WO2015010728A1

WO2015010728A1 - Methods and apparatus for removing fluid from a well

Info

Publication number: WO2015010728A1
Application number: PCT/EP2013/065545
Authority: WO
Inventors: Tord Jensen
Original assignee: Statoil Petroleum As
Priority date: 2013-07-23
Filing date: 2013-07-23
Publication date: 2015-01-29

Abstract

Apparatus and methods of removing fluid from at least one underwater well are described, the fluid being received in the well from a subsurface region of the Earth. In at least one embodiment, compressed first gas is combined with the received fluid in the well to provide gas-assisted flow through a section of the well to facilitate removal of the received fluid. Second gas is then separated from the flow and is compressed to produce the compressed first gas, with the separation and compression of the second gas being performed under water.

Description

Methods and apparatus for removing fluid from a well

Field of the invention The present invention relates to the removal of fluid from a well, in particular with the assistance of gas lift.

Background Wells are typically provided in the subsurface of the Earth in order to extract fluids from the subsurface. In oil and gas production, it is sought to extract hydrocarbon fluid from the subsurface. The natural pressure conditions in the subsurface are often such that the hydrocarbon fluid flows naturally from the lower section of the well, at the reservoir region, up through the well to the surface. In some wells however, it is necessary stimulate the flow of fluid to help lift the fluid to the surface. This can be performed by "gas lift" which comprises injecting compressed gas into the hydrocarbon fluid, at one or more locations along the well, to improve the flowability of the fluid to help remove the hydrocarbons from the well. This can be particularly helpful where the hydrocarbon fluid comprises heavy oil. The weight of the fluid column in the well becomes lighter with increasing gas content. Hence, the wellhead pressure increases when the density is lowered by the gas.

With reference to Figure 1 , there is shown a traditional arrangement 1 by which hydrocarbons produced from a subsurface reservoir 2 can be removed from a subsea hydrocarbon production well 3. Compressed gas is supplied to the well from a topside facility, in this case a production vessel 5 along gas supply line 4, and is received at an injection location 6 along the well. At this location, the compressed gas is injected into the production tubing provided inside the well. The gas thereby combines with the hydrocarbon fluid inside the tubing, generating a gas-assisted flow 7 to help lift the hydrocarbons up through the tubing and out of the well at an upper end 8 at the seabed. The fluid of combined hydrocarbons and injected gas flows out of the well and is conveyed along a fluid return pipeline 9 back to the vessel 10. On the vessel, the returned fluid from the well is processed. Typically, this includes separating the gas and liquid contained in the fluid and then compressing the gas so that it can be conveyed to the injection location 6 via the supply line 4, and used to provide "lift gas" to generate the gas-assisted flow. In this way, the returned lift gas from the injection step can be separated and re-used in the well to provide gas-assisted flow.

In the case of wells which require insertion of gas to lift hydrocarbons from the well, significant losses in gas pressure can occur along the supply line to the injection location. Typically, a production vessel is provided to service several wells. In many fields the wells are located far apart, and may be located in deep water. This puts demands on the capacity of the vessel to compress gas such that the pressure loss is compensated for, and to provide space for the necessary equipment and future equipment or upgrades, etc. This is particularly an issue where wells that are serviced by the vessel are far apart from each other or from the vessel, and may prevent new wells from being connected to the vessel. It may be a challenge to place a vessel in an efficient position and to be provided with the appropriate equipment to service the wells efficiently.

Summary

According to a first aspect of the invention, there is provided a method of removing fluid from at least one underwater well, said fluid being received in the well from a subsurface region of the Earth, the method comprising the steps of:

(a) combining compressed first gas with the received fluid in the well to provide gas-assisted flow through a section of the well to facilitate removal of the received fluid;

(b) separating second gas from the flow; and

(c) compressing the separated second gas to produce the compressed first gas of step (a); wherein steps (b) and (c) are performed under water.

According to a second aspect of the invention, there is provided apparatus for removing fluid from at least one underwater well, said fluid being received in the well from a subsurface region of the Earth, the method comprising:

combining means for combining compressed first gas with the received fluid in the well to provide a gas-assisted flow through a section of the well to facilitate removal the received fluid;

underwater separating means arranged to separate second gas from the gas-assisted flow; and at least one underwater compressor arranged to compress the separated second gas to produce said compressed, first gas.

According to a third aspect of the invention, there is provided a method of removing fluid from at least one underwater well, said fluid being received in the well from a subsurface region of the Earth, the method comprising the steps of:

(a) providing gas-lifted fluid flow from the well;

(b) separating gas from the gas-lifted flow, the separation being performed under water;

(c) compressing the separated gas to produce compressed gas, the compression being performed under water; and

(d) using the compressed gas to produce the gas-lifted flow in step (a).

The gas-lifted fluid flow may be a gas-assisted flow through a section of the well to facilitate removal and/or lift of the received fluid. Step (a) may be performed by combining the compressed gas with the received fluid in the well.

According to a fourth aspect of the invention, there is provided apparatus for performing the method of the third aspect.

Further features of the above aspects are set out in the claims appended hereto.

Each or any of these aspects may include further features as mentioned in relation to any other aspect, or as otherwise contained in the description, drawings or claims. Features from different embodiments may be combined in other embodiments in any appropriate way.

The inventors have identified various limitations associated with traditional solutions. Underwater gas separation and compression can be advantageous. This can provide significant benefits compared with prior art solutions for providing gas-assisted removal of fluid from the well. In particular, the process capacity of hydrocarbons can be significantly improved and fluid production infrastructure made more efficient, both in terms of space and equipment on a surface production vessel and ability to service multiple gas lift wells. The invention can enable removal of gas at the seabed adjacent or possibly close to the well which can reduce the total friction losses compared with many traditional arrangements.

Description and drawings

There will now be described, by way of example only, embodiments of the invention with reference to the accompanying drawings, of which:

Figure 1 is a schematic representation of apparatus for removing fluid from an underwater well, according to the prior art;

Figure 2 is a schematic representation of apparatus for removing fluid from an underwater well, according to an embodiment of the invention; Figure 3 shows a multi-well arrangement using the apparatus of Figure 2;

Figure 4 shows another multi-well arrangement using the apparatus of Figure 2; and

Figure 5 is a flow diagram of a method according to an embodiment of the invention.

With reference now to Figure 2, there is shown apparatus 1 1 by which hydrocarbon fluid produced from a subsurface reservoir 12 can be removed from a subsea hydrocarbon production well 13. Features which correspond with like features to those in Figure 1 have the same numerals but incremented by ten. Compressed gas (first gas) is supplied to the well from a subsea gas compressor 20 along gas supply line 14, and is received at an insertion location 16 along the well. At this location, the compressed gas is inserted, e.g. injected, into the production tubing provided inside the well. The gas is combined with the produced hydrocarbon fluid inside the tubing, generating a gas-assisted flow 17 to help lift the hydrocarbon fluid up through the tubing and out of the well at an upper end 18 at the seabed. The produced hydrocarbon fluid comprises oil extracted from a hydrocarbon reservoir, into which a lower end of the well extends, in the subsurface region. The oil may be of any kind, and in some cases can be heavy oil. Completion equipment is provided in the well to allow fluid contained in the geological formation in the subsurface region to flow into the lower end of the well and into the production tubing. The combined hydrocarbon and inserted gas (combined fluid) flows out of the well at the upper end and along a fluid return line 19 back to a separator 22, also provided subsea, on the seabed.

The separator is used for removing gas from the gas-assisted flow. The removed gas (second gas) is supplied to the compressor 20 via a gas supply line 21 between the separator and the compressor. The compressor is used for compressing the removed gas. The compressed gas is conveyed to the well to the insertion location 16 and is combined with the fluid in the well. The step of removing gas results in removed gas for supplying to the compressor and in downstream production fluid for supplying to a downstream production facility at the surface. The downstream production fluid (without the removed gas) typically contains the produced hydrocarbon liquid, or components therefrom. The downstream production fluid is conveyed through the facility return line 23 to a topside processing facility 24, for example provided on a platform such as a floating production storage offshore (FPSO) vessel or other floating platform.

The compressor and separator are preferably located as close as possible to the well or wells that they serve, e.g. in the event of multiple wells at an equidistant point between them. Each of the separator and compressor are configured to be located on the seabed at or adjacent the well, for instance. In doing so, frictional losses in the pipelines leading away from the well can be minimised.

In practice typically, only some fraction of the gas in the fluid is removed. The gas in the fluid can comprise the inserted gas used for provding the gas lift or comprise gas which is not inserted as such, but which is naturally present in the hydrocarbon fluid from the formation, or mixtures of both. It is not necessary to remove all gas from the fluid. Typically, the object is to extract enough gas from the fluid to supply to the insertion location for providing gas lift. Since not all gas needs to be removed, the separator requirements can be less strict, as compared with traditional well stream separators that are typically configured to generate high specification export gas.

It will be noted that the subsea compressor 20 can be driven by an electric motor 25, in which case a power cable 26 is provided from the topside facility to provide the electric motor with power to operate the compressor. In addition, an optional facility gas supply line 27 is seen in Figure 2 for supplying gas from the topside facility to the injection location 16 along the well if required. This may be useful to help kick start fluid flow from the well before the subsea gas compression is started in wells that do not flow without gas lift. It may also be necessary to supply additional gas through the supply line 27 if the well fluid alone does not contain enough gas to generate the gas lift. Gas could be supplied in different ways for example by supplying it from a surface platform, service vessel or from gas accumulators in which gas is stored, etc.

Although injection of compressed gas for producing lift is shown to take place at one location in the Figure 2, it will be noted in general that injection of gas at further locations along the well may be appropriate.

In some embodiments, the compressor is configured to handle wet gas from the separator. Thus, the separated gas may contain a small amount of liquid, i.e. may be "wet gas". The separator 22 is preferably a simple and compact arrangement. In order to provide a suitable gas that the compressor can accept, a subsea gas scrubber could be used in some embodiments to remove liquid in line 21 carried over from the compact subsea gas separation unit 22 before entering the subsea gas compressor 25. This may be useful for example to reduce liquid content in the gas from the separator, so that the gas which enters the compressor is within the liquid tolerance range of the compressor. This may be applicable for example if the liquid tolerance of the compressor is low, e.g. a "dry gas" compressor, or if the initial separation of gas from the fluid by the separator 22 is relatively crude.

In embodiments where the compressor can accept wet gas, the performance requirements of the separator can be relatively relaxed, in that the removed gas does not have to be dry.

By removal of the gas at the seabed, compression and separation capacity topside may not be needed or may be dedicated to other uses. An increase in the export capacity may be gained where subsea gas lift is retrofitted to an existing gas lift well. It will be appreciated that the compressed gas can be inserted through the wall of production tubing using a gas lift valve. The production tubing is provided in the well and receives the hydrocarbons from the formation therein. The gas lift valve is provided on the production tubing, for example in the wall, so that compressed gas can be inserted through the wall from the outside to the inside of the tubing.

Various flow valves are shown in Figure 2, so that production of fluid from the well can be controlled by controlling the valves. In addition, flow valves are provided to be able to direct flow optionally along a bypass line past the separator 22, for example for performing tests or maintenance.

Turning to Figure 3, an arrangement of production well templates across a region of the seafloor is indicated by reference numeral 30. The wells are connected to a floating production facility 31 . A production well 33 is configured in the same way as well 13 described above in relation to Figure 2, the numerals of like features being incremented by twenty. A compressor station 40 and a separator arrangement 42 are located on the seabed close to the well template. The compressor station includes a compressor which is used to deliver compressed gas into the well along the supply line 34. The separator arrangement 42 is arranged to receive gas-assisted flow from the well and separate gas from the fluid. The removed gas is supplied to the compressor and compressed. Thus, gas from the well is compressed and re-used continuously via the loop 48 as production of hydrocarbons progresses. Downstream production fluid is conveyed through the facility line 43 back to the vessel for further processing. In this example, compressed gas is also supplied from the vessel to the well 55, through gas supply lines 50a-c. The compressed gas is routed to the well 55 via well templates 53 and 54, each of these wells also being supplied with the compressed gas to provide gas lift. An advantage in this case is that that the gas supply lines 50a-c from the vessel do not need to extend all the way to the well 33.

Turning to Figure 4, another example of an arrangement of production well templates across a region of the seafloor is indicated by reference numeral 60. The arrangement includes the same wells as in Figure 3, denoted by the same numerals but incremented by thirty.

In this example, the separator arrangement 72a is located so as to receive gas-lifted flow from both the wells 63 and 85. Flow lines 68a, 68b out of the wells join each other to provide a common line for containing the flow from both wells, upstream of the separator arrangement 72a. Another separator arrangement 72b is provided to receive gas-lifted flow from the wells 83 and 85. Each separator arrangement 72a,72b is arranged to receive their respective gas-lifted flow from the well and separate gas from the fluid. The separated gas is fed to a compressor station 70. Thus, the compressor station, and the compressor(s) provided therein, may be arranged to receive gas separated from gas-lifted flows from different wells. Compressed gas from the compressor(s) is delivered from the compressor station into the wells 84 and 85 along the supply lines 64a, 64b respectively. Part of the compressed gas in line 64a is conveyed to an injection subsurface location along the wellbore of each of the wells 84, 85 for injection. A second part of the injected gas is passed onward from the template of well 85 to the well 63 where portion the second part is injected at an injection location along that well. Likewise, a first portion of the compressed gas provided through line 64b is sent into the well 84 for injection, and a second portion is injected passes onward and is injected in well 83 to provide lift.

Downstream production fluid (left over after removal of gas and containing hydrocarbons produced from the formation) is conveyed through the facility lines 73a,b back to the vessel for further processing. As can be seen, the facility line 73a carries downstream production fluid from the wells 63 and 85, whilst the facility line 73b carries downstream production fluid back to the vessel from the wells 83 and 84.

An advantage in this variant compared with that of Figure 3, is that long compressed gas supply lines 50a-c are not required, as the compressed gas can be supplied to the necessary wells 63, 84 and 85 by separating gas from two streams of fluid and using a local compressor station close to the wells. The compression requirements on the vessel can therefore be further reduced.

An example method for removing the produced fluid from a well has the following steps S1 to S5, with corresponding references being shown in Figure 5: S1 . Gas-assisted flow is provided through a section the production tubing in the well. S2. The produced fluid, including hydrocarbons extracted from the Earth's subsurface, is lifted to the top of the well (e.g. the well head) by way of the gas-assisted flow.

53. Gas is separated from the flow. The separation is performed at a location downstream of the well, at which point the gas-assistance is no longer required.

54. The separated gas is compressed subsea, for example using a compressor nearby the separation location. S5. The compressed gas is combined with produced fluid in the well, e.g. via injection through gas lift valve, at a combining location along the well, between the upper and lower end of the well, in order to produce the gas assisted flow in S1 .

Various modifications may be made without departing from the scope of the invention herein described.

Claims

CLAIMS:

1 . A method of removing fluid from at least one underwater well , said fluid being received in the well from a subsurface region of the Earth, the method comprising the steps of:

(b) separating second gas from the flow; and

(c) compressing the separated second gas to produce the compressed first gas of step (a) ;

wherein steps (b) and (c) are performed under water.

2. A method as claimed in claim 1 , wherein step (c) is performed at or adjacent to the well.

3. A method as claimed in claim 2, wherein step (c) is peformed using at least one underwater compressor.

4. A method as claimed in claim 3, wherein the well has a well template, and the compressor is provided on a compressor frame separate from the well template.

5. A method as claimed in any claim 3 or 4, wherein the compressor is a wet gas compressor.

6. A method as claimed in claim 1 , wherein step (b) is performed at or adjacent to the well.

7. A method as claimed in any preceding claim , wherein step (b) is performed using at least one underwater separator.

8. A method as claimed in any claim 7 when dependent upon claim 3, wherein the well has a well template, and the separator and the compressor are provided on a frame which is separate to the well template.

9. A method as claimed in claim 7, wherein the well has a well template, and the separator is provided on a separator frame separate from the well template.

10. A method as claimed in any preceding claims, wherein either or both of steps (b) and (c) are performed at a distance away from the well of up to 500 m.

1 1 . A method as claimed in any preceding claim , wherein said second gas is a fraction of total gas in said flow.

12. A method as claimed in any preceding claim , wherein said second gas alone provides the necessary supply of gas to produce the gas assisted flow in step (a), such that additional gas to that present in the flow is not required.

13. A method as claimed in any preceding claim , wherein the at least one underwater well comprises first and second underwater wells, and steps (a) and (b) are performed with respect to each of first and second wells, and step (c) is performed using a common compressor or compression facility arranged to receive the separated second gas and produce the first gas from both the first and second wells.

14. A method as claimed in claim 13, which further includes combining the second gas associated with the first and second wells, and receiving the combined second gas at the compression facility.

15. A method as claimed in claim 14, wherein step (c) comprises compressing the combined second gas to produce a common supply of the compressed first gas with respect to the first and second wells.

16. A method as claimed in any preceding claim , wherein the at least one underwater well comprises first and second underwater wells, and steps (a) to (c) are performed separately with respect to each of the first and second wells, step (c) being performed using first and second compressors or compression facilities respectively to produce the first compressed gas for the first and second wells.

17. Apparatus for removing fluid from at least one underwater well, said fluid being received in the well from a subsurface region of the Earth, the method comprising: combining means for combining compressed first gas with the received fluid in the well to provide a gas-assisted flow through a section of the well to facilitate removal the received fluid;

underwater separating means arranged to separate second gas from the gas- assisted flow; and

at least one underwater compressor arranged to compress the separated second gas to produce said compressed, first gas.

18. A method of removing fluid from at least one underwater well , said fluid being received in the well from a subsurface region of the Earth, the method comprising the steps of:

(a) providing gas-lifted fluid flow from the well ;

(d) using the compressed gas to produce the gas-lifted flow in step (a).

19. Apparatus for performing the method of claim 18.

20. An underwater compressor for use in the method of any of claims 1 to 16, or claim 18, arranged to compress the separated gas so as to produce the compressed gas for providing the gas-assisted flow.