T174 Experimental, Field, and Modeling Studies of Geological Carbon Sequestration II

Tuesday, 29 October 2002
1:30 PM - 5:30 PM

REACTIVE TRANSPORT MODELING OF GEOLOGIC CO2 SEQUESTRATION

Paper number: T174-1
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Abstract

Geologic sequestration represents a promising strategy for isolating CO2 waste streams from the atmosphere. Successful implementation of this approach hinges on our ability to predict the relative effectiveness of subsurface CO2 migration and sequestration processes as a function of key reservoir and cap-rock properties, which will enable us to identify optimal target formations and evaluate their long-term isolation performance. Quantifying this functional relationship requires a modeling capability that explicitly couples multiphase flow and kinetically controlled geochemical processes. We have developed a unique computational package that meets these criteria by integrating a state-of-the-art reactive transport simulator (NUFT) and supporting geochemical software and databases (SUPCRT92 and GEMBOCHS). We have used this capability to model saline-aquifer disposal at Statoil's North-Sea Sleipner facility during both prograde (active-injection) and retrograde (post-injection) phases of the process.

Simulation results suggest that in the near-field environment of Sleipner-like settings roughly 85% by mass of injected CO2 remains and migrates as an immiscible fluid phase (subject to hydrodynamic and structural trapping), about 15% dissolves into formation waters (solubility trapping), and <1% precipitates as carbonate minerals (mineral trapping). Although seemingly negligible, mineral trapping has enormous strategic significance. We have identified four distinct mechanisms: siderite-magnesite precipitates within inter-bedded and cap-rock shales, dawsonite cementation occurs throughout the intra-aquifer plume, and siderite-magnesite-calcite rind forms along both lateral and upper plume boundaries. Local porosity and permeability are reduced by each of these mechanisms; however, such reduction is most extreme in clay-rich shales, owing to their relatively large Fe and Mg concentrations. In our 20-year simulations, initial porosity and permeability of the basal cap-rock shale have been reduced by 8% and 22%, respectively. Hence, the strategic significance of mineral trapping: it continuously improves seal integrity and therefore containment of the voluminous immiscible plume and solubility-trapped CO2.