Wells – Processes – Placing or shifting well part
Reexamination Certificate
2000-04-07
2001-08-21
Tsay, Frank S. (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S376000, C166S077100
Reexamination Certificate
active
06276457
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a means and method for emplacing a string of coil tubing in a wellbore.
BACKGROUND OF THE INVENTION
It is common oilfield practice to emplace a string of coil tubing in a completed oil or gas wellbore. The coil tubing may be used for any of a variety of purposes. For example, it can be used for chemical injection; steam injection, service as a bubble tube for measuring downhole pressure, sand clean-out, solvent spotting or circulation, or for carrying sensor instrumentation for measuring downhole pressure or temperature. The present invention was developed in connection with using coil tubing for carrying sensor instrumentation downhole.
Coil tubing has a relatively small diameter. The diameter can vary between ⅛ inch and 2 inch. As a result, a string of coil tubing is pretty flexible. It has a tendency to spiral or corkscrew as it is being run into a wellbore. Also, it does not lend itself to being forced through wellbore tight spots, sand plugs and the like. These problems are magnified when trying to run the coil tubing in to the toe end of a horizontal wellbore, such as a wellbore to be used in a steam-assisted gravity drainage (“SAGD”) project. (A horizontal wellbore usually extends downwardly from ground surface to a hydrocarbon-containing reservoir and then bends to extend, generally horizontally, into the reservoir. The wellbore is described as having a “heel” (at the bend) and a “toe” (at the far end of the wellbore). The section of wellbore between heel and toe is often referred to as the “production interval”).
As previously indicated, it is known to emplace a coil tubing instrumentation string in the horizontal section of a wellbore to measure formation temperature or pressure and relay this information to ground surface through cable means. From this information, the operator can develop a temperature or pressure profile extending the length of the production interval. However this requires that the string extend from the heel to the toe of the horizontal wellbore section.
So one problem to be addressed is how to better insert a coil tubing string to the desired landing point in a wellbore. In the case of a wellbore having a horizontal production interval, the problem is how to better insert the string so that it reaches the toe end of the wellbore. However, the solution to the problem needs to ensure that, once the coil tubing string is in place downhole, it is present as a freely and independently movable string.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a locking assembly comprising two interlocking members. One member is secured to the bottom end of a relatively large diameter and substantially rigid production or steam injection tubing string (hereinafter referred to as the “primary string”). The other member is secured to the bottom end of a relatively small diameter and more flexible coil tubing string. The locking assembly is used to secure the bottom ends of the two strings together at ground surface. The strings are then run into the wellbore together. The primary string functions to pull the coil tubing string along with it. The primary string is better able to penetrate through obstructions in the wellbore and reach the desired landing point. Thus the likelihood of landing the coil tubing string at the desired landing point is improved. In many cases the desired landing point is in the toe end of a horizontal wellbore.
One of the interlocking members is formed of a material which melts when exposed downhole to an elevated temperature for sufficient time. The elevated temperature can be provided by circulating a hot fluid, such as steam, into the vicinity of the shear sub. Alternatively, the reservoir itself may be at a temperature sufficient to cause melting.
In either case, once the shear sub is landed downhole and exposed to elevated temperature for sufficient time to melt the meltable member, the two strings can then be separated.
The invention gives the well operator the opportunity to pull either string independently after deployment and separation. If the coil tubing string is an instrumentation coil tubing string, it can be independently removed for repairs or for transfer to another well. If the primary string needs to be removed or landed at another point along the wellbore, without moving the secondary string, this is now feasible.
In one aspect, the invention is a method for emplacing a coil tubing string having a bottom end in a wellbore having a horizontal section, said section having toe and heel ends, comprising providing at ground surface a primary tubing string and a coil tubing string, each having a bottom end, the primary tubing string having a larger diameter and being stronger and more rigid than the coil tubing string; securing the coil tubing string bottom end to primary tubing string bottom end with first means secured to one string bottom end and second means secured to the other string bottom end, said first and second means being interlocked by a pair of solid members, one of which is meltable at downhole elevated temperature; running the two strings into the borehole with the coil tubing string secured to the primary tubing string and landing their bottom ends adjacent the toe end of the wellbore; melting the meltable member; and separating the coil tubing string from the primary tubing string.
In another aspect, the invention is an assembly for running into a wellbore, comprising a coil tubing string having a bottom end; a tubing string having a bottom end; the primary tubing string having a larger diameter than the coil tubing string; and a locking assembly securing the two bottom ends together, said assembly comprising first means secured to one string bottom end and second means secured to the other string bottom end, said first and second means being interlocked by a pair of solid members, one of the members being convertible from a solid form to a liquid form when exposed to a liquefying agent.
REFERENCES:
patent: 4523645 (1985-06-01), Moore
patent: 4585066 (1986-04-01), Moore et al.
patent: 4597440 (1986-07-01), Pottier
patent: 4945995 (1990-08-01), Tholance et al.
patent: 5318129 (1994-06-01), Wittrisch
patent: 5709269 (1998-01-01), Head
Chhina Harbir Singh
Moffatt Terrence George
Mombourquette Ivan G.
Alberta Energy Company LTD
Millen White Zelano & Branigan P.C.
Tsay Frank S.
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