Assessment of Vapor Extraction (VAPEX) process performance in naturally fractured reservoirs

The Vapour Assisted Petroleum Extraction (VAPEX) process, a newly developed Enhanced Heavy Oil Recovery process, is a promising EOR method for certain conventional non-fractured heavy oil sandstone reservoirs such as those in Canada, but its applicability on low permeable Naturally Fractured Reservoirs (NFR) such as those in the Middle East and Persian Gulf still remained as a question. Previous studies show that the foremost concern for VAPEX application in the case of NFR is the low non-economical production rates. The aim of the present work is to study the effect of fractures geometrical properties such as orientation (vertical or horizontal), density, spacing, location and networking on the performance of the VAPEX process in low permeable naturally fractured laboratory scale models. To approach the problem, a simulation model was developed and validated according to the previously published VAPEX conventional and fractured experiments. Further, this validated model has been modified to include the inhabitant countercurrent drainage mechanism of VAPEX which has not been considered in the previously published fractured models of VAPEX. Simulation analysis showed that contrary to the horizontal fractures, VAPEX process recovery enhanced in the presence of vertical fractures as compared to the case of conventional model. Fracture spacing was an important parameter on the performance of VAPEX since higher production rates achieved in the case of higher density of vertical fractures. Contrary to this, oil recovery decreased in the case of higher density of horizontal fractures inside the model. Vertical fractures improved the recovery performance of the model in the case of networked fractures as compared to the case of horizontal fractures model. Finally the effects of operational parameters such as vertical offset between two stacked wells and also the application of staggered wells configuration in the case of networked fractures have been investigated. Simulation results confirmed the importance of these parameters to enhance the recovery performance of VAPEX in the presence of fracture network. (C) 2010 Elsevier B.V. All rights reserved.