METHOD AND KIT FOR REMOVING TRAPPED HYDROCARBONS

Abstract

A method of removing trapped hydrocarbons from pipework, the pipework comprising a through pipe (1) extending from an inlet to an outlet, and at least one up-pipe (2a, 2b) extending upwardly from the through pipe. The method comprises: flushing the through pipe with a water-based liquid (6) which has a density less than hydrocarbons; wherein the water-based liquid comprises a plurality of rigid containers, such as microspheres, the rigid containers each having a sealed void containing a gas. in this way, hydrocarbons in the up-pipes may be removed without hot-tapping them. The flushing may be performed by directing pipeline pigs (5a, 5b) in front of and behind the water-based liquid. The pigs may be a cross-linked gel, based pipeline pig with elastomeric properties. A kit of parts for such a method is also disclosed.

Claims

1. A method of removing trapped hydrocarbons from pipework, the pipework comprising a through pipe extending from an inlet to an outlet, and at least one up-pipe extending upwardly from the through pipe, and in fluid communication therewith, the method comprising: flushing the through pipe with a water-based liquid which has a density less than hydrocarbons; wherein the water-based liquid comprises a plurality of rigid containers, the rigid containers each having a sealed void containing a gas.

2. A method as claimed in claim 1, wherein the water-based liquid has a specific gravity of less than 0.98 g/cm.sup.3.

3. A method as claimed in claim 1, wherein the rigid containers comprise microspheres.

4. A method as claimed in claim 1, including directing a pipeline pig into the through pipe, along with the water-based liquid.

5. A method as claimed in claim 4, wherein the pipeline pig is a crosslinked gel-based pipeline pig with elastomeric properties.

6. A method as claimed in claim 1, including directing a pipeline pig train into the through pipe, the pipeline train comprising the water-based liquid, a first pipeline pig in front of the water-based liquid, and a second pipeline pig behind the water-based liquid.

7. A method as claimed in claim 6, wherein each pipeline pig is a cross-linked gel-based pipeline pig with elastomeric properties.

8. A method as claimed in claim 1, wherein the water-based liquid comprises miscible solvents.

9. A method as claimed in claim 1, wherein the water-based liquid includes a long chain soluble polymer to act as viscosifying agent, such that the water-based liquid has a viscosity at a 300 rpm dial reading of between 150 (0.15 Pa.Math.s) and 300 (0.3 Pa.Math.s) and at a 3 rpm dial reading of between 15 (1.5 Pa.Math.s) and 100 (10 Pa.Math.s).

10. A method as claimed in claim 1, wherein there is a plurality of up-pipes between the through pipe inlet and through pipe outlet.

11. A method as claimed in claim 10, wherein during a single pass of the water-based liquid from the through pipe inlet to the through pipe outlet, it is in fluid communication with each up-pipe of the plurality of up-pipes.

12. A method as claimed in claim 1, wherein the method includes a pre-flush using a different water-based liquid, the different water-based liquid having a density greater than that of hydrocarbons, before flushing the through pipe with the water-based liquid which has a density less than hydrocarbons.

13. A method as claimed in claim 1, wherein the through pipe is provided on an offshore oil and gas facility.

14. A kit of parts for the method as claimed in claim 4, comprising the water based liquid with the plurality of rigid containers and at least one pipeline pig.

15. A kit of parts as claimed in claim 14, wherein the pipeline pig is a crosslinked gel-based pipeline pig with elastomeric properties.

16. A method as claimed in claim 1, wherein the water-based liquid has a specific gravity of less than 0.90 g/cm.sup.3.

17. A method as claimed in claim 2, wherein the rigid containers comprise microspheres.

18. A method as claimed in claim 3, including directing a pipeline pig into the through pipe, along with the water-based liquid.

Description

[0033] Embodiments of the present invention will now be described by way of example only and with reference to accompanying figures, in which:

[0034] FIG. 1 shows a schematic cross-sectional diagram of a section of a process plant;

[0035] FIGS. 2 to 4 are a series of sequential views showing a pig train arrangement moving through the FIG. 1 process plant, in accordance with the present invention.

[0036] FIG. 1 shows a cross-sectional diagram of a section of a process plant 10 comprising a main through pipe 1 and two up-pipe sections 2a, 2b. After a water flush, hydrocarbon fluid 4 is trapped in the up-pipe sections 2a, 2b due to its lower density compared with water 3.

[0037] In FIG. 2, a pig train 8 is introduced upstream of the trapped hydrocarbon fluid 4. The pig train 8 comprises two gel pigs 5a, 5b placed such that, along with the main pipe 1, they define a section therebetween which is filled with a water-based liquid 6 having a lower density than the hydrocarbon fluid 4.

[0038] In use, the pig train 8 is moved towards the up-pipe sections 2a, 2b by action of pumped water behind the pig 5a. In FIG. 3, the water-based liquid 6 within the pig train 8 is in fluid communication with the first of the up-pipe sections 2a. Since the water-based liquid 6 has a lower density than hydrocarbon fluid 4, the hydrocarbon fluid 4 is displaced by some of the water-based liquid 6, out of the first up-pipe section 2a and into the section of the main pipe 7 between the pigs 5a, 5b, and sealed from the rest of the main pipe 1.

[0039] In FIG. 4, the pig train 8 comprises hydrocarbon fluid 4 that had been displaced out of section 2a and the remaining water-based liquid 6. The fluids are segregated by the action of gravity such that the hydrocarbon fluid 4 is located below the water-based liquid 6. The pig train 8 reaches the second up-pipe section 2b filled with hydrocarbon fluid 4. Similarly, the hydrocarbon fluid 4 is displaced out of the second up-pipe section 2b and into the section of the main pipe 7, and contained between the gel pigs 5a, 5b. At this stage, the pig train 8 comprises hydrocarbon fluid 4 that had been displaced out of sections 2a, 2b, overlaid with the remaining water-based liquid 6.

[0040] Once the pig train 8 passes the up-pipe sections 2a, 2b the hydrocarbon fluid 4 is fully displaced therefrom leaving the upright sections 2a, 2b filled with non-hazardous water-based liquid 6. The pig train 8 is then moved away from the upright sections 2a, 2b to conveniently transport the hydrocarbons away from the up-pipes 2a, 2b and out of the through pipe 1. Upon encountering a waste receptacle, the fluids are released thereto from the pig train 8, with the water-based liquid 6 overlaying the hydrocarbon fluid 4, thus rendering the up-pipes of the process plant 10 safe.

[0041] The pig train 8 comprising the water-based liquid 6 and gel pigs 5a, 5b provides a safer and more effective method of removing trapped hydrocarbon fluid from up-pipe sections 2a, 2b than the other methods known in the art.

[0042] Thus, for certain embodiments, the section of the process plant 10 may be cleaned and rendered safe in a single pass.

[0043] The waste receptacle (not shown) is provided at the outlet of the through pipe 1, downstream of the upright sections 2a, 2b. Upon discharge of fluids from the pig train 8 into the waste receptacle, the water-based liquid 6 floats atop the hydrocarbon fluid 4 in the receptacle (because of its lower density) thus acting as a safety barrier to the release of volatile hydrocarbon vapour. The barrier can be increased by adding quantities of the water-based liquid 6 to the waste receptacle. Once the treatment is complete, the waste can be processed, water and hydrocarbon fluid 4 can be drawn off and the water-based 6 fluid can be reused.

[0044] The gel pigs 5a, 5b can form a tight seal against the inner walls of the main pipe 1, thereby providing a swabbing action. They are also able to contain fluids within the pig train 8, while being movable through long stretches of pipeline of varying diameters and able to navigate through any encountered geometric changes therein.

[0045] The gel pigs 5a, 5b can negotiate short radius bends of 1.5D with the ability to regain their original shape. With an operating temperature range of −25 and 140° C., the gel pigs 5a, 5b can be propelled through the main pipe 1 by gas or liquids and do not require pig launchers or receivers.

[0046] One composition of the gel pigs 5a, 5b is sold by Aubin Ltd under the trade name EVO-Pig LG. Suitable pigs are described, but not limited to those disclosed in UK Patent Application number GB2538966, the disclosure of which is incorporated herein by reference, in its entirety.

[0047] The exact composition of the water-based liquid 6 may be adjusted. Any non-hazardous bulk fluid immiscible with the hydrocarbon fluid may be used as the continuous phase, especially mixtures of water with other water miscible solvents, such as glycols and alcohols. For this embodiment, the water-based liquid 6 comprises: water acting as the continuous phase, a long chain water-soluble polymer which acts as a viscosifying agent preferably imparting non-Newtonian rheological properties to the fluid forming the gel, and microspheres which lower the fluid bulk density to less than 0.7 kg/litre, and therefore below the range of density values characteristic of the trapped hydrocarbon fluid 4. Examples of suitable the long-chain water-soluble polymer Xanthan gum, Carboxymethylcellulose and its derivatives, and Guar and its derivatives. In any case, the water-based liquid is preferably non-hazardous and environmentally acceptable.

[0048] The volume of the water-based liquid 6 provides sufficient excess over the sum of the volumes of trapped hydrocarbons, usually of the entire up-pipe sections 2a, 2b. Optionally, sufficient water-based liquid 6 may also be included such as to cover the entire surface area of the inlet of the waste receptacle.

[0049] Multiple upright sections can be treated sequentially in this manner, limited only by the volume of water-based liquid 6 provided in the pig train 8. As such, the process may be extended to main pipes with multiple up-pipes which can be treated in one pass. The method may be repeated as necessary for the whole process plant or offshore facility.

[0050] In another embodiment, the section of the process plant 10 is flushed with the water-based liquid 6 following or before the insertion of a single gel pig into the main pipe 1. The single gel pig can be one of the gel pigs 5a, 5b. This embodiment has similar advantages to the previous embodiment, but it requires the use of a single pig instead of two pigs.

[0051] In yet another embodiment, the section of the process plant 10 is flushed with the water-based liquid 6 without the use of gel pigs 5a, 5b. This embodiment has similar advantages to the previous embodiments, but it does not require the use of pigs.

[0052] In alternative embodiments, where pigs are used, a cup-pig such as a conical cup-pig may be used instead of the gel pigs shown here.

[0053] Modifications and improvements can be incorporated herein without departing from the scope of the invention.