A METHOD OF STORING ETHANE

Abstract

A method of storing ethane includes storing ethane in a number of storage pipes as a liquid at ambient temperature conditions. The storage pipes may be provided on a tanker.

Claims

1. A method of storing ethane, the method comprising storing ethane in a plurality of storage pipes as a liquid at ambient temperature conditions.

2. A method as claimed in claim 1, wherein the ambient temperature conditions are between 0 C. to 40 C.

3. A method as claimed in 1, wherein the liquid ethane is stored at pressure conditions between 35 barg to 49 barg.

4. A method as claimed in claim 1, wherein each of the storage pipes has a nominal diameter of between 40 inches-60 inches (1.0 m-1.5 m), and/or wherein each storage pipe has a length of 10 m to 30 m.

5. (canceled)

6. A method as claimed in claim 1, where each of the storage pipes comprises an X452, X46, X52, X56, X60, X65, X70 or X80 pipe in accordance with the API SPEC 5L specification.

7. A method as claimed in claim 1, wherein each of the storage pipes is formed from a rolled pipe with, a single longitudinal seam.

8. A method as claimed in claim 1, wherein the plurality of storage pipes is provided on a transportation vehicle, wherein the transportation vehicle is a ship, vessel and/or tanker.

9. (canceled)

10. A method of transporting ethane, the method comprising storing ethane as claimed in accordance with claim 8, and transporting the ethane with the vehicle.

11. A method of enhancing hydrocarbon production, the method comprising: transporting ethane in accordance with claim 10 to a site of a dry gas pipeline; and injecting the ethane into the dry gas pipeline.

12. A method as claimed in claim 11, wherein the step of injecting the ethane into the dry gas pipeline comprises directly injecting the ethane from the transportation vehicle to the dry gas pipeline.

13. A method as claimed in claim 11, comprising offloading the ethane from the transportation vehicle to a second plurality of storage pipes provided at a storage facility situated at the site of the dry gas pipeline, storing the ethane as a liquid at ambient temperature conditions in the second plurality of storage pipes at the storage facility, and wherein the step of injecting the ethane into the dry gas pipeline comprises injecting the ethane from the plurality of storage pipes at the storage facility and into the dry gas pipeline.

14. A method according to claim 11, wherein the step of injecting ethane into the dry gas pipeline comprises pumping the ethane into the dry gas pipeline with a booster pump.

15. A method as claimed in claim 11, wherein injecting the ethane into the dry gas pipeline comprises static mixing of the ethane with the dry gas in the dry gas pipeline.

16. A method as claimed in claim 11, wherein the dry gas pipeline is an offshore dry gas pipeline and wherein the transportation vehicle is a ship, vessel and/or tanker.

17. A plurality of storage pipes configured to store ethane therein as a liquid at ambient temperature conditions.

18. A plurality of storage pipes according to claim 17, comprising liquid ethane at ambient temperature conditions stored within the plurality of storage pipes.

19. A transportation vehicle comprising a plurality of storage pipes as claimed in claim 17.

20. A transportation vehicle according to claim 19, wherein the transportation vehicle is a ship, vessel and/or tanker.

21. A storage facility comprising a plurality of storage pipes as claimed in claim 17.

22. A storage facility as claimed in claim 21, wherein the storage facility is an offshore floating storage facility.

Description

[0051] Certain preferred embodiments of the invention will now be described, by way of example only, and with reference to the following figures, in which:

[0052] FIG. 1 is a schematic of a system comprising a tanker, an offshore floating facility and an offshore subsea dry gas pipeline; and

[0053] FIG. 2 shows the tanker of FIG. 1 in greater detail.

[0054] FIG. 1 depicts a system in an offshore setting, the offshore system comprising a subsea dry gas pipeline 4 running along the seabed 3. The system further comprises a tanker 2 floating at sea level 1 above (i.e. at a site) of the subsea dry gas pipeline 4. Further details of the tanker are described below with reference to FIG. 2.

[0055] The tanker 2 is positioned adjacent an offshore floating facility 6 and is releasably connected thereto via a conduit 5. The offshore floating facility 6 itself is situated adjacent a floating turret 8 and is connected to the turret 8 via conduit 7. The turret 8 is connected to a riser 9 which extends downwardly from the turret 8 and connects to the pipeline 4.

[0056] The tanker 2 as can be seen in FIG. 2, comprises a plurality (several hundred) storage pipes 23 divided between several cargo holds 25 on the tanker 2. The storage pipes 23 are vertically arranged on-board the tanker 2 and are configured to store liquid ethane therein at ambient temperature conditions and at pressures of approximately between 40 barg-45 barg (the exact pressure of storage being dependent on the ambient temperature conditions). Each storage pipe 23 is formed from a section of pipe having an X52 specification and that is sealed at either end via a suitable hemispherical cap.

[0057] The offshore floating 6 facility, whilst not shown in FIG. 1, also comprises a plurality of storage pipes that are correspondent to the storage pipes 23 provided on the tanker 2. The plurality storage pipes on the offshore floating facility 6 are thus vertically arranged and are configured to store liquid ethane therein at ambient temperature conditions and at pressures of between 40 barg-45 barg (the exact pressure of storage being dependent on the ambient temperature conditions). Each storage pipe on the offshore floating facility 6 is formed from a section of pipe having an X52 specification and that is sealed at either end via a suitable hemispherical cap.

[0058] The turret 8 comprises a booster pump (not shown). The function of the booster pump will become clear from the below discussion. A static mixer (not shown) is also provided at the interface between the riser 9 and the pipeline 4. Again, the function of the static mixer will become apparent from the below.

[0059] The system as depicted in FIG. 1 is used to enhance the energy content of the dry gas passing through the subsea dry gas pipeline 4. This is achieved by injecting ethane into the dry gas flowing within the pipeline 4 which, as will be appreciated, increases its energy content.

[0060] This process involves the tanker 2 travelling to a site remote from the dry gas pipeline 4 to collect a volume of ethane (e.g. from a hydrocarbon production system situated remote from the dry gas pipeline). The ethane is liquefied at ambient temperature conditions at between 40 barg to 45 barg and is then loaded into the storage pipes 23 on the tanker 2 for storage therein as an ambient temperature liquid. Once the storage pipes 23 have been filled, the tanker 2 then travels to a site of the dry gas pipeline 4 where it attaches to the conduit 5 to thereby connect to the offshore floating facility 6 (e.g. as shown in FIG. 1). Once the conduit 5 has been attached to the tanker 2, the liquefied ethane stored within the storage pipes 23 is offloaded from the tanker 2 to the storage pipes on-board the offshore floating facility 6. Once the storage pipes 23 have been emptied of liquid ethane, the conduit 5 is detached from the tanker 2 and the tanker 2 is then permitted to travel away from the site, e.g. to pick up a further load of ethane.

[0061] The offshore floating facility 6 acts as a buffer storage of ethane for injection into the dry gas pipeline 4 and provides an effectively continuous supply of ethane thereto. The liquid ethane at ambient temperature conditions stored within the pipes aboard the offshore floating facility 6 is transferred to the turret 8 via the conduit 7. At the turret 8, the liquid ethane (at a pressure of 40 barg to 45 barg) is further pressurised to a pressure of 180 barg using the booster pump. This permits injection of the ethane into the dry gas pipeline 4, where the dry gas is flowing at a pressure of 180 barg under the influence of a compressor. Once pressurised by the booster pump, the ethane is then injected via the riser 9 into the dry gas pipeline 4. On entry into the dry gas pipeline 4, the liquid ethane passes through the static mixer which promotes vaporisation and blending of the ethane within the dry gas flowing through the pipeline 4.

[0062] After injection, the ethane content of the dry gas in the pipeline 4 is increased which, in turn, increases the energy content of the gas within the pipeline.

[0063] The offshore floating facility 6 provides a buffer storage of ethane for effective continuous injection as noted above. The offshore floating facility however is not required in all embodiments of the invention, e.g. where continuous injection of ethane is not required or where the frequency of tankers 2 travelling to the site of the dry gas pipeline is sufficient to meet the continuous demands of injection. Thus, the offshore floating facility 6 may be entirely omitted and injection may occur directly from the tanker 2 to the pipeline 4.