Breakthrough curves for Ca 2+ , Mg 2+ and Na + compared with experimental results from Voegelin et al.

No abstract

[1] Injection of CO 2 may perturb subsurface temperatures, leading to a dynamic temperature system in the storage formation and adjacent seal strata. In most cases, the individual effects from wellbore dynamics, solvation reactions, and phase changes are incremental, but collectively these relevant processes may cause significant temperature changes compared to ambient conditions. In this work, we evaluated several potential nonisothermal effects resulting from CO 2 injection activity. These include the Joule-Thomson (heating and cooling) effect, exothermic CO 2 dissolution, and heat changes associated with concomitant water vaporization. Results suggest that three effects: a) the adiabatic (de-) compression of CO 2 , b) the frictional energy losses, and c) conductive heat exchange between the injected CO 2 and surrounding fluid/rock, govern the resulting CO 2 thermal profiles within an injection well. In addition, as supercritical-phase CO 2 comes into contact with formation brine, the CO 2 will dissolve into the aqueous phase, and such dissolution is exothermic at typical conditions for CO 2 sequestration. However, we still seek a better understanding of heat effects associated with water vaporization into the supercritical-phase CO 2 . Finally, sensitivity studies, simulating supercritical-phase CO 2 injection into a 1-D radially symmetric domain, are conducted to evaluate the magnitude of different heat disequilibrium potentials and spatial location in the CO 2 plume affected by thermal processes. In addition, time-scales associated with migration rates of temperature fronts, pressure pulses, and dissolved-and supercritical-phase CO 2 profiles are investigated with a function of heat capacities of rock, different effective thermal conductivities, permeabilities, and porosities. Our results demonstrate that adiabatic CO 2 compression occurring in injection wells could have the most significant impact on the temperature change whilst the exothermic CO 2 dissolution occurred at the largest spatial domain.

[1] We present the results from a series of numerical simulations to explore systematic k heterogeneity effects on both CO 2 trapping mechanisms and buoyancy-driven CO 2 migration. For this purpose, we generated various permutations of two-dimensional numerical models of subsurface porous media: homogeneous, random, homogenous with a low-permeability (k) lens, and isotropically/anisotropically correlated k fields. For heterogeneous cases, we used a sequential Gaussian simulation technique to generate ten realizations in each model permutation. In each simulation, the amounts of mobile, residually, and aqueously trapped CO 2 were calculated, and the spatial distributions of the CO 2 plumes were quantified using first and second spatial moments. Simulation results from both homogeneous and random k fields suggest that the amount of residually trapped CO 2 increases as the mean effective k increases. These results imply that the overall velocity distribution, which governs the sweeping area of the supercritical-phase CO 2 plume, is a critical factor for controlling residual CO 2 trapping. However, as overall velocity (or effective k field) increases, we predict that the CO 2 plume potentially reaches the caprock more quickly. In addition, results also show that the decrease of variance in ln k increases the amount of residually trapped CO 2 . In simulations of anisotropically correlated k fields, the vertical CO 2 migration distance due to buoyancy shortens as the horizontal correlation length becomes greater. In addition, as the horizontal correlation length becomes greater, residual CO 2 trapping increases and mobile CO 2 decreases because the CO 2 plume spreads farther laterally (i.e., it sweeps a larger area). In summary, results of these analyses suggest that heterogeneous k fields with greater anisotropic correlation ratios potentially maximize residual CO 2 trapping and minimize buoyancy-driven CO 2 migration. Our findings also suggest that when heterogeneous k fields have a certain structure such as a low-k lens or other hydraulic barriers (e.g., faults), the amount of residually trapped CO 2 may increase and depend more on the geometry of geological structures than the magnitude of effective k.

We describe PFLOTRAN, a recently developed code for modeling multi-phase, multicomponent subsurface flow and reactive transport using massively parallel computers. PFLOTRAN is built on top of PETSc, the Portable, Extensible Toolkit for Scientific Computation. Leveraging PETSc has allowed us to develop-with a relatively modest investment in development effort-a code that exhibits excellent performance on the largest-scale supercomputers. Very significant enhancements to the code are planned during our SciDAC-2 project. Here we describe the current state of the code, present an example of its use on Jaguar, the Cray XT3/4 system at Oak Ridge National Laboratory consisting of 11706 dual-core Opteron processor nodes, and briefly outline our future plans for the code.