Water control in gas wells is a major measure to enhance gas recovery. The work is concentrated on finding a highly selective polymer to reduce water production without affecting gas production from gas wells in low-permeability reservoirs. This paper presents the conceptions of residual resistance factors (RRF's) to both wetting and nonwetting phases and the laboratory experimental and field trial results of relative permeability modifiers for water control in gas wells.
Relative permeability modifiers are the products of selectively reducing the permeability to water phase rather than to the permeability to oil or gas phase. Some high-molecular-weight water-soluble polymers are considered as relative permeability modifiers and known to block water in production wells effectively. Using chemicals to block water in producing wells will run the risk of reducing well productivities and blocking of bearing zones correspondingly. Fortunately, laboratory tests and field results have shown that some polymers and polymer gels can selectively reduce water mobility by reduction of relative permeability to the water without significant effect on the relative permeability to oil or gas phase. The chemicals will give rise to a great potential to improve oil/gas recovery and reduce water-treatment costs in the petroleum industry.
Fletcher and Owens measured polymer/oil relative permeability curves using six different polyacrylamide polymers in both water-wet and oil-wet cores. The water relative permeability curve for water-wet systems was much lower after polymer contact than that before polymer contact. No significant effect on the oil permeability curve was observed. Dunlap et al. reported that after amphoteric polymeric material treatment the water relative permeability achieved a reduction factor of 2 to 9 with little effect on the oil relative permeability. It was suggested that the material had strong absorption on the formation. Zaitoun and Kohler reported that a new polyacrylamide can reduce water relative permeability while increasing the permeability to gas applied in water/gas system. Nevertheless, a few field applications of relative permeability modifiers have been reported in the petroleum literature, especially for water-cut reduction in gas wells.