Interest in the subsea deployment of multiphase pumps and wet-gas compressors has grown as companies search for methods to improve recoveries and economics for subsea wells. Subsea pressure boosting technologies are also seen vital in providing access to deepwater oil and stranded gas reservoirs. While multiphase pumping has been proven onshore, operators have been hesitant to deploy this technology subsea due to the high costs and inherent risks associated with the first application of a new technology. This paper examines various types of subsea multiphase pumps and wet-gas compressors and discusses the special issues associated with subsea operation. Multiphase pressure boosting requires wide torque and speed range due to significant load changes, triggered by changes in the gas volume fraction (GVF). This paper introduces and describes a hydrodynamic variable speed drive that can be utilized with both multiphase pumps and wet-gas compressors. This variable speed drive is arranged between a fixed speed motor and the multiphase boosting device and appears to offer several distinct advantages for subsea operation. The Voith Turbo EL6 torque converter was installed and tested with a twin-screw pump under multiphase condition. Results of testing under slug flow conditions are presented along with observations regarding the use of torque converter for speed control.
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