Recovery Type Pipeline Service Pig
A method of providing a pig for assisting in the recovery of coiled tubing string from a pipeline including an attachment to the coiled tubing intermediate the ends of the coiled tubing string, one or more sealing cups which have a preferred sealing direction from the distal end of the coiled tubing string to the proximate end of the coiled tubing string, allowing flow past the sealing cups from the proximate end of the coiled tubing to the distal end of the coiled tubing with a check valve, providing for flow through the pig from the distal end of the coiled tubing to the proximate end of the coiled tubing with a predetermined pressure loss, and using the predetermined pressure loss to generate a force to assist in recovering the coiled tubing string from the pipeline.
This invention relates to the method of removing a blockage in pipelines at an extended distance from the access point utilizing cup type seals which are in an inverted position facilitating the recovery of the conveying tubing string.
BACKGROUND OF THE INVENTIONA majority of offshore oil and gas is produced form platforms which are erected on the seafloor and extend to above the water surface. Oil and gas is typically transported to and from these offshore platforms along pipelines laid on the seafloor. When these pipelines arrive to or depart from one of these platforms, a bend is used at the intersection of the seafloor and the platform and a vertical section of pipe or riser extends up to the platform deck. At the platform deck will be valves and piping to communicate the pipeline with equipment and/or wells on the deck of the platform.
Subsea pipelines which transport oil tend to have the waxy components of the oil come out of solution and bond to the wall of the pipeline, up to in some cases completely blocking the pipelines. In consistence, the waxy blockage appears to be exactly like black shoe polish. In most cases, a layering on the walls of the pipeline is seen and a cleaning pig passes through the pipeline to remove the waxy layering. In some cases instead of simply cleaning the layer of wax off the pipeline wall, it chips it off until it accumulates into a blockage.
When subsea pipelines which transport gas encounter the proper pressure/temperature combination and there is some water in the pipeline, a hydrate is formed. The hydrate looks a lot like crushed ice and will form quickly to create a blockage to stop the flow in the pipeline.
In either of these cases the flow of production is stopped and causes an expensive loss of production. In the case of a hydrate blockage, the operator can simply wait a few days, weeks, or months and the hydrate will melt naturally if pressure is bled off from one end or the other of the pipeline. In the case of the waxy or paraffin blockage, it is permanent until fixed.
As “fixing” these problems typically required mechanical drilling of the blockage, hot oil injection, or chemical dissolving of the blockage, communication to the blockage in the pipeline must be established. The characteristic way to establish this communication is by inserting a string of coiled tubing. A hose would work as well, but the strings of coiled tubing for up to 5 miles in length exist in the market. The hoses do not exist in the market at this length, and would be very expensive in comparison if they did.
Crawford U.S. Pat. No. 6,651,744 shows a coiled tubing string with a thruster pig (10) attached to the end for this purpose and illustrates in FIG. 12 the coiled tubing reel (150), and various other pieces of required equipment. Of note is a 5D bend section (15) which is at the intersection of the seafloor pipeline and the vertical riser. “5D” means that the bend radius of the centerline of that pipe section is 5 times the outer diameter of the pipeline. Sending equipment down the vertical pipe section around the 5D bend and then going out up to 5 miles is a very difficult goal to achieve, and is a common requirement of many offshore pipelines. If you imagine that in a 4.5 inch outer diameter pipeline this bend radius is 22.5 inches, then the steel coiled tubing must negotiate this bend.
The first problem in navigating this bend is that bending 1 to 1% inch outside diameter coiled tubing to a radius of 22.5 inches substantially bends and unbends the coiled tubing as it passes, both going and coming back which has a deteriorating effect on the coiled tubing. Secondly, the high loading on the inside of the pipeline bend and the outside diameter of the coiled tubing when it is being plastically bent tends to cause galling on both pipes, which destroys the integrity of whichever one(s) is galled. Thirdly, the force of pulling the coiled tubing back through the bend from its extended travel position is added to the force of pulling the coiled tubing back, pulling the pig back, and swabbing the fluid behind the coiled tubing back. At some point, you simply cannot pull the coiled tubing back and have caused a worse problem than the blockage itself.
When any or all of these factors is a concern, the only solution is to pick the pipeline up off the seafloor, saw it in half, and attach expensive connectors to the pipeline. This allows the operator to go directly into the end of the pipeline without having to pass a difficult bend. A complication to this is that before the operator can saw the pipeline in half, the pressure must be completely removed from the pipeline. Additionally, as you are sawing into a pipeline with at the least gas fumes in it, you may cause a spark.
An additional problems when going around the pipeline bends is that any equipment to pass the bend must be by definition very short or it simply will not pass and the bending of the coiled tubing tends to import moment loading on the equipment, such as the thruster pig at the end of the coiled tubing.
Offshore platforms with vertical riser pipes have been utilized in the offshore industry as long as it has existed, since the mid 1950's. Coiled tubing became available as an oilfield service tool in the mid 1960's and the marriage of these two systems happened shortly thereafter. The industry is still dealing with the problem of how to reasonably get the coiled tubing around the bends, and the most common answer today is to expensively pick the pipeline up and avoid the problem.
BRIEF SUMMARY OF THE INVENTIONThe object of this invention is to provide a method of installing a protective liner in the bend between a subsea pipeline and a vertical pipe riser at a platform.
A second object of this invention is to provide a method of protecting a thruster pig from the side forces resulting from the bend in the coiled tubing after going through the bend between a subsea pipeline and a vertical pipe riser at a platform.
A third objective of this invention is protect the sealing cup of a thruster pig from being heavily worn on one side due to the weight of the thruster pig.
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Bore 134 has check valve 150 with stronger spring 152 which will cause a predetermined pressure differential across thruster pig assembly 120 when flow is coming in the direction of arrows 154A-E. This predetermined pressure differential will combine with the cross sectional sealing area within the pipeline to give a predetermined force to assist the coiled tubing in being recovered from the pipeline. Rather than long lengths of coiled tubing being drug back by pulling around a bend such as was indicated at 16, it can be pulled by the force across one or more thruster pig assemblies 120. The dominant force in coiled tubing will be tension without the column buckling tendency, but some limited force can also push the coiled tubing ahead of the pig.
Thruster pig assembly 120 is illustrated as being welded into the coiled tubing string but other options are available. Slip type connectors and threaded connectors are available in some cases. Specifically in the case of slip type connectors, coiled tubing can be run through the thruster pig assembly until the appropriate connection point, the slips set, and then the pig can be run with the coiled tubing. Design requirements of this type pig make it increasingly difficult to pass 5D bends, and tend to be limited to applications with larger radius bends.
Sealing cups 160 comprise a metal seal carrier 162 and a resilient cup member 164. O-ring type seal 165 seals between the metal seal carrier 162 and the pig 166. The two sealing cups 160 have an inner spacer ring 167 with O-ring type seals 168 and 169 which allows the two sealing cups 160 to be identical and perform the additional benefit of redundant sealing. It will be noted that there is a gap inside each of the sealing cups 160 as the internal bore 170 of the sealing cups 160 is larger than the outer diameter 172 of pig body 166. Pig guide bushings 180 and 182 are of a low friction material mount to pig body 166 and assist the thruster pig assembly to slide along the pipeline, but as they must be smaller than the internal diameter of the pipeline, they will slide eccentrically to the centerline of the pipeline. This means that if sealing cups 160 are rigidly mounted to pig body 174, they will be pressed more tightly on one side that the other, accentuating the wear on that side and limiting the service life of the thruster pig assembly 120. However, sealing cups 160 are mounted in such a way as to have clearances to allow the sealing cups 160 to remain concentric to the pipeline bore and give a uniform lower stress to the resilient cup members 164. This means rather than the resilient cup members 164 having to support the weight of all the metal parts of the thruster pig assembly and handle any moments caused from the coiled tubing, they simply glide in a centralized state.
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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 providing a pig for assisting in the recovery of coiled tubing string from a pipeline comprising:
- providing an attachment to said coiled tubing, intermediate the ends of said coiled tubing string,
- providing one or more sealing cups which have a preferred sealing direction from the distal end of said coiled tubing string to the proximate end of said coiled tubing string,
- allowing flow past said sealing cups from said proximate end of said coiled tubing to the distal end of said coiled tubing with a check valve,
- providing for flow through said pig from said distal end of said coiled tubing to said proximate end of said coiled tubing with a predetermined pressure loss, and
- using said predetermined pressure loss to generate a force to assist in recovering said coiled tubing string from said pipeline.
2. The method of claim 1 further comprising said attachment to said coiled tubing string is welding said pig into said coiled tubing string.
3. The method of claim 1 further comprising providing a set of slips which engage the outer diameter of said coiled tubing string as said attachment to said coiled tubing string.
4. A pig for assisting in the recovery of a coiled tubing string from a pipeline comprising:
- an attachment to between said recovery pig and said coiled tubing intermediate the ends of said coiled tubing string.
- one or more sealing cups which have a preferred sealing direction from the distal end of said coiled tubing string to the proximate end of said coiled tubing string,
- a one or more sealing cups which have a preferred sealing direction from the distal end of said coiled tubing string to the proximate end of said coiled tubing string,
- a check valve to allow flow past said one or more sealing cups from said proximate end of said coiled tubing to said distal end of said coiled tubing,
- a relief valve to allow flow past said sealing cups from said distal end of said coiled tubing to said proximate end of said coiled tubing with a predetermined pressure loss, and
- using said predetermined pressure loss to generate a force to assist in recovering said coiled tubing string from said pipeline.
5. The method of claim 4 further comprising said attachment to said coiled tubing string is welding said pig into said coiled tubing string.
6. The method of claim 4 further comprising said attachment to said coiled tubing string is a set of slips which engage the outer diameter of said coiled tubing string.
Type: Application
Filed: May 17, 2013
Publication Date: Nov 20, 2014
Inventor: Benton Frederick Baugh (Houston, TX)
Application Number: 13/897,114
International Classification: E21B 37/00 (20060101);