Note: Descriptions are shown in the official language in which they were submitted.
CA 02871085 2014-10-21
WO 2013/159203
PCT/CA2013/000411
Slip Assembly
Field of the Invention
The present invention relates to a slip assemblies and methods for gripping
casing joints and casing strings.
Background
Slip assemblies are well known in the down-hole drilling and oil and gas
industry.
Slip assemblies are used to grip casing sections or strings, also called
tubulars or piping,
for a number of purposes including drilling, making up or breaking out casing
strings and
performing operations to produce oil from the well. Casing strings are made up
by
connecting multiple threaded casing sections together and feeding them into
the
wellbore. Rotation of a first casing into a second casing is conducted until
the thread
male and female ends engage one another.
The gripping mechanism of the slip assembly must be able to carry large loads
and
in certain operations including make up or break out operations do so while
rotationally
gripping the casing section or casing string. The components of the slip
assembly must
also cooperate to set and unset with ease and to maintain a fully set position
on the
casing section or casing string during torqueing and rotation.
While a number of prior art patents including US 6,631,792, US 7,891,469 and
US
7,775,270 teach slip assemblies with means of guiding a slip into engagement
with a
casing section. However these patents do not address means of maintaining
gripping of
the casing during rotation and torqueing of the slip assembly for any number
of
operations including casing make up and break out or any operation involving
rotation
and torqueing where axial loads may exist.
A need and interest therefore exists in the art to develop improved slip
assemblies and gripping systems and methods for making up casing strings.
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Summary
A gripping system is taught for gripping oil well casing, casing string or
other
string comprising one or more slips cammed against one or more inclined
recesses when
the gripping system is rotated to enhance gripping engagement of the casing.
A further gripping system is taught for gripping oil well casing, casing
string or
other string comprising one or more slips received into one or more inclined
recesses.
A method is taught for gripping casing sections or casing strings. The method
comprises the steps of receiving a slip into each of one or more inclined
recesses of a
gripping system, setting said one or more slips on the casing section and
rotating the
gripping system to cam said one or more slips against said one or more
inclined
recesses, wherein cannming said one or more slips against said one or more
inclined
recesses serves to enhance gripping engagement on the casing.
A further method is taught for gripping casing sections or casing strings. The
method comprises the steps of receiving a slip into each of one or more
inclined
recesses of a gripping system, setting said one or more slips on the casing
section and
rotating the gripping system.
Brief Description of the Drawings
The present invention will now be described in greater detail, with reference
to the
following drawings, in which:
Figure 1 is an isometric view of a part of the slip assembly of the present
invention;
Figure 2 is an isometric view of further parts of the slip assembly of the
present
invention;
Figure 3 is an isometric view of yet further parts of the slip assembly of the
present
invention;
Figure 4 is an isometric view of yet further parts of the slip assembly of the
present
invention; and
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Figure 5 is a top plan view of one embodiment of the present slip assembly.
Description of the Invention
The slip assembly of the present invention, also called a gripping system can
be
used in conjunction with a number of tools known in the field of oil well
completion and
production. These tools include but are not limited to elevators, spiders,
flush mount
spiders, snubbing tools, bucking units and back up tongs. The present slip
assemblies
can be used in relation to any operations involving hoisting and rotation of a
casing
string or casing section or in any operation in which a casing string, casing
section or
tubular of any kind is torqued or rotated while under axial loading forces.
These
operations include but are not limited to casing make up or break out
"drilling with
casing", snubbing operations and horizontal wellbore operations.
The slip assemblies of the present invention are preferably actuated by one or
more cylinders (not shown) that extend to set one or more gripping members of
the slip
assembly and retract to release said gripping members. Other means of
actuation are
also possible and would be understood by a person of skill in the art to be
encompassed
by the scope of the present invention
The present slip assembly or gripping system 14 is now described with
references to Figures 1 to 5.
The seat 16 of the gripping system 14 preferably comprises an array of one or
more separate inclined elements 30 for receiving slips 18.
In a further preferred embodiment, the inclined elements 30 comprise one or
more integral or non-integral means of laterally retaining the slips 18 in the
inclined
elements 30, in such a way that the slips 18 are prevented from falling or
tipping
towards a central bore of the casing gripping system 14. Examples of non-
integral
retaining means include but are not limited to strips, plates, clips, cages,
bars, tabs and
rings that can be removably attached to at least a portion of the slip 18 and
at least a
portion of the seat 16 to laterally retain the slip 18 to the inclined element
30. Integral
retaining means can include but are not limited to mating profiles on at least
a portion
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of the slip 18 and on at least a portion of the inclined elements 30 that
connect to hold
the slip 18 to the inclined element 30; such mating profiles can include
shiplap profiles,
tongue-and-groove profiles, dovetail profiles or other profiles well known in
the art.
As seen in Figures 1 and 2, the inclined elements 30 can more preferably be in
the form of an array of one or more inclined recesses 90 that correspond to a
rear face
32 of the slips 18, thereby generating radially inward movement of the slips
18 to grip
the casing joint 10 as the slips 18 are disposed longitudinally within
inclined recesses 90,
without the need for separate tracks, cam followers, springs or other means.
Preferably, the inclined recesses 90 have a cylindrical geometry and part-
circular
cross section to match a cylindrical geometry and part circular cross section
of the slips
18. It is also possible for the inclined recesses 90 and slips 18 to have
cross sections that
are partial rectangles, partial squares, partial ovals, partial rhomboids and
partial
triangles or other cross-sectional geometries.
In a preferred embodiment, the inclined recesses 90 can comprise an integral
retaining means along at least a portion of the axial length of the inclined
recess 90. In
one example, at least a portion of longitudinal edges 92 of the inclined
recesses 90
comprise an integral throat, tab or strip that act to restrict the size of the
mouth 94 of
the inclined recess 90, to thereby capture slips 18 and laterally retain slips
18 from
falling or tipping into the central bore of the seat 16.
In a further preferred embodiment, the inclined recesses 90 are machined to a
cross sectional geometry that restricts the mouth 94 of the inclined recesses
90 to be
smaller than the widest cross section of the slip 18. In this embodiment the
recesses 90
function to partially circumferentially capture the slips 18. To effect this
embodiment,
at least a portion of the axial length of the inclined recesses 90 is machined
such that
the desired cross sectional geometry converges to restrict mouth 94. In the
preferred
case of a partial circle cross-section, at least a portion of the axial length
of the inclined
recess 90 is formed as more than half of a circle, otherwise put, more than a
semi-circle,
to provide a restriction to mouth 94 such that the slip 18 cannot fall into
the central
bore of the seat 16.
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In a preferred embodiment of the present invention, the slips 18 and the
recesses 90 interact in such a way as to enhance gripping forces on the casing
section 10
during rotation. In a preferred embodiment, the slips 18 are caused to cam or
wedge
into the recesses 90 to thereby maintain a firm penetration of the dies 20 in
the slips 18
and a firm grip of the outer surface of the casing section 10 by the dies 20
during casing
make up or break out operations.
Most preferably slips 18 are nominally smaller in cross section than inclined
recesses 90. When the slips 18 and dies 20 of the present gripping system 14
are set on
the casing section 10 to be made up, the top drive is rotated to rotate
gripping system
14. During rotation, gripping torque causes the slightly smaller slip 18 to
advantageously rotate slightly. This results in a line of force in which the
dies 20 are
forced into a front face 36 of the slips 18, in turn forcing a rear face 32 of
the slip to cam
into and against the inclined recesses 90. This serves to further frictionally
arrest the
dies 20 into the slips 18, and the slips 18 into the inclined recesses 90, and
thereby
enhances frictional engagement of the dies to the casing section 10 during
make up and
break out operations.
Although present seat 16 is preferably shown as having a conical form, it
would
be well understood by a person of skill in the art that numerous alternative
forms of
seats 16 are possible that would cause the slips 18 to bias radially inwardly
as they move
axially down the seat 16. For example, the seat 16 may alternatively have a
cylindrical
form comprised of one or more inclined elements 30.
Preferably, the inclined recesses 90 are uniformly spaced around the seat 16.
Most preferably, the inclined recesses 90 are arranged in diametrically
opposing pairs.
The dies 20 of the present invention are illustrated in a preferred embodiment
in
Figures 2 and 3. Most preferably each slip 18 comprises three dies 20 arranged
axially
along the slip 18. Support means are provided to support the dies 20 on the
slips 18. A
most preferred embodiment of dies 20 and slips 18 is depicted in Figures 3 and
4, in
which independent axial load transfer keys or tongues 34 are formed on a front
face 36
of the slip 18 that are received in corresponding load transfer grooves 38
formed on a
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rear face 40 of the dies 20. A front face 42 of the dies 20 can have any
number of
profiles and gripping surfaces well known in the art to engage and grip a
range of casing
joint diameters. The profile may be concave or may be any suitable profile to
capture a
tubular member when the die 20 comes in contact with such member. Examples of
such
profiles are well known in the art and would be understood by a skilled
practitioner to
be included in the scope of the present invention. If concave, the profile of
the front
face 42 of the dies 20 may preferably have a singular radius of curvature, or
a
compound radial profile comprising one or more profile sections each having
the same
or different radii of curvature with either the same or different centers. The
surface of
the front face 42 of the die 20 may be smooth or may be textured, scored,
etched or
ridged to provide further gripping of the casing joint 10.
In the foregoing specification, the invention has been described with a
specific
embodiment thereof; however, it will be evident that various modifications and
changes
may be made thereto without departing from the scope of the invention.
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