INVESTIGATING THE CO2 SEQUESTRATION POTENTIAL OF THE MORROW-B SANDSTONE IN THE FARNSWORTH, TEXAS HYDROCARBON FIELD THROUGH NUMERICAL MODELS AND EXPERIMENTAL ANALYSIS

The Farnsworth Unit (FWU), a depleted hydrocarbon field in Ochiltree County, Texas, is an ongoing research site of the Southwest Partnership for CO₂ Sequestration (SWP). The present study is a part of the SWP research effort and is focused on using numerical reactive transport modeling and batch reaction experiments to evaluate the CO₂ sequestration potential of the Morrow B Sandstone reservoir in the western half of the FWU in conjunction with enhanced oil recovery. The numerical models incorporated detailed site-specific reservoir properties and fluid injection histories, accounting for the flow of multi-phase fluids, heat transport, solute transport, and chemical reaction. The models were calibrated against eight years of production data, after which they were used to forecast reservoir behavior to 1000 years. The models predict modest increases in reservoir pressure during the initial 25-year period of injection of water and CO₂, after which fluid pressure gradually returns to pre-injection levels. The models predict dissolution by oil to be the largest sink for the injected CO₂, followed by dissolution by the formation water, the precipitation of carbonate minerals, and the formation of an immiscible gas phase, respectively. Most of the CO₂ sequestration is limited to a radius of within a few hundred meters of the injection wells. CO₂ sequestration by carbonate mineral precipitation grows continuously in importance over time, approaching dissolution by water and oil in importance by the end of the 1000-year simulation period. Most of the carbonate mineral precipitation consisted of dolomite, with essentially negligible amounts of ankerite, siderite, and magnesite. Calcite, a native reservoir mineral, was predicted to dissolve throughout the simulations. Concerning other native reservoir minerals, quartz was predicted to precipitate whereas clinochlore was predicted to dissolve, while albite, kaolinite, and illite did not undergo significant changes in abundance. These predicted changes in mineral abundance do not lead to significant changes in reservoir porosity or permeability. Batch reaction experiments involving thin sections of the Morrow B Sandstone immersed in variably CO₂-charged formation water are currently underway to test theoretical predictions of changes in mineral abundance.