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MOBO – An Alternative Type of Subsea Boosting
Conference Paper · March 2013
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MOBO – AN ALTERNATIVE TYPE
OF SUBSEA BOOSTING
Felipe Ehlke Anastacio
Product Engineer | Subsea Controls
felipe.anastacio@akersolutions.com
Leandro Fischer
Product Engineer | Subsea Controls
leandro.fischer@akersolutions.com
Juliano Pimentel
Engineering Manager | Subsea Controls
juliano.pimentel@akersolutions.com
AkerSolutions™
Francisco Sobania Street, 1300.
Curitiba,
Brazil
Offshore Asia 2013
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Abstract – The heavy oil reservoirs in South America represents 61 percent of the known
technically recoverable heavy oil in the world (40 billion barrels) [1] , with this information we
can affirm that the main challenge is not finding resources, but to have the ability to extract this
oil in the shortest amount of time to make it commercially viable. Today one of the most
promising methods of heavy oil recovery is through subsea pumping system.
Subsea pumping systems are used in the UK North Sea, South China, Africa,
Equatorial Guinea and in almost every place where there is a heavy oil reservoir. One of the
most common types is the Electrical Submersible Pump (ESP) that is used to increase the
production flow by depleting the well faster than it would be by regular pressure well flow.
One of the issues with ESP is the constant maintenance intervention required due to the low
lifetime (3 to 5 years usually). Any intervention generates an operational risk and requires a
halt in the production system. In Brazil where are located about 14 billion barrels of proven
oil reserves in 2012, with 90 percent consisting in heavy grade oil[2]. A successful case of
recovery used in Jubarte and Golfinho field is a pumping module (MOBO) which is installed
in a dummy satellite well, that allows topside intervention without stopping the production
through a bypass line.
This paper will explain the MOBO System regarding its technical advantages as:
- Being able to continue production during an intervention on the ESP;
- The specifically designed and recently qualified electrical system (5/8.7kV U0/U)
which includes a penetrator with a double seal barriers;
- A better solution for ESP systems regarding to safety and work over operation;
- Low time intervention (3 days average for installation) and a higher level of safety
for the operation;
This project was initially deployed in eight wells (2 in Golfinho field and 6 in Jubarte
field), with a good response from customer, a second phase of the project was developed and
we will also present the differences between MOBO Phase I project and MOBO Phase II as
to:
- Engineering improvements (cost reduction, lessons learned and higher pump power
supply demands which required new qualification);
- Future drivers of development for this kind of equipment;
The main objective of this article is to present an alternative type of equipment for
subsea boosting operations which may result in easier, safer and faster intervention in the
field.
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Keywords — Subsea boosting, MOBO, ESP, heavy oil recovery, subsea
equipment;
I. INTRODUCTION
Heavy oil (API gravity less than 20º) reservoirs are believe to be by the geologists [3] the
residue of formerly light oil reservoirs which were degraded by bacteria, evaporation and other
natural processes. The revenue generated from the exploration of heavy oil tends to be
considerably lower due to higher refining costs, production and transportation; however as the
resources of heavy oil represent such a significant amount, it must be considered as an important
revenue source by all operators.
Provided the heavy oil lower revenue, the operating companies have to find alternative
ways to increase profit margins on those fields, as to decrease the operational costs (OPEX). One
of the several alternatives is to use “artificial lift” technologies which increases the oil recovery
ratio.
Following Hubbert’s Peak Theory [4], any geographical oil containing (oil field) has a
rate of production tending to be a bell-shaped curve, but how short or wide will this plot be will
depend on the technologies used for the oil extraction which can maximize the production flow.
Figure 01 – The Hubbert Curve – [5]
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The technique that we will address in this paper is the artificial lift using ESP (Electrical
Submersible Pump), which is one amongst many artificial lift techniques and has its advantages
Advantages
and disadvantages as compared on the table below.
Rod Pumps
Electric
Submersible Pump
Venturi Hydraulic
Pump
Gas Lift
Progressing
Cavity Pump
Simple, basic design
Extremely high
volume lift using up to
1,000kw motors
High Volumes
Solids tolerant
Solids and
viscous crude
tolerant
Unit easily changed
Unobtrusive surface
location
Can use water as
power fluid
simple to operate
Downhole telemetry
available
Remote power
source
Can achieve low BHFP
Tolerant high well
elevation
Tolerant high well
deviation
Can lift high temperature,
viscous oils
corrosion / scale
treatments possible
Tolerant high GOR
reservoir fluids
Pump off control
Disadvantages
Large volumes in high
Energy efficient
PI wells
Unobtrusive
surface location
Simple maintenance
with downhole
motor
Tolerant high well
deviation
Wireline maintenance
Friction in crooked
Not suitable for low
volume wells
High surface
pressures
Lift gas may not be
available
Elastanes swell in
some crude oils
Pump wear with solids
production (sand, wax,
etc)
Full workover required
to change pump
Sensitive to change in
surface flowline
pressure
Not suitable for
viscous crude oil or
emulsions
Pump off control
difficult
Cable susceptible to
Free gas reduces pump
damage during
efficiency
installation with tubing
Free gas reduces
pump efficiency
Cable deteriorates at
high temperatures
Power oil system
hazardous
Obtrusive in urban areas
Downhole corrosion
inhibition difficult
Heavy equipment for
offshore use
Problems with
Susceptible to gas
rotating rods
freezing / hydrates at (windup and after
low temperatures
spin) increase
with depth
Casing must
withstand lift gas
pressure
Gas and solids
intolerant
Increased production
casing size often
required
Figure 02 – Comparison between artificial lift technologies – [6]
Usually ESP systems are installed inside the production well and are installed on a pump
hanger (a.k.a. tubing hanger) of a Wet Christmas Tree. This paper has the objective of presenting
a new type of equipment called MOBO (a term derived from the Portuguese for "boosting
module") which uses the ESP technology but it is not installed on the production wellhead,
providing more flexibility to work over, more reliability and higher operational uptime.
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II. MOBO AS A SUBSEA SYSTEM
A. MOBO Overview in a Subsea System
For a complete understanding of the MOBO system, it is necessary to understand the
different equipment constituting the system and its interaction with other subsea
equipment/elements. To provide a better understanding of the overall system, it will be splitted
in the main equipment below which are laid subsea:
-
BAB (Boosting Adaptor Base)
-
MOBO (Module of Boosting)
-
ULB (Umbilical Launching Base)
-
Capsule (divided into sections)
-
VCM (Vertical Connection Module)
-
PH (Pump Hanger)
-
PES (Power Electrical System)
Figure 03 – MOBO Complete Stack-Up System and flow diagram [Aker Solutions –
Equipment Operation manual]
B. VCM (Vertical Connection Module)
The VCM is the connection module hence the main function is to connect the flexible
lines from topside to subsea equipment. In Brazil, the VCM is used in every equipment that has
a production flow, that includes Manifolds, Xmas Trees and MOBOs. It is deployed with the
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production flow line terminated from the topside and is installed vertically on a production hub
located on the equipment. It has a directional gate valve to control the oil production and a ROV
panel which allows the equipment to be mechanically locked into the hub.
For the MOBO system, two identical VCMs are used. The first one, suction VCM, is
installed on the BAB on the suction line (equipment intake) and connects the MOBO with the
Xmas Tree, where the oil flows with the well pressure. The second one, discharge VCM, is
installed on the discharge line (equipment outflow) and connects the MOBO to the FPSO in
order to collect the oil production after being pumped by the ESP.
Figure 04 – VCM Model [Aker Solutions – Equipment Operation manual]
C. BAB (Boosting Adaptor Base)
As explained before, the MOBO system is not installed on the production wellhead but
in a dummy satellite well which will not be deeper than 50 meters (enough length to
accommodate the capsule) down into the seabed and can be installed using the Torpedo Base
technique.[7]
The BAB is the equipment installed on top of the 30” dummy wellhead and has the
function of allowing the installation of the VCMs on the hubs. The internal piping allows the
outflow of the production from the VCMs, which through a specific valve commanded sequence
can be either routed through the MOBO to the ESP or routed to the “bypass line” where the oil
will flow straight to the discharge VCM and then to the flow line.
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Figure 05 – BAB Model [Aker Solutions – Equipment Operation manual]
The bypass line is meant to allow the production to flow if a work over is required in the
ESP. The production will then flow with gas injection (GI), from other Xmas Tree. If the bypass
valve is closed, the production will flow to the MOBO through the flow line to the capsule
where the ESP is installed.
Figure 06 – BAB piping detail [Aker Solutions – Equipment Operation manual]
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D. MOBO (Module of Boosting)
The MOBO equipment has the function of receiving the oil production through the flow
line mandrel from the BAB and direct it to the Pump Hanger where the ESP is allocated. The
MOBO has two mechanical gate valves to control the production that goes in and out to the
Pump Hanger. With those valves, it is possible to lock the fluid inside the capsule where the
ESP is allocated and bring the MOBO to the surface for an eventual maintenance without having
any oil leak to the environment.
The MOBO has two main interfaces: with the flow line mandrel from the BAB and with
the Pump Hanger which is the connection to the ESP. It is important to notice that the MOBO
has its mechanical connector locked on top of the Pump Hanger at the surface and it is not
unlocked by any means subsea, establishing a connection between equipment a ”dry mate” type.
Figure 07 – MOBO Model [Aker Solutions – Equipment Operation manual]
The production flows to the MOBO from the BAB trough the Flow Line Connector and
into the Pump Hanger suction bore, which is located externally from the ESP, filling the capsule
and submerging the ESP into production oil.
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Figure 08 – MOBO Cut view with flow direction [Aker Solutions – Equipment
Operation manual]
E. Pump Hanger
The Pump Hanger, is where the ESP is hanged/installed inside the capsule on the
dummy well. It has three bores that get in contact with the production fluid. The first one is the
suction bore, where the oil comes from the MOBO and floods the internal capsule where the
ESP is. The second is the discharge bore, where the pressurized oil that went through all the
pump stages come back to the MOBO and is exported to the FPSO. The third one is for the
electrical connector which is integrated in the ESP motor lead cable.
The ESP is torqued into the "saver sub", on the discharge bore, which is a replaceable
pipe section with the same threaded interface as on the Pump Hanger. The main function of the
saver sub is to avoid the pump hanger full replacement in case of any thread problems while
torque is applied to the ESP, so if any damage is made to the threads during the torque process,
the saver sub can be easily replaced.
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Figure 09 – Pump Hanger Model [Aker Solutions – Equipment Operation manual]
The Locking Sleeve at figure 09 is used to rotate clockwise and lock the Pump Hanger
on the top of the Capsule where the ESP is accommodated.
F. Capsule
The capsule is a set of five pipe sections (4 long and 1 short) with diameters of 20”
which function is to accommodate the ESP inside the dummy well. During the operation the
capsule is flooded with oil so the pump can work in its normal condition. On the top of the
capsule is installed the Pump Hanger where the oil flows in, and later on, flows out pressurized
by the pump.
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Figure 10 – Capsule with Pump Hanger detail [Aker Solutions – Equipment Operation
manual]
G. ULB (Umbilical Launch Base)
The ULB is an individual equipment which interfaces with the MOBO system supplying
all the electrical and hydraulic power for the system operation. The ULB is deployed with the
umbilical which feeds the MOBO and the Xmas Tree. The umbilical used on the project has the
power copper cables, signal and hydraulic lines.
Figure 11 – Umbilical Example for a MOBO System [8]
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Inside the ULB the power cables are diverted from the main pipeline trough the pipeline
spool cut to an UTU (Umbilical Termination Unit) back end. Also, four hydraulic lines (2 for
control + 2 for Chemical Injection) are diverted to a stab plate on the panel. All other functions,
which are not used on MOBO, are directed to the Xmas Tree as the electrical twisted pairs and
other hydraulic functional lines.
Figure 12 – Umbilical Launching Base [Aker Solutions - Equipment Operation manual]
The connection from the ULB to the MOBO system is made using an electrical power
jumper and a 4-way hydraulic jumper which are ROV operated after the deployment of the ULB
and the MOBO. The electrical power jumper is deployed with the BAB and the hydraulic
jumper is deployed with the ULB.
H. PES (Power Electrical System)
One of the main achievements of this project was to qualify a 5.0 / 8,7kV (U0/U) - IEC
60502-2 - Category C, medium power system which was fully modular. In other words, it could
be replaced without having any termination services as soldering, crimping or curing processes
what could generate risks specially offshore, causing downtime. All the integration services
(Umbilical to UTU and ESP Cable to Pump Hanger Connector) are made onshore and the
resulting products are loaded into the rig for the installation process.
All the components of the PES are listed according its numbering below:
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Figure 13 – MOBO Power Electrical System [Siemens Tronic - Spectron 8 Power System for MOBO / BAB]
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1. UTU - Umbilical Termination Unit
As described, the UTU is where the power cables from the umbilical are
installed to provide the electrical power needed for the ESP. The umbilical is connected through
a pressurized hose to a power receptacle on the panel.
2. Test ROV Plug (with resistors)
This ROV plug connector has an Y resistor network connecting its pins. The
values of the resistors in this case are 10, 20 and 30 Ω (ohms). It is mated to the UTU receptacle
on the panel for electrical testing. When the plug is mated, it is possible to check the umbilical
phases and integrity measurement.
Figure 14 – Typical Y Resistor network
3. Parking Receptacles
These receptacles are used only to assist the ROV maneuvers during the
installation of the Infield Power Jumper.
4. Infield Power Jumper
This is the only electrical flying lead that connects the ULB to the MOBO
system. For this project it has a 25m length since this was the distance between the ULB and
MOBO. During the equipment assembly, this jumper is parked and accommodated in a "8"
shape at the BAB as it is easier to the ROV to unroll it subsea.
5. Test ROV Plug (isolated phases)
This ROV plug connector has no electrical connection between its pins. Its
function is to allow insulation testing (5000V@10 min) [9] on the umbilical.
6. Parking Test Receptacle (with resistors)
It has the same resistor network as item 2, but the test receptacle allows testing
the umbilical with the Infield Jumper connected. That is available to be possible to identify
which part of the system the failure occurred, in case of any electrical failures.
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7. MOBO Jumper
The MOBO Jumper is constituted of a power receptacle on the MOBO panel
(7.1), a pressurized hydraulic hose with the electrical cables (7.2), a penetrator (7.3) which is
locked in the MOBO main body and a MOBO base plug connector (7.4) which is mated to the
Pump Hanger connector. The penetrator has the important function of preventing the water
ingress and also the oil escape as it is a secondary barrier from the oil inside the capsule.
Between the penetrator and the MOBO interface there is a metal-to-metal seal (7.5) which does
not allow the oil to escape. This same seal is used on the pump hanger connector (8.1).
The MOBO Jumper is fully modular which means that can be dismounted as one piece
equipment from the MOBO and easily replaced.
8. Pump Hanger Connector
The Pump Hanger Connector is mounted in one of the 3 bores in the Pump
Hanger. It has the function of connecting the MOBO power system to the ESP motor lead. The
connector is the first barrier against the oil that is inside the capsule. This connector can be
divided into two parts: front end and back end. The back end is where the ESP motor lead is
terminated and is individually defined for each project as the supplier of the ESP may be
different. Some special tests may be required during qualification as the oil type may change
from project to project. For this MOBO project it was required a Rapid Gas Decompression
(RGD) [10] test due to the gas build up on the base of the pump hanger during the oil flow in the
capsule. Because of this test, the connector termination process includes a special soldering on
the cable creating a metal seal inside the connector. This termination is made onshore before the
full equipment delivery to the client to be installed.
Figure 14 – Pump Hanger Connector [Siemens Tronic - Pump Hanger Receptacle GA]
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9. Monitoring Power Jumper
The Monitoring Power Jumper is an electrical flying lead with a JIC 6
connection in one end to be connected to any electrical connector available at the rig which will
mate with the work over umbilical. The main function is to allow the monitoring of the ESP and
of the electrical system during the subsea deployment of the equipment. After the complete
installation this jumper is retrieved with the MOBO Installation tool.
10. Parking Test Receptacle (isolated phases)
It has no electrical connection between its pins as item nº5. But the test
receptacle allows testing the umbilical with the Infield Jumper connected. That is available to be
possible to identify on which part of the system has the failure occurred, in case of any electrical
low insulation resistance.
III. MOBO INSTALLATION & WORK OVER
The MOBO system installation can be made in two different scenarios. The first scenario
is installing the BAB in advance which gives the opportunity to bring the VCM's installation
forward and to start production trough the by pass line without the use of ESP and on a later
stage, the MOBO with the capsule and ESP. From the records made by the client, the most
efficient MOBO installation took 3 days (72 hours) from the start of the equipment assembly
offshore until the start of the rig demobilization.
The second scenario is to install the system all together (except the ULB which is
launched with the umbilical), which would include BAB, MOBO, Capsule and ESP. During the
installation the first step is to move the BAB to the moon pool area. The capsule sections are
torqued on each other vertically and allocated inside the BAB. The next step is to torque the ESP
sections and connect it to the Pump Hanger which will be locked at the end of the capsule and
will seal the ESP inside. After that the MOBO will be locked on top of the Pump Hanger and
will make the flow connection between BAB and P.H..
After the MOBO connection, the equipment is ready to be deployed. At the sea bed the
equipment will be guided into the dummy wellhead by the capsule tip which makes the
alignment between equipment and wellhead much quicker.
After the equipment lock at the wellhead, a ROV shall be deployed to connect the
hydraulic and electrical jumpers between the MOBO System and the ULB. With the jumpers
connected, the system is ready to operate after the ESP topside system is installed in the FPSO.
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For any ESP work over, the pump can be retrieved inside the capsule which is hanged on
the MOBO, with that there is no need of any interference in the production well where the
Christmas tree is installed. That creates a much safer way of intervention as it is not direct into
the production well.
IV. FUTURE DRIVES
Today the MOBO system has two main competitors in which can be considered as future
alternatives for the ESP technology.
The first competitor is basically a Horizontal Wet Christmas Tree (HWCT) with an ESP
straight to the production well. The main advantage is that it exists economic savings when
building the field layout as it will have just one equipment (HWCT) for each well instead of two
(MOBO and WCT). The main disadvantage is that in every intervention into the well, will cause
the production stop due to the necessity of retrieving the ESP and any other system inside the
well, which may cause an operational risk.
The Horizontal ESP Skid is a new technology which is being proved to be easier to
install as it can be installed by boat and there is no need for a rig with drill pipe [11]. The
difference that allows this kind of installation is that the ESP is allocated horizontally inside the
equipment, which is a huge frame for protection. The horizontal position allows the ESP to be
retrieved by cables. Another advantage is that no dummy well is needed as the ESP will not be
allocated below the sea bed, which potentially saves cost during the drilling phase.
Figure 15 – MOBO System (left)[12] and Horizontal ESP Skid (Right)[11]
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V. MOBO PHASE I X MOBO PHASE II
The client record shows, a second phase was developed for this type of system. As the
equipment engineering was ready, the main focus was in reduce cost, weight, decrease fluid
friction loss and to avoid the oil temperature loss. The accomplishments from this effort are
listed below.
Main differences between equipments:
MOBO Phase I
MOBO Phase II
Design
Electrical
System
4,7/8kV (Schlumberger Diamould)
5/8.7kV (Siemens Tronic)
BAB
- Flow line configuration not optimized
with high fluid friction loss;
- Flow line without elbows which
decreased fluid friction loss;
- New structure due to the new
flow line configuration;
MOBO
- Aprox. weight: 10 ton;
- Flow line configuration not optimized
with high fluid friction loss;
- Gate valves, lock connector and lifting
hub were separated from the main
body;
- Aprox. weight: 7.8 ton
- Flow lines without elbows which
decreased fluid friction loss;
- New structure due to the new
flow line configuration;
- Gate valves, lock connector and
lifting hub were integrated to the
main body;
VCM
- Aprox. weight: 2.5 ton;
- No secondary resident mech. unlock
system;
- Aprox. weight: 2.15 ton;
- Added Swivel;
- Added secondary resident mech.
unlock system;
- Internal pressure 3600 psi;
- Length 48m;
- Internal pressure 5000 psi;
- Length 50.7m;
- Added external thermal
insulation;
- Increased pipe thickness to
2000m;
CAPSULE
Table 1 – Comparison between MOBO Phase 1 and MOBO Phase 2
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VI. REFERENCES
[1] Richard F. Meyer and Emil D. Attanasi - Heavy Oil and Natural Bitumen-Strategic Petroleum Resources. Available at: http://pubs.usgs.gov/fs/fs070-03/fs07003.html
[2] Energy Information Administration (EIA) - Brazil Country Analysis Briefs. Available at:
http://www.eia.gov/countries/cab.cfm?fips=BR
[3] Ian M. Head, D. Martin Jones & Steve R. Later - Biological activity in the deep subsurface
and the origin of heavy oil, 2003.
[4] Kenneth S. Deffeyes - Hubbert's Peak: The Impeding World Oil Shortage, 2008.
[5] Association for the Study of Peak Oil –Hubbert Curve. Available at: ASPOITALIA.NET
[6] Heriot-Watt University – Selection of Artificial Lift Types, section 5.5. Available at:
http://seipg.files.wordpress.com/2011/04/criterios-de-seleccic3b3n-de-tipos-delevantamiento-artificial.pdf
[7] E.F. Nogueira, A.T Borges, C.J.M. Junior and R.D. Machado - Torpedo Base - A New
Conductor Installation Process, OTC 17197, 2005.
[8] Prysmian - FDT-0607 Umbilical Datasheet.
[9] ET-3000.00-1516-823-PEK-007 Rev A - Petrobras technical spec. “Medium Voltage
Power Electric System 8kVx220A, Pumping Module (MoBo) with BCSS.
[10] Norsok M710 - Qualification of non-metallic sealing materials and manufacturers, rev 2,
section 7.3, 2001.
[11] Roberto Rodrigues and Alex Dal Pont - O desafio da instalação de Módulos de
Bombeamento submarino, preferencialmente sem Sonda, 23º National Offshore and Naval
Construction Congress, 2010. [PORTUGUESE REFERENCE]
[12] Stuart L. Scott – Artificial Lift, 2008, page 66.
VII. CURRICULUM
Felipe Ehlke Anastacio has a Bachelors of Science degree in Electrical Engineering from UP
(Positivo University – Brazil). Since 2009, he has been working at AkerSolutions as a subsea
control systems engineer. Before his current position in the oil and gas industry, he acted in the
power turbine design for sugarcane refining for 1 year.
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Leandro Fischer has a Bachelors of Science degree in Mechanical Engineering from UFSC
(Federal University of Santa Catarina - Brazil). Since 2011, he has been working at
AkerSolutions as a subsea control systems engineer. Before his current position in the oil and
gas industry, he acted in the machinery industry for 1 year.
Juliano Pimentel has a Master of Science in Electronic Engineering from ITA (Technological
Institute of Aeronautics – Brazil). He has been in the Subsea Engineering for nearly 10 years,
currently working at AkerSolutions and previously for FMC Technologies.
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