Subsea separation has successfully been implemented on the Troll and Tordis fields operated by Statoil, Pazflor (Total), Marlim (Petrobras), and Perdido and Parque das Conchas/BC-10 (Shell). One objective of subsea separation is to separate gas and liquid to optimize working conditions for subsea pumps enabling high recovery factors. The objective of this work was to qualify a two-stage, compact, inline gas-liquid separation system with full turndown and slug handling capabilities, consisting of already proven components: one Gas-Liquid Cylindrical Cyclone (GLCC) and one InLine DeLiquidiser.CompactSep and its separator components and control system were qualified through a comprehensive, large-scale, real fluid and high pressure test programme at K-lab, a Statoil large scale test facility in Norway. This was done in a Joint Industry Project with Statoil as operator and Chevron, Petrobras, Total, and FMC Technologies as participants. The tests were performed with realistic fluids -59°API condensate and 25°API crude, recombined with natural gas -and at realistic pressure conditions, from 25 to 90 bar, with and without inlet slug flow. The separation requirements for the CompactSep system were a liquid output with gas volume fraction GVF Ͻ 0.1 and gas output with gas volume fraction GVF Ͼ 0.995 downstream the separator system. The pressure drop limits were 2 bar (soft target) and 5 bar (hard limit). Separate and stricter requirements were set for the system's individual separator components.The main results were: a wide operating range where the performance requirements were fulfilled, 99% to 99.9% separation efficiency, gas qualities (GVF) between 0.995 and 0.999, and liquid qualities (GVF) between 0.02 and 0.1. The operational boundaries were challenged to determine the onset of liquid carry over and gas carry under. The actual operating range exceeded the design and performance predictions. The system handled slugging and start-up scenarios. The control system stabilized the process with relatively slow control valves.The work developed and qualified an inline separator system with full turndown and slug handling capability. Qualification was performed at a wide range of realistic conditions and with high quality reference and performance measurements. Comparison of CompactSep and conventional subsea separation stations shows significant cost and weight reductions for the compact solution. What can be done subsea can be done topside. The CompactSep separator is a viable alternative to conventional vessels for topside applications where size and weight must be limited.

Several fields on the Norwegian Continental Shelf are in the decline phase with an increasing production of water and gas, often in combination with reduction in production pressure. The available area and weight for installation of new equipment on the platforms is often limited, and it is important to minimize both the operational and capital costs. Compact, inline separation devices can be a key technology for mature fields, and also for subsea fields at large water depths where the weight is critical. The Statoil operated Gullfaks licence has identified compact separation as a key technology to increase the oil recovery. Due to low foot print and low operating cost the technology can aid prolonged production from the reservoir. The technology will also make it easier to use the existing infrastructure at Gullfaks for tie-in of new fields. A survey identified a need for both compact gas/liquid as well as compact oil/water separation. Statoil has chosen to test and develop relevant units in close co-operation with vendors of compact separation equipment. All the tested technologies are based on cyclonic separation devices with low or moderate pressure drops. Statoil is carrying out an extensive qualification program where selected compact solutions for several unit operations are developed and tested at real operating conditions. The tests have been done in high pressure laboratory flow loops as well as offshore at the Gullfaks field. The compact technology has been tested for a wide operational window, showing that efficient processing of well stream can be achieved using compact separation equipment. The results from this work leads to the conclusion that compact technology has a large potential both in replacing conventional gravity separators topside and for deep water subsea separation. Introduction Several oil fields world wide are in the decline phase with an increasing production of water and gas, often in combination with reduction in production pressure. Increasing water cut means that water occupies a large part of the separator volume, which otherwise could have been used for 3rd party processing or for low pressure production. Due to low weight, low foot print and use of piping code, compact separation units can provide new processing capacity at existing installations as well as debottlenecking of existing separation equipment. The Norwegian offshore field Gullfaks is one of the fields that have reached tail-end production. They started up in 1986 and with a peak production of 600.000 bpd oil in 1994. In 2008 the oil production was reduced to 92.000 bpd. The Gullfaks field consists of three concrete platforms, see illustration in Figure 1. The oil is stored in the concrete cells and loaded into shuttle tankers on the field, while associated gas is piped to the Kårstø gas treatment plant on the Norwegian west coast, and then further to continental Europe. Three satellite fields have been developed with subsea wells remotely controlled from the Gullfaks A and C platforms. The recovery factor on Gullfaks is 59 per cent, however the aim is to increase it to 62 per cent.