HYDRATE REMOVAL IN HYDROCARBON WELLS

Abstract

A process for removing an obstruction (13) caused by gas hydrates or water ice from the tubing (12) of a hydrocarbon production or injection well or a riser using a microwave. The process comprises passing a microwave generating and emitting tool (5) on wireline (8) down the tubing (12) and supplying electrical power to the tool via the wireline (8) or from a battery to produce microwave energy and direct it to the gas hydrate and/or water ice deposit (13), thereby melting deposit and unblocking the well.

Claims

1. A process for removing an obstruction caused by gas hydrates or water ice from tubing of a hydrocarbon production or injection well or a riser, wherein the process comprises: a) passing a microwave generating and emitting tool on wireline down the tubing; b) supplying electrical power to the microwave generating and emitting tool either from a battery package in the tool or via the wireline, to produce microwave energy and direct it to a gas hydrate and/or water ice deposit; thereby at least partially melting and/or decomposing the gas hydrate and/or water ice deposit.

2. The process according to claim 1, wherein the electrical power supplied to the tool is between 500 and 10,000 Watts, optionally between 1,000 and 5,000 Watts, such as about 2,000 Watts.

3. The process according to claim 1, wherein microwave energy is directed distally along the tubing by the tool.

4. The process according to claim 1, wherein, after melting or decomposing a portion of hydrate or ice, the tool is advanced through the melted or decomposed hydrate or ice, along the well or riser, to melt or decompose further hydrate or ice.

5. The process according to claim 4, wherein the weight of the tool is sufficient to advance it along the tubing until it reaches solid hydrate or ice.

6. The process according to claim 1, wherein the hydrate or ice is in a subsea well.

7. The process according to claim 1, wherein the tool is delivered from a surface vessel with a wireline facility.

8. The process according to claim 1, wherein the said deposit comprises a region of water ice and a region of hydrate.

9. The process according to claim 1, wherein the process includes recovering the tool by directing microwave energy proximally to melt or decompose re-formed hydrate or ice to allow the tool to be withdrawn.

10. The process according to claim 1, wherein the process includes sensing slackening of tension in the wireline or sensing proximal acceleration of the tool and then activating a braking system to restrain proximal movement of the tool.

11. A tool for removing an obstruction caused by gas hydrates or water ice from tubing of a hydrocarbon production or injection well or a riser, wherein the tool is adapted for delivery on wireline into the tubing and wherein the tool comprises: a) a microwave generator adapted to receive electrical power from a battery pack in the tool or via the wireline; and b) a microwave antenna adapted to deliver microwave energy in a distal direction when the tool is located in the tubing.

12. The tool according to claim 11, including a ground/earth contact member arranged to contact the interior surface of the tubing of so that the tubing acts as a Faraday cage.

13. The tool according to claim 11, wherein the microwave generator has an input power rating between 500 Watts and 10,000 Watts, optionally between 1,000 Watts and 5,000 Watts, such as about 2,000 Watts.

14. The tool according to claim 11, wherein the tool comprises two or more antennas for directing microwave energy distally.

15. The tool according to claim 11, wherein the tool comprises an antenna for directing microwave energy proximally.

16. The tool according to claim 11, wherein the tool comprises: a) a sensor for sensing slackening of tension in the wireline or a sensor for sensing proximal acceleration of the tool; and b) a system for braking the tool in response to sensed slackening of tension in the wireline or in response to sensed proximal acceleration.

17. The tool according to claim 16, wherein the system for braking comprises a braking member engageable with the interior tubing wall to restrain movement of the tool.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] A more complete understanding of the present invention and benefits thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings.

[0042] FIG. 1 is a schematic showing a light well intervention vessel deploying a microwave tool on wireline into a subsea well in a method according to the invention; and

[0043] FIG. 2 is a schematic representation of a downhole microwave tool according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0044] Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

[0045] As shown in FIG. 1, a light well intervention vessel 1 may be deployed at the surface 2, having wireline capability including a reel of wireline and associated equipment shown generally at 3, together with an electric power supply 4. A microwave tool shown generally at 5 is lowered to the seafloor 6 on wireline 8. On the seafloor 6 is a wellhead 7 with a wireline riser 9 extending upwardly from the wellhead 7 and a well with casing 23 extending through the seafloor. Production tubing 12 extends through the casing. The wireline 8 passes into the subsea wellhead 7 and then into the well tubing 12, via the wireline riser 9. The operation of introducing the wireline 8 into the wellhead 7 may be assisted by a remote operated subsea vehicle (ROV) 10 controlled by an umbilical 11 from the vessel 1. All these items and their operation are familiar to those skilled in this field, and will not be described in detail.

[0046] The microwave tool 5 is shown in the well tubing 12 adjacent a blockage 13 comprising hydrate. The tool 5 is shown in slightly more detail in FIG. 2, where similar reference numerals denote the same components as in FIG. 1. The tool in fact is several meters long; the aspect ratio has been changed in the drawings to aid clarity. The tool 5 comprises a robust housing 18. Within the housing 18 is a microwave generator 16 connected to an electric power line 17 within the wireline 8, which draws electric power from the supply 4 on the vessel. In an alternative embodiment of the invention, power may be supplied from a battery in the tool.

[0047] The microwave generator is designed to generate microwave signals with frequency 2.45 GHz and to emit microwaves from antennas 14 in a distal direction (i.e. down the well). The well tubing 12 acts as a Faraday cage and/or waveguide containing the microwave energy and directing it along the tubing 12 in a distal direction towards the hydrate deposit 13. The device is earthed to the tubing 12 by means of flexible contacts 19. Two antennas 14 are shown; it is preferable to have two or more antennas since the standing wave generated by a single antenna may have dead spots. Two or more antennas may be arranged so as to reduce or eliminate dead spots.

[0048] When flow from a producing well is reduced or even stopped and it is believed that a build-up of hydrates and/or water ice in the well may be the cause, a so-called riser-less light well intervention vessel (RLWI vessel) is brought in. A microwave tool, as described above, may be lowered on wireline from the vessel. The wireline comprises a coaxial arrangement of load-bearing braided wire, with a central electrical conductor wire. A subsea remotely operated vessel (subsea ROV) is deployed from the RLWI vessel and used to open the necessary valves and access points and to help manipulate the microwave tool into the wellhead and allow it to be lowered into the well. The tool continues to be lowered under its own weight through the well until it encounters an obstruction, believed to be hydrate and/or water ice. Powered from the power supply on the RLWI vessel, the microwave tool generates and delivers microwave energy focused down the well towards the hydrate/water ice blockage. The input power drawn by the microwave tool is approximately 2 kW, which is within the capacity of the type of wireline used. If necessary, a higher-powered microwave generator could be used, depending on the type of wireline employed.

[0049] The hydrate or ice deposits are normally formed only a few metres into the well (or riser), often just below the downhole safety valve if in a well. It is therefore a relatively quick operation to pass the wireline into the well as far as the deposit. The capacity of wireline to carry electric power can depend on the length of line; because only a short length is required, it may be within specification to deliver up to 10 KW of electric power to the microwave device. However, it is also possible that lower power devices may be sufficient, e.g. as low as 500 Watts. With modern lithium ion batteries, these power levels can also be reached.

[0050] Microwave generators are inherently efficient. The well casing may act to reflect and contain microwave energy within the well, and the antenna and waveguide on the tool can direct the energy to the desired location. Microwave energy of 2.45 GHz almost exclusively excites water molecules. All of these factors mean that the energy transmitted down the wireline is likely to be transferred with high efficiency into the water ice or hydrate causing the blockage, resulting in fast liquefaction of the ice/hydrate and removal of the blockage.

[0051] As water/hydrate is liquefied, the tool is allowed to continue its descent under its own weight, passing through the liquefied hydrate/water and directing microwave energy distally, towards new un-liquefied hydrate/water until the blockage is completely removed.

[0052] Once the blockage is removed, the wireline is withdrawn and the well put back on production. A proximal antenna 15 is provided and energy from the microwave generator 16 may be selectively applied to this antenna if it is determined that the tool is stuck in the well. In this event it is possible that hydrate or ice has re-formed above the tool and obstructed withdrawal of the tool; directing energy proximally may melt the re-formed ice or hydrate and allow the tool to be withdrawn. The control of which antenna to energize may be via signals passed down the wireline to the device.

[0053] The tool is equipped with a brake 20 that may be engaged with the interior surface of the tubing 12 to arrest undesirable movement of the tool. When a hydrate or ice deposit is melted, it is possible that the fluid beyond the deposit is at relatively high pressure. This may result in the tool being forced upwards (proximally), potentially at high speed. This is undesirable and can be dangerous, so the main purpose of the brake 20 is to prevent such movement. The tool is equipped with a sensor 22 for sensing when tension in the wireline 8 is reduced, indicating that the tool may be subject to an upward force. A brake actuator mechanism 21, powered via the wireline, engages the brake on receipt of a signal from the sensor 22.

[0054] It is also envisaged that the system could be used with offshore dry wellheads located on an offshore platform, or with onshore wells where low temperatures may cause hydrates and/or water ice to form in hydrocarbon wells. In offshore dry wellheads, where a riser extends between the wellhead and the seafloor, hydrates may form in the riser as well as in the well itself. The invention is equally applicable to these situations, where access to the wellhead is relatively simple compared to a subsea wellhead. In these situations too, the use of a microwave energy generating and emitting tool is likely, the inventors believe, to result in much shorter times for decomposing and/or melting hydrate and/or water ice deposits causing blockages in wells or risers.

[0055] Hydrates may form in onshore wells that pass through permafrost. In this situation, melting of the hydrates using heat is undesirable since the rig/wellhead is built upon the permafrost and to partially melt it could disturb the foundations of the rig. For this reason, wells passing through permafrost are in fact normally insulated to prevent the permafrost being affected. Microwave melting of hydrates, as discussed above, should contain the microwave energy within the tubing and thus nor affect the permafrost.

[0056] In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as a additional embodiments of the present invention.

[0057] Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.

[0058] It should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiments of the present invention.

REFERENCES

[0059] All of the references cited herein are expressly incorporated by reference. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. Incorporated references are listed again here for convenience: [0060] 1) U.S. Pat. No. 4,678,034, Eastlund, et al., Well heater, (1987). [0061] 2) U.S. Pat. No. 4,856,593, Mathews, R. R. & Clark, C. R., Inhibition of hydrate formation, (1987). [0062] 3) U.S. Pat. No. 6,307,191, John J. Waycuilis, Microwave heating system for gas hydrate removal or inhibition in a hydrocarbon pipeline, (2001). [0063] 4) U.S. Pat. No. 7,975,763, Banerjee, D. K. & Stalder, J. L., Process for enhanced production of heavy oil using microwaves, (2008). [0064] 5) U.S. Pat. No. 8,365,823, Dreher, et al., In-situ upgrading of heavy crude oil in a production well using radio frequency or microwave radiation and a catalyst, (2009). [0065] 6) U.S. Pat. No. 8,431,015, Smith, K. W. & Banerjee, D. K., Wellhead hydrocarbon upgrading using microwaves, (2009). [0066] 7) U.S. Pat. Nos. 8,464,789, 8,720,547, 8,689,865, 8,720,548, 8,720,549, 8,720,550, 8,905,127, Banerjee, et al., Process for enhanced production of heavy oil using microwaves, (2010). [0067] 8) U.S. Pat. No. 8,555,970, Wheeler, et al., Accelerating the start-up phase for a steam assisted gravity drainage operation using radio frequency or microwave radiation, (2009). [0068] 9) U.S. Pat. No. 9,004,164, Dreher, et al., In situ radio frequency catalytic upgrading, (2011).