System for increasing oil pressure from a well

Abstract

There is disclosed a system for increasing the pressure of produced oil from a well, the system comprising:• an inlet (11) for receiving oil from the well (4);• an outlet (13) for the oil; and• a pump (20) provided between inlet and the outlet for increasing the pressure of the oil from the inlet to the outlet, characterised in that the pump is integrated in, connected to or at least partially housed within a suction anchor (18).

Description

[0001] SYSTEM FOR INCREASING OIL PRESSURE FROM A WELL

[0002] The present invention relates to a system for increasing oil pressure from a well. In particular the invention relates to system using a pump to increase oil pressure from a well. The invention also relates to a production assembly including such a system.

[0003] The reduction in oil pressure from a well over time is a common phenomenon in the life of an oil reservoir. Several factors contribute to this decline in pressure. As oil is extracted from the reservoir, the pressure within the reservoir decreases. Initially, oil wells often experience a natural flow of oil due to the pressure in the reservoir. However, as more oil is produced, the pressure decreases, and the natural flow diminishes. Oil reservoirs typically contain a mix of oil, water, and gas, and as oil is produced, there may be an influx of water or gas into the well. Water and gas have different compressibility than oil, and their movement can affect the overall pressure in the reservoir. The formation surrounding the reservoir have a certain compressibility and as oil is extracted, the formation may compact, leading to a reduction in pore space and subsequently decreasing the reservoir pressure. Some reservoirs have a natural gas cap above the oil zone. As oil is produced, the gas cap expands to fill the void left by the extracted oil. This expansion can also contribute to a decline in pressure.

[0004] It is known to use pumps, such as electric submersible pumps (ESP), in oilwells to increase pressure and facilitate production of oil. The ESP is often submerged into the wellbore, typically deep within the well, and is designed to push fluids, including oil, to the surface. However, installing ESPs by retrofitting them into the well can present significant challenges, including limited space and available power downhole, also taking into account that such pumps are usually quite large, even if they can be customized to specific wellbore dimensions. Attempts have also been made to install pumps in satellite wells, to which oil from a producing well is circulated to be boosted / pressure-increased, before sent to surface. However, drilling an additional well for the sole purpose of making such a pressure-increase is time consuming and very expensive. Access to the pumps, such as for maintenance or replacement, is also challenging. More recently, it has been proposed to install booster pumps on skids on the seabed, which provides improved access to the pumps. However, a skid is not a sufficiently stable connection point / anchor for a riser to connect the pressure-boosted, produced oil to a surface offtake installation. Such a stable connection point will therefore have to be installed separately.

[0005] The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

[0006] The object is achieved through features, which are specified in the description below and in the claims that follow.

[0007] The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

[0008] In a first aspect the invention relates to a system for increasing the pressure of produced oil from a well, the system comprising:

[0009] - an inlet for receiving oil from the well;

[0010] - an outlet for the oil; and

[0011] - a pump provided between inlet and the outlet for increasing the pressure of the oil from the inlet to the outlet, wherein the pump is integrated in, connected to or at least partially housed with a suction anchor.

[0012] By using a suction anchor, a combined base or housing for the pump and a solid connection point for an outlet line for produced oil, such as a riser or another pipeline is provided. The pump may be connected to the inside or outside of the suction anchor, such as inside a pipe extending through the suction anchor or in a storage volume inside the suction anchor as will be explained below. In one embodiment, the pump may be an electrical submersible pump (ESP). ESPs are known for their high efficiency in converting electrical power into mechanical energy for fluid lifting and can be equipped with variable speed drives, allowing operators to adjust pump speed to match changing well conditions. This latter feature enhances operational flexibility and efficiency. ESPs can be tailored to specific system conditions, including depth, temperature, and fluid properties and may operate continuously, providing a consistent and reliable means of lifting fluids from the system. Properly designed and installed ESP systems can have relatively low maintenance requirements, especially when compared to some alternative artificial lift methods.

[0013] It should however be noted that the present invention is not limited to the use of ESPs. In alternative embodiments, depending i.a. on the pressure boosting requirements and the available space and infrastructure, rod / beam pumps, progressing cavity pumps, jet pump systems, hydraulic piston pumps, hydraulic submersible pumps etc. may be used in the claimed system.

[0014] In one embodiment, the suction anchor may have a top portion formed with an opening therethrough, wherein the system further comprises a pipe inserted into the opening. The pipe may e.g. be a guide pipe, a conductor, or a surface casing. In certain embodiments, two or more of the mentioned pipes may be provided and concentrically arranged. The pipe(s) may be installed through and hung off in the suction anchor subsea or the pipe(s) may be integrated with the suction anchor topside before subsea deployment.

[0015] In one embodiment where conductor and surface casing are installed through the suction anchor, the stable nature of the suction anchor further allows the connection of a BOP run from a mobile drilling platform. The suction anchor provides a means to cope with the static and fluctuating (fatigue) loads that are exerted by the BOP. Similarly, loads from production, both static and fluctuating (fatigue), risers may be taken by the suction anchor. Although the application of a mobile drilling unit is not required, it could be beneficial to have the possibility to be able to do so in certain circumstances.

[0016] In one embodiment, an outer pipe may be integrated with the suction anchor topside before deployment, while an inner pipe may be installed once the suction anchor is in- stalled in the seabed. In one embodiment, the suction anchor may be a CAN® as commercially available from the present applicant. A CAN-basic has an integrated guide pipe, while a CAN-ductor comes with an integrated conductor.

[0017] In one embodiment the pump may be installed inside the (inner) pipe. The flow of oil from the inlet may e.g. be downwards in an annulus outside the pipe, and then up centrally inside the pipe through the pump and out through the outlet. The pipe may be a first pipe, and the annulus may be formed between the outside of the first pipe and the inside of a second pipe concentrically surrounding the first pipe. As such, the second pipe may be a guide pipe or a conductor, and the first pipe may be a conductor or a surface casing. The pipe (or pipes) may extend from the opening in the top of the suction anchor and down to below a lower end of a skirt of the suction anchor. In an alternative embodiment, one or more pipes may be connected to the suction anchor on the outside of the skirt so that the suction anchor as such remains unpenetrated by the pipes. The pump may be placed in this external pipe. In yet another embodiment, the pipe (or pipes) may be located inside the suction chamber of the suction anchor. "Inside" being defined as the pipe(s) extending downwardly from an opening in lid of the suction anchor, towards before lower end of the suction anchor skirt without extending all the way down to the skirt.

[0018] In one embodiment, the system may be provided with a riser connection. The suction anchor provides a rigid and robust anchor node for the riser connection. In principle, the riser connection may be provided anywhere on the suction anchor as long as it is in fluid connection with the outlet. The riser connection, which may e.g. be a flexible riser joint, may be provided on top of a valve assembly, such as a small valve tree ("Christmas tree") provided in connection with the outlet. The valve assembly may e.g. be provided on top of the suction anchor on a wellhead of the system. The valve assembly may be connected to the wellhead via a standard wellhead connector, such as an H4 connector and the riser connection may also be connected to the valve assembly by a similar or another standardised connector. Loads coming from the attached riser are significantly higher compared to loads coming from flow lines. Where riser elements are subjected to loads due to waves, currents, and movements of the floating production facility over the lifetime of the construction, flowline loads are limited to much smaller amounts, for example reoccurring temperature changes or one or more tie-in operations.

[0019] In an alternative embodiment, the pump may be included in or otherwise connected to valve assembly being provided with a connector, such as an H4 connector. The standardised connector and integration into an assembly will simplify lifting, installation, and removal of the valve assembly as a whole from a light-weight intervention vessel or a rig. The valve assembly may also include the inlet and the outlet and may optionally include a connector for a standardised running tool. In one embodiment the valve assembly may be installed by first integrating or installing a conductor through the opening in the suction anchor. The conductor may be pre-installed in the suction anchor such as in the mentioned CAN-ductor®. A surface casing or similar, with sufficient length to house the pump / ESP, may be hung off inside the low-pressure housing at the top of the conductor. The upper portion of the surface casing defines a high-pressure wellhead housing. The pump may then be installed in the surface casing, and the pump valve assembly may be locked and sealed in place in the high-pressure housing. The valve assembly will normally also include a connection for a power cable for operation of the pump. The valve assembly may include one or more valves between the inlet and outlet. The valve(s) may be check valve(s) that prevents backflow from the pump and which opens automatically when the pump and valve assembly is properly installed, and circulation starts. As an alternative or addition, one ore more valves may also be provided at the inlet and / or outlet that may be opened once the pump module is locked and sealed in place. A plurality of valves may in certain embodiments be required to satisfy barrier requirements. The valves at the in- let / outlet may be ROV-operable valves or hydraulicly operable valves, but a not limited to such. The outlet may be connected to an oil receiving facility / offtake by means of a pipeline, a riser, or another type of conduit.

[0020] In a second aspect, the invention relates to a production assembly for increasing the pressure of oil from a well, the production assembly comprising:

[0021] - a system according to the first aspect of the invention where a suction anchor is installed in a seabed;

[0022] - a producing well having an outlet for produced oil in fluid connection with the inlet of the system; and

[0023] - an offtake for oil in fluid connection with the outlet of the system.

[0024] In one embodiment a closed volume formed between the inside of the suction anchor and the seabed may provide a storage volume for oil and other produced fluids from the well upstream of the pump. The storage volume may e.g. be formed by the volume between a pipe, such as a guide pipe or conductor, extending centrally through the suction anchor, the surrounding skirt, and the seabed. In one embodiment, the suction anchor may deliberately not be penetrated fully into the seabed. E.g. a stick-up corresponding to 30-70%, such as 50% of the length of the skirt of the suction anchor, may remain above the seabed, thereby providing a substantive storage volume. An advantage of this is that it enables use of more robust pumps with larger diameters compared to conventional downhole pumps, which will also increase service life of the pump. In one embodiment, it may also be possible to separate oil from produced water in the storage volume, such as by a filter or other separation means. Water may be re-injected into an injection well or be pumped to a separate water treatment facility. Different pumps may be provided for pumping of oil and water and / or the intake of one or more pumps may be movable between the oil and water fractions. In addition or as an alternative, some of the soil inside the suction anchor may be washed out to provide the mentioned closed volume, whereby a storage volume maybe provided without any significant stick-up. In certain embodiments, a membrane may be provided to prevent soil from mixing with the produced fluids.

[0025] In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein:

[0026] Fig. 1 shows a system and a production facility according to the present invention; and

[0027] Fig. 2 shows an alternative embodiment of a system according to the present invention;

[0028] In following reference numeral 1 will be used to denote a system according to the first aspect of the present invention while reference numeral 10 refers to a production assembly according to the second aspect of the invention. Any positional indications refer to the position shown in the figures. In the figures, same or corresponding elements are indicated by same reference numerals. For clarity reasons, some elements may in some of the figures be without reference numerals. A person skilled in the art will understand that the figures are just principal drawings. The relative proportions of individual elements may also be distorted.

[0029] Fig. 1 shows, very schematically, a system 1 and a production assembly 10 according to the invention. A well 2 is producing oil from a reservoir 4. A flow of oil and other produced fluids is indicated with arrows extending vertically upwards from the reservoir 4 to a wellhead 6 with a valve assembly 8 on top. From the valve assembly 8, the flow of oil and other produced fluids is shown flowing to the right through a pipe 9 towards the system 1. As explained above, the pressure of the produced oil is insufficient for natural / un- assisted flow to surface and a pressure boost is necessary. In the system 1, the oil (and other produced fluids) flow into an inlet 11 provided in a system valve assembly 12, which may typically be a smaller valve assembly / valve tree ("Christmas tree") than the one on the producing well 2. The system valve assembly 12 is also provided with an outlet 13 for pressurised oil as will be explained below. From the inlet 11 at the system valve assembly 12 the oil flows downwardly in an annulus 14 between the outside of a first pipe 15 and the inside of a second pipe 16. In the shown embodiment, the first, inner pipe 15 is a surface casing, while the second, outer pipe 16 is a conductor integrated into a suction anchor 18 installed in a seabed S. The suction anchor 18 may be a CAN-ductor® commercially available from the present applicant. A pump 20, herein the form of an electric submersible pump (ESP), is installed inside the first pipe 15, as can be seen in the enlarged horizontal cross-section A-A. The oil flows downwardly in the annulus 14 and, when reaching the lower end of the first and second pipes 15, 16, upwardly centrally in the first pipe 15, through the pump 20. The pump 20 increases the pressure of the oil. If a significant pressure increase is required and / or if limited place is available for the pump 20, two or more pumps may be installed in series. Downstream of, i.e. above, the pump 20 in the drawing, the oil with increased pressure flows further upwardly through a system wellhead 22 to which the system valve assembly 12 is connected by means of a not shown standardised connector, such a H4 connector. The oil flows out through the outlet 13 in the system valve assembly 12 and further up through a riser connection 24, which is also connected to the system valve assembly 12 via a standardised connector, such as an H4 connector. A riser 26 extends from the riser connection 24, typically via a not shown flexible riser joint, to an offtake installation 27, here shown as a storage tanker floating at sea level T. Alternatively, the oil may be sent to another suitable receiving facility. The suction anchor 18 serves both as a housing and mechanical fundament for the pump 20 and as a rigid and reliable anchor node for the system valve assembly 12 and the connected riser 26.

[0030] Fig. 2 shows an alternative embodiment of a system 1 according to the invention. Here the suction anchor 18 also has an integrated conductor 16, such as in the mentioned CAN- ductor®. A surface casing 15 has been landed and locked into the conductor 16. However, in contrast to what was shown in Fig. 1, the pump 20 is integrated or otherwise connected to a valve assembly 28 that is deployed from surface, typically from a light-weight intervention vessel, as a whole and locked an sealed into a high-pressure housing 30 of the surface casing 15, the high-pressure housing 30 being landed and latched to a low- pressure housing 32 of the conductor 16, as will be understood by a person skilled in the art. It should be emphasized that the figure is highly schematic and that locking of the valve assembly 28 by means of a locking profile 35, here a H4 connector, to an outer profile 34 of the high-pressure housing 30 is only shown on the left-hand side of the drawing for simplicity. The pump 20 may be installed first before the valve assembly 28, or together with the valve assembly 28.An inlet 11, in the form of an inlet conduit 36 extends from the upper portion of the pump module 28, through the locking profile 35 of the pump module 28 and downwardly inside the surface casing 15. Towards the lower end of the surface casing 15, the inlet conduit 36 makes a 180° bend and mates with an intake 38 of the pump 20. A check valve 40 is optionally provided upstream of the intake 38. The oil further flows through the pump 20, up towards upper part of the pump module 28 and to the right in a conduit 41, extending through locking profile 35, and out through the outlet 13. In the shown embodiment, both the inlet 11 and outlet 13 are provided with valves 42 closing off the respective conduits 36, 41 before the pump module 28 is locked and sealed in place. To fulfil barrier requirements, a plurality of valves may be provided on each side, and disconnection of the valve assembly 28 from the high pressure housing 34 may be done between valves in a pair of valves on each of the inlet and outlet sides. The valves 42 may e.g. be operable by means of an ROV or may hydraulically operable. The valve assembly is also provided with a connection 43 for a power cable as well as a connector 44 for a running tool at its upper portion for easy installation and removal of the pump module 28 as a whole.

[0031] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any ref- erence signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0032] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

C l a i m s1. System for increasing the pressure of produced oil from a well, the system comprising:- an inlet for receiving oil from the well;- an outlet for the oil; and- a pump provided between inlet and the outlet for increasing the pressure of the oil from the inlet to the outlet, c h a r a c t e r i s e d i n that the pump is integrated in, connected to or at least partially housed within a suction anchor.

2. System according to claim 1, wherein the pump is an electrical submersible pump.

3. System according to claim 1 or 2, wherein the suction anchor has a top portion formed with an opening therethrough, wherein the system further comprises a pipe inserted into the opening.

4. System according to claim 3, wherein the pump is arranged inside the pipe.

5. System according to claim 4, wherein the pipe extends from the opening through the top portion of the suction anchor and to below a lower end of a skirt of the suction anchor.

6. System according to any one of the preceding claims, wherein the system is provided with a riser connection.

7. System according to any one of the proceeding claims, where in the pump is included in or connected to a valve assembly, the valve assembly being provided with a BOP connector, such as an H4 connector.

8. Production assembly for increasing the pressure of produced oil from a well, the production assembly comprising:- a system according to any one of the preceding claims where the suction anchor is installed in a seabed;- a producing well having an outlet for produced oil in fluid connection with the inlet of the system; and- an offtake for oil in fluid connection with the outlet of the system.

9. Production assembly according to claim 8, wherein a closed volume formed be- tween the inside of the suction anchor and the seabed, provides storage volume for produced fluids from the well upstream of the pump.

10. Production assembly according to claim 9, wherein the closed volume is provided with a separator for separating oil from produced water.

11. Production assembly according to claim 10, wherein the system is connected to the offtake via a riser.

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