OTC 23552

Marlim 3 Phase Subsea Separation System – Challenges and Solutions for the Subsea Separation Station to Cope with Process Requirements R.T.C. Orlowski, M.L.L. Euphemio, F.G. Castro, C.A. Andrade, F.M.F. Guedes, L.C.T. da Silva, R.G. Pestana and G.C. de Cerqueira, Petrobras, I. Lourenço, A. Pivari, A. Witka, H. Folhadella, L. Pacheco, S. Kronemberger and J. Vilela, FMC Technologies

Copyright 2012, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 30 April–3 May 2012. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.

Abstract This paper presents the experience brought from the oil-water subsea separator project developed for the Marlim field, known as SSAO Marlim. Here, it will be addressed the inherent arising challenges from a project of a subsea separation equipment, from the subsea mechanical design perspective, with special focus to the additional requirements to the normally presented in conventional subsea equipment for oil and gas production. It will be part of the discussion the architecture selected for the system and the main challenges imposed by:

⎯ Separation process (gas-liquid, liquid-liquid and sand removal system); ⎯ Requirements for modularization, installation and retrieval of subsea components; ⎯ Installation concept.

Introduction The oil-water subsea separator is installed in a water depth of approximately 870m in the Marlim field, located in the Campos basin, Brazil. The subsea separation station has an envelope of 29m length, 10.8m width, 8.4m height and an overall assembly weight in-air of 392ton, and it will receive production from selected well, separate produced water from oil and sand and re-inject it into Marlim production reservoir via a centrifugal pump. The water separation happens into a Pipe SeparatorTM based on a gravitational concept, while water polishment to meet quality requirements, i.e. reduce oil content in water to acceptable levels for the re-injection into reservoir, is performed by cyclonic equipment. The equipment also has a sand management system which the main aim is to minimize the operational impact induced by solids production. Figure 1 illustrates the oil-water subsea separation system of Marlim.

Figure 1 - Artistic view of oil-water subsea separation system of Marlim

SSAO

FPSO

Production Well

Injection Well

Water depth: 870m

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Figure 2 presents a simplified version of the subsea separator process engineering flow diagram. The main process equipment considered in Marlim project is also indicated.

Figure 2 – Engineering flow diagram of SSAO Marlim Once getting into the subsea separation station, the production flow is routed to an inline multiphase sand remover (A) responsible to remove the bulk part of produced solids. The main objective of this equipment in the system is to minimize the frequency of flushing and cleaning operations of the pipe separatorTM and the outlet vessel, due to sand settlement in these components.

Downstream multiphase sand remover (A), a set of vertically arranged pipes, named as harp (B), is responsible for the free gas removal from the production flow. This equipment thus is responsible for the gas-liquid separation in the system. Right downstream of it, there is a pipe separatorTM (C) of around 60meters long responsible to perform great part of the oil separation from water (liquid-liquid), that will be completed inside the outlet separation vessel (D) - located at the very end of the pipe separator loop. In this outlet separator the phases are extracted: oil is recombined with the separated gas and free flow in multiphase stream to topsides stationary production unit (SPU), while separated water still with oil content above limits for reservoir re-injection is routed to a polishment system. The water polishment system comprises another inline sand remover (E) and two stages of hydrocyclones (F). The sand remover (E) reduces the amount and size of particles to the level required for re-injection into the reservoir, but has also the additional function to protect the downstream equipment such as hydrocyclones and water injection pump from erosion.

The two stages of hydrocyclones (F) have the function to reduce the amount of oil in water to acceptable levels for the re-injection into reservoir.

The boost of pressure to allow water re-injection is provided by a centrifugal pump (G), while a subsea oil in water monitoring device (H) verifies the quality of the water to be re-injected. Two additional sampling lines located subsea and connected to the topside facilities also allow the verification of water quality for re-injection. Modularization of Subsea Station A subsea system project needs to consider many different aspects in order to assure not only the operation of equipment according to the technical requirements previously established, but also to enable access the equipment subsea, for its recovery to surface for maintenance. Besides that, the project needs to foresee the possibility to reinstall such equipment in their original place at the subsea system, once activities at the surface are concluded. To make this possible, the subsea system is divided in modules, making the subsea recovery and reinstallation operations easier to be performed.

The criteria adopted to define which components need to be in or out a retrievable module considers many aspects such as failure rate brought from previous field proven applications or technology qualification testing programs, and the criticality of the lost of proper functioning of the component and consequently the impacts on the overall system. Taking this as the main basis for design, the Marlim subsea separation system has adopted the premise to have the possibility to recover to surface all subsea sensors, hydraulically actuated valves and process equipment.

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In addition to the aspects above mentioned, the modularization design on the SSAO Marlim had to have a level of compactness of subsea components inside retrievable modules as a main driver to reduce the overall subsea separation station weight and dimensions and meet the restrictions imposed by the offshore installation and intervention vessels available in Petrobras fleet.

One of the first tasks on the development of a subsea separation system project is the “translation” of the process and instrumentation diagram (P&ID), produced fundamentally on process and process controls requirements, to the “subsea language” in order to incorporate aspects from installation, operation and remote intervention. The result of this translation, referred here as the “Modularized P&ID”, allows the identification of the need to add and or remove components such as isolation valves, by-passes, among other features. The “Modularized P&ID” also allows the grouping or repositioning of equipment, organizing them in such a way to facilitate the access to internal components of the modules for maintenance or repair. After the modularization study performed for the SSAO Marlim project, it was possible to conclude that the best arrangement for the system would be the option with ten (10) retrievable modules, which are listed and described below (refer to Figure 3):

⎯ By-pass module: Allows the flow of production through the separation stages of subsea separation station or directly to the topside platform connected to the SSAO;

⎯ Multiphase sand remover module (desander module): Comprises the multiphase inline sand remover and has the

function to remove the sand present in the multiphase flow from production well. In order to optimize the subsea arrangement, this module also comprises the choke responsible to balance the delta pressure at the subsea separation system outlet and allow the rejects of sand removers and hydrocyclones to be routed to topsides via oil export line;

⎯ Pipe Separator module: The bigger module in the system. This module comprises the separation components

responsible for the gas-liquid separation – the harp, and for the liquid-liquid separation – pipe separatorTM and outlet section vessel;

⎯ Water sand remover module (desander module): First module at the water polishment system. Comprises the

inline sand remover responsible to assure the maximum amount of sand and maximum sand particles of sizes will not be re-injected into reservoir;

⎯ Hydrocyclones module: Comprises two stages of hydrocyclones, responsible to reduce the amount of oil in the water

to acceptable levels to be re-injected into reservoir. The ejector and additional chokes used for the hydrocyclones rejects controls are also located in this module;

⎯ Pump module: Holds the water injection centrifugal pump, responsible to assure the boost of pressure to the water to

be re-injected into reservoir. The water injection centrifugal pump also provides pressure for reservoir fracturing (when needed) and high flow for flushing operations in the system;

⎯ Water injection choke module: Comprises the chokes and hydraulic on-off valves responsible for the management

of water injection lines (routing water flow to the injection well when water quality is met, or routing flow to topsides when quality is out of specification). The flow meter responsible to totalize the amount of water re-injected and the water quality monitoring systems are also located in this module;

⎯ Recirculation and Flushing module: This module comprises the valves and all components required for the sand

removal operations for the pipe separatorTM and outlet separator vessel; ⎯ Electro-hydraulic module for multiplex control (EHCM): The two (2) EHCMs located in the subsea separation

system are similar to the ones used in subsea manifolds. The EHCM comprises the SCM and hydraulic, electric and chemical injection distribution system of the separation system.

Besides that, the system still has three (03) vertical connection modules (VCMs) and three (03) umbilical termination modules (UTMs). These components allow the SSAO Marlim connection to the production and water injection wells, and also to the topsides production platform.

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Figure 3 – Modularization of SSAO Marlim system Challenges Inherent to Marlim Subsea Oil-Water Separation System The primary processing of fluids on the seabed has brought to the Subsea Engineering some requirements not present in previous subsea projects, or at least unusual to the conventional projects developed by the industry. Aspects such shearing effects on fluids particles, control system applied to closed network, balance of pressure between fluid streams inside subsea equipment among many other, became present on daily basis due to the requirements set by the subsea separation equipment design. If compared to a conventional equipment for oil production (ex. Subsea manifold), the SSAO for Marlim has experienced many new challenges, in some cases as a result of the process of separation of fluids, in other cases as a result of the requirements set in order to assure flow of fluids inside subsea equipment; or at last, due to the need to develop new components to perform specific functions imposed by the separation stages of the system. In the following paragraphs the main challenges faced during the development of the project are presented from the mechanical system design perspective. Optimization of piping routing arrangement upstream the pipe separatorTM All piping routing upstream the gas-liquid separator – the harp, had to be designed in order to minimize turbulences or disturbances to the multiphase flow. The main objective was to assure the correct pre-conditioning of incoming flow is met, in order to facilitate the separation of free gas from liquid stream, avoiding undesired mixing of phases in upstream separator stages. Many computational models were built aiming the verification of flow dynamics of fluids, and to assurance the best piping routing and most effective positioning of each component inside the retrievable modules.

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As a main result from this design approach, it is possible to observe in Figure 4 for instance, the use of gentle curves, angles and geometries instead of sudden changes on the direction at the multiphase flow piping segments of pipe separator module. However, at the piping segments downstream the pipe separatorTM, where requirements for the fluid conditioning are not that strict and fluid is essentially free of gas, it is possible to observe a higher level of compactness on the layout of retrievable modules (refer to Figure 4: Recirculation and Flushing module). In many cases it was necessary to specify special fabrication processes in order to achieve the desirable geometry that would cope with separation requirements. As an example of that, we can mention the use of Hip process – hot isostatic pressure, which is basically the use of powder metal imposed to very high pressures to form shapes or geometries with high level of complexity.

Figure 4 – Pipe separator module piping (left) / Recirculation and flushing module piping (right) Inclination limits for the separation operation One of the most challenging requirements imposed to the SSAO Marlim project team was the need to assure the leveling of the subsea station after its subsea installation. The maximum inclination angle regarding the horizontal plane of the station considered within acceptable limits for the separator operation without putting in risk the oil-water separation efficiency was of 0.5-degree. The maximum inclination angle here informed is more restrictive than the ones normally used for the conventional equipment, where the limits for inclination are mainly given by the connection system of modules, flexible flowlines and umbilicals. In order to evaluate if the inclination requirement above mentioned could be met with the technologies currently used for subsea equipment of similar magnitude, a detailed study over the subsea separator foundation system was triggered. The following activities were considered in this investigation:

⎯ Complete study over historical data regarding inclination deviations of subsea equipment installed in production

fields operated by Petrobras, where a foundation design similar to the one used in the SSAO Marlim project was used;

⎯ Detailed bathymetry survey at the target installation location of the subsea separator in order to better evaluate the seabed topography;

⎯ Collection of seabed samples at the installation location in order to determine soil resistance characteristics. With the conclusion of the activities described above, and analysis of the results achieved, it was possible to conclude that the mechanical design for the separation station should consider the use of a flat foundation capable to compensate the seabed topography at the SSAO installation location, i.e. a seabed slope of 2.3-degree (refer to Figure 5).

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Figure 5 – SSAO Marlim foundation system Besides that, due to the evaluation on historical data regarding inclination deviation of equipment of same magnitude as the SSAO Marlim, already installed subsea, it was observed that, even with the actions identified for the foundation design, there were still some risks of not having the subsea separation station properly leveled after its installation. In other words, even with the actions taken, the maximum inclination of 0.5-degree could be exceeded. In order to eliminate this possibility, it was designed and fabricated an active leveling system for the pipe separator module, with the capacity to compensate a leveling deviation of 1.0-degree in any direction. With the incorporation of this feature to the subsea station design, the maximum acceptable deviation of leveling due to later accommodation of structure to seabed was increased from 0.5-degree to 1.5-degree, which is sum of the maximum capacity of leveling system and the maximum acceptable inclination tolerated by separator design. The leveling system incorporated to the subsea station mechanical design assures the horizontal leveling of the station via four (04) mechanical jack systems distributed along the pipe separatorTM, and four (04) leveling points at the separator module structure to allow the use of a hydraulic tool associated with a mechanical locking system (refer to Figure 6). Shop tests were performed in order to validate the leveling system design and leveling capacity, assuring it is fit for the purpose it was designed for.

Figure 6 – Active leveling system

I II

I – Hydraulic tool II – Adjustable support

Foundation

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Requirements for flow assurance inside the subsea station The flow assurance inside the subsea separation station of SSAO Marlim is very important in order to have the system availability as high as possible and consequently the oil production maximized. A shut down of production in a subsea system, can off course imply in a huge impact into the field development economics depending on the amount of time the system is off, and also require a lot of work in order to restart production in a safely manner. As an example, hydrates can cause the blockage of a valve by the freeze out of process fluid in its internals. For the SSAO Marlim separation system, this became even more challenging, since the equipment piping will be in many situations, filled in with different fluids. Some of the piping will be filled in with oil and gas, while some other segments will be filled in with water, depending on the location of them in the system. After a detailed investigation on the hydrate formation curve of Marlim crude, it was concluded that hydrates would start to appear if oil temperature falls below 15oC. Based on that, detailed operational procedures were developed in order to assure hydrates will not form either in a shut down or start-up conditions. In order to provide enough time for these procedures routines to be triggered out, thermal insulation was specified mainly for the multiphase piping and for the piping connected to the separated water lines. A total of 6 hours was defined as the total time to have hydrate remediation actions in place. MEG injection was specified in order to flush all multiphase piping at the separation station once system is shut down. A total of two (02) MEG injection points were placed in the by-pass module, in order to allow the operations of flushing and flooding the station once system is shut down, providing the mitigating action to remediate formation of hydrates in the system. However, if even with all the procedures described above hydrates appear, the corrective action defined for the SSAO system is to depressurize from topside the production inlet and outlet flowlines to the SSAO. Additional information on the flow assurance strategy defined for the SSAO Marlim can be found in the SSAO Marlim Flow Assurance OTC paper 23694. Necessary subsea components for the oil-water separation system During the development of SSAO Marlim, it was identified the need to design and qualify new types of components, not used before in a subsea environment. Such equipment included in this group is presented in the list below:

⎯ Separation Equipment; ⎯ Sand removal system for the outlet separator vessel; ⎯ Ejectors; ⎯ Flow orifices (orifice plates); ⎯ Special flow restrictors for the control of the multiphase sand remover reject; ⎯ Vortex breakers to minimize hydrate formation risk at the connection points between the multiphase flow circuit and

separated water flow circuit of the system (refer to paper OTC 23694).

Figure 7 – Sand flushing ejector (left), special flow orifice (center) and sand removal system for the outlet separator vessel (right) Due to the uncertainties brought from the application of new technologies for oil separation at the seabed, a specific qualification program was elaborated in order to allow the gain of better knowledge upon the equipment technology to be used and to enable the design adjustments and validation. This technology qualification program (TQP, refer to paper OTC 23417) validated all the separation and sand management equipment for use in the Marlim project. However, with the results achieved on the TQP, it was identified the need to perform complementary tests in some of the specific mechanical components aiming the risk mitigation during the design and operation phases of the system. This was the case of the test to map the performance of the ejectors, where the ejector curve was raised, enabling a better understanding of its operational limits, and the definition of set points of the chokes in the control system. Due to lack or unavailability of an ideal test bench, in other words, a test rig capable to deal with high flow rates and pressures such as the Marlim separator, a test matrix at reduced scale was defined, keeping the representativeness of tests specified with regards to the actual application in field operation conditions.

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Another case to be mentioned is the capability of some components to have a high erosion resistance due to the high flow velocities found at some points of the system, and the high quantity and granular distribution of sand imposed by the project (100ppm on mass basis and particles sizes ranging from 4micra to 2mm). As a result of the high velocities of flow and sand content, it was necessary to qualify special ceramic materials, with high erosion resistance, for the flow orifices and ejectors nozzles. The ceramic materials selected were imposed to a series of tests in order to verify the material loss when subjected to the incidence of sand at high velocity and different impingement angles. Erosion tests were also performed to the hydrocyclones liners in order to define the better coating material to be used for the project (refer to paper OTC 23417).

The SSAO Marlim subsea separation station uses chokes as the main actuation component of the closed loop control network of the system. This new function for this component has required a detailed study in order to identify the operation conditions of each choke in the system would be subjected to, as well as the design and testing requirements that would be specified during their procurement process. In this new function application, the additional requirements identified for the chokes in the system are listed below:

⎯ Need of higher accuracy on the choke Cv curve in order to allow good controllability; ⎯ Good erosion resistance due to the possibility to operate with fluid with high concentration of solids; ⎯ Choke design capable to avoid cavitation even when operating at high differential pressure conditions (upstream to

downstream); ⎯ High robustness in order to cope with sporadic operation conditions with reverse flow.

It is important to observe that the association or not of requirements above presented, depends upon the location and function of the choke in the separation system. In other words, not necessarily all requirements above listed apply to all chokes of the system. In order to meet the operational requirements and conditions, for the total of ten (10) chokes present in the system, four (4) different models of assembly were used. The models selected also include double-stage trim chokes, to avoid cavitation in points of the system where component had to produce an elevated pressure reduction (delta pressure). Installation of Subsea Station The Marlim oil-water subsea separator project had as one of the main drivers the weight and envelope dimensions optimization in order to enable its installation via an available installation vessel that belongs to Petrobras fleet. The installation crane barge BGL-1 was identified among other installation vessels evaluated as the best available resource to perform the operation. The BGL-1 has a dynamic positioning system and a crane with driving blocks that can reach 600 to 1000ton SWL. However in order to perform installation with a load of this magnitude, the installation depth is limited to 300 meter. Since the operational limit of the BGL-1 crane was less than the SSAO Marlim water depth for installation, Petrobras has preferred to adopt an installation method used for the installation of their first subsea manifolds in deep water depths (refer to paper OTC 8237). This methodology consists in lowering the equipment to the target water depth using an arrangement of cable segments. These segments of cables comprise two (2) 6-inch diameter cables disposed in parallel, with a total length of approximately 35 meter. Successive segments of cables are connected one to each other using link plates, thus the lowering of equipment is conducted gradually till touching down to the seabed. During connection of two sucessives segments of cable, the total arrangement is supported by cantilevers welded to the vessel’s deck, thus releasing the crane for the lifting of another segment of cables. The SSAO Marlim installation operation has been performed running twenty three (23) link plates connection operations, from the deck of the barge to the final landing at a water depth of 870 meter. The following sequence presents a step by step description of the methodology used for the lowering of the equipment, and Figure 8 illustrates each of the steps followed.

– Step 1: SSAO Marlim overboarding and equipment lowering just below the splash zone; – Step 2: Hang-off the two-sling arrangement on the deck cantilevers and start-up of lifting of next cables segments; – Step 3: Connection, via link plates, of the following segments of pipes to the installation arrangement supported at

the deck cantilevers;

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– Step 4: Lifting of the entire system via barge crane, and lowering of assembly for the hang-off at the upper extremity of the following segments of cables;

– Step 5: Repeat first four (4) previous steps for the lowering of the equipment up to the water depth of 860m; – Step 6: Lower to the final depth paying out rope from the crane.

Figure 8 – Steps of the methodology adopted for the installation of SSAO Marlim In order to determine the environmental and operational window for the SSAO Marlim subsea installation, it was performed a series of coupled numerical analysis, considering the characteristics of the installation vessel (RAO – response amplitude operator), and the hydrodynamic parameters obtained from the tests of the SSAO reduced model (mock-up) performed in a installation analysis laboratory (refer to Figure 9).

Figure 9 – Reduced scale model of equipment during tests to determine hydrodynamic coefficients The results, summarized in Table 1, indicated that for the environmental conditions at the Campos basin, the installation of the equipment with the proposed methodology would be viable however some restrictions should have been considered in order to proceed with the installation operation in a safely way. Once SSAO separation station installation is concluded, the following phases to be executed are the interconnection of the station to the topside floating production unit and to the production and water injection wells, the installation of the separated water reinjection pump, and the commissioning / pre-operation activities.

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Table 1 – Allowable significant wave height (Hs) and peak periods (Tp) for each installation stage

Hs (m) Allowable Tp (s)

Overboarding Splash Zone Hang off on the vessel crane

Hang off on the deck cantilever

1.5 All All All All 1.6 All All All All 1.7 > 5s > 5s All All 1.8 > 5s > 5s < 8s < 8s 1.9 > 5s > 5s < 8s < 8s 2.0 > 6s > 6s < 8s < 8s

Conclusions As a result of the SSAO Marlim subsea separation project it is possible to conclude that the requirements imposed by the separation system design imply in a different way to develop the subsea mechanical system design. As described above, some components that are commonly used in conventional subsea projects, and have their operation capabilities well understood by the oil industry, are now subjected to new operation conditions where they have never been before. In many of these cases, alternative components that would fit better for the application are either not available yet for subsea application or even do not exist. In addition to that, subsea separation projects, such as the SSAO Marlim, have established new routines to progress with the system engineering. To the conventional mechanical calculations such as the ones using FEA (finite element analysis modeling) for checking stresses and deformations, that are usually run while evolving with the project engineering, it was added new disciplines such as fluid dynamics in order to adjust the subsea mechanical design to the separation system design and provide the better configuration to extract the best separation performance as possible. Flow assurance design has also turned to be an important task while developing the mechanical system layout. Depending on the operational procedures, the subsea station arrangement may need to be modified in order to assure production flow will be transported to topsides in any situation. When it comes to the fabrication perspective, since subsea processing projects are at the vanguard of the oil industry, many gaps are still to be filled. Some of the the equipment suppliers are still trying to understand the challenges in going subsea with a project of such a nature and complexity. Quality requirements usually accepted for topside applications may not be enough once going to the subsea environment. This will require the development of more robust and reliable components, new materials, new methodologies for producing in a safe and reliable way separated oil stream to topsides, and a different way to design the subsea system making it still compact and within the limits for installation with conventional vessels. Acknowledgments The authors would like to thank Petrobras and FMC Technologies Inc. for permission to present the information contained in this paper. We would like also to extend our gratefulness to all colleagues who, directly or indirectly contributed to this work. References 1. Capela, C. et al.: “Marlim 3 Phase Subsea Separation System – Subsea Innovative Process Design Validated by Comprehensive

Technology Qualification Program”, Offshore Technology Conference, paper OTC 23417, 2012. 2. Duarte, D. G. et al.: “Marlim 3 Phase Subsea Separation System – Challenges and Innovative Solutions for Flow Assurance snd Hydrate

Prevention Strategy”, Offshore Technology Conference, paper OTC 23694, 2012. 3. F.E. Roveri, M.C. de Oliveira and M.J. Moretti: “Installation of a Production Manifold in 2000ft Water Depth Offshore Brazil”,

Offshore Technology Conference, paper OTC 8237, 1996. 4. Euphemio, M.L.L., Oliveira R.C.G., Nunes, G.C., Capela Moraes, C.A., and Ferreira, L.V. “Subsea Oil/Water Separation of Heavy Oil:

Overview of the Main Challenges for the Marlim Field - Campos Basin”, Offshore Technology Conference, paper OTC 18914, 2007. 5. Figueiredo, M.W., Kuchpill, C., Caetano, E.F., “Application of Subsea Processing and Boosting in Campos Basin”, Offshore

Technology Conference, paper OTC 18198, 2006. Abbreviations EHCM = Electro-hydraulic Module for Multiplex Control FEA = Finite Element Analysis FPSO = Floating Production, Storage and Offloading Unit Hs = Allowable Significant Wave Height MEG = Mono Ethylene Glycol P&ID = Process and Instrumentation Diagram RAO = Response Amplitude Operator SCM = Subsea Control Module SSAO = Marlim 3-Phase Subsea Separation System (for the terms in Portuguese)

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Tp = Peak Period TQP = Technology Qualification Program UTM = Umbilical Termination Module VCM = Vertical Connection Module