U.S. patent application number 11/512198 was filed with the patent office on 2008-03-06 for pipe guides and methods of guiding pipes in snubbing units.
Invention is credited to Kelly Funk.
Application Number | 20080053661 11/512198 |
Document ID | / |
Family ID | 39133553 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080053661 |
Kind Code |
A1 |
Funk; Kelly |
March 6, 2008 |
Pipe guides and methods of guiding pipes in snubbing units
Abstract
An hydraulic snubbing unit has a pair of hydraulic cylinders for
moving travelling snubbing slips towards and away from stationary
snubbing slips to snub a pipe through the snubbing unit, the
hydraulic cylinders having spaced, parallel cylinder rods. A pipe
guidance apparatus has pipe guides between the stationary snubbing
slips and the travelling snubbing slips, the pipe guides each
having a pair of cylinder rod openings spaced apart from one
another and slidably receiving the rods of the hydraulic cylinders
and a pipe guidance opening located between the cylinder rod
openings and slidably guiding the pipe, and a pipe guide spacer
having extendable and contractible interconnections between the
pipe guides. In a contracted condition of the pipe guide spacer,
the interconnections are contracted and the pipe guides are moved
into proximity to one another by the simultaneous movement of the
cylinder rods slips towards the stationary slips, and in an
expanded condition, the interconnections are extended and the pipe
guides are moved apart from one another by the simultaneous
movement of the cylinder rods away from the stationary slips to
provide lateral support of the pipe at intervals along the
pipe.
Inventors: |
Funk; Kelly; (Nanaimo,
CA) |
Correspondence
Address: |
LONG AND CAMERON
SUITE 1401 - 1166 ALBERNI STREET
VANCOUVER
BC
V6E 3Z3
US
|
Family ID: |
39133553 |
Appl. No.: |
11/512198 |
Filed: |
August 30, 2006 |
Current U.S.
Class: |
166/380 ;
166/77.51; 166/85.5 |
Current CPC
Class: |
E21B 19/24 20130101;
E21B 19/00 20130101; E21B 19/16 20130101 |
Class at
Publication: |
166/380 ;
166/77.51; 166/85.5 |
International
Class: |
E21B 19/00 20060101
E21B019/00; E21B 19/16 20060101 E21B019/16 |
Claims
1. A pipe guidance apparatus for guiding a pipe during snubbing of
the pipe, comprising:-- a. a plurality of pipe guides; b. the pipe
guides each having a pair of jack rod openings spaced apart from
one and a pipe guidance opening located between the jack rod
openings for slidably guiding the pipe; c. the jack rod openings
being mutually aligned and the pipe guidance openings being
mutually aligned; and d. a pipe guide spacer; e. the pipe guide
spacer comprising extendable and contractible interconnections
between the pipe guides; and f. the pipe spacer having a contracted
condition, in which the interconnections are contracted and the
pipe guides are moved towards one another, and an expanded
condition, in which the interconnections are extended and the pipe
guides are moved apart from one another.
2. A pipe guidance apparatus as claimed in claim 1, wherein the
extendable and contractible interconnections comprise two parallel
sets of tubular members, the tubular members of each of the sets
being telescopically extendable and retractable relative to one
another and each of the sets of tubular members being provided, at
one end of the set, with a pull member for telescopically extending
the tubular members.
3. A pipe guidance apparatus as claimed in claim 2, wherein an
outermost one of the tubular members of each set of tubular
members, at an opposite end of the set, has an abutment for
retaining the remainder of the set on contraction of the set.
4. A pipe guidance apparatus as claimed in claim 2, wherein each of
the pull members has, at one end thereof, an anchor member located
within an innermost one of the tubular members of the respective
set of tubular members, said innermost tubular member having an end
abutment engageable by the anchor member to telescopically extend
said respective set of tubular members on extension of the pull
member from the innermost tubular member.
5. A pipe guidance apparatus as claimed in claim 4, wherein each of
the tubular members has, on one end thereof, a further anchor
member and at an opposite end thereof a further end abutment, the
further end abutment of each of the tubular members being
engageable by the further anchor member of another of the tubular
members to effect the telescopic extension of the tubular
members.
6. A pipe guidance apparatus as claimed in claim 5, wherein the
further end abutments are formed by end caps on the tubular
members.
7. A pipe guidance apparatus as claimed in claim 5, wherein the
further anchor members comprise annular collars on the tubular
members.
8. In an hydraulic snubbing unit having stationary snubbing slips,
travelling snubbing slips and a pair of spaced, parallel hydraulic
jacks for moving the travelling snubbing slips towards and away
from the stationary snubbing slips to snub a pipe through the
snubbing unit, the hydraulic jacks comprising hydraulic cylinders
and jack rods extending from the cylinders, the improvement
comprising: a pipe guidance apparatus for guiding a section of the
pipe between the stationary snubbing slips and the travelling
snubbing slips; the pipe guidance apparatus comprising:--a
plurality of pipe guides between the stationary snubbing slips and
the travelling snubbing slips; the pipe guide guides each having a
pair of cylinder rod openings spaced apart from one another and
slidably receiving the jack rods of the hydraulic cylinders and a
pipe guidance opening located between the cylinder rod openings and
slidably guiding the pipe; and a pipe guide spacer; the pipe guide
spacer comprising extendable and contractible interconnections
between the pipe guides; and the pipe spacer having a contracted
condition, in which the interconnections are contracted and the
pipe guides are moved into proximity to one another by movement of
the travelling slips towards the stationary slips, and an expanded
condition, in which the interconnections are extended and the pipe
guides are moved apart from one another by movement of the
travelling slips away from the stationary slips.
9. An hydraulic snubber unit as claimed in claim 8, wherein the
extendable and contractible interconnections comprise two parallel
sets of tubular members, the tubular members of each of the sets
being telescopically extendable and retractable relative to one
another, and each including a connecting member for telescopically
extending and contracting the tubular members, the connecting
members each having one end connected for movement with the
travelling slips and an opposite end extending into the tubular
members.
10. An hydraulic snubber unit as claimed in claim 8, wherein each
of the connecting members has at one end thereof an anchor member
located within an innermost one of the tubular members of the
respective set of tubular members, said innermost tubular member
having an end abutment engageable by the anchor member to
telescopically extend said innermost tubular member.
11. An hydraulic snubber unit as claimed in claim 10, wherein each
of the tubular members of each set, other than an outermost one of
the tubular members, has on one end thereof a further anchor member
and each of the tubular members has at an opposite end thereof a
further end abutment, the further end abutment being engageable by
one of the further anchor members to effect the telescopic
extension of the tubular members.
12. An hydraulic snubber unit as claimed in claim 8, wherein the
extendable and contractible interconnections comprise two parallel
sets of telescopically extendable and retractable tubular member
connecting the pipe guides in a ladder-like assembly.
13. A method of guiding a pipe as the pipe is being snubbed through
snubbing unit having stationary snubbing slips, traveling snubbing
slips and hydraulic jacks for moving the traveling slips towards
and away from the stationary slips, the hydraulic jacks comprising
hydraulic cylinders and jack rods extending from the hydraulic
cylinders, the jack rods being connected to the traveling snubbing
slips, the method comprising the steps of:--gripping the pipe by
the travelling snubbing slips during movement of the pipe through
the snubbing unit; extending and retracting the hydraulic jacks to
displace the travelling snubbing slips relative to the stationary
snubbing slips and thereby to displace the pipe through the
snubbing unit; and guiding a section of the pipe extending between
the stationary snubbing slips and the travelling snubbing slips by
laterally restraining the pipe section at intervals spaced apart
along the section of the pipe.
14. A method as claimed in claim 13, in which the step of guiding a
section of the pipe comprises guiding the pipe by pipe guides
spaced apart along the section of the pipe, and which further
includes moving the pipe guides towards one another on movement of
the travelling slips towards the stationary slips and moving the
pipe guides apart from one another on movement of the travelling
slips away from the stationary slips.
15. A method as claimed in claim 14, which includes guiding the
pipe guides along the pipe by sliding engagement of the pipe guides
with the jack rods of the hydraulic cylinders.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to pipe guides for use in
snubbing units for snubbing pipes into and from live underground
well bores, to snubbing units provided with pipe guides and to
methods of guiding pipes through snubbing units.
[0003] 2. Description of the Related Art
[0004] Snubbing units, which are used to "snub" or feed pipes into
and from underground wells, employ stationary snubbing slips or
grippers and traveling snubbing slips to alternately grip and
release a pipe as the traveling snubbing slips are moved towards
and away from the stationary snubbing skips, so that the pipe is
moved upwardly or downwardly by a "hand-over-hand" gripping of the
pipe.
[0005] Traditional pipe guidance apparatus on snubbing units used
today typically employ two interlocking and telescoping tubes
positioned between the stationary snubbing slips and the traveling
snubbing slips. Inherent problems with this type of guiding system
include the space and weight of the pipe guidance systems and the
heights which they add to the snubbing units. Also, approximately
one half of the effective stroke of the snubbing unit is lost and
snubbing operations therefore become much less efficient than would
be the case if full snubbing strokes could be taken.
[0006] A pipe that is being snubbed into or out of a live well
against the forces (compressive loads), which are generated from
the well pressure over the cross-sectional area of the pipe being
removed from or inserted into the well bore, can only support a
limited amount of compressive force before the pipe buckles. The
longer the length of exposed pipe between the point at which the
traveling snubbing slips grip the pipe and the point at which the
pipe is exposed outside of the well bore determines the allowable
compressive load before buckling takes place. For example a 2-foot
long section (window) of exposed and unsupported pipe under a
compressive load can withstand a far greater compressive force,
before major axis buckling occurs, than a 10-foot unsupported
section subject to the same compressive load.
[0007] There are two types of bucking that can occur when a pipe is
under a compressive load:-- [0008] 1. Major Axis buckling occurs
without of yielding the pipe and is therefore known as elastic
buckling. This happens when compressive loads on the pipe are as
such that the pipe buckles outwardly, at an exposed, i.e. laterally
unsupported, section of the pipe as a result of not being supported
laterally. [0009] 2. Local buckling requires the pipe to yield and
is therefore known as inelastic buckling. This happens when the
pipe may very well be supported laterally but the compressive load
is as such that the pipe is effectively crushed vertically.
[0010] When snubbing against well pressures without pipe guidance
apparatus, a reasonable safety factor to prevent buckling can be
obtained by not exposing a section of pipe longer than the pipe can
support from the generated forces with friction related to the seal
point maintaining the well pressure. Additional factors, such as
the speed at which the pipe is inserted into or removed from the
well, are all part of typical pre-job calculations which are needed
to predetermine the maximum allowable length of pipe that can be
exposed while manipulating the pipe without possible bucking. Once
these calculations have been made, a snubbing operator uses short
strokes to move the pipe into or out of the well, never allowing
more unsupported exposure than calculated.
[0011] With this type of snubbing operation, a safety factor is
only maintained if the snubbing operator stays within the
calculated parameters. The operation is therefore subject to human
error in the event that the operator uses too long a stroke of the
pipe, which could result in the pipe rocketing out sideways at an
exposed, i.e. laterally unsupported, section of the pipe. This type
of error, although not common, can easily occur, since operators
are under constant pressure to complete snubbing operations as
quickly as possible and they therefore generally push the limits by
attempting to take strokes which are as big as possible. Often, an
operator will take a stroke long enough to see the pipe bow as it
is being snubbed into or out of the well. This bowing occurs just
short of the pipe reaching its compression limit. The result of
bucking of the pipe can be catastrophic, with potential loss of
control of the pipe and the well and loss of life. The
short-stroking operation is not only dangerous but slows the
operation down as compared to longer strokes of exposed pipe that
could be taken if the pipe was supported externally by means of a
pipe guidance apparatus.
[0012] Hydraulic snubbing units generally comes in two
configurations, namely a self-contained, stand-alone configuration,
and a rig-assist snubbing unit.
[0013] The self contained stand-alone configuration works well for
live wells, where the overall height of the equipment is not all
that important because there is typically no spatial limitations in
order to handle the pipe that is to be inserted or removed from the
live well.
[0014] With a rig assist-snubbing unit, however, the overall height
is critical because the snubbing unit must work within the height
restraint of the top of a derrick forming part of a rig in
conjunction with which the snubbing unit is being operated. The
distance between the top of the snubbing unit and the inside
working area from the top of the rig derrick in many cases
eliminates the option of having pipe guidance apparatus, because
the additional height that the apparatus would add to the snubbing
unit would not allow sufficient space for lengths of pipe to be
handled. Consequently, the operators have resorted to performing
the dangerous short stroking operation on high-pressure wells, as
described above.
BRIEF SUMMARY OF THE INVENTION
[0015] According to the present invention, there is provided a pipe
guidance apparatus for guiding a pipe during snubbing of the pipe,
the pipe guide having a plurality of pipe guides, each with a pair
of jack rod openings spaced apart from one for sliding engagement
with a pair of parallel, spaced hydraulic jack rods, which laterlly
restrain the pipe guides when the apparatus is in use, and a pipe
guidance opening located between the jack rod openings for slidable
guiding engagement with the pipe. The jack rod openings are
mutually aligned and the pipe guidance openings are also mutually
aligned. The pipe guidance apparatus includes a pipe guide spacer
comprising extendable and contractible interconnections between the
pipe guides. The pipe spacer has a contracted condition, in which
the interconnections are contracted and the pipe guides are moved
towards one another, and an expanded condition, in which the
interconnections are extended and the pipe guides are moved apart
from one another.
[0016] In a preferred embodiment of the present invention, the
extendable and contractible interconnections comprise two parallel
sets of tubular members, the tubular members of each of the sets
being telescopically extensible and retractable relative to one
another and each of the sets of tubular members being provided at
one end of the set with a connecting member, e.g. a rod, for
telescopically extending the tubular members.
[0017] Also in accordance with the present invention, there is
provided an hydraulic snubbing unit having stationary snubbing
slips, traveling snubbing slips and a pair of spaced, parallel
hydraulic jacks for moving the traveling snubbing slips towards and
away from the stationary snubbing slips to snub a pipe through the
snubbing unit, the hydraulic jacks comprising cylinders having jack
rods. The hydraulic snubbing unit is provided with a pipe guidance
apparatus for guiding a section of the pipe between the stationary
snubbing slips and the travelling snubbing slips, and the pipe
guidance apparatus comprises a plurality of pipe guides between the
stationary snubbing slips and the travelling snubbing slips, the
pipe guide guides each having a pair of jack rod openings spaced
apart from one another and slidably receiving the jack rods, and a
pipe guidance opening located between the cylinder rod openings and
slidably guiding the pipe. The pipe guidance apparatus includes a
pipe guide spacer comprising extendable and contractible
interconnections between the pipe guides, the pipe spacer having a
contracted condition, in which the interconnections are contracted
and the pipe guides are moved into proximity to one another by the
movement of the traveling slips towards the stationary slips, and
an expanded condition, in which the interconnections are extended
and the pipe guides are moved apart from one another by the
movement of the traveling slips away from the stationary slips.
[0018] In the preferred embodiment of the invention, the extendable
and contractible interconnections comprise two parallel sets of
tubular members, the tubular members of each of the sets being
telescopically extensible and retractable relative to one another,
and each including a connecting member for telescopically extending
and contracting the tubular members, the connecting members each
having one end connected for movement with the traveling slips and
an opposite end extending into the tubular members.
[0019] Also according to the present invention, there is provided a
method of guiding a pipe as the pipe is being snubbed through
snubbing unit having stationary snubbing slips, traveling snubbing
slips and spaced, parallel hydraulic jacks for moving the traveling
slips towards and away from the stationary slips, the hydraulic
jacks comprising hydraulic cylinders having jack rods connected to
the traveling snubbing slips, the method comprising the steps of
gripping the pipe by the traveling snubbing slips during movement
of the pipe through the snubbing unit, extending and retracting the
hydraulic cylinders to displace the traveling snubbing slips
relative to the stationary snubbing slips and thereby to displace
the pipe through the snubbing unit, and guiding a section of the
pipe extending between the stationary snubbing slips and the
travelling snubbing slips by laterally restraining the pipe section
at intervals spaced apart along the section of the pipe.
[0020] Prefereably, the pipe is guided by pipe guides spaced apart
along the section of the pipe, and the pipe guides are moved
towards one another on movement of the travelling slips towards the
stationary slips and apart from one another on movement of the
travelling slips away from the stationary slips by sliding
engagement of the pipe guides with the jack rods of the hydraulic
cylinders.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention will be more readily understood from the
following description of an embodiment thereof given, by way of
example only, with reference to the accompanying drawings, in
which:--
[0022] FIG. 1 shows a view in elevation of a pipe snubbing unit
provided with an extendable and contractible pipe guidance
apparatus according to the present invention, with the pipe
guidance apparatus in a contracted condition;
[0023] FIG. 2 shows a view corresponding to that of FIG. 1 but with
the pipe guidance apparatus in an extended condition;
[0024] FIG. 3 shows a plan view of a pipe guide forming part of the
pipe guidance apparatus of FIGS. 1 and 2;
[0025] FIG. 4 shows a view in side elevation of the pipe guide of
FIG. 3;
[0026] FIGS. 5 and 6 show views in vertical cross-section through a
set of tubular members forming part of the pipe guidance apparatus
of FIGS. 1 and 2 in a contracted condition and an extended
condition, respectively: and
[0027] FIG. 7 shows a broken-away view in perspective of a
connection between one of the tubular members of FIGS. 5 and 6 and
an associated guide plate.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Referring firstly to FIGS. 1 and 2 of the accompanying
drawings, there is shown a pipe snubbing unit, indicated generally
by reference numeral 10, for snubbing a vertical pipe 12 into or
from an underground well (not shown).
[0029] The snubbing unit 10 has stationary snubbing slips or pipe
grippers 14, provided with an underlying blow-out preventor 16,
travelling snubbing slips or pipe grippers 18 and a pair of
hydraulic jacks 20 for moving the travelling snubbing slips 18
vertically towards and away from the stationary snubbing slips
14.
[0030] The jacks 20 each comprise an hydraulic cylinder 22 from
which extends an jack rod 24, the lowermost end of the hydraulic
cylinder 22 being mounted on a middle plate 26, and the uppermost
end of the jack rod 24 being connected to a travelling plate 28 on
which the travelling snubbing slips 18 are mounted.
[0031] In operation of the snubbing unit 10, the jack rods 24 move
the travelling snubbing slips 18 vertically up and down relative to
the stationary snubbing slips 14, while the stationary snubbing
slips 14 and the travelling snubbing slips 18 alternately grip the
pipe 12. In this way, the pipe 12 is fed into or from its well by
the snubbing slips 14 and 18 by a "hand-over-hand" operation of
those slips.
[0032] The snubbing unit 10, as described above, and its operation
are well known in the art and, therefore, are not described herein
in greater detail.
[0033] To provide lateral support for a section 30 of the pipe 12
extending between the stationary snubbing slips 14 and the
traveling snubbing slips 18 when the traveling snubbing slips 18
are displaced by the hydraulic jack rods 24 from the stationary
snubbing slips 14, the snubbing unit 10 is equipped with a pipe
guidance apparatus indicated generally be reference numeral 32 in
FIG. 1, the components of which are shown in greater detail in
FIGS. 3-7.
[0034] The pipe guidance apparatus 32 includes four pipe guides 34,
one of which is shown in FIGS. 2 and 3.
[0035] Each pipe guide 34 includes an elongate guide plate which,
as can be seen from FIG. 4, has a pair of parallel flat end
portions 38, a central portion 40 which is parallel to the flat end
portions 38, and a pair of intermediate portions 42 which extend
between and at an inclination to the end portions 36 and the
central portion 38. Each intermediate portion 42 is provided, in
one of its edges, with a pair of threaded holes 45.
[0036] Each of the end portions 38 is formed with a circular jack
rod opening 44, and each circular jack rod opening 44 is provided,
at opposite sides of its respective end portion 38, with an annular
slide member 46, which is secured to the end portion 38 by screws
48.
[0037] The circular jack rod openings 44 slidably receive the jack
rods 24, as shown in FIGS. 1 and 2, so that the pipe guides 34 are
guided and retained laterally of the jack rods 24 by slidable
engagement with the jack rods 24 and are free to slide
longitudinally of the jack rods 24. The jack rods 24 hold the pairs
of jack rod openings 44 in mutual alignment and thereby also hold
pipe openings 50 in mutual alignment.
[0038] The pipe openings 50, which are provided with annular slide
members 52 secured to the central portion 40 by screws 54, slidably
receive, guide and laterally restrain the pipe section 30,
extending between the stationary snubbing slips 14 and the
traveling snubbing slips 18, so that the pipe section 30 is
prevented from buckling.
[0039] Referring now to FIGS. 2, 5 and 6, the pipe guides 34 are
connected to one another by pipe spacers indicted generally by
reference numeral 55 in FIG. 2. The pipe spacer 55 includes two
sets of interconnections which are formed by two sets of
telescopically extensible and retractable tubular members 54a-54d,
as shown in greater detail in FIGS. 5 and 6. The pipe guidance
apparatus therefore has a collapsible ladder-like assembly, formed
by the rung-like pipe guides 34 and the stile-like sets of tubular
members 54a-54d.
[0040] The pipe spacer 55 has a contracted condition, in which the
interconnections comprising the sets of tubular members 54 are
contracted and the pipe guides 34 are moved into proximity to one
another by the movement of the traveling snubbing slips 18 towards
the stationary snubbing slips 14 as shown in FIG. 1, and an
expanded condition, in which the sets of tubular members 54 are
telescopically extended relative to one other and the pipe guides
34 are moved apart from one another, as the traveling snubbing
slips are moved away from the stationary snubbing slips 14 by the
hydraulic jacks rods 24, as shown in FIG. 2. In the expanded
condition of the pipe spacer 55, in which the pipe guides 34 are
spaced apart along the pipe section 30, longitudinally of the pipe
12, for laterally supporting the pipe section 30 at these spaced
apart positions as shown in FIG. 2.
[0041] The two sets of tubular members 54a-54d are each provided
with a connecting member in the form of a rod 56 for telescopically
extending and contracting the tubular members 54a-d. Each of the
rods 56 has an upper end 58 connected to the traveling plate 28,
and thereby connected for movement vertically with the traveling
snubbing slips 18, and a lower end 60 extending into the innermost
tubular member 54a. When the traveling snubbing slips 18 are
displaced upwardly, away from the stationary slips 14 by extension
of the jack rods 24 from their cylinders 22, the rods 56 pull the
associated tubular members 54a-54d so as to telescopically extend
the latter.
[0042] As shown in FIGS. 5 and 6, the lower end 60 of the rod 56
has an a metal annular anchor member 62a, which is secured to the
lower end 60 by a nut 64 in threaded engagement with the lower end
60. The anchor member 62a includes an annular rubber cushion 66,
which is provided on the lower end 60 at the side of the anchor
member 62 opposite from the nut 64.
[0043] The tubular members 54a-54d have caps 68a-68d in threaded
engagement with the upper ends of the respective tubular member
54a-54b. Each of the caps 68b-68d is formed with a circular opening
70b-70d for slidably receiving a respective one of the tubular
members 54b-54d, while the cap 68a of the innermost tubular member
54a has a circular opening 70a for slidably receiving the rod 56.
Each of the tubular members 54a-54c has an annular anchor member
62a-62c, welded to its exterior at a spacing from its lower end,
the annular anchor members 62a-62c being provided with annular
cushions 62a-62c of resilient material, e.g. rubber.
[0044] Since the caps 68a-68d are secured by threaded engagement
with the tubular members 54a-54d, the caps 68a-68d can be readily
unscrewed and removed from the tubular members 54a-54d to allow
replacement of the annular cushions 62 and 62a-62c and for other
maintenance and repairs.
[0045] The caps 68a-68d serve as end abutments on the tubular
members 54a-54d, so that when the rod 56 is drawn upwardly relative
to the innermost tubular member 54a, by upward displacement of the
traveling snubbing slips 18 as described above, the rubber cushion
66 of the anchor member 62 is moved into abutment with the end cap
68a, which causes the innermost tubular member 54a to be
telescopically extended from the next tubular member 54b.
[0046] The cushion 66b of the tubular member 54b is then moved
upwardly into abutment with the end cap 68a, which causes the
tubular member 54b to be telescopically extended from the tubular
member 54c. The tubular member 54c is then telescopically extended
in a similar manner from the outermost tubular member 54d, thereby
extending the pipe guide spacer 55 into the extended condition
shown in FIG. 2.
[0047] The lower end of the tubular member 54d is closed by a
circular plate 72, which is welded to the lower end of the tubular
member 54d. When the traveling snubbing slips 18 reverse their
direction of movement and move towards the stationary snubbing
slips 14, the rod 12 acts as a push rod and is telescopically
retracted into the innermost tubular member 54a. The tubular
members 54a-54c are then telescopically retracted into the
outermost tubular member 54d until the lower ends of the tubular
members 54a-54c abut the circular plate 72, as shown in FIG. 6.
[0048] FIG. 7 shows a connection between one of the guide plates 34
and its associated tubular member 54a. This connection is provided
by a metal strip 76, which is secured, by screws 77 in threaded
engagement with the holes 45 (FIG. 4), to an edge of one of the
inclined portions 42 of the guide plate 34. The metal strip 76 is
connected to the cap 68a by a metal plate 78, which is welded to
the metal strip 76 and to the cap 68a.
[0049] The remaining tubular members 54b-54d are connected to their
guide plates 34 by connections which are similar to that shown in
FIG. 7, and which have metal plates which correspond to the metal
plate 78 of FIG. 7 but which are of different dimensions to
accommodate the different diameters of the tubular members
54a-54d.
[0050] When the above-described pipe guidance apparatus 32 is in
use, the section 30 of the pipe 12 which is exposed between the
stationary snubbing slips 14 and the traveling snubbing slips 18 is
automatically guided and laterally restrained by the mutually
spaced pipe guides 34 when the traveling snubbing slips 18 are
moved away from the stationary snubbing slips 14 by the hydraulic
jack rods 24, which causes the pipe spacer 55 to become extended
without any intervention by an operator. Therefore, the maximum
allowable stroke by which the pipe 12 is snubbed can be employed
but no judgement with respect to the length of stroke nor any other
intervention by an operator is required to prevent buckling of the
pipe section 30. Human error in determining the stroke length is
therefore avoided and, consequently, highly efficient snubbing of
the pipe 12 without buckling of the pipe 12 can be achieved. Also,
the height of the snubbing unit 10 is not affected by the provision
of the snubbing unit 10 with the pipe guidance apparatus 32.
[0051] The anchor members 62a-62c are staggered along their tubular
members 54a-54c, as shown in FIGS. 5 and 6, to compensate for the
heights of the caps 68a-68c, so that the tubular members 54a-54c
are extended by equal lengths when the pipe spacer 55 is in its
extended condition.
[0052] The pipe guides 34 shown in the drawings are each formed
with a depressed central portion 40 to conform to the shapes of the
slips between the stationary snubbing slips 14 and the travelling
snubbing slips 18 when the snubbing unit is collapsed and thereby
to avoid adding additional height to the snubbing unit. Otherwise,
the pipe guides could, for example, be flat.
[0053] The tubular members are provided, at their lower ends, with
annular metal rings 74a-74d, which are welded to the exteriors of
the tubular members 54a-54d and which serve to provide internal
stabilization of the apparatus.
[0054] As will be apparent to those skilled in the art, various
modifications may be made in the above-described embodiment of the
present invention within the scope of the appended claims.
* * * * *