Numerical Simulation Study of Water Shut-Off Treatment Using Polymers

Abstract

Abstract Polymers are frequently used to treat high water-cut producing wells in an effort to reduce water production. The application of polymer solution was reported to be successful in some cases but disappointing in others. This study applies numerical simulation to investigate the effectiveness of the polymer treatment for reducing water production from oil wells with water coning and from waterflood producers. The results of the study show that near-wellbore, non-gel type polymer treatment in lowering water production can only be effective for a period of time. The water production will gradually rise to and exceed the pre- treatment level. An effective treatment requires deep polymer penetration in the formation to reduce water coning and the water production from waterflood producers. Water coning heightens at high production rates, low perforation intervals, high oil-water viscosity ratios, etc. The polymer treatment is not very effective for the wells with severe water coning problems. Introduction The economic life of an oil well in a waterflood project or aquifer water- drive field normally ends when too much water is produced from the well. Besides the mechanical methods, such as cement plugs, chemical methods by polymer injection are frequently used to treat the high-water-cut producing well in an effort to reduce water production. Polymers are applied either in the form of polymer solutions or as monomer solutions to form polymer gels in situ. Application of polymer solution to reduce water production was reported to be highly successful in some cases but somewhat disappointing in others. Causes of discrepancies were the subjects of several studies, most of them involving lab experimentation and field tests. This study, on the other hand, applies numerical simulation to predict how the long-term production is affected by the polymer treatment under various reservoir and operational conditions. The principle of the non-gel type polymer treatment is based on the findings that polymer solutions can substantially decrease the permeability of a reservoir rock matrix to water while only slightly reducing the permeability to oil. In one study, the relative permeability to brine was reduced by as much as 60 to 95 percent whereas the relative permeability to oil was only reduced less than 15 percent. Others also reported a several fold reduction in water relative permeability with little effect on oil relative permeability due to polymer solution injection. P. 129^