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A theoretical investigation of factors affecting the gas phase transport of evaporating organic liquids in the unsaturated zone is presented. Estimates of density-dfiven advective gas flow using a simple analytic expression indicate that significant advective gas flow will result from the evaporation of volatile liquids in soils having a high permeability. Numerical simulations using a two-dimensional cylindrical geometry and including the effects of phase partitioning between the solid, gas, water, and organic liquid phases show that mass transfer due to density-dfiven flow may dominate the gas phase transport of some organic chemical vapors in the unsaturated zone. 2159

DISCLATMERThis document was prcparcd as M account of w o k sponsored by the US& Stam G o v u n m a r While this document is belicvd IO ABSTRACTT2VOC is a numerical simulator for three-phase, three-component, non-isothermal flow of water, air, and a volatile organic compound (VOC) in multidimensional heterogeneous porous media. Developed at the Lawrence Berkeley Laboratory, T2VOC is an extension of the TOUGH2 general-purpose simulation program.This report is a self-contained guide to application of T2VOC to subsurface contamination problems involving nonaqueous phase liquids (NAPLs). It gives a technical description of the T2VOC code, including a discussion of the physical processes modeled, and the mathematical and numerical methods used. Detailed instructions for preparing input data are presented along with several illustrative sample problems.

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Dissolution of CO 2 into brine is an important and favorable trapping mechanism for geologic storage of CO 2 . There are scenarios, however, where dissolved CO 2 may migrate out of the storage reservoir. Under these conditions, CO 2 will exsolve from solution during depressurization of the brine, leading to the formation of separate phase CO 2 . For example, a CO 2 sequestration system with a brine-permeable caprock may be favored to allow for pressure relief in the sequestration reservoir. In this case, CO 2 -rich brine may be transported upwards along a pressure gradient caused by CO 2 injection. Here we conduct an experimental study of CO 2 exsolution to observe the behavior of exsolved gas under a wide range of depressurization. Exsolution experiments in highly permeable Berea sandstones and low permeability Mount Simon sandstones are presented. Using X-ray CT scanning, the evolution of gas phase CO 2 and its spatial distribution is observed. In addition, we measure relative permeability for exsolved CO 2 and water in sandstone rocks based on mass balances and continuous observation of the pressure drop across the core from 12.41 to 2.76 MPa. The results show that the minimum CO 2 saturation at which the exsolved CO 2 phase mobilization occurs is from 11.7 to 15.5%. Exsolved CO 2 is distributed uniformly in homogeneous rock samples with no statistical correlation between porosity and CO 2 saturation observed. No gravitational redistribution of exsolved CO 2 was observed after depressurization, even in the high permeability core. Significant differences exist between the exsolved CO 2 and water relative permeabilities, compared to relative permeabilities derived from steady-state drainage relative permeability measurements in the same cores. Specifically, very low CO 2 and water relative permeabilities are measured in the exsolution experiments, even when the CO 2 saturation is as high as 40%. The large relative permeability reduction in both the water and CO 2 phases is hypothesized to result from the presence of disconnected gas bubbles in 123 460 L. Zuo et al. this two-phase flow system. This feature is also thought to be favorable for storage security after CO 2 injection.