Stimulation in High Water-Cut Wells: Treatment Optimization Using a Fluid Placement Model

Abstract

This work discusses application of an advanced placement model for optimizing stimulation treatments in high water-cut wells. Stimulation treatments in high water-cut wells are challenging because they can lead to an undesired increase in water production. Associative polymers have been successfully used as diverters for addressing this challenge, and effective treatments have been performed based on experience and guidelines. However, further optimization of such treatments can be achieved using fluid placement models. Model-based treatment design has been described previously but has not been comprehensively applied for diversion by associative polymers. In this work, a transport model was developed for relative water permeability reduction by associative polymers and diversion of stimulation fluids in the pay zone. The model accounted for the mass transport and adsorption of the polymer in the formation. The transport model was integrated into a near-wellbore (NWB) fluid placement model to simulate fluid distribution in a heterogeneous layered reservoir and the effect on total skin, production/injection profiles, and surface/bottomhole pressures (BHPs) during the treatment. The paper describes case studies based on actual field treatments to demonstrate the application of the integrated model for optimizing stimulation treatments. Acid-to-diverter stage volumes, number of diverter stages, polymer concentration, and injection rates are identified as important design parameters. Based on model results, it is observed that polymer placement results in increased total skin in water-bearing zones, leading to lower post-treatment water production. Further, the optimum number and volume of diverter stages for effective diversion vary with injection rate and are governed by the non-equilibrium polymer adsorption behavior and the self-diversion effect during placement. It is concluded a single treatment design might not be suitable across multiple wells, and well-specific optimization of the pumping schedule is necessary. Because multiple parameters affect the treatment, simultaneously leading to results that are not intuitive, the placement model should be used for the treatment design. This paper discusses application of an advanced fluid placement model, which provides insight into the diversion by associative polymers during stimulation treatments. The model is useful for optimizing stimulation treatments in wells with high water cut and reducing costs associated with undesired water production.

Rock/Fluid/Polymer Interaction Mechanisms: Implications for Water Shut-off Treatment

“…As the RPM injection rate increases, the adsorption amount and the adsorption hydrodynamic thickness gradually increase, consequently causing more permeability reduction. ,, It has been reported that extensional flows can stretch and orientate the chains/macromolecule of flexible polymers (such as polyacrylamide and poly­(ethylene oxide)). This is also called shear-induced elongation. ,,− Polymer molecules can be imagined as entangled coils.…”

“…Wall effects have been recognized as an important post-treatment factor. Generally, it is agreed that wall effects appear due to the presence of the layer of the adsorbed polymer on the pore walls. ,− ,,,,,,,− The wall effect of RPMs can cause a noticeable reduction to water relative permeability but a minimum effect on oil/gas relative permeability due to the physical or chemical properties of the adsorbed layer . It is claimed that the wall effect is expected to induce one or a combination of subeffects that altogether determine the outcome of RPM treatment, and these include the following:…”