Evaluation of Compact Steam/Water Separation Equipment for Gas/Oil Systems

Abstract

Abstract The possibility of using existing steam/water separation equipment for compact gas/oil separation applications has been evaluated and is believed feasible. A single separator pair operating at 880 psia is estimated to have a separation capacity of 28,000 BPD oil and 15 MMSCFD gas for a water drive reservoir, and 17,000 BPD oil and 15 MMSCFD gas for a gas drive reservoir. Larger capacities are expected at lower pressure. Efficient separation is expected over a wide range of flows, liquid levels, and pressures. The vertical orientation of the separator allows it to be contained within a 24-inch diameter pressure vessel. Potential areas where this compact separation equipment may be beneficial include primary separation for minimum facility platforms, vertical high pressure gas/liquid separation, retrofit/add-on capacity, combined slug suppression and preseparation, gas/liquid separation for floating production systems and subsea applications. The major benefits are expected to be its compactness, small footprint and weight, and the modularity of the design. Introduction The development of offshore gas and oil reserves continues to move into deeper waters and marginal fields, The economics of many of these fields does not justify the use of conventional fixed leg platforms. Consequently, many of the fields tie-back to existing host platforms where available production capacity can be used, In some cases a minimum facility platform will be located between the wellhead and the host with some amount of processing taking place on this smaller platform. When a host with adequate production capacity is not available, options such as floating production facilities are considered. In recent years these have become widely used for small fields and deep water. Subsea processing may also be considered. One of the subsea processing techniques uses subsea separation and single-phase pumping to facilitate the transport of fluids from the subsea completed wells to a distant location for further processing. The ability to tie-in to an existing host platform can be limited by available processing capacity. Modifications to the processing stream are often required to maximize the capacity for the available space. Minimum facility platforms by their definition are to be compact, yet they typically use large, heavy production equipment. Floating production systems must cope with the motions of the vessel and during severe sea conditions this can lead to a shutdown of the production equipment. Subsea separation faces challenges in equipment reliability and ensuring a robust design due to its limited access. Clearly, the future economic development of gas and oil reserves will require innovative solutions in the area of separation technology. Because of Babcock & Wilcox's parent company, McDermott International, involvement in deepwater development, the possibility of applying compact steam/water separation technology to gas and oil production was evaluated. When the feasibility of this technology is demonstrated, it will represent a cost-effective solution for several gas/oil applications. Description of Steam/Water Separation Equipment High-efficiency separation is critical in most boiler applications to prevent water droplet carryover into the superheater, minimize steam carryunder in the water, and to prevent the carryover of solids dissolved in entrained water droplets from entering the superheater and turbine where damaging deposits may form. Steam-water separation typically takes place in two stages. The primary separation removes nearly all the water from the steam, however the steam leaving the primary separator still typically contains to much liquid in the form of contaminant containing droplets for satisfactory superheater and turbine performance. Therefore, the steam is passed through a secondary set of separators, or scrubbers, for final water droplet removal. P. 351