Large heavy oil resource presents in reservoirs containing overlying gas cap. However, production from such reservoir is challenging. At the moment there is no proven recovery technique that can be successfully applied to these viscose oil reserves. Recently, vapour extraction process (Vapex) is introduced as an attractive alternative method for such problematic reservoirs.

The objective of this study is to investigate the applicability of Vapex process in reservoirs containing gas cap. This paper is grouped into two parts (i) developing a validated numerical model via experimental data to carry out sensitivity analysis of different parameters which are expensive and difficult to perform on experimental setup (ii) screening study of the Vapex process to real reservoir by using simulation model.

The results show that small gas cap can even be advantageous in this process and improves the recovery by expending the interfacial mass transfer rate and the inter-well communication. In addition, there is a threshold value for the ratio of initial gas to oil volume which beyond that the process loses its efficiency. Moreover, increasing the lateral spacing between the injector and producer is not beneficial in the presence of a small gas cap.

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