Summary In this paper we present the development and implementation of automatic operation and control for a pump/hydrocyclone produced-water-treatment system to maximize oil/water-separation efficiency. A so-called perturb-and-observe (P&O) algorithm is adapted for a novel centrifugal pump to continuously optimize the point of operation. The novel pump coalesces and increases the size of oil droplets in the produced water, resulting in a unique relationship between the coalescing effect and the point of operation, and allowing for the successful implementation of the P&O algorithm. The algorithm was implemented in two different setups, one measuring the droplet-size distribution between the hydrocyclone and the pump, and the other measuring the oil concentration downstream of the hydrocyclone. The latter was considered the most robust because it required no prior knowledge of the system. Nonetheless, both setups achieved satisfying results and compared favorably with a third setup, where the optimal point of operation was predicted using measurements of the upstream produced-water characteristics.

Summary A novel centrifugal pump that increases oil-droplet sizes in produced water has been developed. This paper investigates a concept of pumping-pressure optimization, with respect to downstream separation efficiency, for the new pump. The investigation shows that the coalescing centrifugal pump always increased the separation efficiency of a downstream hydrocyclone. Furthermore, it is shown that the pumping pressure can be adjusted to maximize the improvement. Experimental results demonstrate how pumping conditions that minimize the volume fraction of droplets with a diameter smaller than the cut size of the hydrocyclone maximize the separation efficiency. Finally, it is demonstrated how the concept of pumping-pressure optimization can be implemented in a typical produced-water-treatment plant.

Summary Hydrolyzed polyacrylamides (HPAMs) are used as mobility-control agents to improve the macroscopic sweep efficiency of oil reservoirs. To maximize their viscosifying power, very-high-molecular-weight (MW) 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. 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. The work also demonstrates that the creation of pressure drop through viscous pipe friction is very ineffective with regular tubes, most likely because of the drag-reducing effect of polymer. In addition, the arrangement of very long, straight, or coiled pipes in parallel is impractical and bulky. This paper further presents the development of a novel valve technology that solves these challenges. First, through the unique use of spiraling flow channels with optimally designed reducer and expansion zones, machined on the surface of disks, shear forces and thereby polymer degradation is controlled. Second, by arranging numerous such disks to form a disk stack, any target capacity can be met efficiently. Third, the disk-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- to 45-bar pressure drop, compared with 60 to 80% for a standard valve.

This paper presents three variable step size P&O algorithms for optimizing the separation efficiency of a coalescing pump/deoiling hydrocyclone produced water treatment system. By continuously adjusting the pumping pressure, and subsequently the coalescing effect, the algorithms are used to minimize the oil concentration downstream the hydrocyclone. Due to the variable step size, the algorithms react rapidly to changes in the upstream produced water characteristics, at the same time as they reduce (or eliminate) steady-state oscillations. Based on both simulation and experimental testing, the study discusses advantages and disadvantages of the algorithms.

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