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Abstract Recent deepwater projects are considering Subsea Gas-Liquid Separation aspotential technology to unlock oil reserves. Eni e&p is currently workingon R&D and development studies to evaluate the benefit of this technologyfor a number of representative assets in its deepwater portfolio. The paper presents several findings of this original analysis. Case studies arerepresentative of a wide range of potential applications: from secondarytiebacks in standard deepwater depth to 1500 m water depth oil developmentapplications and heavy/difficult oil cases to condensate/gas fieldsapplications. The results are presented with the comparisons between standard deepwaterarchitectures and configurations based on Subsea Gas-Liquid separation in termsof flowassurance strategy, field layout, capital costs and benefits for theoperators in terms of potential additional recovery and production. SubseaGas-Liquid separation may become an enabling technology for deepwaterdevelopments if oil industry is able to resolve and mitigate possible risksassociated. INTRODUCTION Subsea processing coupled with innovative field architectures are one of themost attractive tools currently being utilized and considered by the oil andgas industry to open new opportunities and achieve more effective exploitationof offshore fields. Every day new oil and gas reservoirs are being discoveredin unconventional and remote areas in deep and ultra-deep water, typically farfrom existing treating and storage facilities. Subsea processing technologiesare becoming faster and faster applicable options to improve technical andeconomic performance of those challenging subsea field developments, improvingthe reserves recovery and operation strategy, and, in some cases, reducing theassociated development CAPEX. The term " subsea processing" can be defined as any treatment of the producedfluids performed on the seabed prior to reaching the offshore installation andthe conventional surface process facility. Different devices have beenqualified and installed to boost the raw wellstream, like subsea multiphasepumps and wet gas compressors. In the last ten years, technologies to separatethe gas phase from a liquid stream and produced water from hydrocarbons rapidlyevolved thanks to great efforts on qualification program and testing campaign. Moreover, a few installations of separation and boosting devices have beenachieved, presenting really encouraging results but not neglecting operationalissues they have encountered during field life.

Abstract The use of subsea technologies and innovative field architectures as development solutions for oil and gas fields is fast becoming a reality. In the last ten years more than half of new global oil and gas reserves have been discovered offshore, especially in deepwater. This paper shows the selection path followed systematically for the proper technical and economical solution selection, passing through concept screening and case-specific conceptual studies. A typical case study will be presented in this paper, showing the advantages to be gained in using the proposed selection exercise, including flow assurance strategies, for the development of challenging new upcoming reserves deepwater. The values presented are for a generic offshore development. The purpose is to pinpoint the limits of existing technologies, identify new subsea architectures implementing upcoming subsea processing solutions and compare and illustrate the performances of several configurations for a development in about 1000 m of water, through a case study. A problematic oil will be considered, having a density in the range of 20–30 °API, a GOR in the range of 200–400 scf/bbl, wax and hydrate formation risk. Total liquid flowrate in the example is around 50,000 bbl/d, selected in order to be out of giant project frame. Conventional loop, single production line, electrical heating, gas/liquid separation, subsea liquid or multiphase boosting are the scrutinized solutions, applied considering on site or long distance topside facilities and upward or downward production line path. The analysis reported in this paper evidences the technical feasibility and when benefits are obtainable implementing subsea processing technology on offshore oil and gas fields. The principles described could be the base to perform a multi-parameters study for real case technology selection. This paper examines the drawbacks, limitations and advantages of various field architectures and technology solutions, that may be considered for deepwater oil development. It covers the different production phases, from start-up to tail production, without forgetting flow assurance issues, typical of long satellite tie-back lengths in deep waters. INTRODUCTION In the last ten years more than half of new global oil and gas reserves were discovered offshore, especially in deepwater [1]. Usually such hydrocarbons reservoirs are located in remote areas, far from existing facilities. Traditional development solutions to exploit this kind of reserves are no longer applicable, due to both technical and economical constraints. Technologically advanced solutions are needed in order to efficiently produce oil and gas from satellite fields to overcome technical and economical difficulties. Especially for marginal fields, containing relatively small amounts of reserves in place, increasing the overall recovery factor is crucial to make the field economically sustainable. Marginal fields means too small to support the investment required for a conventional standalone development or too depth and far from existing facilities to be produced by means of conventional surface production technologies. Therefore marginal fields are more challenging to exploit in a cost-effective manner. The only way to unlock these reserves is to minimize the investment for facilities that will extract and process the hydrocarbons.