Slim hole stage cementer and method

Wells – Processes – Cementing – plugging or consolidating

Reexamination Certificate

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Details

C166S291000, C166S153000, C166S154000, C166S177400

Reexamination Certificate

active

06651743

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to small-diameter or “slim hole” stage cementers and to related equipment, such as an inflatable packer collar. The slim hole stage cementer of the present invention is designed to facilitate improved drill-out operations.
BACKGROUND OF THE INVENTION
Stage cementers (“cementers”) are used in the petroleum production industry during wellbore-tubular cementing operations. Stage cementers, as that term is used herein, includes (1) stage cementer tools, and (2) stage cementers with inflatable packer collar tools.
Stage cementers intended for use in “slim-hole” or small diameter casing strings, i.e., casing strings with nominal diameters of 4½″ inches and smaller, create special problems because of their size. Small diameter cementers inherently present significant problems, both operationally and during drill-out. In relatively larger diameter cementers, many of the problems inherent in the design of the tool may be easily resolved because of the relatively large diameter. Compared to larger diameter cementers, small diameter cementers may present operational challenges not present in the larger tools. As a consequence, stage cementers have conventionally been one type of tool in which the small diameter tools may be more expensive to manufacture because of difficulties inherent in working with reduced diameter components.
Prior art slim-hole stage cementers have been successfully used in the past, but these stage cementers may be very expensive to manufacture, challenging to operate, and difficult to drill out after use. With mechanically-operated stage tools, undrilled portions of a partially drilled out plug may free fall to a lower position within the casing in the wellbore. In addition, drill-out of the moving opening seat may break the seat into several large chunks or pieces. Drilling-up the free floating remnants of an opening seat may be very difficult and risky, with use of the small diameter work strings required to operate inside the small diameter casing. Such small diameter work strings inherently have limited weight on bit and torque capabilities.
A small diameter stage cementer with an inflatable packer collar has, to the knowledge of the applicant, never been manufactured or sold. Stage cementers for nominal casing sizes greater than 4½ inches do not generally present many of the problems associated with small diameter/slim-hole stage cementers.
With the increased cost of drilling, improved wellbore completion technologies, and the need to reduce well drilling costs, slim-hole drilling is becoming increasingly popular. Such popularity has been especially recognized in remote areas. In order to improve realization of the objectives for drilling small diameter wellbores, and to meet the demands for improvements in small-diameter wellbore equipment and procedures, there is a need for an improved stage cementer for use within oilfield casing having a nominal outside diameter 4½ inches or less. Other problems with prior art stage cementers include the difficulty of drilling out the drillable components of the tool after the cementing operation is complete, while still providing a reliably useable and operating tool.
In a larger, more conventionally sized cementer, drill-out of the opening and closing seats may be accomplished relatively easily, in that the internal diameter of the cementer permits use of relatively large drill collars, thereby facilitating applying a relatively substantial weight on bit. If a seat is broken up or free falls, it may be chased by the bit and thereafter effectively drilled up downhole. Such practice is very difficult, relatively expensive, and time consuming in slim-hole casings. Drilling out a slim-hole stage cementer is commonly performed with a slim-hole string, such as 1⅝ inch drill pipe or coiled tubing. Either type of string permits severely limited weight on the bit and limited torque to be transmitted through the drill string to the drill bit.
Other problems are also present in small diameter packer collars configured or manufactured like larger diameter cementers or packer collars. Conventionally sized hydraulically opened stage cementers typically include a cylindrical, sleeve or tubular-shaped outer case surrounding a concentrically positioned, tubular-shaped, inner case, forming a concentric annulus there-between. In a packer collar tool, a port is provided through both cylinders/cases, with the portion of the port through the outer case including a secondary opening device affixed therein, such as a rupture disk, to plug or seal that portion of the port. In operation of the cementer, an opening sleeve is moved to an opened position, exposing the port in the inner case to the interior of the cementer. Thereby, fluid may be pumped from within the casing, through the port in the inner case, through the concentric annulus, and cause inflation of a packer element, positioned on a lower end of the packer collar. The secondary opening device must withstand the inflation fluid pressure without opening until after packer element inflation is complete.
Thereafter fluid pressure is increased causing the secondary opening device to rupture or open, such that the cementing operation may proceed. Cementitious fluid is then pumped through the port in each of the inner and outer cases. Thus, the port in the inner case functions as both a cementing port and an inflation port, and the port in the outer case functions only as a cementing port. The ports may share a common port axis.
Problems arise with small diameter hydraulically operated stage collar cementers and packer collar cementers designed as described above. To effectively and safely place the cement in the wellbore in timely fashion before the cement begins to thicken a minimum fluid pump rate must be obtained through the cementing ports. As a result, the cementing ports in the cementer's concentric sleeves has a relatively large diameter, as compared to the diameter of a port required to merely inflate the packer. Consequently, in a small diameter tool, the loss of steel or tool material to provide the required port cross-sectional area may limit the tensile working strength of the cementer. This effect may be even more pronounced where the tensile bearing sleeve is the inner sleeve, as this sleeve has an even smaller ID and OD than the outer sleeve, and wall thickness increases are prohibitive to permit a required minimum throughbore ID. The result is a limitation to the amount of casing that can be run below the stage cementer, and/or a limit to the amount of tension that may be pulled in the casing for straightening purposes prior to cementing.
There is thus a need for an improved small diameter stage cementer, a small diameter stage cementer with inflatable packer collar, and a stage cementer, which facilitates improved subsequent drill-out operations. An improved small diameter stage cementer and a method of operating a stage cementer with an inflatable packer collar are subsequently described. The stage cementer and method of this invention thus overcome many of the difficulties and shortcomings of the prior art.
SUMMARY OF THE INVENTION
According to a preferred design, both the improved slim-hole stage cementer of the present invention and the combination stage cementer and inflatable packer collar open hydraulically, as do some existing prior art cementers. This hydraulic actuation is a departure, however, from the numerous prior art designs for small diameter, mechanically operated stage cementer tools, which typically require an opening plug to seat on an opening seat to open the ports. Since the present cementer tool is hydraulically opened, this is a significant advantage in tool operation and in cementing, saving time and equipment. A hydraulically operated tool also has the advantage of not requiring drill-out of an opening plug.
Improved drill-out of the cementer according to the present invention is facilitated in one sense, by constructing the drillable portions of the tool,

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