Salt precipitation due to supercritical gas injection: I. Capillary-driven flow in unimodal sandstone

• Published in: International journal of greenhouse gas control 2015-12, Vol.43, p.247-255
• Main Authors: Ott, H., Roels, S.M., de Kloe, K.
• Format: Article
• Language: English
• Subjects: CO2 storage; Counter-current flow; Dry-out; Micro-CT imaging; Precipitation; Sandstone
• ISSN: 1750-5836; 1878-0148
• DOI: 10.1016/j.ijggc.2015.01.005

•Impact of salt precipitation in injectivity during supercritical CO2 injection.•Macroscopic solute transport to the injection point by capillary-driven counter-current flow.•Experimental observation of kinetic effects of water evaporation in sandstone.•Numerically derived dimension of the drying zone.•Experimentally derived permeability–porosity relationship for salt precipitation in unimodal sandstone. Drying and salt precipitation in geological formations can have serious consequences for upstream operations in terms of injectivity and productivity. Here we investigate the consequences of supercritical CO2 injection in sandstones. The reported findings are directly relevant for CO2 sequestration and acid–gas injection operations, but might also be of interest to a broader community dealing with drying and capillary phenomena. By injecting dry supercritical CO2 into brine-saturated sandstone, we investigate the drying process and the associated precipitation of salts in a capillary-pressure-dominated flow regime. Precipitation patterns were recorded during the drying process by means of μCT scanning. The experimental results and numerical simulations show that under a critical flow rate salt precipitates with an inhomogeneous spatial distribution because of brine and solutes being transported in counter-current flow upstream where salt eventually precipitates. A substantial impairment of the absolute permeability has been found, but despite high local salt accumulation, the effective CO2 permeability increased during all experiments. This phenomenon is a result of the observed microscopic precipitation pattern and eventually the resulting K(ϕ) relationship. The findings in this paper are related to unimodal sandstone. In a companion paper (Ott et al., 2014) we present data on the distinctly different consequences of salt precipitation in dual- or multi-porosity rocks.