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In recent years, companies have executed project-specific qualification programs for subsea-processing technologies. This paper summarizes the results of a qualification program that included a multiphase, subsea-separation system for shallow-water applications. The intent of this qualification program was to develop subsea-separation technologies for the global subsea portfolio, rather than for a specific project. To meet this goal, a separator design was chosen that would meet performance targets over a wide range of operating conditions. Subsea processing is not a new concept; however, recent economic considerations have led to more applications, ranging from simple single-phase or multiphase boosting to separation/boosting to future compression projects.
Abstract As oil fields mature, the produced water content of the production stream will often increase over time, and produced water management will eventually become a bottleneck in production. Subsea separation of produced water enables prolonged lifetime of brown field installations, increased recovery rates and more energy efficient production. In addition, implementation of subsea water separation will also enable future tie-ins to existing facilities, and reduce the need for new and expensive transport lines. Existing installed subsea produced water bulk separator technologies are limited to gravity and compact gravity vessels, such as Troll and Tordis, and the Marlim pipe separator. These are large installations, which are costly to manufacture, transport and install. In addition, the gravity and compact gravity vessels are not suited for deep-water installations, and there is a need for novel solutions to both reduce the weight and size of bulk water separators, making the technology more attractive for new business cases. In order to investigate improved subsea bulk water separation technologies, a multiphase oil-water test loop has been developed at the Norwegian University of Science and Technology (NTNU). Facility test fluids are ExxsolD60 and distilled water with wt%3.4 NaCl. In this paper, a new separator design, utilizing multiple parallel pipes will be presented. The design allows reduction of required wall thickness at large water depths, shorter residence times and hence a shorter separator length compared to traditional gravity based technologies. Initial performance data of a constructed medium scale prototype will be reported, including separation efficiency estimations over a range of flow rates, water cuts (WC) and water extraction rates (ER). Tested flow rates vary from 250L/min to 750L/min at 30%, 50% and 70% WC. Water extraction rates are varied from 50% to 100% of the inlet water rate. Based on this initial test campaign, the concept proves promising, displaying good separation efficiencies (>98%) for both water continuous and oil continuous inlet flows at moderate flow velocities. At higher flow rates, performance decreases, and water extraction rates must be limited in order to maintain high efficiencies. Photos of flow conditions at the water outlet are included, providing a visualization of the occurring two-phase flow phenomena inside the separator. The presented concept adds to an expanding portfolio of proposed subsea separation solutions, and displays a new way of utilizing parallel pipes to achieve oil-water bulk separation.
Abstract Over the past 10 to 15 years subsea processing has been globally established as a market segment within the subsea development arena, and subsea separation has been a vital part of this development with Troll C, Tordis SSB, Pazflor and others. The track record of these installations have been outstanding, some of them with documented uptime of more than 99%. Still focus in the market seems to turn towards more ‘clean’ pumping or compression solutions at a time where the boosting technology options increases, while separation seems to be linked to more complexity and higher capex and are often not included as an option in evaluating a field. Still, subsea separation has some distinguished qualities that cannot be matched by other IOR methods. The more obvious scenarios are linked to flow assurance issues such as hydrate or slugging conditions in a field, but in addition some fields with very low production pressure or very long transportation distance to shore. Equally important is the operators need for flexibility in the design to cover for uncertainty in the production over the life of field and to count for future unexpected situations. This could be for a greenfield, redevelopment of a brownfield, or in general uncertainties about future sand or water production. Subsea separation is a simple way of mitigating these uncertainties, while at the same time increasing the operational envelope of the overall system compared to a pump or compressor alone. The paper will present examples of how separation can hugely add value compared to boosting alone by using simple, robust technology, resulting in more predictability an increased Net Present Value (NPV) for the operator.
Abstract Production fluid typically leaves a well in multiple phases, including: oil, gas, water, and solids. It is necessary to separate these components in order to recover the oil and gas, treat the water, dispose of sand, etc. In the past decade there has been a trend to move processing equipment to the seabed. As offshore production continues to be developed in deeper water, it is imperative to develop separator technology that will be designed for the hydrostatic forces and large amounts of produced water that is expected to occur over time. This paper explores two novel subsea linear pipe designs that allow subsea processing to be accomplished more cost effectively than existing technologies. The process undertaken for designing the two novel subsea linear pipe separation technologies: (gas-liquid) and (gas-liquid-solids) is described. To validate the efficiency and effectiveness of these two systems, a Computational Fluid Dynamics (CFD) analysis and cost analysis have been performed for each separator to provide both a realistic view of the actual separation efficiency of the systems, as well as comparative cost efficiency to existing technology in use today. Separators utilizing the pipe classification can be made lighter and cheaper when compared to existing subsea separation modules. In addition, they can be fabricated out of standard pipe sizes, thus cutting costs due to high availability and ease of fabrication. These factors are made even more attractive when modularized for ease of installation and field expansion. Applications of the process and design of these special separators are discussed along with their potential advantages in offshore deepwater seabed based developments. With continued research and testing, the gas-liquid and gas-liquid-solid linear pipe separator designs have the potential to reshape the subsea separation industry.
Sand production occurs from wells commingled with crude oil and produced water. For a subsea separation unit, the produced sand concentration as well as the particles size and the subsea equipment design are the main parameters to be considered when designing the most suited sand handling system. A sand management philosophy has then to be defined case by case. Within a subsea produced water separation station using the Saipem SpoolSep for bulk separation, the sand could be handled at several production points using different technologies and approaches :
• Upstream the bulk separator using multiphase desanding systems allowing the removal of the largest particles from the well stream.
• Inside the SpoolSep, which is designed considering a sand-dedicated volume to ensure the required separation performances even if a sand bed is formed, knowing that the modularized spools could be replaced if needed. Moreover, if necessary each spool could be flushed to remove settled particles by fluid flowing.
• Within the produced water treatment stage, downstream the bulk separator where cyclonic desanders could be used to achieve the water quality specifications in terms of SiW concentration and particle cut off diameter.
• The slurries coming from the different stages (multiphase desander, bulk separator, water treatment) could be exported continuously through the multiphase line up to the surface facility using ejectors or specific pumps or could be stored subsea before export.
The paper presents the sand management philosophy and technologies which could be used in a subsea separation unit with the SpoolSep for bulk separation of produced water.
Abstract Many producing assets in the world have reached the so-called mature phase of development. Some of these assets have been producing for 30 to 40 years or more, which is typically beyond the design life, and have reached a water to oil ratio of 3 to 9 or more. There are many issues that affect the productivity and economic viability of these fields. Some of the challenges include integrity uncertainty in the wells, flow lines, and facilities; production bottlenecks due to the shift in gas, oil and water ratios; erosion/corrosion; increased sand production and handling costs; high chemical consumption and treatment costs; and obsolete monitoring and control systems that are incompatible with new technologies and which contribute to the need for a large number of operations staff. Generally operators are faced with the commercial decision whether to sell the asset to a low cost operator, reinvest in the asset, or incur the cost of decommissioning. While the number and complexity of these challenges are significant, there are nevertheless a number of viable options for extending the economic life of such assets. Hydrocarbon recovery and production from these fields can be enhanced by infill drilling; acid and fracture stimulation; by implementing a range of remediation techniques such as recompletion with smart systems to reduce water and solids influx to surface facilities; and by the implementation of improved and enhanced recovery methods. Selecting the optimal strategy requires a holistic perspective on subsurface issues, wells, and surface facilities, and an ability to make projections of integrated performance. This is greatly facilitated by first developing a root cause understanding of the reservoir and production fluid characteristics, and second, the use of analysis tools that allow quick and reasonably accurate assessment of options. In order to increase value from matured fields, the goal is to increase oil recovery from the historical average of 35% and to optimize production by improving the operational efficiency. To achieve this goal, in this paper we will put forward two key imperatives that extend the life of a mature field: (1) Finding and accessing the by-passed oil and (2) Maintaining High uptime during Asset production and operation. In this paper, several mature fields in Europe, Far East and Middle East are analyzed and presented in order to: –highlight the root causes for either low production and or higher operating costs; –assess the impact of both surface and subsurface uncertainties in multiple development planning scenarios; –develop the best strategies and options for improved reservoir, well and facilities management; –demonstrate the contributions of implemented new technologies that optimized performance of artificial lift, minimized downtime by well intervention and reduced operational costs by fluids flow assurance in well and surface facilities; and –list the technical and economical challenges that still face the industry.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 25367, "Qualification of a Subsea Separator With Online Desanding Capability for Shallow-Water Applications," by M.D. Olson, E.J. Grave, and J.C. Juarez, ExxonMobil Upstream Research, and M.R. Anderson, ExxonMobil Development, prepared for the 2014 Offshore Technology Conference, Houston, 5-8 May. The paper has not been peer reviewed.
In recent years, companies have executed project-specific qualification programs for subsea-processing technologies. This paper summarizes the results of a qualification program that included a multiphase, subsea-separation system for shallow-water applications. The intent of this qualification program was to develop subsea-separation technologies for the global subsea portfolio, rather than for a specific project. To meet this goal, a separator design was chosen that would meet performance targets over a wide range of operating conditions.
Subsea processing is not a new concept; however, recent economic considerations have led to more applications, ranging from simple single-phase or multiphase boosting to separation/boosting to future compression projects. There has been a modest number of subsea-separation applications in the Norwegian North Sea, in the Gulf of Mexico, off the west coast of Angola, and most recently in the Campos basin of Brazil. Future subsea projects that have been announced include two compression and liquid-boosting units that will be installed in the Norwegian North Sea. These two projects, and a few of the installed units, use the simplest form of subsea separation: two-phase gas/liquid separation.
The most notable projects that have installed three-phase subsea separators, which remove a produced-water stream, include the Troll C pilot unit, Tordis in the North Sea, and, most recently, Marlim offshore Brazil.
Shallow-Water, Three-Phase Separator Design
In the preliminary separator design, bulk separation was provided by two inlet vane diffusers (IVDs) installed on the two inlet nozzles. In this design, the IVDs diffuse the momentum of the inlet in a gradual manner such that the liquid phases are not sheared into smaller droplets, which can lead to liquid droplets entrained in the gas or the formation of stable oil/ water emulsions. Downstream of the inlet section, a series of perforated baffles was provided to straighten the flow paths in the oil/water phases in an attempt to maximize the separation length and minimize recirculation or stagnant zones. In the preliminary separator design, there were no separation internals downstream of the perforated baffles in the settling section. High-efficiency oil/ water-separation internals, such as platepack coalescers or vessel-based electrostatic grids/coalescers, were avoided because of reliability concerns.
A water-retaining weir was included in the design to separate the oil/water outlet compartments. With this design, a single level detector, such as a nucleonic device, can be installed upstream of the weir and can be used to measure both the gas/liquid- and the oil/water-interface levels.
Olson, M.D. (ExxonMobil Upstream Research Company) | Grave, E.J. (ExxonMobil Upstream Research Company) | Juarez, J.C. (ExxonMobil Upstream Research Company) | Anderson, M.R. (ExxonMobil Development Company)
Abstract ExxonMobil Development Company (EMDC) recently completed a qualification program which included a multiphase, subsea separation system for shallow-water applications. This paper summarizes the results from this qualification program. Developments and advances in subsea processing technologies and the application of such technologies have been fueled by recent economic considerations in the oil and gas industry, as fields are maturing and operating companies strive to maintain oil and gas production. To-date, companies have executed project-specific qualification programs which take years of upfront engineering. The intent of this qualification program was to develop subsea separation technologies for the "global" subsea portfolio, rather than a specific project. To cover the "global" subsea portfolio, a separator design was chosen that would meet separation performance targets over a wide range of operating conditions. For subsea applications, availability and reliability is critical, as unplanned intervention costs are extremely high; therefore, only certain internals were recommended to avoid plugging and fouling issues. Also, the separator was equipped with sand handling internals, including sand jetting headers and sand removal cyclones, to allow online fluidization and removal of accumulated sand. Qualification activities included the development of a subsea processing template, design validation of a multiphase separator design using Computational Fluid Dynamics (CFD) and performance tests with model fluids and "live" fluids, and performance tests on the sand handling equipment. High-level results from these tests are shared. Prior to the qualification programs, experience with subsea separation technologies, and subsea processing as a whole, within ExxonMobil was limited to being an active partner with subsea processing projects such as Tordis and Pazflor. Following the execution of the aforementioned qualification programs, technical risks have been mitigated, such that it is now possible to be confident in applying these technologies in the "global" subsea portfolio. This will enable ExxonMobil to reduce the cost and schedule impact of upfront engineering on future subsea processing projects. In the ever-changing business environment of the oil and gas industry, this may become a preferred approach to bring unproven technologies to maturity when the business need is well-established.
Abstract This paper initially discusses the tendency to wider the conceptual envelop of subsea systems in oil production installations. From the conventional boosting systems to more complex gas/oil/water separation equipment and even polishing devices for coarsely separated fluid stream, there is nowadays a tendency to increase the complexity of subsea production systems far beyond manifolds and other maneuver stations. In sequence the pros and cons of subsea processing as an alternative to conventional topside primary processing are also discussed. Restrictions of the subsea environment and the consequent requirement for unconventional solutions and equipments comparing to topside traditional separation equipment are also mentioned. The limitations of the expression " subsea processing" are emphasized and both advantages and technological gaps of new " building blocks" for processing plant for topside and subsea application are discussed. Besides, operational aspects are also addressed so as to emphasize the new challenges subsea systems pose to operation crew: some important paradigm changes should be captured by operators when changing from a topside plant to a subsea system. The problems arising from having a new subsea system connected to an old production unit in a brown field are also discussed. The drive for the qualification of new conceptions and new equipment is approached not only for subsea use but also for the new generation of topside production facilities. The paper tries to bring some conclusions on the means to allow further development - filling up the gaps - and qualification of the new " compact" or " in-line" building blocks for subsea processing plants. However, it must be emphasized that the focus of this work is on processing technology not on equipment or marinization technologies. Thus, subsea engineering (hardware) qualification is beyond the scope of this work. 1. Introduction In offshore oil and gas production systems, subsea equipment started with wellhead components and flow distribution manifolds three or four decades ago. Some time later, boosting systems (including dynamic equipment - pumps either monophase or multiphase, and, eventually compressors) were conceived as means of turning feasible production of remote marginal fields with long tie backs to production platforms. But even these initiatives were initially assumed as part of the strategy of flow assurance in the offshore production fields. The concept of primary processing of produced fluids was kept in accordance with the usual expression " surface oilfield operations" and that " surface", in the offshore case, was considered as being provided by the deck on the offshore production unit. Seabed was not regarded as supporting site for primary processing facilities. The idea of having at least part of the primary processing (mainly phase separation) at the subsea environment was driven by the necessity of boosting liquid and gas streams to flow to a greater distance - again flow assurance demand. Subsea separation was initially regarded as potentially complicated from the operational point of view, and as a consequence, in parallel to the new conceptions of subsea gas-liquid separation, an impulse on the development of multiphase pumping system was also boosted.
Hannisdal, Andreas (FMC Technologies) | Westra, Remko (FMC Technologies) | Akdim, Mohamed Reda (FMC Technologies) | Bymaster, Adam (Exxon Mobil Corporation) | Grave, Ed (ExxonMobil Upstream Research Co.) | Teng, Daniel Terng (Woodside Energy)
Abstract Offshore deepwater discoveries have driven the development of new compactseparation technologies, a core aspect of subsea processing. Compact separatorsare much smaller than conventional separators and have the potential tosignificantly reduce capital expenditure for deepwater developments. Unfortunately, reducing the size of separators generally reduce the separationperformance and the robustness to handle fluctuations in flow rate andcomposition. It is therefore essential to find an acceptable balance betweenthe realized reduction in overall capital expenditure and reduced tolerance tofluctuating conditions. To maximize the economics of a subsea development, itis important to understand how the technology selection impacts performance, risks, costs, and ultimately the attractiveness of deepwater subsea processing. Proactive technology screening and qualification are required. This paperpresents one of several ongoing joint industry projects to develop and screenseparation technologies for deepwater applications, the DEMO 2000 project: NextGeneration Deepwater Subsea Gas-liquid Separation System. An overview ofavailable technologies for separation in deep water is disclosed, includingcyclonic separators, compact gravity-type separators, and slug dampeningtechnologies. Their characteristics, typical performance and maturity level arediscussed. Finally, the program activities are explained and some highlightsfrom the separation test program are shared. Introduction Value Drivers for Subsea Gas-liquid Separation In recent years, subsea processing, and more specifically subsea separation, has been recognized as one of the most promising technology developments in theoffshore industry. With the recent success at Perdido [Ju et al., 2010], Parquedas Conchas (BC-10) [Iyer et al., 2010; Deuel et al., 2011], and Pazflor[Eriksen, 2012], subsea separation is attracting interest from industry becauseof its ability to increase production, enhance recovery, and improve fieldeconomics on a commercial scale. Subsea separation is, in general, stillconsidered an emerging technology area; therefore the benefits and capabilitiesmust be clearly demonstrated to infuse acceptance and confidence as thepreferred development option. McClimans and Fantoft  and Di Silvestro etal.  have presented a detailed review of the value drivers for subseagas-liquid separation, which is the topic of this paper. In summary, subseagas-liquid separation has proven to provide strong business incentives withenabling capabilities, including (i) more efficient liquid boosting, (ii)longer range gas compression from subsea to onshore, (iii) cost efficienthydrate management, (iv) effective riser slug depression, (v) and access tochallenging field developments that otherwise would be abandoned or notdeveloped (due to their remote location, harsh conditions, longer tie-backrequirements, or low reservoir drive). The main drivers are discussedbelow.