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CO2-induced chemo-mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

Greenhouse Gases: Science and Technology

Aman, Michael; Espinoza, D.N.; Ilgen, Anastasia G.; Major, Jonathan R.; Eichhubl, Peter; Dewers, Thomas D.

The injection of carbon dioxide (CO2) into geological formations results in a chemical re-equilibration between the mineral assemblage and the pore fluid, with ensuing mineral dissolution and re-precipitation. Hence, target rock formations may exhibit changes of mechanical and petrophysical properties due to CO2 exposure. We conducted batch reaction experiments with Entrada Sandstone and Summerville Siltstone exposed to de-ionized water and synthetic brine under reservoir pressure (9–10 MPa) and temperature (80°C) for up to four weeks. Samples originate from the Crystal Geyser field site, where a naturally occurring CO2 seepage alters portions of these geologic formations. We conducted micro-scratch tests on rock samples without alteration, altered under laboratory conditions, and naturally altered over geologic time. Scratch toughness and hardness decrease as a function of exposure time and water salinity up to 52% in the case of Entrada and 87% in the case of Summerville after CO2-induced alteration in the laboratory. Imaging of altered cores with SEM-EDS and X-ray microCT methods show dissolution of carbonate and silica cements and matrix accompanied by minor dissolution of Fe-oxides, clays, and other silicates. Parallel experiments using powdered samples confirm that dissolution of carbonate and silica are the primary reactions. The batch reaction experiments in the autoclave utilize a high fluid to rock volume ratio and represent an end member of possible alteration associated with CO2 storage systems. These types of tests serve as a pre-screening tool to identify the susceptibility of rock facies to CO2-related chemical-mechanical alteration during long-term CO2 storage. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

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TYPE Journal Article YEAR 2018
ScopusOSTIDOI

Density Fluctuation in Aqueous Solutions and Molecular Origin of Salting-Out Effect for CO2

Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

Ho, Tuan A.; Ilgen, Anastasia G.

Using molecular dynamics simulation, we studied the density fluctuations and cavity formation probabilities in aqueous solutions and their effect on the hydration of CO2. With increasing salt concentration, we report an increased probability of observing a larger than the average number of species in the probe volume. Our energetic analyses indicate that the van der Waals and electrostatic interactions between CO2 and aqueous solutions become more favorable with increasing salt concentration, favoring the solubility of CO2 (salting in). However, due to the decreasing number of cavities forming when salt concentration is increased, the solubility of CO2 decreases. The formation of cavities was found to be the primary control on the dissolution of gas, and is responsible for the observed CO2 salting-out effect. Finally, our results provide the fundamental understanding of the density fluctuation in aqueous solutions and the molecular origin of the salting-out effect for real gas.

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TYPE Journal Article YEAR 2017
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Results 51–75 of 112
Results 51–75 of 112