Summary Progressing into deeper water and more hostile environments in the search for new oil and gas reserves has placed an increasing demand on the 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 deoiling hydrocyclone and discusses system design, early operational experiences, and test results from the first full-scale commercial application of the four-in-one hydrocyclone concept on the Murchison platform. In addition, and of perhaps more significance, early results from field tests of the larger 60-mm [2.4-in.] cyclones on the Hutton tension leg platform (TLP), where conventional equipment was adversely affected by platform motion, are discussed. Introduction Produced water represents an increasing portion of the total produced fluids during the life of a field. Although the treatment of produced water offers no direct economic incentive, a considerable portion of both engineering and operations time is spent modifying and maintaining produced-water cleanup systems to ensure satisfactory operation. In the Murchison field, although the existing system performed adequately, albeit through labor-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 important, the platform could not achieve the U.K. Dept. 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 cleanup revealed that the hydrocyclone separator warranted serious consideration. Our first experience with hydrocyclones was with pilot plant trials of the Serck-Baker Oilspin developed as a result of an extensive research program conducted at Southampton U. While these tests, carried out on the Murchison and Hutton platforms in early 1985, were not an unqualified success, they demonstrated the equipment's potential and enough encouragement for us to commit to the first full-scale commercial application of the Vortoil trademark four-in-one 35-mm [1.4-in.] hydrocyclone later that year. The Vortoil hydrocyclone, developed by an Australian company but based on the original Southampton U. design, was considered to be a more refined and advanced product capable not only of achieving the required performance but also of reducing the nursemaid attention associated with more traditional equipment. The many operational advantages of Vortoil make it ideally suitable for a retrofit it situation. However, the true worth of hydrocyclone technology should be realized 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.

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Summary Dubai Petroleum Co. (DPC) performed two in-situ offshore separator retrofit projects during 1989-91. Significant cost savings were achieved over the alternatives of separator replacement, addition, or modification onshore. The retrofits were accomplished without production loss or compromised operating safety. DPC's experience demonstrates that in-situ offshore facility modifications can be done successfully and simultaneously with normal operations. Improved performance after the retrofits strongly supports the need for properly designed internals to realize the full potential of a separator. Although the two retrofits share a common objective, they differ significantly in design, planning, and execution. First, a three-phase separator critical for uninterrupted production was modified during a 6-day scheduled fieldwide shutdown using only "cold work." This was followed by the conversion of a two-phase, double-barrel separator to three-phase service without a field shutdown. The work took place during 6 months with the use of "hot work." The success of both field modifications was attributed to innovative engineering and careful planning. Introduction Production is gathered from 67 platforms offshore Dubai, through a network of subsea multiphase pipelines to the central facilities at Fateh and S.W. Fateh (Fig. 1). Gas is separated and compressed for gas lift and pipeline export. Water is removed, processed, and disposed overboard. Separated oil from the S.W. Fateh central facilities is pumped to Fateh for further stabilization, dehydration, storage, and tanker offtake in three "khazzans." Khazzans are large, openbottom, underwater storage containers that resemble inverted champagne glasses. The oil floats on top of the water within the khazzans and displaces seawater out the bottom as more oil is introduced. During the 6 or more hours that the oil resides in the khazzans, its basic sediment and water (BS&W) is reduced to less than 0.5% for tanker sale. Before 1987, all production separators in the system operated in the two-phase mode. They removed the gas from the produced fluid before it was sent to the khazzans. Oil and water separation took place entirely in the khazzans. This method of water separation and disposal was abandoned for three-phase separation when water production increased to levels that exceeded the capacity of the khazzans.

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