Simulation of Compositional Gravity-Drainage Processes

The amount of wetting phase that is recovered by gravity drainage when the displacing fluid is not in chemical equilibrium with the initial fluid involves a complex interplay of gravitational, diffusive, and capillary forces. Previously, in Part 1 in a series of papers, we proposed analytic solutions for capillary/gravity equilibrium (CGE) in compositional gravity drainage and estimated the total recovery of wetting phase (DiCarlo and Orr 2007). In Part 2, we presented the results of experiments in an analog brine/isopropanol (IPA)/isooctane (IC(8)) system in which the vertical profile of the components was measured destructively after 3 weeks of drainage (DiCarlo et al. 2007). Here, we present numerical simulations of compositional gravity drainage. We find that the CGE solutions are approached asymptotically as the simulation grid is refined for a simplified phase diagram. For vaporizing drainages, a bank of wetting fluid is found to be created from early times in the drainage because of wetting fluid imbibing back into swept regions. We show that including hysteresis in the capillary pressure curve limits the creation of the wetting-fluid bank. We compare the numerical simulations to the experimental observations and find that the simulations match well for condensing drainages but not for vaporizing drainages, similar to what is seen for the CGE solutions.