(147e) Evolution of Transport and Mechanical Properties of Mt Simon Sandstones Due to Interaction with Brine/CO2

Authors: 
Shi, Z., University of Southern California
Sun, L., University of Southern California
Jessen, K., University of Southern California
Tsotsis, T., University of Southern California
When sandstone rocks are exposed to CO2-saturated brine, their transport and mechanical properties can change due to brine/CO2-induced chemical reactions. The present study investigates the change in the flow-through characteristics, porosity and the mechanical behavior of Mt. Simon Sandstone samples caused by exposure to brine/CO2. The cores, extracted from the Mt. Simon formation, were first characterized for their mechanical and transport properties, and then aged in CO2-saturated brine at pressures of 2500 psi and temperature of 50⁰C for one to two weeks. Following that, tests were carried out to measure the change in transport and mechanical properties of the samples. Our experiments show that the porosity of the Mt. Simon samples slightly increases after the exposure to CO2/brine. On the other hand, the permeability increases quite substantially (depending on the confining environment) upon exposure to CO2/brine. Industrial CT and Micro CT scanning were used to monitor the evolution of the pore structure during exposure. Measurements of the flow-through pore size distribution (PSD) are indicative of changes occurring consistent with the observed increases in permeability. Nitrogen adsorption tests (BET), before and after incubation, show a significant loss of pore volume in the mesoporous range that is indicative of clay dissolution. Weakening of the materials was observed based on the mechanical properties studied, a result that is consistent with the observed dissolution of clays that play a central role in the cementation of the quartz grains. The compositions of the brines used in the experiments were analyzed, and increases in concentration of most cations were found after incubation with the Mt. Simon cores, also consistent with mineral/clay dissolution, which is in line with the porosity, transport, and mechanical property measurements and electron microscopy analysis of the same samples.