Abstract
Gas shut off technology for wells with a high gas/oil ratio is extremely valuable to improve oil production and reduce environmental pollution. Foam treatments have been applied to reduce unwanted gas inflow. However, results have not always been favorable. This paper presents a field case supported by a modeling study of successful foam shut-off treatments carried out in the South Chinese Sea. This study shows that the possibility of success of gas-shut-off treatments can be greatly enhanced by having a good understanding of the process parameters. In the Champion field, Brunei, an increasing number of oil wells are shut in due to high gas/oil ratio. In November 1998, three wells were treated with a surfactant/polymer (foam) solution in water, co-injected with nitrogen. In two wells the gas/oil ratio was substantially reduced but also a significant loss in oil productivity was observed, which partly restored in the course of time. The treatments were based on laboratory core flow experiments under reservoir conditions. The experiments served to design the field trials and as input data for simulations with a numerical radial well model, which was used to interpret the field trials. The reduction in gas mobility by a factor between 2 and 10 as observed in the field is consistent with the results of the laboratory experiments.
The study identifies the permeability and temperature window and the type of geological setting and well configuration for which the applied foam system will be successful. This is essential to screen potential candidate wells. It will be shown that in future treatments less damage to the oil productivity and lower costs are possible by omitting nitrogen gas and by reducing the injected volumes.
