Process for remediating hydrates from subsea flowlines

Abstract

A process for removing hydrate formations from a flowline includes connecting a manifold to the flowline, passing an inert gas across a pair of inlets of the manifold so as to create a reduced pressure across the pair of inlets that is less than a pressure of a fluid in the flowline, opening a valve between the pair of inlets and the flowline so as to expose the pressurized fluid in the flowline to the reduced pressure across the pair of inlets, disassociating hydrates in the flowline by exposure to the reduced pressure across the pair of inlets, and flowing the fluid and the disassociated hydrates from the flowline into the outlet of the manifold and outwardly of the manifold through at least one of the pair of inlets.

Claims

1. A process for removing hydrate formations from a flowline, the process comprising: connecting a manifold to the flowline, the manifold having a pair of inlets and an outlet; passing an inert gas across the pair of inlets so as to create a reduced pressure across the pair of inlets that is less than a pressure of a fluid in the flow line; opening a valve between the pair of inlets and the flowline so as to expose the pressurized fluid in the flowline to the reduced pressure across the pair of inlets; disassociating hydrates in the flowline by exposure to the reduced pressure across the pair of inlets; and flowing the fluid and the disassociated hydrates from the flowline into the outlet of the manifold and outwardly of the manifold through at least one of the pair of inlets.

2. The process of claim 1, further comprising: connecting the outlet by a conduit to the flowline.

3. The process of claim 1, further comprising: connecting the pair of inlets to a supply of inert gas by separate tubes.

4. The process of claim 1, the valve being connected to either the flowline or to the manifold.

5. The process of claim 1, the step of flowing comprising: flowing hydrocarbons and the disassociated hydrates by a pressure of the inert gas toward a surface location.

6. The process of claim 5, the step of flowing further comprising: flowing hydrocarbons and the disassociated hydrates by a pressure of the inert gas toward a surface location through a coiled tubing.

7. The process of claim 1, further comprising: closing the valve between the pair of inlets and the flowline after the disassociated hydrates are removed from the flowline.

8. The process of claim 6, further comprising: removing water from the coiled tubing through an orifice of the manifold by introducing the inert gas through the coiled tubing.

9. The process of claim 8, further comprising: opening the valve between the pair of inlets and the flowline so as to allow the disassociated hydrates to flow into the water-removed coiled tubing.

10. The process of claim 1, the flowline selected from the group consisting of jumpers, pipelines, conduits and tubing.

11. The process of claim 1, the pair of inlets being in valved relation to the outlet and in valved relation with each other.

12. The process of claim 1, the inert gas being nitrogen.

13. The process of claim 1, further comprising: supplying the inert gas from a surface location through tubing to the manifold.

14. The process of claim 8, the orifice of the manifold selected from the group consisting of a choke valve, a needle valve, and a throttling valve.

15. The process of claim 1, further comprising: connecting a first tubing to one of the pair of inlets and extending the tubing to a surface location; and connecting a second tubing to the other of the pair of inlets and extending the second tubing to the surface location.

16. The process of claim 15, further comprising: pumping the inert gas through the first tubing by a first pump at the surface location; and pumping inert gas through a second tubing by a second pump at the surface location.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of the process of the present invention.

(2) FIG. 2 is a detailed view of the configuration of the manifold is used in the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) Referring to FIG. 1, there is shown the process 10 for the removal of hydrates from a subsea flowline. The process 10 utilizes a manifold 12, a conduit 14 connected to an outlet 16 of the manifold 12, a first tubing 18 connected to a first inlet 20 of the manifold 12, a second tubing 22 connected to a second inlet 24 of the manifold 12, and a flowline 26. FIG. 1 shows that the flowline is connected to a well jumper 28 and ultimately to a well 30 by way of various connections. Similarly, the flowline 26 is connected by another jumper 32 to another location at the sea floor.

(4) In FIG. 1, it can be seen that the first inlet 20 is connected by a line 34 to the outlet 16. The second inlet 24 is connected by a line 36 to the outlet 16. An orifice 38 is positioned on the manifold 12 and is cooperative with separate lines 40 and 42 extending respectively between the first inlet 20 and the second inlet 24. Each of these lines has suitable valves thereon so as to control fluid flow. The orifice 38 can be an adjustable choke valve, a needle valve, a throttling valve, or of a similar construction. The orifice 38 can suitably open so as to allow release of fluids into the subsea environment. The orifice 38 can also be utilized for controlling pressures and flow rates of fluids in the various lines. The orifice 38 can be suitably actuated by an ROV or by automatic controls.

(5) The tubing 18 is connected to the first inlet 20 and extends upwardly to a surface location, such as a production vessel. A supply of an inert gas 44 is connected to the tubing 18. A suitable pump can be provided so as to deliver the inert gas through the tubing 18 toward the inlet 20. Another supply of inert gas 46 is connected to the tubing 22 so as to be delivered to the second inlet 24. As used herein, is possible that only a single supply of inert gas be provided in relation to at least one of the tubings 18 and 22. The tubings 18 and 22 are in the nature of coiled tubing that can be supplied from a production vessel.

(6) The conduit 14 can be in the nature of a pipe, a tube, coiled tubing, a jumper, or other type of fluid-passing line. Conduit 14 has one end connected to the outlet 16 of the manifold 12 and another end interconnected to the flowline 26.

(7) The method of the present invention first involves the step of connecting the manifold 12 to the flowline 26. This is established by connecting the conduit 14 to the outlet 16 of the manifold 12 and then connecting the opposite end of the conduit 14 to the flowline 26. In this circumstance, the various valves that connect the outlet 16 to the inlets 20 and 24 are closed. The next step is to pass the inert gas across the pair of inlets 20 and 24 by way of lines 40 and 42 so as to create a pressure across the inlets 20 and 24 that is less than a pressure of the fluid in the flowline 26. Thirdly, a valve within the manifold 12 is opened so as to expose the pressurized fluid in the flowline 26 to the reduced pressure across the pair of inlets 20 and 24. Depending upon which valves are open, this differential pressure will cause fluids to flow from the flowline 26, through the conduit 14, into the outlet 16, and through the lines within the interior of the manifold 12 so as to ultimately pass outwardly of the manifold 12 through one of the inlets 20 or 24. The exposure of the hydrates of the flowline 26 to the reduced pressure across the pair of inlets 20 and 24 will disassociate the hydrates in the manner described herein above. The fluid from the flowline 26, along with the disassociated hydrates, will flow outwardly of the manifold 16 through one of the tubings 18 or 22. In other words, there is a constant flow of inert gas from one of the tubings 18 and 22 toward the other of the tubings 18 and 22. This inert gas flow will create a gas lift so as to force the fluids from the flowline 26 upwardly and outwardly of the manifold 16 so as to be collected by a vessel at the surface of the body of water.

(8) In the present invention, during the installation of the tubings 18 and 22, it is inherent that there will be an accumulation of seawater within these tubings. As such, it is necessary to evacuate the water from the tubings prior to the gas lift of fluids. This is accomplished by opening the orifice 38 and introducing the pressure of the inert gas through each of the tubings 18 and 22. This forces the water out of the interior of the tubings 18 and 22. Once the water is removed from the tubings 18 and 22, the valves can be closed. This will create an ambient pressure of air within the tubings 18 and 22. Since ambient pressure is less than the pressure of the fluid within the flowline 26, when the valves connected to the flowline 26 are opened, this differential pressure will draw the fluids from the flowline 26 into one of the tubings 18 or 22. Once pressure is equalized within the tubing, the pressure of the inert gas can then be introduced so as to force the fluids and disassociated hydrates upwardly and outwardly of the tubing.

(9) FIG. 2 is a detailed view showing the manifold 12. The manifold 12 is designed to be located at a subsea location and proximity to the flowline. As can be seen, the first inlet 20 extends through a wall 60 of the manifold 12. The second inlet 24 also extends through the wall 16 of the manifold 12. Line 34 extends from the first inlet 20 so as to be connected by valves 62 and 64 to the outlet 16. The outlet 16 extends through a wall 66 of the manifold 12. A pressure transducer 68 can be located within the manifold 12 so as to measure pressures within the lines on the interior of the manifold 12.

(10) The second inlet 24 is connected by line 36 to the outlet 16. A valve 70 is positioned on line 36. If it is desired that fluid flow from the inlet 24 should flow to the outlet 16, then valve 70 will be open, valve 64 will be open and valve 62 will be closed. If it is desired to have fluid flow through the inlet 20 and through the line 34 toward the outlet 16, the valves 62 and 64 will be open while the valve 70 remains closed.

(11) The first inlet 20 is connected by line 40 to the orifice 38. The second inlet 24 is connected by line 42 to the orifice 38. A valve 72 is located on line 40 so as to control fluid flow therethrough. Similarly, a valve 74 is located on line 42 so as to control fluid flow therethrough. Ultimately, if it is desired to flow inert gas from inlet 20 toward inlet 24, valves 72 and 74 will be open and the orifice 38 will be open so as to allow fluid flow between the lines 40 and 42.

(12) As described above, the flow of inert gas under a reduced pressure between the inlets 20 and 24 creates a zone of reduced pressure. Ultimately, when the valve 64 is opened and either of the valve 62 and 70 are opened, then the fluid and hydrates within the flowline will be open to a zone of reduced pressure so as to be drawn toward this zone of reduced pressure through the outlet 60, and through the valve 64. If the valve 70 is open, then the hydrocarbons will flow toward the inlet 24 and outwardly therethrough. Alternatively, if the valve 70 is closed and the valve 62 is open, then the hydrocarbons with flow through line 34 and outwardly of the manifold 12 through the inlet 20.

(13) In the present invention, nitrogen, or other gases, serve to remove the bulk fluid column from a riser connected to the subsea equipment. The reduction in pressure allows a hydrate to disassociate (or melt). However, in order to maintain a low-pressure in the system, the fluids (i.e. oil, gas and water) developed from the melting hydrate need to be removed. Other systems have used a subsea pump that is troublesome for high gas volume fluids. This leads to longer disassociation durations. The manifold of the present invention utilizes continuous injection of nitrogen (or similar gas) into the manifold to gas lift the fluids back to the intervention vessel.

(14) The manifold has a special features/provisions to facilitate this operation without adding additional down lines. The manifold has the ability to change-out the gas lift injection valve (or orifice) by ROV. It does not need to recover the system.

(15) The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.