NO20160416A1

NO20160416A1 - Flexible subsea pump arrangement

Info

Publication number: NO20160416A1
Application number: NO20160416A
Authority: NO
Inventors: Knut Møgedal; Gunder Homstvedt
Original assignee: Aker Solutions Inc
Priority date: 2016-02-19
Filing date: 2016-03-11
Publication date: 2017-08-21
Also published as: GB2563780B; BR112018016538A2; GB201906609D0; BR122020003256B1; US20190040718A1; GB2563780A; CA3014535A1; GB2575534B; GB2575534A; BR112018016538B1; GB201815147D0; NO20181211A1

Description

FLEXIBLE SUBSEA PUMP ARRANGEMENT

Field of the invention

The present invention relates to subsea pumping of hydrocarbon fluids from subsea wells and subsea hydrocarbon production systems.

Background of the invention and prior art

Subsea pumping is crucial for increased recovery and production rate of oil and condensate. Thereby, subsea pumping can increase the value of an offshore field significantly. However, the technology for subsea pumping is complicated. Due to the location of the equipment for subsea pumping, reliability is a vital issue. Cost is also a vital issue, in particular when oil prices are low.

A demand exists for subsea pump arrangements resulting in lower cost over the life of such equipment. This includes not only the initial cost for the equipment itself, but also the cost for installation, repair or replacement of the equipment, possible upgrading or modifications, and even effects on adjacent subsea equipment.

Based on ongoing incentives to reduce cost, some significant attempts are made to install downhole pumps in a subsea environment. Such pumps, called Electric Submersible Pumps (ESP) are widely used as arranged downhole into wells, for artificial lift in wells. Due to their mature design and sales quantity they can be regarded as a commodity item at reasonably low cost. However installing them for subsea use, which means not downhole into a well but subsea on or near the seabed, pose a significant challenge. Some of this work is described or illustrated in the prior art publications listed below.

The most relevant prior art publications identified are:

[1] US 7150325 - "ROV Retrievable Sea Floor Pump" by Baker Hughes Inc. describes a retrievable pump in a caisson.

[2] US 7565932 - "Subsea Flowline Jumper containing ESP" by Baker Hughes

Inc. describes an ESP (Electrical Submersible Pump) arranged inside the horizontal section of a flowline.

[3] US 2010/0119382 - "Subsea Pumping System with Interchangeable Pumping Units" by Schlumberger describes a retrievable ESP arranged in a pipe mounted onto a base.

[4] US 7516795 - "Subsea Petroleum Production System Method of Installation and Use of Same" by Petrobras describes two ESPs arranged in a skid mounted onto a base.

[5] US 7314084 - "Subsea Pumping Module System and Installation Method" by Petrobras - describes a vertical arrangement to install an ESP subsea. A horizontal orientation of an ESP is mentioned, but no further details are described other than arranging the ESP in a closed tubular body arranged onto a single base.1

[6] WO 2015/199546 A1-"System for subsea pumping or compressing " by Aker Subsea AS - describes a system for a flowline installed ESP pumping system. The system has two bases separated some substantial distance apart for landing and connecting the system to the flowline. A buoyancy and stiffening arrangement with the pipe-enclosed ESP is described to limit the stresses and deflection in the system.

The present invention is a further development of the teaching of said prior art publications.

Summarv of the invention

The invention provides a subsea pump arrangement, comprising a base module and a pump module, distinguished in that the pump module is separated in horizontal direction from the base module and is not supported or only partially supported by the base module.

With the subsea pump arrangement of the invention, all heavy equipment in less demand for replacement or maintenance are located on and supported by the base module, whilst the pump module, comprising ESPs or subsea pumps in larger demand for replacement or maintenance, is located horizontally apart, as a module low in weight, easily accessible and particularly adapted for easy

and safe installation and retrieval.

The phrase "the pump module is separated in horizontal direction from the base module" means separated in direction in principle 90° from vertical. Said separation provides improved access for installing and retrieving the pump module, resulting in faster, safer and less expensive installing and retrieving. Except for possible and often preferable trawl protection structure, access from above is without restriction.

The phrase "the pump module is not supported or only partially supported by the base module" means that the weight of the pump module is not or only in part supported by the base module. The pump module comprises a pump module support structure and optional other features for limiting or eliminating the pump module weight that is supported by the base module.

The connection between the pump module and the pump base is preferably arranged with flexible flowlines or steel tube flowlines that has an elongated section creating flexibility to bending without causing excessive stress or fatigue concern.

The subsea pump arrangement of the invention can have numerous embodiments, comprising features as described, illustrated or claimed in this document in any operative combination.

Preferably, the base module comprises a foundation, an inlet coupling part, an outlet coupling part, a bypass line with a bypass valve arranged between the inlet coupling part and the outlet coupling part, and at least one pump module coupling part between said inlet coupling part and outlet coupling part, and isolation valves and guideposts.

In addition, the base module preferably comprises a fluid conditioner unit (FCU) or an arrangement therefore, between the inlet coupling part and the at least one pump module coupling part, a liquid collection unit (LCU) or an arrangement therefore, between the at least one pump module coupling part and the outlet coupling part, and a recirculation line with an adjustable choke, the recirculation line arranged between the LCU and the FCU.

Most preferably, the pump module comprises a U-shaped flow conduit or pipe with inlet and outlet in only one end, the pump module comprising at least one pump arranged in said conduit or pipe, and a pump module support structure. Preferably, the pump module is horizontally oriented as installed, containing two oppositely but horizontally oriented ESP's, one in each horizontally oriented leg of a U shaped pipe or conduit.

Preferably, the pump module comprises connector parts for inlet and outlet in only one end. Preferably said connector parts are oriented vertically downwards with the pump module as installed, comprising a dual bore connector part, two separate single bore connector parts for inlet and outlet, respectively, or one or more multi-bore connector parts, the base module comprising matching connector parts oriented vertically upwards with the base module as installed, the mated connector parts as installed connect the base module operatively to the pump module. The connectors are preferably damp or collet connectors operable by ROV, preferably a single dual bore or multi-bore damp connector.

The pump module preferably comprises a stiffening structure, comprising one or more of a truss structure, stiffening ribs, stiffening beams or pipes, and additional U-shaped conduits or pipes with or without pumps and connector parts for later inline coupling, or other stiffening structure.

One embodiment of arranging such a stiffening structure is, as illustrated in the attached figures, by welding two steel plates onto the sides of the horizontal pipe sections of the U-shaped pipe assembly. The plates have materials removed to reduce weight, but in such a way that a truss-like pattern is created. These plates attached to the two pipes are thereby forming a very stiff structure and still keeping the weight low. An alternative arrangement is to weld beams/plates in-between the horizontal pipe sections of the U-shaped pipe assembly to create a truss-like structure. This can be done by welding in plates håving a 90 degree and typically a 20 degree angle to the pipe axis between the two pipes axially separated apart. Reference to figure 5 is made to illustrate the arrangement. For those skilled in the art it is clear that alternative arrangements can be made to maintain stiffness and still keep the weight low while integrating the two flow pipes in the arrangement.

Preferably, the pump module comprises load-limiting elements, comprising one or more of buoyancy elements, gas filled tanks or gas filled pipe elements or other load limiting structure.

The base module comprises a foundation, preferably comprising one or more of a pile, a suction anchor or a mud mat.

Preferably, the pump module comprises an adjustable support structure, for example comprising an ROV torque tool operable support structure height adjustment.

Preferably, the pump module comprises an ROV panel with or without ROV docking structure, said panel comprising ROV receptacles or sockets with connectors or bores for hydraulics and electrics for flow assurance and electric power to the pump.

The subsea pump arrangement preferably comprises transmitters for inclination, a water level or bubble level or bullseye, height/position for the pump module, and/or other instrumentation, and guide funnels.

The pump module support structure preferably is releasable and connectable by ROV, alternatively said support structure is fixed to the pump module.

In an alternative embodiment, using a subsea pump instead of an ESP, the pump module is horizontally oriented as installed, containing one or two subsea pumps horizontally oriented in a U shaped pipe or conduit. Alternatively, the one or two subsea pumps are vertically oriented in a vertically oriented U shaped pipe or conduit.

However, most preferably, one or two ESPs are horizontally oriented in a horizontally oriented U shaped pipe, with the pipe legs as load carrying members in a truss arrangement where the pipe legs are interlinked with steel members. This arrangement results in a very stiff pump module structure giving good support for the long ESP rotor assembly, ensures good rotor-dynamic performance and long service life.

The two pipe legs of a U shaped pipe or conduit, containing one or two ESPs or subsea pumps are preferably horizontally oriented but arranged vertically above each other, with a truss structure between the pipe legs, which provides a very stiff, lightweight structure with improved stability and stiffness for handling during installation and retrieval.

Preferably, the pump module comprises sections with flexible connection flowlines near the coupling between the pump module and the base module, to allow for some subsidence of the pump module support structure without creating undue stress.

The pump module preferably comprises a U shaped pipe or conduit, with distance between the legs of the U, which provides easier handling, increased stiffness (easy to include truss structure) and optional integration of buoyancy, compared to prior art solutions. Including the horizontal pipe sections containing one or more pumps as part of the stiffening arrangement is a vital part in reducing the pump module weight as no other longitudinal parts are needed to achieve the required stiffness.

Since connection is arranged only in one end of the pump module, the other end is free to move axially due to change in temperature and pressure in the pump module for various operational conditions. Arranging the support structure at an axial distance of approximately 2/3 of the overall length from the connector also significantly reduces the deflection and stress in the pipes. Since the free end acts as a counter-weight, the pipe arrangement has an almost stiff anchor at the location of the support structure.

Since the pump module has a connection only in one end, and fixed or preinstalled adjustable pump module support structure, no metrology is required prior to installation. This eliminates a survey trip with the installation vessel that otherwise would have been required, reducing cost and installation time.

Reduced size, length and weight contribute to the advantages provided with the invention. Arranging the pump module couplings or coupling parts on only one side facilitates installation and retrieval, allowing use of for example a single dual or double single-bore damp connector, reducing the number of critical fluid connector coupling operations to a single coupling operation. Compared to the standard design, as described and illustrated in prior art [2] US 7565932 and [6] WO 2015/199546 A1, the pump module length is typically reduced by 20% and the weight reduction is typically 25 %. If the subsea pump arrangement requires a fluid conditioning system, the weight reduction is typically 55%. A significant reason for this saving is eliminating the gooseneck arrangement that is typically required in prior art solutions. Such axial flexibility arrangement in the prior art is required to allow for temperature and pressure elongation plus the adjustment required to adapt to the distance between the two connection stations after installation.

The arrangement of the invention is more suitable for including trawling protection than prior art arrangements as the unit can be arranged with low vertical height limiting the snagging profile of the protected equipment.

Figures

Figure 1 is a schematic illustration of an embodiment of a subsea pump arrangement of the invention, comprising two ESPs. Figure 2 illustrates the principal arrangement of the embodiment illustrated in figure 1, as top and side views, respectively. Figure 3 illustrates a pump module with dual ESPs of an arrangement of the invention, during installation. Figure 4 illustrates the subsea pump arrangement comprising an alternative stiffening arrangement for the pump module. Figure 5 illustrates the subsea pump arrangement comprising trawling protection.

Detailed description

Figures 1 and 2 illustrate how the subsea pump arrangement of the invention has a modular and different design than prior art systems.

The principle is to locate all heavy items that are in lesser need for regular service onto a larger base module (1). The ESP is enclosed in a pipe interconnected with a return pipe to ensure stiffness. This unit is called the pump module (2) and is coupled to the base module (1). The base module (1) has a foundation (5) that is resting on the sea floor either on a pile, suction anchor or mud-mat depending on the soil conditions. The pump module (2) is partly resting on the base module and partly on a pump module support structure (6) with a foundation (7) onto the sea floor.

The well flow (3) is fed through a flowline via an inlet connector (10) at the base module. The boosted flow (4) is routed out of the base module through an outlet connector (11). The flow is routed from the base module (1) to the pump module (2) via a dual bore connector (21).

The base module (1) comprises the components that are not likely to need much maintenance. More specifically, the base module comprises the following components:

■ In and outlet flow line connections (10 and 11)

■ By-pass line (12) with a bypass valve (13)

■ A fluid conditioning system with

□ Fluid conditioning unit (14) for gas/liquid homogenizing and mixing □ Liquid collection unit (15) for gas/liquid separation and liquid collection □ Recirculation line (16) with adjustable choke (17)

■ Pump module connector (21) or pump module connector part, allowing connection to the pump suction and discharge being arranged with flexible

connection flow lines (18)

■ Isolation valves (19 and 20) for the pump input/output connections

■ Guide posts (27) for easier landing and coupling of the pump module (2) during installation

The pump module (2) only comprises the essential parts to caterfor the ESP(s): ■ A horizontally oriented U shaped pipe (22, 23) where one leg is the first canister or first pipe leg with 1. stage ESP (24) and the other leg is the second canister or second pipe leg with 2. stage ESP (25). If only one pump is needed, the second canister or pipe leg is an empty return transfer pipe, typically of smaller diameter than the first canister or leg. The ESPs are horizontally oriented, but oppositely directed, in respective horizontally oriented canisters or pipe legs.

■ Base module connector (21) or base module connector part

■ An ROV panel (26) for power connection to the ESPs plus any hydraulic or electric connections needed for flow assurance or instrumentation. ■ Support members (29) connecting the two canisters/pipes (22 and 23), as a truss structure, securing stiffness to limit sagging of the ESPs to ensure good rotor-dynamic stability of the motor/pump-rotor.

■ Guide funnels (28) for landing onto the guide posts (27).

■ It is preferable that the pump module comprises no fluid conditioning unit, in contrast to prior art solutions. This means that the U shaped pipe do not comprise an integrated fluid conditioning volume orfunction. The result is an improved advantage with respect to weight, size and ease of handling during installation and retrieval, enhancing the advantages of the invention. ■ It is preferable that the pump module comprises no fluid separation unit or fluid phase collection unit, in contrast to prior art solutions. This means that the U shaped pipe do not comprise an integrated fluid separation or collection volume orfunction. The result is an improved advantage with respect to weight, size and ease of handling during installation and retrieval, enhancing the advantages of the invention.

The pump module has flow connection only in one end. The free end is supported in the vertical direction via a support structure (6) resting at a small base (7) at the seafloor. This support structure is typically attached and hinged to the pump module and thereby installed together with it. The support will be released to its landing position during the final phase of the installation process. A height adjustment mechanism can be included in the case of a soft soil condition. An ROV operated mechanical screw adjustment is indicated in figure 2. Alternative height adjustment arrangements can be utilized.

Lifting for installation of the pump module (2) with two ESPs in series is illustrated in Figure 3. Figure 4 illustrates the subsea pump system comprising an alternative arrangement for stiffening of the pump module. The figure also illustrates an arrangement with only one ESP and a smaller diameter return pipe or U pipe leg. Figure 5 illustrates how trawling protection can be arranged. One protection structure (31) is arranged for the base module and another (32) for the pump module. Said structures are typically supported by a suction anchor (30), but could also be supported by a pile or otherwise to take the loads that can occur during trawling. Minimising the height of the system is important; therefore the pump module is arranged close to the sea floor. Hatches (33) that can be opened by an ROV are located along the protection structure to allow access during installation, retrieval or service. This figure illustrates one arrangement, but for those skilled in the art it is obvious that different arrangements can be made taking advantage of the low height above the sea floor.

The subsea pump arrangement of the invention provides at least the following advantages: ■ Thermal expansion of the pump module is allowed by håving one end free to move in the axial direction without including large goosenecks thereby limiting the installation size and weight ■ No need for metrology for locating the connection points of the pump module since they are connected through a single connector or two connectors at one end only ■ The pump module support structure will be attached to the pump assembly and installed together with it. It can however be detached and left in place when the pump module is retrieved for service. Support height is preferably ROV adjustable if soil condition is soft or undetermined. The support leg preferably can be axially positioned at approx. 2/3 of the overall distance from the connector along the pump module for optimum support achieving minimum sagging. ■ Flexibility is built into the feed and return-pipes at the connector. The height of the pump module support structure is therefore not critical. This is an important feature as it is likely that some sinking into the seabed soil can occur over time.

■ Installation time is minimized since only two units need to be installed.

■ A light invention vessel can be used for retrieval and installation of the pump module due to low weight ■ By-pass is arranged on the base module, avoiding any by-pass jumper ■ If trawling protection is needed, the pump module can be located at or very close to the seafloor covered with trawling protection structure like the ones used for protecting subsea installations and pipelines. ■ The length and weight reduction of the pump module is very significant compared to using a jumper arrangement to install a single ESP. The length is typically reduced by 20% and the weight reduction is typically 25 %. If the pump module requires a fluid conditioning system, the weight reduction is typically 55%. ■ Less weight and cost impact when upgrading to a higher pressure rating since the pump module has pressure containing items with smaller diameter compared with the jumper arrangement with fluid conditioning vessels included ■ The pump modules as illustrated can be exchanged with a standard vertical subsea pump module or other pump module, retraining the essential features of the invention, allowing standardization of the base module for a range of subsea pumps

In the case where only one ESP is to be installed, substantial weight can be removed by using a small diameter pipe as return-line. If the soil condition is stable, the level adjustment mechanism can also be removed. This is shown in figure 4. A weight reduction of more than 50% can be achieved by this arrangement compared with a flow line jumper where the fluid conditioning system and the by-pass line also have to be arranged between the landing bases.

The base module preferably comprises the Fluid Conditioning Unit (FCU, 14) and the Liquid Collection Unit (LCU, 15) as retrievable units. If there is no need for fluid conditioning in the early phase of the production, the base module can be installed with the piping and connectors in place, but without the FCU and LCU included. Both the manifold and the FCU and LCU would have to be installed with retrieval connectors in such case. When gas fraction is increasing and there is a need for fluid conditioning, the FCU and LCU can be installed afterwards.

The subsea pump arrangement of the invention can include any feature or step as here described or illustrated, in any operative combination, each such operative combination is an embodiment of the present invention. Furthermore, the invention also provides a method of installing or retrieving a subsea pump arrangement of the invention, or a pump module thereof, and use of the subsea pump arrangement for subsea pressure boosting, both of said method and said use can include any feature or step as here descried or illustrated, in any operative combination, each such operative combination is an embodiment of the present invention. For example, the pump module can be installed using an ROV for coupling and optional height adjustment based on measured parameters from the instrumentation of the subsea pump arrangement. The connector for coupling base module and pump module can comprise power and/or control connectors in addition to pump inlet and outlet bores, simplifying the arrangement and method even further.

Claims

1. Subsea pump arrangement, comprising a base module and a pump module,characterised in thatthe pump module is separated in horizontal direction from the base module and is not supported or only partially supported by the base module.

2. Subsea pump arrangement according to claim 1, wherein the base module comprises a foundation, an inlet coupling part, an outlet coupling part, a bypass line with a bypass valve arranged between the inlet coupling part and the outlet coupling part, and at least one pump module coupling part between said inlet coupling part and outlet coupling part, and isolation valves and guideposts.

3. Subsea pump arrangement according to claim 1 or 2, wherein the base module comprises a fluid conditioner unit (FCU) or an arrangement therefore, between the inlet coupling part and the at least one pump module coupling part, a liquid collection unit (LCU) or an arrangement therefore between the at least one pump module coupling part and the outlet coupling part, and a recirculation line with adjustable choke, the recirculation line arranged between the LCU and the FCU.

4 Subsea pump arrangement according to any one of claim 1-3, wherein the pump module comprises a U-shaped flow conduit or pipe with inlet and outlet in only one end, comprising two oppositely oriented ESP's, one in each leg of said U shaped pipe or conduit, said legs and ESPs are horizontally oriented.

5. Subsea pump arrangement according to any one of claim 1-4, wherein the pump module comprises a connector part for inlet and outlet in only one end, said connector part is a dual bore connector part oriented vertically downwards with the pump module as installed, matching a dual bore base module connector part oriented vertically upwards with the base module as installed, the mated connector parts as installed connect the base module operatively to the pump module.

6. Subsea pump arrangement according to any one of claim 1 -5, wherein the pump module comprises a stiffening structure, comprising one or more of a truss structure, stiffening ribs, stiffening beams or pipes, and additional U-shaped conduits or pipes with or without pumps and connector parts for later inline coupling.

7. Subsea pump arrangement according to any one of claim 1 -6, wherein the pump module comprises load limiting elements, comprising one or more of buoyancy elements, gas filled tanks or gas filled pipe elements.

8. Subsea pump arrangement according to any one of claim 1 -7, wherein the base module comprises a foundation comprising one or more of a pile, a suction anchor or a mud mat.

9. Subsea pump arrangement according to any one of claim 1 -8, wherein the pump module comprises a support structure, height adjustable, releasable and connectable with an ROV.

10. Subsea pump arrangement according to any one of claim 1 - 9, wherein at least one of the base module or pump module comprises sections with flexible connection flow lines, including or near to a coupling part for coupling the pumping module to the base structure.