Countercurrent Flow Enhances CO2 Accumulation During Upward Migration in Storage Aquifers
8 Pages Posted: 17 Apr 2019 Last revised: 20 Apr 2019
Date Written: September 30, 2018
Using high-resolution numerical simulation, we model the purely buoyant flow of CO2 in a two-dimensional (2D) closed aquifer domain. The domain is composed of two heterogeneous layers with different average permeabilities. The high permeability layer is overlain by the low permeability layer, and each layer has heterogeneous capillary pressure functions correlated with geostatistically-assigned permeabilities. Initially, CO2 is emplaced at the bottom with a given column height and then allowed to rise. During CO2 upward migration, two types of CO2 accumulations are observed: one accumulation is capillary-barrier trapping, and the other is permeability-retarded. More importantly, capillary-trapped CO2 interacts with the permeability-retarded CO2. The former CO2 trapping exhibits a much higher saturation, which causes the latter CO2, under countercurrent flow (i.e., CO2 rises and while water falls), to move upward much slowly. Thus, accurate evaluation of CO2 upward migration should consider the interaction between capillary-trapping and permeability-retardation.
Keywords: countercurrent flow; concurrent flow; CO2 accumulation; buoyant flow; geological carbon sequestration
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