Effect of Fracture Spacing on VAPEX Performance in Heavy Oil Fracture Systems

The vapor extraction (VAPEX) process, a solvent-based enhanced oil recovery process has been found promising for some heavy oil reservoirs. In this work, the VAPEX process is studied using a compositional simulator on a number of single-block and multiple block fractured systems. PVT data of one of an Iranian heavy oil reservoir are used to tune the equation of state. Effects of fracture spacing on the performance of process were studied. It was found that the fracture network enhances the VAPEX process in low-permeability systems by increasing the contact area between solvent and oil contained in the matrix blocks. Also, the fracture network reduced the instabilities in the system pressure and damped pressure surges in the system during the VAPEX process. In addition, results showed that solvent traverse between fracture network delayed the onset of solvent breakthrough and provided more residence time for the solvent to be in contact with heavy oil. In other part, effect of well location on the performance of process was studied. It was found that the oil production decreased as the well spacing increased. When the injection and production wells were far from each other, the oil production was governed by displacement for quite a long time rather than the gravity drainage enhanced by the VAPEX process. Also, improper location of the injection and production wells may results in the shortcut between injector and producer, which would lead to early solvent breakthrough and increased gas production through the system. The well location is a critical issue when applying the VAPEX process in fractured systems.