Polymeric damage is due to inconsistent or incomplete breaks of stimulation fluids as well as dynamically formed filter-cakes produced by drill-in fluids or drilling muds. Several methods have been employed with limited success to remove polymeric damage in an effort to increase well productivity.
Prior treatments to remove this type of damage consist either of bleach (sodium hypchlorite) or acids. In case of horizontal wells with slotted liners or screens bleach or acids are not preferred. Additional expensive trips have become mandatory when coiled tubing or drill-pipe are utilized for spotting the treatment. Additionally, the mineralogy of some formations precludes the use of acids.
Recent extensive research was conducted to develop a treatment which could effectively reduce this type of polymeric damage in either horizontal or fracture stimulated wells. Core flow evaluations and regained conductivity testing have shown that multi-fold improvements can be achieved even at elevated temperatures exceeding 250 °F and over a wide pH range.
A case study of several low productivity wells suffering from polymeric damage was conducted. Post-frac production histories and return flow analysts were evaluated to characterize the damage and guide the remedial treatment design. A detailed study of field case histories including 11 fracture stimulated wells, which were suffering from polymeric damage, are presented and demonstrate how multi-fold improvements in well productivity could be achieved.
Polymeric damage to proppant pack and formation permeability can significantly decrease well production. Insufficient gel degradation of drilling, completion, or stimulation fluids and dynamically formed filter cakes are responsible for impaired hydrocarbon recovery.1–3
Polymers are frequently employed within this industry for drilling, completion and stimulation operations. The polymers used are selected based upon their ability to provide viscositication, proppant transport and/or suspension, fluid loss control and zonal isolation. Yet the very properties for which they are chosen also make them difficult to break down following their application. Unbroken filter cake and insoluble high molecular weight polymer fragments are just two forms of damage produced by polymers. It is these residual effects of polymers that are responsible for reducing productivity through damage to a formation's permeability and conductivity.
Hydraulic fracturing is one application through which significant polymer damage can occur. Treatments usually require gel systems utilizing high polymer loadings, yielding tremendous viscosity, in order to propagate the fracture and transport proppant therein. Due to the effects of fracturing treatments, such as fluid leak-off and fracture volume reduction upon closure, the polymer becomes concentrated on the formation face and within the proppant pack. At times the concentration of this polymeric filter cake becomes so high that breaker additives are no longer able to thoroughly degrade it. The goal then becomes the reduction or removal of the polymer damage in order to obtain optimum productivity in the most cost-effective manner.
Filter cakes are dense and are a practically insoluble concentration of polymer deposited on the fracture face. Concentrations of tilter cake can range from about 10 to greater than 25 times the surface polymer concentration depending on the formation permeability and fluids efficiency.4,5
