Solution-Gas Drive in Heavy Oil: Field Prediction and Sensitivity Studies Using Low Gas Relative Permeability
Authors: Kumar R. , Pooladi-Darvish M. 
Published: March 2010

Abstract
The favourable behaviour of heavy oil reservoirs under solution- gas drive has intrigued the oil industry for a long time. Many mechanistic models have been proposed to explain this behaviour. This paper investigates one of the theories that attributes the low producing GOR and high recovery of heavy oil to low gas mobility.
A simulation study was carried out on a commercial black oil simulator to match the "typical" production data of heavy oil fields in Lindbergh and Frog Lake. Sensitivity studies were carried out to investigate the effect of gas relative permeability on oil recovery. The effect of sand production, which is an integral part of heavy oil production in Western Canada, was also investigated. A parameter was used in the simulator to account for the increased permeability due to sand production.
The results indicate that the field performance can be matched by using low gas mobility and incorporating improved permeability due to sand production. Neither of them alone was sufficient for matching the field performance. The use of a low gas mobility was successful to explain high pressure-gradients in the field, by acting as a pressure maintenance mechanism, and leading to a high recovery under solution-gas drive.

Intruduction
PanCanadian has been one of the major operators in the Lindbergh and Frog Lake heavy oil fields of northeast Alberta(1). The production in these fields is from the Upper Mannville group. The producing formations contain oil of 12 – 14 ° API with in situ viscosities of 3,000 – 10,000 cp. The fields have shown recovery much in excess of what can be predicted by applying conventional flow equations. Many heavy oil wells under primary production have produced about 15% of the original oil in place (OOIP) in 10 years(1). The primary oil production in these fields is accompanied by sand production and is called "Cold Production." A typical well in the Lindbergh and Frog Lake fields under depletion has produced an average of 9,200 m3 of oil and about 230 m3 of sand in 1,000 days(1).
Several tests have been carried out to determine the mechanism responsible for the favourable behaviour of these reservoirs. Metwally and Solanki(1) presented a simulation model to match the field production behaviour. The authors postulated that reservoir porosity and permeability are increased due to sand production. Additionally, the authors showed that a pressure support mechanism needs to be incorporated to match recovery data; an external aquifer was therefore incorporated into the model.
Similar to Metwally and Solanki(1), we use a commercial simulator to match the production data. We show that the use of low values for gas relative permeability results in pressure maintenance and substantial oil production. Accounting for the low gas mobility along with the improved permeability resulted in a match of the field data. Sensitivity studies are reported, which show that both the effects of low gas mobility and improved permeability are required for a match.