How To Apply the Flow Velocity as a Design Criterion in RPM Treatments

Abstract

Summary The effect of water control using relative permeability modification (RPM) depends strongly on the well's flow rate because the permeability reduction decreases as the flow velocity increases. This will affect the volume and the properties of the injected RPM fluid. This paper discusses how the velocity-dependent permeability reduction can be accounted for in the job design. The approach is to introduce a velocity-dependent permeability reduction and to solve the Darcy law for non-Newtonian flow. Coreflood experiments report permeability reduction as residual resistance factors (RRFw and RRFo). In scaling up to field situations, the reduction in productivity is a better measure. Designing an RPM treatment to a fixed reduction in water productivity demonstrated that low-volume, high permeability reduction is better than larger volumes with lower permeability reduction. In highly productive wells, there may be situations where certain RPM systems fail to reduce the water productivity adequately. By including pressure constraints on the injection of the RPM fluid, the planned pumping schedule is derived. The criteria for increased oil production are reported as a balance between (1) increased drawdown based on the water-cut reduction and improved lift and (2) reduction in oil productivity. The critical oil productivity depends on the water productivity, initial water cut, density difference between the water and the hydrocarbon phases, and true vertical depth (TVD). It is clearly demonstrated that the potential for increased oil production increases by increasing the ratio between the oil- and the water-productivity reduction (M). In addition, M increases as RRFw increases and the treatment volume decreases. The time to restore the productivity from the oil zone, the cleanup time, can be understood through the fractional-flow theory. In theory, the cleanup time can be derived from relative permeability curves or the saturation profiles during the oil back production. Also, the cleanup time was reduced by the use of low-volume, high water-permeability reduction.