Hydrocyclones: A Solution to Produced Water Treatment

In light of the progression into deeper water and more hostile environments in the search for new oil and gas reserves, an increasing demand is being placed upon industry to develop lighter, more compact and more efficient process equipment to replace their traditional counterparts. A recent application of cyclone technology for liquid-liquid separation of oil from produced water has shown considerable promise during extensive field testing. This paper outlines the basic construction and principle of operation of the de-oiling hydrocyclone and discusses system design, early operational experiences and test results from the first full scale commercial application of the 4 in 1 hydrocyclone concept on Conoco's Murchison Platform. In addition, and of perhaps more significance, early results from field tests of the larger 60mm cyclones on the Hutton TLP, where conventional equipment was adversely effected by platform motion are discussed. INTRODUCTION Produced water represents an increasing portion of the total produced fluids as time progresses in a field's life. Although offering no direct economic incentive, a considerable portion of both engineering and operations time is spent modifying and maintaining produced water clean up systems to ensure satisfactory operation. In the case of the Murchison field, although the existing system performed adequately, albeit through labour intensive operation, optimum reservoir development required water injection capacity beyond the original design basis. Consequently this created the need to upgrade the capacity of the produced water treatment system. A similar upgrade in water handling capacity was required for the Hutton field, but more importantly the platform could not achieve the U.K. Department of Energy specification for overboard effluent of 40 ppm with the originally installed equipment. Investigations into alternatives to the traditional flotation cells/plate separators for oily-water clean up revealed that the hydrocyclone separator warranted serious consideration. Conoco's first experiences with hydrocyclones was with pilot plant trials of the Serck-Baker Oilspin developed as a result of an extensive research program conducted at Southampton University. While these tests which were carried out on the Murchison and Hutton platforms in early 1985 were not an unqualified success, they demonstrated the equipments potential and Conoco was sufficiently encouraged to commit to the first full-scale commercial application of the 'Vortoil' 4 in 1 35mm hydrocyclone later that year. The 'Vortoil' hydrocyclone developed by BWN, an Australian company, but still based on the original " Southampton design was considered to be a more refined and advanced product not only capable of achieving the required performance but also as a means of reducing the nurse maid attention associated with more traditional equipment. The many operational advantages of 'Vortoil' make it ideally suited for a retro-fit situation. However, the true worth of hydrocyclone technology should be realised on future marginal developments where space and weight are a premium and on floating structures like the Hutton TLP where motion sensitivity is a problem.