Multiphase simulations of CO2 injectivity with and without brine extraction constrained by brine reinjectivity to optimize CO2 storage in the Illinois Basin

We developed a methodology to estimate maximum CO2 injection rates in subsurface layers across wide geographic areas using inverse modeling-based optimization techniques. We first defined geographic areas where groundwater was too saline to meet the standard for drinking water and where sufficient confining units existed above and below the injection layers. We then assumed concurrent CO2 injection into a system of wells on a consistent 25 km x 25 km spacing across the entire modeled area. Taking advantage of symmetry, we modeled each 25 km x 25 km injection area using a mesh shaped as a right-angle prism measuring 12.5 km by 12.5 km on the two orthogonal sides of the triangle. The domain therefore represents one eighth of the injection volume. This domain was divided into 10 rows of grid blocks of equal thickness. In the lateral directions, grid blocks measured 125 m by 125 m. The mesh contained 10 rows of grid blocks, each of which was set to a thickness equal to one-tenth of the layer thickness at the hypothetical injection area being modeled. Fifty years of CO2 injection were simulated into one of the bottom corners that formed a 45-degree angle in the plan view, and in some simulations water extraction was simulated from the other triangular corner. Pressure buildup was monitored at the CO2 injection location as well as the grid block at the corner of the domain that takes the shape of a right angle in the plan view (i.e., the corner grid block that takes the shape of a square prism). The injection rate was automatically adjusted to meet a maximum pressure buildup to 80% of the fracturing pressure, estimated as the least principal stress, at the injection location. A secondary constraint of 1 bar maximum pressure increase at the far-field boundary grid block after 50 years of injection was applied. We demonstrated this method on four stratigraphic layers in the Illinois Basin, which is a well-known CO2 injection target with a large estimated CO2 storage capacity. CO2 storage could be optimized by extracting brine from the injection layer and injecting it into a different one, which was the reason for implementing pressure increase mitigation via brine extraction in some cases. We also tested the effects of different brine extraction locations, either from the bottom grid cell only or from the entire thickness of the layer. Finally, we investigated the effects of geologic heterogeneity and anisotropy by running optimization simulations in which the porous media porosity and permeability were calculated as functions of depth.

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  "010:12"
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[
  "geospatial"
]