Fiber Reinforced Sealing Element
TECHNICAL FIELD
[0001] This disclosure relates generally to a sealing element for a rotating control
device (RCD) used in rotary drilling systems, and particularly to a fiber reinforced
sealing element for the RCD.
BACKGROUND
[0002] During drilling, an earth-boring drill bit is typically mounted on the lower
end of a drill string and is rotated to form a wellbore by rotating the drill string. During
this process erratic pressures and uncontrolled flow known as formation "kick" pressure
surges can emanate from a well reservoir, potentially causing a catastrophic blowout.
Because formation kicks are unpredictable and would otherwise result in disaster, flow
control devices known as blowout preventers ("BOPs") are required on most wells drilled
today. BOPs are often installed redundantly in stacks, and are used to seal, control and
monitor oil and gas wells.
[0003] One common type of BOP is an annular blowout preventer. Annular BOPs
are configured to seal the annular space between the drill string and the wellbore annulus.
Annular BOPs are typically generally toroidal in shape and are configured to seal around
a variety of drill string sizes, or alternatively around non-cylindrical objects such as a
polygon-shaped Kelly drive. Drill strings formed of drill pipes connected by largerdiameter
connectors can be threaded through an annular BOP. Annular BOPs are not
designed to be stationary while maintaining a seal around the drill string as it rotates
during drilling because rotating the drill string through an annular BOP would rapidly
wear it out, causing the blowout preventer to be less capable of sealing the well.
[0004] In some drilling operations, a rotating control device (RCD) located on top
of the BOP stack is used in managed pressure and underbalanced drilling to interface
between high and low pressure regions of drilling operations. During this type of drilling
the well bore is held at pressures that are well above atmosphere which creates the
problem of how to get the drill pipe into the well without the loss of well pressure and
fluid. The RCD forms a seal between the well bore and the drill pipe so that the drill
string can move vertically and rotationally without the loss of well pressure.
[0005] The key component in the RCD, which allows for the separation of high
and low pressure regions, is the RCD sealing element. The RCD sealing element is
comprised of a core and an elastomeric body. The core is molded into the upstream end
of the elastomeric body and is used to fasten the element to the RCD. Cores can be made
in many shapes and sizes and fabricated from many materials. For example, an RCD core
can be made from steel and is referred to as a cage. An RCD sealing element may also be
referred to as a stripper rubber.
[0006] A drill string of varying diameter is passed through the center of an RCD
sealing element. RCD sealing elements are currently made so that the inside diameter of
the RCD sealing element is smaller than the smallest outside diameter of any part of the
drill string passed through it. As the various parts of the drill string move longitudinally
through the interior of the stripper rubber a seal is continuously maintained.
[0007] RCD sealing elements seal around rough and irregular surfaces such as
those found on a drill string and are subjected to conditions where strength and resistance
to wear are very important characteristics. However, RCD sealing elements often have a
short life expectancy, especially when they are used in wells that have high well bore
pressures. Loads exerted on the outside of the element body by the high pressure region
of the well cause the element to deform and press against the drill pipe. High frictional
loads result from the pipe being stripped through the element as it is deformed against the
drill pipe. High pressures in the well can accelerate RCD sealing element failure.
Common modes of RCD sealing element failure include side wall blow through, vertical
and horizontal cracking and chunking away of the interior region of the sealing element
body also known as "nibbing".
[0008] Conventional prior art sealing elements in rotating control devices (RCDs)
tend to split or experience chunking when encountering harsh loading conditions due to
poor tear resistance. Further, over time the sealing element may become worn and may
become unable to substantially deform to provide a seal around the drill string.
Consequently, the sealing element must be replaced, which may lead to down time during
drilling operations that can be costly to a drilling operator.
DESCRIPTION OF DRAWINGS
[0009] The details of one or more embodiments of the disclosure are set forth in
the accompanying drawings and the description below.
[00010] FIG. 1 is a cross sectional view of a rotating control device.
[0001 1] FIG. 2 is a cross sectional view of a rotating control device sealing
element in the rotating control device of FIG. 1.
[00012] FIG. 3 is a schematic view of a fiber-reinforced elastomer to be
used in a rotating control device sealing element.
[00013] FIG. 4 is a cross sectional view of a rotating control device sealing
element comprising a fiber-reinforced elastomer.
[00014] FIG. 5 is a cross sectional view of a rotating control device sealing
element comprising fiber-reinforced elastomers of varying fiber concentration.
DETAILED DESCRIPTION
[00015] In the rotating control device (RCD) sealing element of the present
disclosure the body comprises the majority of an RCD device and is the component
responsible for creating a seal between the drill pipe threaded through the RCD and the
interior of the wellbore below the RCD. Materials for making the elastomeric body
include polyurethane, natural rubber, nitrile rubber and butyl rubber. In use, the RCD
sealing element is held inside the RCD and the drill pipe stabs through the RCD sealing
element when it enters the RCD, creating an interfacial seal capable of separating the
high pressure region of the well bore from the atmospheric pressure region of the rig
floor. The interfacial seal is created when the drill pipe enters the RCD sealing element
and deforms the inner diameter of the RCD sealing element to fit over the larger diameter
of the drill pipe. While attached, the drill pipe penetrating the RCD sealing element is
capable of vertical motion as well as rotational motion. The RCD sealing element is also
able to expand to fit over tool joints as new sections of drill pipe are added to the drill
string.
[00016] This disclosure also relates to a method of improving the material
properties of the elastomeric RCD element body by introducing a fibrous reinforcing
material into the elastomer. During the preparation of the elastomer raw material, fibers
can be added so that the performance characteristics of the finished element are altered.
Elements that have been molded with reinforced elastomer can have improved strength,
resistance to tear and abrasion while still exhibiting good elongation.
[00017] The elastomer used to form the RCD sealing element of the present
invention contains polyurethane. Rubber and polyurethane do not have identical material
properties. Natural rubber has excellent elastic memory, that is it will return its original
shape after being compressed or stretched. Polyurethane has a substantially lower
memory than rubber. Compression Set is a measure of memory. In one implementation,
the polyurethane described herein has a compression set of approximately 62% while
rubber compounds can have a compression set of 6% or lower. Polyurethane is affected
by temperature differently than rubber. Polyurethane breaks down in the presence of
water while remaining strong in the presence of oil, rubber is the opposite.
[00018] The molding process is significantly different between rubber and
cast polyurethane; rubber is injected into a mold with high pressure and high temperature
while cast urethane is simply poured into a mold and heated in an oven. Since the
molding process is different the technique for adding reinforcing fibers is also different.
Since, unlike with rubber molding the mold is not filled under high pressure, fibers can
be connected to the inside of the empty mold and oriented horizontally, vertically,
radially or in any combination desired prior to the filling of the mold. Concentration and
placement of the reinforcing fibers in elastomers containing polyurethane can be
carefully controlled, thus allowing regions of the element to be targeted with more
reinforcing material and other regions to be given very little or no reinforcing material.
[00019] A major limitation to the capabilities of prior art RCDs is the
amount of well pressure at which they can they can operate, with the capabilities of
current RCD sealing elements as a major limiting factor. An advantage of the RCD of
this disclosure is providing an RCD sealing element that can operate at higher pressures
than current RCD sealing elements.
[00020] Often RCD sealing element life is short which can result in
frequent element replacement during drilling operations. It is well-known that rig time
can be very expensive, especially when drilling operations are performed in deep water.
Typical deep water daily rig costs can range between $400,000 and $900,000 a day. If an
RCD sealing element can last for drilling a complete borehole section, the approximate
two hours rig time for an element change out equates to a rig downtime saving of
$33,000 to $75,000. Improving element life with an element with improved life and
durability according to this disclosure will reduce costs. This cost saving will be achieved
by fewer elements being required to complete an operation, as well as saving in much
more costly rig down time. Improving element life will also result in a reduction of
nonproductive time for the rig since the rig must be shut down each time an element is
changed out.
[00021] Referring to Figure 1, one implementation of the RCD 100
includes an RCD sealing element 105 (also sometimes referred to in the art as a "stripper
element" or "stripper rubber"). The RCD sealing element 105 acts as a passive seal that
maintains a constant barrier between the atmosphere above and wellbore below. An
interior surface 106 of the RCD sealing element 105 seals against a drill string 110. The
drill string 110 extends from a drilling rig (not shown) through the sealing element 105
and into the wellbore (not shown).
[00022] A drill string typically includes multiple drill pipes connected by
threaded connections located on both ends of the drill pipes. Although the threaded
connections may be flush with outer diameter of the drill pipes, they generally have a
wider outer diameter. For example, as shown in Figure 1, drill string 110 is formed of a
long string of threaded pipes 103 joined together with tool joints 115. The tool joints 115
have an outer diameter 116 that is larger than the outer diameter 111 of the pipes 103. As
the drill string is longitudinally translated through the wellbore and the RCD 100, the
RCD sealing element 105 squeezes against an outer surface of the drill string 110,
thereby sealing the wellbore. In particular, the inner diameter of the RCD sealing element
105 is smaller than the outer diameter of the items passed through (e.g., drill pipes, tool
joints) to ensure sealing.
[00023] A side view of an exemplary RCD sealing element 105 is shown in
Figure 2. The RCD sealing element 105 has a base end 120 and a nose end 130. The base
end 120 is typically attached to a mandrel (not shown) running through the center of the
bearing assembly, however it could also be attached to a stripper housing that does not
include a bearing. The mandrel is attached to the bearing housing via two sets of
bearings. The element is then screwed onto the mandrel or bolted to the mandrel; this
allows the element to rotate with the drill string during drilling operations. For example,
holes 121 are provided for set screws to lock the element to the mandrel once the element
has been threaded onto the mandrel. However there are multiple other techniques used to
mount the RCD sealing element to the RCD. This disclosure shall not be limited to this
style of core but rather encompass all styles of core.
[00024] The nose end 130 has an inner diameter 134 that is smaller than the
inner diameter of the base end 120 to provide a tight seal against the drill string 110. The
outer diameter 122 of the base end 120 may be larger than the outer diameter 132 of the
nose end 130. Similarly the inner diameter 124 of the base end 120 may be larger than the
inner diameter 134 of the nose end 130.
[00025] Prior art RCD sealing elements are often made from of a single
elastic material which is flexible enough to deform to fit around and seal the varying
diameters. Sealing element material may include but not be limited to natural rubber,
nitrile, butyl or polyurethane, for example, and depends on the type of drilling operation.
The RCD sealing element 105 of the present disclosure is made from a polyurethane
based elastomer and is flexible enough to deform to fit around and seal the varying
diameters of drill pipe 110 (e.g., diameters 11land 116 shown in Figure 1).
[00026] To alter the performance characteristics of various RCD sealing
element body materials, the addition of reinforcing fibers of many kinds and sizes may be
used. Fibers may include but are not limited to cotton, polyester, glass fiber and polyvinyl
alcohol (PVA). Fibers may be of varying deniers and lengths and may be combined in
any combination of denier and length. For example, an elastomer may be reinforced with
fibers of uniform length and varying denier or an elastomer may be reinforced with fibers
of varying length and uniform denier. Any combination of length and dernier is
permissible. In one embodiment, fibers may have a length of 1/8" to 5" and a denier of
1200 to 1800.
[00027] As shown in Figure 3, reinforcing fibers 205 can be added to the
elastomer raw material 210 to form a resultant composite material 200. This composite
material 200 can be comprised of both uniformly distributed fibers and non-uniformly
distributed fibers. Fibers 205 can be randomly oriented, or may be non-randomly oriented
(i.e., oriented radially, oriented longitudinally, or oriented at some other angle or
combination of angles).
[00028] The concentration of reinforcement fibers 205 within the elastomer
material 210 can be varied to alter the properties of the composite material 210, allowing
for the customization of element material properties. For example, as shown in Figure 4,
an RCD sealing element 250 may be molded with an elastomer that has a uniform
concentration 255 of fibers throughout. Any fiber concentration is permissible, although
fiber concentration ranging from 1% to 20% is preferred. Element properties that will be
altered by the addition of reinforcing fibers include but are not limited to the following:
tensile strength, elongation, stress-strain modulus, tear strength, compression set and
Taber abrasion.
[00029] Alternatively, an RCD sealing element may be molded with an
elastomer material that has a non-uniform concentration of reinforcing fibers along the
length (i.e., along a longitudinal or axial axis) of the RCD sealing element. For example,
shown in Figure 5, an RCD sealing element 270 has a higher concentration of
reinforcement fibers at its base 320 and a lower concentration of fibers at its nose 330.
Any combination of fiber concentration is permissible. For example, more than two
concentrations (i.e., three different fiber concentrations) are shown in Figure 5 : a region
with high concentrations of fiber reinforcement 272, a region with moderate
concentrations of fiber reinforcement 274 and a region with low concentrations of fiber
reinforcement 276.
[00030] In a varying fiber concentration RCD sealing element 270, each
region of fiber reinforced element material exhibits material properties are different from
the other regions. The particular material properties can be selected to optimize
performance of different regions of the RCD sealing element 270. For example,
resistance to pressure is a critical material property needed at the base end 320.
Additional tensile and compressive strength near is required near the base end 320 for
resisting the tendency of the RCD sealing element 270 to blow out when high pressure
builds on the exterior surface of the RCD sealing element 270. To increase strength, a
high concentration of fibers 272 is used in the base end 320 of the RCD sealing element
270. Resistance to deformation resulting from external pressure is also essential to the
long life of RCD sealing element 270. Since the inner diameter at the base end 320 is
much larger than the ID at the nose end 330 the amount of elongation required at the base
end 320 is much less than the amount of elongation required at the nose end 330. Since
high elongation is not required in the base section 320 a higher concentration of fibers
can be used, for example 20%, thus giving increased strength and wear resistance. In the
middle section 274 moderate elongation is required so a concentration of approximately
5-10% may be used to increase strength and wear resistance while allowing for required
elongation. In the nose section 276 where the greatest elongation is required and wear
resistance is less important a lower concentration of approximately 1-5% can be used.
[00031] The nose end 330 of the RCD sealing element 270 requires greater
flexibility in order for the smaller inner diameter 334 of the nose end 330 (compared to
the wider diameter 324 of the base end 320) to deform around the diameters of the
wellbore components passed through (e.g., drill pipe diameter 111, tool joint diameter
116). Lower concentration fibers 276 enhance wear resistance but still allow deformation
or elongation. Preferably the fibers in the nose area 272 have a concentration 276 ranging
between about 1% to 20%. The result is an the RCD sealing element 270 which has a
higher resistance to pressure as well as longer wear in the area that contacts the wellbore
components.
[00032] In one embodiment, fibers are added to the liquid polyurethane and
the mixture poured into the mold results in a uniform distribution of fibers with random
orientation.
[00033] In another embodiment, the fibers are longitudinally suspended
from the top of the mold so that they hang down throughout the length of the element
running parallel to the central axis of the element. When the mold is filled the
polyurethane will fill in around the suspended fibers and cure with the fibers inside of the
element.
[00034] In a further embodiment the fibers are connected to the mold core
and extended to the mold shell. This would orient the fibers in a radial direction. Again
the mold would be filled and the polyurethane allowed to cure.
[00035] Another embodiment involves filling the mold with the liquid
polyurethane and then inserting the fibers into the liquid with an insertion tool. Since the
polyurethane is a highly viscous fluid when it is poured into the mold, a fiber could be
inserted and once released it would stay in the location it was deposited. Fibers could be
inserted in any orientation and concentration desired.
[00036] To fabricate an RCD sealing element of the present disclosure one
or more raw elastomer materials 210 is prepared. Once prepared, the elastomer is molded
around a core to form a complete RCD sealing element. The element is made from cast
polyurethane which uses a mold with a core. The core is used to form the ID of the
element. The RCD sealing element has a steel cage or core molded into its base. RCD
sealing elements can be molded using a single reinforced elastomer, or using multiple
combinations of elastomers with various levels of reinforcement, or no reinforcement at
all. For example, an element may be molded with a highly reinforced region at its base
which transitions into a region of low reinforcement in its middle which transitions into a
region of no reinforcement at its nose. Likewise, elements may be molded with various
combinations of elastomer with the same amount of reinforcement. For example, an
element may be molded with a region of low durometer elastomer and a region of high
durometer elastomer, both with equal amounts of reinforcement. Any combination of
elastomer and reinforcement is permissible.
[00037] In the implementation of this disclosure, the base material in the
elastomer being used to mold an RCD sealing element is primarily polyurethane.
Polyurethane may be used in any combination with natural rubber, nitrile, or butyl.
Polyurethane is a flexible elastomer that can be stretched over the changing outer
diameter of drill pipe and tool joints. To form an RCD sealing element of the current
disclosure, the polyurethane is cast by pouring polyurethane in a liquid state into a mold.
[00038] To create an RCD sealing element with uniform fiber
reinforcement, reinforcing fibers 205 are mixed into the liquid state polyurethane. The
polyurethane-fiber mixture is poured into the mold. Heat and time are then applied to
allow the material to set by heating in a curing oven. To create an element with targeted
regions of fiber reinforcement multiple batches of liquid polyurethane with different
levels of fiber reinforcement are mixed. When filling the RCD sealing element cast, the
appropriate mixture of polyurethane would be used to fill the portion of the cast that is
being target for a specific level of reinforcement.
[00039] Although embodiments of the present disclosure have been
described as having at least two separate portions, wherein each separate portion has a
different fiber reinforcing concentration, it is also within the scope of the present
disclosure for the at least two elastomer materials to partially mix. Approximately a 0.5"-
1" region of mixing can exist between layers. In some embodiments the region of mixing
can be about 0.25" to about 0.5". Alternatively, the region that experiences mixing could
be increased.
[00040] A number of embodiments of the disclosure have been described.
Nevertheless, it will be understood that various modifications may be made without
departing from the spirit and scope of the disclosure. Accordingly, other embodiments are
within the scope of the following claims.

WHATIS CLAIMED IS:
1. A method for making a sealing element for a rotating control device used in rotary
drilling systems, said sealing element having a bore, a base region, and a nose region, said
method comprising:
providing a mold for the sealing element for the rotating control device;
adding fibers at a first concentration to a first liquid elastomer material containing
polyurethane;
placing the first liquid elastomer material having a first concentration of fibers into the
mold;
adding fibers at a second concentration to a second liquid elastomer material containing
polyurethane;
placing the second liquid elastomer material having a second concentration of fibers into
the mold;
heating the fibers and liquid elastomer in the mold;
forming a sealing element having a bore, a base region with a first concentration of
fibers, and a nose region having a second concentration of fibers.
2. The method of claim 1, further comprising placing an elastomer material having a third
concentration of fibers into the mold.
3. The method of claim 1, further comprising selecting fibers from the group consisting of
polyvinyl alcohol (PVA), glass, cotton, or polyester.
4. The method of any of claims 1 to 3 further comprising selecting fibers of 1/8"- 1/2" in
length and 1200-1800 denier.
5. The method of any of claims 1 to 4 comprising orienting the fibers in a random,
horizontal, vertical or radial orientation, or any combination of these orientations.
6. The method of any of claims 1 to 4 further comprising suspending the fibers
longitudinally from the top of the mold parallel to the central axis of the sealing element and
extending to the bottom of the mold prior to placing the elastomer material in the mold.
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7. The method of any of claims 1 to 4 further comprising suspending the fibers radially
from a central core of the mold to an inner surface of an outer wall of the prior to placing the
elastomer material in the mold.
8. The method of any of claims 1 to 4 further comprising inserting the fibers into the liquid
elastomer with an insertion tool.
9. A sealing element for a rotating control device used in a rotary drilling system,
comprising:
said sealing element molded from a polyurethane base elastomer and fibers mixed into
the polyurethane base elastomer;
said sealing element having an inner surface which forms a bore extending axially
through the sealing element;
a base region;
a nose region opposite from the base region, wherein the nose region has an inner
diameter smaller than the inner diameter of the attachment region;
at least one region comprising a first concentration of fibers; and
at least one region comprising a second concentration of fibers.
10. The element of claim 9, wherein the first concentration is higher than the second
concentration.
11. The element of any of claims 9 or 10, wherein the region comprising the first
concentration of fibers is located near the base region of the sealing element.
12. The element of any of claims 9 to 11, wherein the first concentration of fibers is in the
range of l%-20% measured by weight of the elastomer and fiber composite.
13. The element of any of claims 9 to 12, wherein the fibers are randomly oriented in the
sealing element.
14. The element of any of claims 9 to 12, wherein the fibers are uniformly distributed in the
sealing element.
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15. The element of any of claims 9 to 14 wherein the fibers are l/8"-l/2" in length and 1200-
1800 denier.
16. The element of any of claims 9 to 15 wherein the fibers are formed from one of the
members of the group consisting of polyvinyl alcohol (PVA), glass, cotton, and polyester.
17. A method for making a sealing element for a rotating control device used in rotary
drilling systems, comprising:
providing a mold for the sealing element for the rotating control device;
adding fibers at a first concentration to a first liquid elastomer material containing
polyurethane;
placing the first liquid elastomer material having a first concentration of fibers into the
mold;
adding fibers at a second concentration to a second liquid elastomer material containing
polyurethane;
placing the second liquid elastomer material having a second concentration of fibers into
the mold;
heating the fibers and liquid elastomer in the mold;
forming a sealing element having a bore,
wherein the sealing element can stretch to receive a wellbore component in a longitudinal
insertion through the bore,
wherein the fibers enhance a property of the sealing element for extending the service life
of the sealing element, including at least one of increased resistance to outside pressure,
increased resistance to wear, and increased strength,
wherein the fibers are randomly oriented and uniformly distributed in the sealing
element.
18. The method of claim 17, further comprising selecting the fibers from the group consisting
of polyvinyl alcohol (PVA), glass, cotton, and polyesther.
19. The method of claim 17, further comprising selecting fibers of 1/8"- 1/2" in length and
1200-1800 denier.