Numerical Modeling of the VAPEX Process in Heterogeneous Media

Interest in using VAPEX as an alternative to thermal methods to recover heavy oil and bitumen is gaining interest. The main difference between methods is that while thermal methods rely on conduction of heat as well as mass transfer, VAPEX only relies on mass transfer. This limits mass diffusion and convection solely to occur through the pore space, whereas heat from thermal methods can conduct through solids. Therefore, it has been postulated that VAPEX is more sensitive to heterogeneity than thermal methods. The interest here was to see to what extent VAPEX is affected by spatial heterogeneity. The theory generated for the VAPEX process assumes permeability to be a scalar. The idea explored here was for the same permeability distribution, does the spatial heterogeneity affect recovery and to what extent? A two dimensional compositional simulator was constructed with permeability fields varying in the horizontal and vertical directions. The permeability fields were accompanied by appropriately scaled capillary pressures by use of the Leverett J-function. The correlation lengths were varied and the production data was noted to see what effect spatial heterogeneity had on the recovery. Other sensitivity analysis were performed such as injection well location, permeability anisotropy, and coarsening of the permeability field. A random walker was implemented to further understand gravity drainage and to attempt to assess the limitations of grid block size for homogenous and heterogeneous cases.