Wells – Guide for device or conduit – On sucker or pump rod
Reexamination Certificate
2002-02-08
2004-01-20
Bagnell, David (Department: 3672)
Wells
Guide for device or conduit
On sucker or pump rod
C166S174000, C166S241600, C175S325500
Reexamination Certificate
active
06679325
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to casing or tubular centralizers with flexible bow springs for use in bore bole drilling operations, and particularly to centralizers that can be radially compressed to fit within a small annular space and which can later expand to center casing within the bore hole.
2. Description of Related Art
Casing is tubular pipe used to line a bore hole that is drilled to recover naturally occurring oil or gas deposits. A joint of casing is typically about 36 to 44 feet in length, and generally has threaded connections at each end to facilitate coupling to adjacent joints of casing to form a casing string. Casing prevents drilled bore holes from washing out or caving in during subsequent drilling and completion operations. Casing strings are cemented into place in the bore hole by circulating cement from the surface down the interior of the casing string, and then displacing the cement into the annular space between the exterior surface of the casing string and the wall of the bore hole. It is important that the casing string be positioned prior to cementing as closely as possible to the center of the bore hole in order to ensure full circumferential cement placement around the casing and to thereby effectively isolate and seal off penetrated geologic formations and to prevent unwanted fluid flow. It is desirable to install casing periodically to maintain the bore hole, and the length of a casing string that can be effectively installed and cemented into place in the bore hole is limited. Progressively smaller diameter casing strings are lowered into the bore hole through the interior of previously installed and cemented casing. Consequently, progressively smaller diameter casing is installed as the depth of the drilled bore hole increases.
It is advantageous to case the bore hole adjacent to producible hydrocarbon zones with casing of a reasonably large diameter to facilitate completion and production operations. This advantage is achievable using bi-centered drill bits. Bi-centered drilling bits are drilling bits that can be used to drill a bore hole of a size larger than the inside diameter of cemented casing through which the drilling bit passes. For example,
FIG. 1A
illustrates a bore hole having casing
90
with 13⅜ inch outside diameter and 12¼ inch inside diameter. Using conventional drilling bits, the bore hole below the 12¼ inch I.D. casing
90
can be drilled only to 12¼ inch in diameter
71
, and the largest standard size of casing that can be effectively installed and cemented in the bore hole is 9⅝ inch O.D. casing
82
. However, using a bi-centered bit allows drilling the bore hole beneath the end of the 12¼ inch I.D. casing
90
to 14¾ inch diameter
72
as shown in FIG.
1
B. This advance in drill bit technology allows 11⅞ inch O.D. casing
80
to be effectively cemented in place beneath the 12¼ inch I.D. casing
90
as an annulus
75
comparable to the annulus between the 9⅝ O.D. inch casing and the 12¼ O.D. inch bore hole in
FIG. 1A
is obtained around the 11⅞ inch O.D. casing in FIG.
1
B.
The bore hole is easier to drill and complete if larger diameter tools can be used. As wells are drilled to deeper depths, and as more high angle and horizontal wells are drilled, the number of discrete sizes of casing used in the casing system increases, and the available annular clearance between adjacent strings of casing necessarily decreases. For example, referring again to
FIG. 1B
, if a bi-centered bit is used to drill the bore hole below a string of 12¼ inch I.D. casing
90
to 14¾ inch, and if 11⅞ inch O.D. casing
80
is lowered through the 12¼ inch I.D. casing
90
and into the 14¾ inch diameter
72
bore hole, the thickness of the annular clearance
74
between the inside of the (fixed) 12¼ inch casing
90
and the outside of the 11⅞ inch O.D. casing
80
is {fraction (3/16)} inch. The use of bi-centered bits gives rise to the need for a centralizer that substantially radially collapses to fit within the thin {fraction (3/16)} inch annular space
74
, and that can later re-deploy to center the 11⅞ inch O.D. casing
80
in a 14¾ inch diameter
72
bore hole. However, as the thickness of the annular clearance
74
becomes very small, it becomes difficult to obtain optimal pre-cement centralization of casing
80
using conventional bow-spring centralizers because they require excessive annular clearance
74
between adjacent casing strings
90
and
80
.
Bow-spring centralizers are used to center casing inside a drilled borehole in order to obtain uniform annular placement of cement in the casing/bore hole annulus
75
. Bow springs extend radially outwardly from the center bore of the centralizer to provide desirable casing stand-off from the wall
76
of the bore hole. Wide-deployment centralizers are centralizers designed to provide substantial stand-off from a nearby object such as the wall of a bore hole. For example, centering a 11⅞ inch O.D. casing within a 14¾ inch diameter bore hole requires radial stand-off of about 1{fraction (7/16)} inch. By comparison, a limited deployment centralizer may be used to center a 4½ inch O.D. diameter casing within a 5½ inch diameter bore hole, and requires only a radial stand-off of about 0.5 inch. While a limited stand-off centralizer may have bow springs that are sufficiently stiff to resist radially outward collapse upon being pushed into or through a restriction, most wide-deployment centralizers have bow springs that are flexible, and the leading ends of the bow springs must be secured against the casing in order to prevent radially outward collapse of the centralizer ribs. As shown in FIG.
2
A and
FIG. 2B
, bow-spring centralizers are secured to the exterior of the casing and centralizer ribs project radially outwardly therefrom. In order to provide optimal centralization of casing installed at lower depths in the well, it is essential that centralizers be resiliently collapsible to fit within the annular space between the exterior surface of the casing being installed and the interior surface of the larger, installed casing. It is also desirable that the centralizer ribs
42
collapse radially inwardly to achieve a minimum annular clearance, and that the centralizer does not prevent the flow of drilling fluid through the annulus between the smaller and larger casing.
Another factor to be considered in designing a low annular clearance centralizer is the prevention of centralizer rib damage. No wellbore is perfectly vertical and uniform. As casing is lowered into a well, the high strength steel resiliently twists, turns and flexes as it passes through restrictions and bends in the non-linear and non-uniform bore hole. It is important to prevent damage to centralizer ribs by securing the centralizer to the casing in a manner that allows free rotation of the centralizer relative to the casing to which it is secured.
Another factor to be considered in designing low annular clearance centralizers is related to securing the centralizer in place on the exterior of casing that is to be lowered into the well. As the bow springs radially inwardly collapse, the ends of each bow spring must longitudinally separate one from the other. Longitudinal elongation of the centralizer requires that at least one of the collars to which the end of bow springs are secured must remain longitudinally movable relative to the casing on which the centralizer is secured. If the other collar is secured to the casing, then the centralizer will be unidirectional; that is, the centralizer ribs will collapse only when the centralizer passes through a restriction in one direction, and the centralizer ribs will not collapse and pass through the larger casing unless the collar that is secured to the casing is the leading collar to first enter the larger, installed casing. However, a centralizer needs to
Bagnell David
Frank's International, Inc.
Gay Jennifer H
Steele Patrick K.
Streets & Steele
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