Patent Application
20110042102
1. Field of the Invention
This application relates to centralizers to position a pipe string within a borehole. Specifically, this invention relates to a method of and a kit for installing a centralizer on a pipe segment to be made-up into a pipe string, for example, a pipe string of the kind used in oil and gas wells.
2. Brief Description of the Related Art
Centralizers may be secured at spaced intervals along a pipe string to provide radial stand-off of the pipe string from the wall of a borehole. The term “pipe string,” as used herein, may refer to a casing string, a drill string, or any other tubular string made up of a plurality of connected pipe segments. A “centralizer,” as that term is used herein, comprises two spaced-apart end collars aligned one with the other to define a bore there through to be received onto the end of a pipe segment, and a plurality of angularly-spaced ribs that project radially outwardly from the end collars to provide stand-off between the pipe string and the wall of the borehole. In one aspect, the ribs of a centralizer are bow springs that provide variable stand-off between the pipe string and the wall of the borehole. Bow spring centralizers provide an additional advantage in that the bow springs may collapse to pass through restrictions such as, for example, a previously installed pipe string, a wellhead or a borehole irregularity.
A centralizer may position a pipe string within a drilled borehole to provide an annulus radially intermediate the pipe string and the wall of the borehole. In one aspect, positioning the pipe string within the borehole may provide a generally uniform and continuous distribution of cement slurry within the annulus during a step of cementing the pipe string within a targeted interval of the drilled borehole. In another aspect, a centralizer may provide stand-off between the pipe string and the wall of the borehole to prevent unwanted sticking of the pipe string to the wall of the borehole at a portion of the wall at which fluid loss from the borehole into a porous geologic formation may occur. In another aspect, a centralizer may provide stand-off between the pipe string and the wall of a drilled borehole to prevent the wall of the borehole from engaging a device installed on the pipe string generally adjacent to the centralizer. In another aspect, a centralizer may position a slotted or perforated liner within a producing interval of the drilled borehole to optimize feed-in of produced oil and/or gas. It should be understood that centralizers may be used to position a pipe string within a drilled borehole for other purposes and objectives.
Generally, it is desirable to prevent movement, or to limit the range of movement, of a centralizer along a pipe string on which it is installed. In one aspect, one or more stop collars may be coupled to the exterior of a pipe segment adjacent the centralizer to limit or prevent axial movement of a centralizer. For example,
As a pipe string is installed within a targeted interval of a borehole, a bow spring centralizer installed on a pipe segment that is made-up within the pipe string may encounter a restriction that engages the ribs and obstructs or opposes movement of the centralizer past the restriction. The bow spring centralizer may then slide along the advancing pipe segment until an end collar engages a stop collar. If the bow spring centralizer is installed between two stop collars (as illustrated in
By comparison, if a stop collar 22 is disposed intermediate the end collars of a bow spring centralizer, as illustrated in
It may be difficult or impractical to position a stop collar intermediate two end collars of a centralizer using conventional methods. Necessarily, the outer diameter of a stop collar is larger than the inner diameter of the end collars of a centralizer to be positioned using the stop collar to prevent the end collars from moving beyond the stop collar. As a result, a stop collar is typically installed intermediate two end collars of a bow spring centralizer by receiving a first end collar of the centralizer onto the end of a pipe segment, disposing a stop collar (e.g., inserting between two adjacent bow springs) within the bow springs and intermediate the end collars of the bow spring centralizer, rotating the stop collar so that the bore of the stop collar is brought into alignment with the first end collar of the bow spring centralizer that is already received onto the pipe segment and also into alignment with the end of the pipe segment, and receiving the bore of the stop collar onto the end of the pipe segment. After the stop collar is received onto the pipe segment adjacent the first end collar, the centralizer is moved to receive the second end collar onto the end of the pipe segment. The centralizer and the stop collar are then moved together along the length of the pipe segment to the targeted installation location and the stop collar is then secured to the pipe segment to limit the range of movement of the centralizer along the pipe string.
The shortcoming of this method of installation arises from the difficulty in securing the stop collar to the pipe segment after it is positioned intermediate the end collars of the centralizer. In the position shown in
Other types of stop collars are securable to a pipe segment using an adhesive, such as an epoxy adhesive, but these types of stop collars may require even more access for installation than a set screw-type stop collar. As a result, centralizers are more often installed intermediate a pair of stop collars (as illustrated in
What is needed is an improved method of installing a bow spring centralizer on a pipe segment so that the stop collar is intermediate the end collars of a bow spring centralizer. What is needed is a method of installing low-clearance bow spring centralizers on a pipe string to reduce the running force required to run the pipe string into a borehole. What is needed is a kit that can be used to install a bow spring centralizer on a pipe segment so that the stop collar is intermediate the end collars of a bow spring centralizer and/or to reduce the running force required to run the pipe string into a borehole.
Embodiments of the disclosed invention satisfy one or more of the above-stated needs. Embodiments of the invention provide a method of installing a bow spring centralizer on a pipe string so that a stop collar is secured to the pipe string intermediate the end collars of a bow spring centralizer. One embodiment of the method comprises the steps of assembling a bow spring centralizer with first and second end collars on opposite sides of a stop collar installed on a pipe string wherein the range of movement of the centralizer along the pipe string is limited by the stop collar. Another embodiment of the method comprises the steps of assembling a bow spring centralizer with the first and second end collars on opposite sides of a non-flush pipe coupling, wherein the range of movement of the bow spring centralizer along the pipe string is limited by the pipe coupling. Another embodiment of the method comprises the steps of assembling a bow spring centralizer with the first and second end collars on opposite sides of a radially upset portion of a pipe segment, wherein a range of movement of the bow spring centralizer along the pipe segment is limited by the radially upset portion of the pipe segment.
In another embodiment of the method, assembling the low-clearance bow spring centralizer with first and second end collars on opposing sides of the stop collar comprises the steps of (i) slidably receiving a first centralizer portion onto a pipe segment on a first side of an installed stop collar, wherein the first centralizer portion comprises a first end collar, having an inner diameter smaller than an outer diameter of the stop collar, and a first plurality of bow spring segments coupled to the first end collar, (ii) slidably receiving a second centralizer portion onto a pipe segment on a second, opposite side of the stop collar, wherein the second centralizer portion comprises a second end collar, having an inner diameter smaller than an outer diameter of the stop collar, and a second plurality of bow spring segments coupled to the second end collar, and then (iii) coupling the first plurality of bow spring segments to the second plurality of bow spring segments to form a bow spring centralizer having a plurality of bow springs extending between the first and second end collars. Optionally, the first plurality of bow spring segments is coupled to the second plurality of bow spring segments at a midpoint between the first and second end collars. Optionally, the first and second plurality of bow spring segments may be coupled together to form bow springs by welding.
Optionally, a first bow spring segment and a second bow spring segment are positioned to abut (or to be in close proximity across a small gap) and then coupled one to the other to form a bow spring by welding along a weld path at the abutment (or gap) at an angle between about 20 and about 70 degrees to the longitudinal centerline of the bow spring. Optionally, a backing plate may first be welded to an interior side of the abutting interface (or gap) between the first bow spring segment and the second bow spring segment to stabilize the first and second bow spring segments for welding and to facilitate proper positioning of the first and second bow spring segments for being coupled together to form bow springs.
In one embodiment, the first centralizer portion and the second centralizer portion may be formed by cutting each of a plurality of bow springs of a bow spring centralizer intermediate the first and second end collars. For example, in one embodiment of the method, cutting each of the plurality of bow springs of a low-clearance bow spring centralizer at a non-perpendicular angle relative to a longitudinal centerline of the bow spring to form a first centralizer portion and a second centralizer portion provides the first and second centralizer portions that may be positioned, in accordance with embodiments of the method, and then coupled to form a low-clearance bow spring centralizer movable within a range defined by an installed stop collar intermediate the first end collar of the first centralizer segment and the second end collar of the second centralizer segment. Optionally, the non-perpendicular angle is between 20 and 70 degrees relative to the longitudinal centerline of the bow spring.
One embodiment of the invention provides a method of installing a low-clearance bow spring centralizer on a pipe segment comprising assembling a bow spring centralizer with first and second end collars on opposite sides of an installed stop collar wherein the stop collar limits the range of movement of the bow spring centralizer along the pipe segment. For purposes of this description, a “low-clearance” centralizer is one that has sleeve-shaped end collars and bow springs that flexibly collapse to lie generally along the exterior wall of a pipe segment received through the centralizer so that a pipe string that includes the pipe segment may pass through restrictions larger than the diameter of the end collars, and so that the bow springs may flexibly redeploy to position the pipe segment within a portion of the borehole beyond the restriction.
In a further option, the first and second plurality of bow spring segments may be coupled, such as by welding, along a generally linear path 74 disposed at a non-perpendicular angle, e.g., between about 20 and about 70 degrees relative to a longitudinal centerline 76 of the bow spring formed by coupling the aligned first and second bow spring segments 54, 64. It should be understood that the weld path may be non-linear. By positioning the path 74 substantially separated from the end collars 52, 62, heat from welding the first and second bow spring segments 54, 64 to form a bow spring will not damage or otherwise affect pipe segment 20. As heat conducts from the weld interface at path 74 through the slender first and second bow spring segments 54, 64 and toward end collars 52, 62, respectively, the heat rapidly dissipates, e.g., due to the favorable flat cross-section and elongate shape of the first and second bow spring segments 54, 64, which perform like heat dissipation fins. As a result, heat introduced into the first and second bow spring segments 54, 64 at the weld interface 74 favorably dissipates so that any interior and/or exterior pipe coatings, pipe linings and the pipe 20 material itself all maintain their chemical, structural and/or metallurgical integrity and remain uncompromised by heat damage or heat affected zones.
Although the first and second plurality of bow spring segments 54, 64 are illustrated in
Optionally, the first centralizer portion 50 and the second centralizer portion 60 may be formed by cutting through a plurality of bow springs of an assembled centralizer intermediate the first and second end collars 52, 62. The first bow spring segments 54 and the second bow spring segments 64 may be heat treated prior to assembly of the first centralizer portion 50 and the second centralizer portion 60 so that the plurality of bow springs formed by joining the bow spring segments may be installed on a pipe segment and run into a borehole without the need for further heat treating. Although the first and second centralizer portions may be separately manufactured using, for example, dies prepared specifically for the purpose of making first and second bow spring segments, the same result may be achieved by cutting through the bow springs of an existing bow spring and/or the bow springs of a pre-assembled bow spring centralizer.
In one embodiment, the non-perpendicular angle is between about 20 and about 70 degrees relative to the longitudinal centerline of the bow spring. A weld angle within this range may better distribute stresses from flexible working of the bow spring along a longer weld seam instead of concentrating the stress along a shorter, more perpendicular weld seam in a “hinge-effect” bending moment. In accordance with a further option, a backing plate 78 may be welded to an interior side and/or exterior side of the abutting first and second bow spring segments 54, 64, wherein the backing plate 78 covers at least a portion of the weld path 74. Application of the backing plate to the interior side of the abutting first and second bow spring segments 54, 64 may provide access to weld the exterior side. A backing plate 78 may be secured to abutting first and second bow spring segments 54, 64 prior to welding of the path 74 by tack welding to secure the first and second bow spring segments 54, 64 in the abutting configuration for welding.
Although embodiments of the invention are described and shown primarily in relation to a bow spring centralizer, it should be recognized that the methods of the invention are equally applicable to a centralizer having rigid ribs instead of bow springs as the ribs.
The terms “comprising,” “including,” and “having,” as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms “a,” “an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The term “one” or “single” may be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as “two,” may be used when a specific number of things is intended. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.
It should be understood that the term “stop collar,” as used herein, refers to a collar to limit the range of movement of a centralizer movably received on a tubular segment, and that the use of the modifier “stop” within the term “stop collar” should not be considered as limiting the use of the device to secure only stationary or fixed devices. It should be further understood that the inventive method may be used with epoxy-secured, set screw-secured, heat shrunk and any other type of stop collar.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
