Water production from oil and gas wells is an increasing problem for the oil industry. Many solutions to the problem have been proposed and some techniques have been successfully introduced into operations. These successful techniques generally require well interventions to isolate target zones and to place the treatments. However, the associated costs may inhibit the treatments from being economic. A bullhead type chemical treatment that selectively reduces water production appears to be a more attractive alternative. These systems are known as relative permeability modifiers.
This paper focuses on relative permeability modifiers from a reservoir and production engineering perspective. The concepts behind relative permeability and its effect on hydrocarbon production and recovery are briefly discussed. Existing experimental data and history matching were used to obtain relative and modified relative permeability curves. Subsequently, these relative permeability curves were used to identify conditions where relative permeability modifiers can be used with potential for success.
Water production compromises the profitability of oil- or gas-producing wells. On a larger scale the production of unwanted water and gas can reduce the sweep efficiency and consequently reduce the ultimate recovery from hydrocarbon reservoirs. Although prevention is usually more effective than treating, excessive water production is most often treated rather than prevented.
Most water and gas control well interventions make use of selective placement or zonal isolation. For example, if a well has multiple sets of perforations, a full blocking polymer gel system should only be placed in a reservoir zone that produces water. This can be achieved with the use of an inflatable packer, a bridge plug or sand plug. Many wells, however, have a completion that does not allow a selective placement of a water or gas control system. In openhole completions, for instance, it is difficult to use bridge plugs or inflatable packers. Other examples are gravel pack completions where it is difficult to selectively place fluids. ID-restrictions, moreover, can be the limiting factor in the application of bridge plugs or packers and consequently prohibit selective placement.
Several decades of research resulted in chemicals that can reduce the permeability to water without significantly effecting the permeability to oil1,2. These systems are referred to as relative permeability modifiers (RPMs). It is asserted that relative permeability modifiers can be placed in production wells without the need for zonal isolation. The thought behind the use of these systems is that if they are placed in a water-producing zone, the productivity of this zone will be reduced significantly. Since the system is placed without zonal isolation, it will also enter the oil-producing zones. Because the systems are designed to only reduce the water permeability, the productivity of the oil-bearing layers should not be affected. There are, however, limitations on the use of relative permeability modifiers. Several researchers3,4,5 have presented guidelines for the application of relative permeability modifiers. In this paper the authors present refined guidelines and some focal points for future research.