Heavy oil recovery with overlying gas cap

In doing a literature search, I ran across an interesting article (SPE 111367) presented at the 2007 SPE/EAGE Reservoir Characterization and Simulation Conference in Abu Dhabi, where the reservoir history of the subject study included conventional primary depletion with unrecovered heavy oil deposits and a resulting gas cap. While not an uncommon scenario, there has not been a lot of research or methods proven in recovering the more viscous heavy oil in the presence of a large gas cap.

The paper outlines a study that investigated the applicability of the VAPEX process including developing a numerical model via experimental data and a screening study of the VAPEX process applied to real reservoirs by using the simulation model.

The study results showed that while a small gas cap can be advantageous and improve heavy oil recovery, there is a threshold value for the ratio of gas to oil volume (GOR) above which the VAPEX process loses its efficiency.

While more lab and field research is needed, the article would indicate that any application of VAPEX in combination with other heavy oil recovery methods (especially in complex reservoir environments) will be more likely to succeed with improved reservoir characterization and the use of numerical modeling for sensitivity and screening analysis.

Kambiz.