Paper: Field Results of a Short Setting Time Polymer Placement Technique

Newly drilled water injection wells in the Shell operated Jordan University Unit in the Jordan(San Andres) Field of West Texas exhibited thin intervals of high permeability (and poor profiles) soon after injectivity began (Fig. 1). The wells had been selectively acidized (straddle packers were used to isolate each perforation while acidizing) with surface pressures of not more than 500 psi. Since fiberglass casing was cemented across the entire injection interval, the use of cement to squeeze off selected perforations (prior to reacidizing perforations not taking water) was not feasible because of its high density and hard set. A plugging material with a low viscosity and a specific gravity approaching that of fresh water was needed in order to plug the rock matrix near the wellbore. A crosslinked polymer was used because its specific gravity and viscosity approach that of fresh water, and it is a non-particulate. Therefore, the polymer could be used without hydraulically fracturing the rock or "plating out" on the wellbore face. The use of polymers in injection well profile control has been well-documented in previous publications. A different method of application of a crosslinked, stiff gel polymer (American Cyanamid Company AM-9 Chemical Grout) was successfully used to alter injection profiles in the three San Andres dolomite water injection wells. Proven fluid design techniques were successfully used to premix a gel solution and a catalyst solution at the surface ("on the fly") for a downhole (3800 ft) setting time of approximately 20 min. at 90" F. The resulting solution had low viscosity pumping characteristics, yet rapidly increased in viscosity at the desired setting time. Consequently, the solution pumping characteristics were also similar to fresh water. In addition, an under displacement gel placement technique was utilized to assure that uncontaminated polymer was gelled in the pore network (within a radius of 6 to 8 ft) and back into the wellbore. The under displacement technique and reacidizing of old tight perforations were the keys to injection well profile change in the Jordan University Unit. Production history data from wells surrounding the three injectors reflect an increase of approximately 550 BOPD over an 18-month period. The increase in oil production is a direct result of injection well profile improvement. See Table 1 for an economic analysis of the cost of the three worked-over injection wells and of the production results associated with the 16 surrounding producing wells.