Optimizations in the Design and Operation of an Offshore Hydraulic Pumping System

Abstract

ABSTRACT This paper presents an overview of the design and operation of an offshore hydraulic pumping system on UNOCAL's Platform Eva when it was converted from a power oil to a power water system in 1983. Also described is useful economic and operational information obtained from UNOCAL's experience with the system since the switchover. The new system exhibits several special features in the design and operation of an offshore hydraulic power water system. Emphasis was placed on maximizing operational efficiency, cost reduction, safety, and the efficient use of deck space. Platform Eva was refitted with canned electrical submersible pumps, designed within the constraints of limited deck space, electrical switchgear rating, and power fluid properties. An evaluation was performed leading to the selection of produced water as power fluid over fresh water and sea water. Guidelines for good power water quality have been established by UNOCAL's Research Department, specifying fluid solid content, oil content, and lubricity level. A new oil field filter has been introduced and used successfully to achieve the required power water quality and improved downhole pump life. In a joint effort with pump manufacturers, the normal downhole pump life has been improved over 100% with metallurgical and mechanical improvements in the standard pump system. Severe problems with tubing leaks occurred shortly after the switchover from oil to water. These problems were traced to small amounts of CO2 breaking out at low pressures in the turbulent regime of the fluid stream and were eliminated. Failure of splash zone coating caused by thermal stresses and improvements there of are also described. Despite optimizations that improved operational efficiency of the power water system, a comparative analysis of the old and the new systems shows several economical and operational advantages of using power oil over power water as a hydraulic power fluid. The power oil system, however, is potentially a higher safety risk.