insights on the rough progression of matrix porosity. However, for accurate geometry quantification of fine-scale features such as fractures under high confining pressure, higher resolution is needed .…”

Sealing of fractures in a representative CO2 reservoir caprock by migration of fines

“…A decrease in fracture permeability despite a net removal of material along the fracture pathways demonstrated a nonintuitive, inverse relationship between dissolution and permeability evolution in a fractured carbonate caprock. In comparison, CO 2 and brine flow experiments on several fractured low carbonate mudrocks from active or proposed carbon storage sealing formations (Kirtland shale, Eau Claire mudstone, and Tuscaloosa claystone) exhibited minimal changes in recordable fracture properties over the course of extended enriched CO 2 brine flow through the fractures 12 …”

“…In order for geologic CO 2 storage to be acceptable from a scientific, regulatory, and public perception standpoint, risks associated with the technology must be carefully evaluated 9 . Wells and pre‐existing non‐transmissive faults and fractures in caprock have been identified as potential risks for the safe and secure storage of CO 2 injected in reservoirs, as they could serve as conduits for CO 2 and/or brine to migrate from the storage reservoir into overlying aquifers 9–14 . Specific mechanisms that could result in CO 2 leakage from a reservoir include reactivation of faults in the caprock, reactivation of faults hydraulically connected to the reservoir, induced shear failure of the caprock, hydraulic fracturing of the caprock, leakage from the injection well, and exceedance of the capillary membrane seal pressure 15–17 …”

Carbon dioxide storage in unconventional reservoirs workshop: summary of recommendations

“…Bacteria were found to exist in all samples, and iron-rich carbonates and iron hydroxides formed when exposed to supercritical CO 2 . Computed tomography (CT) scanners with resolutions of 240 micrometers to 1 micrometer (Crandall and Bromhal, 2013) are being used to image CO 2 flow at reservoir conditions through Grande Ronde Basalt from the Columbia River Basalt Group, and these images help researchers infer how subsurface CO 2 moves during pilot tests. Experiments on Columbia River Basalt samples at the Pacific Northwest National Laboratory show that mutual solubilities of CO 2 and water can have a large impact on reaction kinetics (McGrail and others, 2011b).…”