The Development of a Low Shear Valve Suitable for Polymer Flooding

Hydrolyzed polyacrylamides are used as mobility control agents to improve the macroscopic sweep efficiency of oil reservoirs. In order to maximize their viscosifying power, very high molecular weight polymers are preferred, which in turn make them very sensitive to shear degradation.

Shear degradation originates from chain stretching and breaking when the solution is subjected to a sudden acceleration. Such extension dominated flow fields are encountered at different locations of surface facilities (mainly in pumps, pipes and valves) and at the wellbore interface. Although CAPEX intensive, the use of one injection pump and line per injector well is a way to control and to minimize polymer degradation. For mature field developments or large fields with long injection lines, it is generally necessary to install a control valve on the wellhead of each well to regulate the injection pressure and flow rate.

In classical chokes used for water flooding, the fluid accelerates strongly in order to create the turbulence required for pressure reduction, which in turn leads to a high degradation of polymer chains. Fundamental development work is presented, where polymer degradation is studied in flow through diffusers and expanders of various geometrical shapes, as well as through straight pipes and pipe coils of various diameters and lengths. Empirical correlations between geometries and polymer degradation are established. In particular, for a given flow capacity, it is found that the optimal geometry of a tube-based throttling device, is a compromise between length, diameter and number of tubes in parallel. Results demonstrate that the creation of pressure drop through viscous pipe friction is very ineffective with tubes of constant diameter, most likely due to the drag reducing effect of polymer flow. In addition, the arrangement of very long, straight or coiled tubes in parallel is impractical and bulky.

A novel valve technology solves these challenges: Firstly, through the unique use of carefully designed contractions evenly spaced in the flow channels, the drag reducing effect is overruled. Secondly, the arrangement of multiple flow channels of certain diameters and lengths, and with optimally designed reducer and expansion zones, resolves itself by using a stack of machined spiral discs. The latter also enables an easy and reliable technical solution for flow and pressure regulation. The efficiency of the new valve technology is demonstrated through small and large-scale prototype tests. Degradation is less than 10% at 40 bar pressure drop compared to 80% for a standard valve.

Hydrolyzed polyacrylamides are used as mobility control agents to improve the macroscopic sweep efficiency of oil reservoirs. In order to maximize their viscosifying power, very high molecular weight polymers are preferred, which in turn make them very sensitive to shear degradation. Shear degradation originates from chain stretching and breaking when the solution is subjected to a sudden acceleration. Such extension dominated flow fields are encountered at different locations of surface facilities (mainly in pumps, pipes and valves) and at the wellbore interface. Although CAPEX intensive, the use of one injection pump and line per injector well is a way to control and to minimize polymer degradation. For mature field developments or large fields with long injection lines, it is generally necessary to install a control valve on the wellhead of each well to regulate the injection pressure and flow rate.

In classical chokes used for water flooding, the fluid accelerates strongly in order to create the turbulence required for pressure reduction, which in turn leads to a high degradation of polymer chains. Fundamental development work is presented, where polymer degradation is studied in flow through reducers and expanders of various geometrical shapes, as well as through straight pipes and pipe coils of various diameters and lengths. Empirical correlations between geometries and polymer degradation are established. In particular, for a given flow capacity, it is found that the optimal geometry of a pipe-based throttling device, is a compromise between length, diameter and number of pipes in parallel. Generally, the work also demonstrates that the creation of pressure drop through viscous pipe friction is very ineffective with regular tubes, most likely due to the drag reducing effect of polymer flow. In addition, the arrangement of very long, straight or coiled pipes in parallel is impractical and bulky.

This paper presents the development of a novel valve technology that solves these challenges. Firstly, through the unique use of spiralling flow channels with optimally designed reducer and expansion zones, machined on the surface of discs, shear forces and thereby polymer degradation is controlled. Secondly, the arrangement of numerous such disc forming a disc-stack, any target capacity can be met efficiently. Thirdly, the disc-stack concept enables an easy and reliable plug-based solution for flow regulation and control. The performance of the new valve technology is demonstrated through small and large-scale prototype tests. At very shear sensitive test conditions, it is demonstrated that polymer degradation of the new valve is less than 10 % at 40–45 bar pressure drop, compared to 60–80 % for a standard valve.