Alterations of Fractures in Carbonate Rocks by CO2-Acidified Brines

• DOI: 10.1021/acs.est.5b01980
• Publication Date: 2015-07-24T02:38:20Z
• Authors: Hang Deng; Jeffrey P. Fitts; Dustin Crandall; Dustin McIntyre; Catherine A. Peters
• Keywords: Channelized; Carbonic acid; Brine

Fractures in geological formations may enable migration of environmentally relevant fluids, as leakage CO2 through caprocks geologic carbon sequestration. We investigated geochemically induced alterations fracture geometry Indiana Limestone specimens. Experiments were the first their kind, with periodic high-resolution imaging using X-ray computed tomography (xCT) scanning while maintaining high pore pressure (100 bar). studied two CO2-acidified brines having same pH (3.3) and comparable thermodynamic disequilibrium but different equilibrated pressures (PCO2 values 12 77 High-PCO2 brine has a faster calcite dissolution kinetic rate because accelerating effect carbonic acid. Contrary to expectations, extents experiments. However, progressive xCT images revealed extensive channelization for PCO2, explained by strong positive feedback between ongoing flow reaction. The pronounced channel increasingly directed small region fracture, which explains why overall was lower than expected. Despite this, simulations large increases permeability high-PCO2 experiment. This study shows that evolution dissolving fractures will be larger faster-reacting fluids. mechanism is not more rock dissolves, would commonly assumed, accelerated channelization.