Surface oil and gas treatment facilities in .service for decades are likely to be oversized due to the natural depletion of their reserx'oirs. Despite these plants might have been designed modularly, meaning they comprise multiple identical units serving the same task, such units operate often in conditions far from the design. This work analyzes the revamping options of an existing upstream gas facility, cho.^en because representative of a wide set of plants. It presents a flexible process simulation model, implemented in the HYSYS environment and dynamically linked to an Excel spreadsheet, which includes the performance maps of all turbomachineries and the main characteristics of the investigated modifications. The model may be used to run simulations for various gas input conditions and to predict the performance over I year of operation and for different possible future scenarios. The first objective is to assess economically the considered options, which shall be applied only if yielding short return times of the investment since the reservoir is mature. Moreover, all options are appreciated adopting a figure of merit, here defined, that compares the overall energy consumption to the one calculated with .•itate-of-the-art technologies. In addition, exergy and environmental analyses are executed.

Surface oil and gas treatment facilities in service for decades are likely to be oversized due to the natural depletion of their reservoirs. Despite these plants might have been designed modularly, meaning they comprise multiple identical units serving the same task, such units operate often in conditions far from the design point and inefficiently. This work analyzes the revamping options of an existing upstream gas facility, which is chosen because representative of a wide set of plants. A flexible numerical model, implemented in the HYSYS environment and dynamically linked to an Excel spreadsheet, includes the performance maps of all turbo machineries and the main characteristics of the investigated modifications in order to run simulation for many gas input conditions and to predict the performance over a year of operation and for different possible future scenarios. The first objective is to assess economically the considered options, which shall be applied only if yielding short return times of the investment since the reservoir is mature. Moreover, all options are appreciated adopting a figure of merit, here defined, that compares the overall energy consumption to that calculated with state-of-the-art technologies. In addition, an exergy and an environmental analyses are executed.

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.

The scope of the paper is to present and discuss results of an extended technology development program regarding very long oil tiebacks architectures (50-100km) and related enabling technologies. The program is based on Eni most recent development projects (started up in the last 4 years) contemplating long tiebacks, new technologies implementation and experimental production periods conducted on those projects. Important field production data and measured performances on development projects have been a key to define the program. Wide ranges of tieback architectures and technologies have been studied. Technology providers and suppliers have been heavily involved. Technology validation and risk analysis approaches were used. Feed design is now ongoing regarding new asset development initiatives. The objectives are to reduce deepwater development costs increasing the distance between new assets and existing production hubs, shallow water areas or even connecting those assets to shore. A cost effective and flexible extra long oil tie back architecture proves to efficiently work on a wide range of applications and a wide range of design basis parameters. Key enablers are boosting, subsea power distribution, multicontrol communication, thermal management technologies, extensive work on reliability and availability and tailored operations procedures. Maturity levels and way forwards to a potential project execution will be discussed in the paper, including projected economics. Recent technology development, qualification and testing together with the experience matured on the most recent deepwater projects allow to seriously consider a "full subsea development approach" at long distances from existing hubs or from shore.