Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02708851 2013-10-02
DUAL STRIPPER ASSEMBLY FOR SLICK CABLE
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The invention relates generally to the field of well head equipment used in
oil and gas well
services. More specifically, the present invention relates to an apparatus
that provides a pressure
seal around a slick cable used in oil field operations.
2. Description of the Prior Art:
The use of so called "wireline" conveyance equipment and procedures are well
known in the oil
and gas industry for running a multitude of different types of well tools and
other well
equipment in oil and gas wells while the wells are under pressure. For
example, in well logging
operations, two basic types of wireline conveyance have traditionally been
used, slickline and
twisted or braided cable. The twisted or braided cable typically consists of a
large-diameter
cable that mechanically supports a hanging instrument. A wireline truck on the
surface will
usually be required for support. A data cable of this type supplies power and
provides a
communication connection down the well to the instrument in the well bore.
Slickline, on the
other hand, is typically a smaller diameter line in the form of a solid wire
on the order of 1/8
inch or smaller, e.g., like piano-wire and does not typically provide real
time data at the well
surface.
Slickline logging tools have been developed in recent years to enable data
collection in deep oil
and gas wells. The well casing is completed by setting pipe and grouting it in
place with
cement. The cement seals the annulus between the soil and the outside diameter
of the pipe.
The top of the pipe is threaded and a blow-out preventer is installed. Some
type sealing device
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will typically be provided on the upper end of the upper tubing section which
will permit the
wireline to move into and out of a lubricator while the lubricator is under
pressure form the
well. A closing valve, such as a gate valve, and a second pipe provide a
sealed enclosure above
the well head. The sealed enclosure is long enough to accommodate a logging
tool with a top
sub attached to the slickline cable. The cable exits the lubricator through a
sealing gland that
enables the slick line to enter the sealed enclosure under pressure. When the
gate valve is fully
opened, the logging tool descends into the well casing, while the sealing
device maintains a seal
with the slick line as the hoist lowers the logging tool into the well bore.
Conventional slickline logging tools are designed with internal recording
memory to log data
during descent and ascent in the hole. After returning from the well, recorded
digital data is
read out on the surface and chart recordings are used to display the data for
analysis. Twisted or
braided cable, on the other hand, may provide real time data communication to
the well surface.
The wireline or cable not only serves to support the tools and other equipment
when running
them into and withdrawing them from a well, but may also be used to apply
forces when
manipulating tools and other equipment present in the well.
Depending upon the particular type of equipment present, the sealing device
referred to above
may take the form of a what is referred to as a stripper, stuffing box,
sealing gland, pack-off
heads, etc. In each case, the device performs the safety function of pressure
containment during
wireline operations. For example, wireline (or slick-line) pack off heads (oil
savers) have been
used by the oil field service industry for many years. A pack off head is
designed to make a
pressure seal around a wireline to contain the well pressure during trips in
and out of the well. If
during wireline operations a well kick were experienced, an unsafe condition
would occur if the
well head was not contained but instead left open to atmosphere. A typical
pack off head
includes a hard rubber insert with a passage where the wire line passes
through the annulus. To
seal around the wireline, the hard rubber insert is axially compressed, which
reduces the cross
sectional area of the passage. Reducing the cross sectional area of the
passage causes the inner
radius of the passage to fit snugly around the outer radius of the wire line,
thus preventing fluid
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flow through the passage. The typical prior art pack off head only functioned
to seal around a
static line. This was due at least in part to the fact that the prior art
braided cable would quickly
destroy the seal if it moved though the energized seal element in use.
Traditionally, pack off heads have been manual or hydraulic. A manual style
pack off head is
usually comprised of a threaded cap that compresses the rubber packing element
as the cap is
screwed down onto the head assembly. This operation is typically perfoimed by
hand. The
hydraulic style pack off head has a hydraulic cylinder that is expanded via
hydraulic pressure
provided by a hand pump connected to the head by a hydraulic hose. The pack
off head
hydraulic cylinder moves as pressure is supplied to it, expansion of the pack
off head hydraulic
cylinder in turn compresses the pack off element to provide a seal around the
wireline.
Despite the advances which have been made in the wireline arts, there
continues to exist a need
for improvements in the area of cable conveyance pressure containment devices
of the type
discussed above. For example, while slick line or braided cable have been
widely used in the
past, new types of Aslick cable@ are now beginning to appear on the scene. The
slick cable will
have a smooth outer diameter in the same manner as traditional slick line,
while allowing real
time data communication with the downhole tool in the well bore in the manner
of traditional
braided cable. Preferably, the new slick cable will be capable of dynamic
movement through the
2 0 seal elements, even when the seal elements are energized to contain
well pressure. The outer
diameter of these types of slick cable will be much larger than traditional
slick line, e.g., larger
than 2 inch. New pressure containment devices are needed which have the
ability to accept
these new types of slick cable.
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,
SUMMARY OF THE INVENTION
The present invention provides a solution to certain of the previously
mentioned deficiencies
noted in the prior art in the form of a dual stripper assembly which is used
in conjunction with a
wellhead situated on a hydrocarbon producing well bore, particularly where the
assembly is used
with a slick cable having a smooth or uniform outer diameter. The assembly
allows dynamic
stripping of the slick cable through the assembly while the well head is under
pressure. The
preferred assembly includes a dual isolation end element body having a hollow
interior. An
isolation sub is received within the hollow interior of the end element body,
the isolation sub
having an interior bore which communicates each of oppositely arranged upper
and lower ends
thereof A cylindrically shaped upper hydraulic cylinder body is mounted on the
upper end of
the isolation sub and end cap, the upper hydraulic cylinder body having a
cylindrically shaped
internal piston chamber with a cylindrical upper piston slidably received
therein. The upper
piston also has a cylindrical interior bore. A cylindrical sleeve member is
received within the
cylindrical interior bore of the upper piston.
A resilient wiper element is closely received within the cylindrical interior
bore of the upper
piston, the resilient wiper element having a central bore appropriately sized
to receive and seal
around a slick cable. The upper element has cylindrical sidewalls and a
convex, cone shaped
upper extent.
A spring retainer guard including a retaining flange is attached to the upper
hydraulic piston for
movement upwardly and downwardly with the upper hydraulic piston. A cone
shaped wiper
retainer is received within the cylindrical sleeve member and has a lower
concave extent which
contacts and mates with the convex cone shaped upper extent of the resilient
wiper element.
The upper retainer also has an upper extent which is contained by the spring
retainer guard. An
externally mounted return spring is received about the exterior sidewalls of
the upper hydraulic
piston between the spring retainer guard at an upper extent and an upper
portion of the hydraulic
cylinder at an opposite lower extent.
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An upper hydraulic port is connected to a source of hydraulic fluid for
communicating hydraulic
fluid to an interior region of the upper hydraulic cylinder body for moving
the upper hydraulic
piston in a downward direction relative to the body. This action, in turn,
compresses the return
spring and causes the wiper retainer to compress the resilient wiper element,
whereby the wiper
element seals around a slick cable passing through the central bore thereof.
The preferred assembly also has a second, lower hydraulic cylinder body, lower
hydraulic piston
and associated resilient wiper element similarly arranged in mirror image
fashion on a lower end
of the dual isolation end element body for use as a backup in case of failure
of the upper wiper
element assembly.
In one preferred version of the dual stripper assembly of the invention, the
slick cable has a
uniform outer diameter, the outer diameter ranging from about 1/8 to about
15/32 inches. The
resilient wiper element is made of an elastomer such as rubber and has an
outer diameter which
is greater than about 2 inches. The wiper element has an interior bore which
is sized for the
slick cable it will receive, allowing dynamic movement of the slick cable
through an energized
wiper element. With these dimensions, the assembly of the invention has been
tested to hold
greater than about 8000 psi pressure in the well bore.
In one version of the assembly of the invention, the lower hydraulic cylinder
body houses a
velocity check valve which is actuated in the case of an unexpected event such
as a cable
breaking to isolate well bore pressure. The assembly is also preferably
provided with an isolator
lock retainer having a pair of internal spline elements which can be installed
to lock the dual
isolation end element body and the isolation sub to prevent relative vertical
movement there
between. Removal of the internal spline elements by pulling out a pair of
external ears allows
the isolation sub, wiper retainers and associated wiper elements to be removed
from the
assembly for maintenance. Removal of the isolation sub, wiper retainers and
associated wiper
elements from the dual isolation end element body allows a slick cable with an
associated cable
head to be pulled freely through the body of the assembly.
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Additional objects, features and advantages will be apparent in the written
description which
follows.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a simplified, perspective view of the dual stripper assembly of
the invention
in place on a well head.
Figure 2 is an exploded view of the dual stripper of Figure 1 showing the
internal
components thereof
Figure 3 is a cross sectional view of the assembled dual stripper of the
invention
showing the operative components thereof
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DETAILED DESCRIPTION OF THE INVENTION
The embodiments herein and the various features and advantageous details
thereof are explained
more fully with reference to the non-limiting embodiments that are illustrated
in the
accompanying drawings and detailed in the following description. Descriptions
of well-known
components and processes and manufacturing techniques are omitted so as to not
unnecessarily
obscure the embodiments herein. The examples used herein are intended merely
to facilitate an
understanding of ways in which the invention herein may be practiced and to
further enable
those of skill in the art to practice the embodiments herein. Accordingly, the
examples should
not be construed as limiting the scope of the claimed invention.
Figure 1 is a simplified representation of the general environment of the dual
stripper assembly
of the invention when in use on a well head. A blowout preventer 11 rests atop
a wellhead 13.
Usually at least two lubricator risers 15, 17 sit atop the blowout preventer
11. The dual stripper
assembly 19 of the invention sets atop the lubricator riser 17 and is
threadedly connected
thereto.
Figure 3 is a cross-sectional view of a preferred version of the dual stripper
assembly 19 of the
invention. The dual stripper assembly 19 includes a dual isolation end element
body 21 having
a hollow interior 23. The dual isolation end element body 21 has a port 87
which is used to
charge an internal reservoir 88 with lubricating grease. An isolation sub 25
is received within
the hollow interior 23 of the dual isolation end element 21. The isolation sub
25 has a stepped
interior bore 27 which communicates with each of the oppositely arranged upper
and lower ends
29, 31 thereof. The exterior of the isolation sub 25 is also stepped and
decreases in external
diameter between upper and lower generally cylindrical regions thereof.
As perhaps best seen in Figures 2 and 3, an isolator lock retainer, designated
generally as 36 in
Figure 2 comprising a pair of internal spline elements 33, 35 can be installed
to lock the dual
isolation end element body 21 and the isolation sub 25 to prevent relative
vertical movement
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there between. The spline elements 33, 35 are received in machined recesses
provided between
the element body 21 and sub 25 and are inserted and removed by means of
external ears (32, 24
in Figure 2).
As best seen in Figure 3, a cylindrically shaped upper hydraulic cylinder body
37 is mounted on
the upper end of the isolation sub 25 and end element body 21. The upper
hydraulic cylinder
body has a cylindrically shaped internal piston chamber 39 with a cylindrical
upper piston 41
slidably received therein. The upper piston 41 also has a cylindrical interior
bore 43 and an
interior threaded upper extent 44. A cylindrical sleeve member 45 is received
within the
cylindrical interior bore 43 of the upper piston 41.
A resilient wiper element 47 is closely received within the cylindrical
interior bore 43 of the
upper piston 41. The resilient wiper element 47 has cylindrical exterior
sidewalls and a convex,
cone shaped upper extent. The wiper element also has a central bore 49 which
is appropriately
sized to receive and seal around a slick cable. The upper element 47 will
typically be formed of
a suitable elastomeric material, such as a suitable rubber. To insure that the
wiper element 47
will seal around the slick cable, it is important that the elastomeric
material be sufficiently
pliable to perform under extreme cold or hot conditions for which it will be
used, and yet be of
adequate resiliency to sustain the pressure applied to it to preclude leakage
between the wiper
element 47 and the slick cable.
A spring retainer guard including a retaining flange 51 has an exterior
threaded surface 52 which
engages the threaded surface 44 of the upper hydraulic piston 41 for movement
upwardly and
downwardly with the upper hydraulic piston. A wiper retainer 53 is received
within the
cylindrical sleeve member 45 and has a lower concave extent 55 which contacts
an upper mating
surface of the resilient wiper element 47. The retainer 53 also has an upper
extent 57 which is
received within an interior region of the spring retainer guard 50. The
retainer 53 has an internal
bore 54 which communicates with the central bore 49 of the wiper element 47.
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A top guide sub 59 having a central bore 60 is threadedly connected to a top
region of the
spring retainer 50 and has an interior recess or bore which retains a series
of packing materials
61 in the form of disk shaped elements which form a lubrication seal at the
upper end of the
assembly. The packing elements 61 have central bores which communicate with
the bore 49 of
the wiper element so that they can receive the slick cable as it passes
through the assembly to
keep the cable clean as it leaves the assembly.
An externally mounted return spring 63 is mounted about the exterior sidewalls
of the upper
hydraulic piston 41 between the flange 51 of the spring retainer guard 50 at
an upper extent
thereof and an upper portion of the hydraulic cylinder 37 at an opposite lower
extent. An upper
hydraulic port 67 is connected to a source of hydraulic fluid through a
conventional fitting 68.
The source of hydraulic fluid will typically be a hydraulic hand pump (not
shown) present on the
rig floor. The port 67 communicates hydraulic fluid from the pressurized
source to the upper
hydraulic cylinder body 37 for moving the upper hydraulic piston 41 in a
downward direction
relative to the body, as viewed in Figure 3. This action serves to compress
the return spring 63
and causes the wiper retainer element 53 to compress the resilient wiper
element 47 radially
inward, whereby the wiper element seals around a slick cable passing through
the central bore
49 thereof.
The slick cable (89 in Figure 2) will generally have a uniform outer diameter
which is about 1/8
inch or greater in diameter. Preferably, the slick cable 89 will have a
uniform outer diameter
which is in the range from about 1/8 to about 15/32 inches, unlike the prior
art Apiano wire@
slick wirelines used in the past. The resilient wiper element 47 will have an
outer diameter
which is greater than about 2 inches. The wiper element 47 is designed to hold
at last about
8000 psi pressure in the wellbore and has been tested to 10,000 psi. The slick
cable which is
capable of being dynamically run through the device will typically have
internal communication
lines for transmitting data from a tool at a subterranean location in the
wellbore in the surface in
real time, unlike traditional slick line used in the prior art.
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As shown in Figure 3, the preferred device of the invention will also have a
second, lower
hydraulic cylinder body, lower hydraulic piston and associated resilient wiper
element similarly
arranged on a lower end of the dual isolation end cap for use as a backup in
case of failure of the
upper wiper element assembly. For example, with reference to Figure 3, the
lower hydraulic
cylinder body 69 contains a lower hydraulic part 76 and has an internally
threaded surface 71
which matingly engages the externally threaded surface of a lower end cap 73.
A lower
hydraulic piston 75 has a ring-shaped piston portion 77 having a sealing ring
area 78 which is
received within the lower hydraulic chamber 69. A lower resilient wiper
element 79 is received
within the bore of a sleeve member 81, as in the case of the upper wiper
element. A wiper
retainer 83 rests atop the resilient wiper element 79 and contacts the lower
end 31 of the
isolation sub 25.
The further details and construction of the lower wiper assembly are generally
a mirror image of
the upper assembly previously described. However, as shown in Figure 3, a
velocity check
valve 85 is located within an internal region of the end cap 73 below the
resilient wiper element
79. The velocity check valve 85 has internal passages and a floating check
ball which would be
actuated in the case of a cable breaking to seal off the relevant internal
passages and isolate the
wellbore pressure.
With reference now to Figure 2, the internal components of the device are
shown in exploded
fashion. It will be appreciated that removal of the internal spline elements
33, 35 allows the
isolation sub 25, wiper retainers 53, 83 and associated wiper elements 47, 79
to be removed
from the assembly for maintenance. Removal of the isolation sub, wiper
retainers and
associated wiper elements also allows a slick cable (89 in Figure 2) within an
associated cable
head 91 to be pulled freely through the body of the assembly.
With reference again to Figure 3, the operation of the device will be briefly
explained with
respect to the upper wiper assembly. In operation, pressure at port 67 forces
piston 41
downwardly thereby compressing the wiper retainer and spring retainer to
compress the spring
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63. The cone shaped wiper retainer 53 presses down on the wiper element 47
causing it to
expand radially inwardly toward the slick cable which may be either static or
moving
dynamically through the wiper element central bore 49. During wireline
operations the wiper
inner passage (bore 49) will experience some wear due to the dynamic movement
of the slick
cable 89 through the energized seal (wiper element 47). Although the wear will
gradually result
in material loss of the inner annulus of the wiper element 47, wiper element
will continue to seal
against the slick cable because of the constant compressive force applied to
it by the wiper
retainer 53. When the upper region of the piston 41 is no longer exposed to
the hydraulic
pressure through the port 67, the spring 63 will return the piston 41 and
spring retainer guard 50
to their original positions. The dimensions and characteristics of the spring
63 are determined
based on the well parameters. When the spring 63 moves the piston 41 to its
original position,
the wiper retainer 53 will cease to apply force to the wiper element 47, and
therefore no longer
compress it.
An invention has been provided with several advantages. The dual stripper of
the invention can
accommodate slick cable of a larger diameter than the slick wireline used in
the past. Unlike the
pack off designs of the prior art which only sealed around a static wireline,
the dual stripper
design of the invention will seal around a dynamically moving slick cable. The
slick cable
causes less wear and tear on the internal wiper elements and yet allows
communication with the
downhole tool in real time, if desired. Because the assembly basically
features a mirror image
of the pack off construction, failure of the upper wiper element can be
compensated by actuation
of the lower wiper element as a backup measure. The externally mounted return
spring and
particular sizing of the wiper element and associated components of the
assembly make it
particularly suited for use with slick cable.
While the invention has been shown in only one of its foi ____________________
His, it is not thus limited but is
susceptible to various changes and modifications.
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