Investigation of the Vapex process in high-pressure fractured heavy-oil reservoirs

In this work, the vapour extraction (VAPEX) process was studied in a multiple block, dual porosity fractured system. The performance of this process is compared with a conventional, non-fractured system under similar rock and fluid properties, bulk volume, pore volume, hydrocarbon volume, and injected pore volume of solvent and solvent injection rate. At early stages of the VAPEX process in fractured system, the solvent-oil interfaces form and develop from all sides of the matrix, and the oil chamber, rather than solvent chamber forms and shrinks in the center of each block. Also, at later stages of the process, the solvent zones from all neighboring blocks combine and form an integrated solvent zone, which is similar to that in the conventional systems. The results showed that in low-permeability carbonate reservoirs, the fracture network provides communications for solvent flow through which the solvent can flow faster and form solvent fingers at early stages, which can reach the blocks located at farther distances from injection well. It was found that the solvent breakthrough starts at he same time in both low-permeability non-fractured system and fractured system. This is because the solvent flows directly through drained areas towards producer in both systems. Further, effect of solvent injection rate on heavy oil recovery in the fractured system was studied in two cases: different injection rate at the same injection time, and different injection rate with the same injected pore volume. It was found that the solvent injection rate should be optimized for a specific system in order to control the solvent breakthrough and to avoid extra operation time and cost.