Field Testing a Low Shear Valve Suitable for Polymer Flooding in a Mother Solution Injection Scheme

Abstract

Summary Hydrolyzed polyacrylamides are used as mobility-control agents in polymer flooding operations to improve the macroscopic sweep efficiency of the oil reservoirs. For this, very high molecular-weight polymers are often preferred to maximize their viscosifying power. In return, these long polymer chains are very sensitive to shear degradation which originates from chain stretching and breaking when the solution is subjected to a sudden acceleration. For a mother solution injection scheme, one polymer injection pump is normally installed on each well to inject tailored viscosities. The injection system avoids viscosity loss by injecting a high concentration polymer solution downstream the choke valve. One drawback of this setup, however, is that CAPEX, maintenance and energy demands are usually higher than for a valve-based scheme. In 2012, the development of a low shear valve suitable for polymer flooding was initiated. By employing unique spiraling flow channels with optimally designed reducer and expansion zones, machined on the surface of discs, shear forces and thereby polymer degradation is controlled. During a prototype test using a very shear-sensitive diluted polymer solution, presented in 2019, it was demonstrated that the polymer degradation through the new valve was less than 10 % at up to 45 bar pressure drop, compared with 60 % for a standard valve. In this paper, results from a field test of the novel low shear valve are presented. The low shear valve was installed on a high-concentration mother solution flow line at the Matzen field in Austria. At a flow rate of 1.6 m³/h and polymer concentration of 11800 ppm, the low shear performance of the novel valve was investigated at up to 35 bar pressure drop. Within the design range of up to 20 bar pressure drop, the viscosity degradation through the valve was not higher than 2.7 %. In conclusion, the low footprint valve was found to be easy to connect and operate, and the low shear performance was well within the design criteria. When employing the novel low shear valve in a mother solution application, the one-pump-per-well injection scheme can be replaced with a larger central pumping station plus one low shear valve per well to control the injection viscosity. In this case, the low shear valve has the same low shear performance as the positive displacement pumps. However, compared to the one-pump-per-well scheme, the central pumping station and low shear valves will result in significantly lower CAPEX and maintenance costs.