Method of prevention of hydrates
The method of prevention of hydrate formation inside a subsea pipe of a first temperature during an increase in flow within the pipe comprising containing a volume of water outside the pipe, heating the volume of water to a second temperature higher than the first temperature such that the pipe is heated to a temperature high enough to stop the formation of the hydrates, and increasing the flow in the pipe.
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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTN/A
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISKN/A
BACKGROUND OF THE INVENTIONThe field of this invention is that of preventing hydrate blockages in subsea pipelines, subsea riser pipes, and subsea equipment installations.
Hydrates are a porous solid which is formed primarily of water with a mixture of gases. It is effectively similar to crushed ice which is stuck together. There is a tendency for hydrates to form in pipelines departing from a subsea gas well, especially during well flow startup.
The temperature of the seawater at depths will often approach 34° F., with the temperature in a non-blowing pipe being the same. When a subsea valve is opened, the gas expansion can cause substantial additional cooling. In these cold and high pressure conditions, hydrates of the gas and water quickly form.
Frequently when the hydrate forms, it forms a blockage. The blockage will typically be somewhat porous. At that time, a high pressure will exist on the upstream side of the blockage and a lower pressure will exist on the downstream side. This means that additional gas will move thru the hydrate and expand and therefore cool as it does. This means that not only can the expansion of this gas keep the formed hydrate cool, but can literally continue to grow additional hydrate blockage.
Attempts have been made to enter the accessible end of the pipeline with a somewhat flexible string of steel coiled tubing to get to the blockage and wash it out. This is an expensive operation due to the cost of the equipment and the time delay in arranging for and deploying the equipment. As the blockage most often occurs at the opposite end from the accessible end, the blockage can be 5 or more miles away. Removal by the use of coiled tubing is further complicated if there are bends in the pipeline, making it more difficult to impossible.
Another method of prevention of the formation of hydrates is to place expensive chemicals at the likely location of the formation of the hydrates. Chemicals such as methanol will reduce the temperature of the liquid/gas combination required for the formation of the hydrates, hopefully below the temperature which occurs during the well startup operations. In addition to the chemicals being expensive, the delivery of the chemicals to the remote location of the likely hydrate formation requires expensive capital equipment.
BRIEF SUMMARY OF THE INVENTIONThe object of this invention is to provide a method for the prevention of the formation of hydrates in subsea pipes when subsea valves are opened.
A second object of the present invention is to provide a method for the removal of hydrates and/or wax blockages which have formed in subsea pipes.
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Prior to the opening of valve 5 and throttling gas into the riser pipe 7, the ROV 32 and belly skid 34 heats seawater to 150° F. and circulates it into the annular area 42, This fills the annular area 42 with 150° F. seawater rather than the 34° F. seawater which would have been in it otherwise. When the valve 5 is opened a hydrate is not formed as it enters an area as hot as you want it to prevent gas and water vapor mixture from going down to a temperature low enough to form hydrates.
Other methods are available for providing a heat source to prevent the formation of hydrates, such as providing electric heaters within the annular area 42. Prior to the opening of the valve 5, electricity could simply be sent to the electric heaters from the surface or from the ROV to heat the seawater 40 in the annular area 42.
The present method of preheating a volume of seawater to prevent the formation of hydrates is shown in these drawings as a part of a vertical riser pipe 7 going to the surface. The method could be equally well used along a horizontal flowline associated with a subsea installation, or the subsea installation itself. In the case of some subsea installations, there is enough piping to allow formation of the hydrates directly on the subsea system.
Hydrates are formed and are remediated at a combination of temperatures and pressures rather than having a single simple temperature or pressure to design equipment in accordance with. For this reason the temperature best to increase the contained water to and the volume of contained water will vary from installation to installation.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
Claims
1. The method of prevention of hydrate formation inside a pipe of a first temperature during an increase in flow within said pipe comprising
- containing a volume of water proximate the outer surface of said pipe,
- heating said volume of water to a second temperature higher than said first temperature such that said pipe is heated to a temperature higher than said first temperature, and
- increasing said flow in said pipe.
2. The invention of claim 1, wherein at least a portion of said pipe is located subsea.
3. The invention of claim 1, wherein said water is seawater.
4. The invention of claim 1, wherein said volume of water is contained in a second pipe which is larger than and generally concentric to said pipe.
5. The invention of claim 1, wherein said pipe is a pipeline taking flow generally horizontally away from a subsea installation of equipment.
6. The invention of claim 1, wherein said pipe is a riser pipe taking flow generally vertically away from a subsea installation of equipment.
7. The invention of claim 1, wherein said pipe is a part of a subsea installation of equipment.
8. The invention of claim 1, wherein said water is heated by a remotely operated vehicle heating seawater and then pumping said heated seawater into the space of said contained water to displace said contained water with heated water.
9. The invention of claim 1, wherein said contained water is heated by electric heating elements within said contained water.
10. In an environmental condition suitable to the formation of hydrates within a pipe, the method of preventing hydrate formation within said pipe comprising
- heating said pipe and a volume of water contained around said pipe to a temperature high enough to prevent the formation of a hydrate.
11. The invention of claim 10, wherein at least a portion of said pipe is located subsea.
12. The invention of claim 10, wherein said water is seawater.
13. The invention of claim 10, wherein said volume of water is contained in a second pipe which is larger than and generally concentric to said pipe.
14. The invention of claim 10, wherein said pipe is a pipeline taking flow generally horizontally away from a subsea installation of equipment.
15. The invention of claim 10, wherein said pipe is a riser pipe taking flow generally vertically away from a subsea installation of equipment.
16. The invention of claim 10, wherein said pipe is a part of a subsea installation of equipment.
17. The invention of claim 10, wherein said water is heated by a remotely operated vehicle heating seawater and then pumping said heated seawater into the space of said contained water to displace said contained water with heated water.
18. The invention of claim 10, wherein said contained water is heated by electric heating elements within said contained water.
Type: Application
Filed: Sep 2, 2008
Publication Date: Mar 4, 2010
Inventors: Paula B. Baugh (Houston, TX), Benton F. Baugh (Houston, TX)
Application Number: 12/231,306
International Classification: E21B 36/00 (20060101);