Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR SEALING AND VENTING PRESSURIZED
CASINGS OF GAS WELLS
BACKGROUND
Technical Field
The present disclosure relates generally to oil and gas wells, and
more particularly to controlling gas leaking from an annular gap between
surface
and production casings thereof.
Description of the Related Art
Historically, hydrocarbon wells for producing natural gas have been
drilled using a larger diameter surface casing inside which is inserted a
relatively
smaller production casing that extends down into the production zone where the
production casing is perforated to permit the production tubing to be fluidly
coupled
to the hydrocarbon source and control flow to the surface. According to Oil
Country Tubular Goods "OCTG" standards, the surface casing typically has a
diameter of 177.8 mm or 7 inches, while the production casing typically has a
diameter of 114.3 mm or 4.5 inches. Once both casings are in place, the
installer
"cements" the annulus that exists between an interior of the surface casing
and an
exterior of the production casing, so as to prevent pressurization of the
casings
from the escape of gas up the annulus.
The importance of the problems associated with uncontrolled gas
leaks is well documented. Uncontrolled gas leaks can also result from tubing
and
casing leaks, poor drilling practices, improper cement selection, inadequate
zonal
isolation and production cycling. Modern regulation of the oil and gas
industry has
resulted in the need to install surface casing vents, including retroactively
installing
surface casing vents on older wells. Many wells experience sustained casing
pressure due to from the uncontrolled migration of gas to the surface,
associated
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with annular flow which results from a number of causes, including inadequate
cementation. With the increase in the importance, and hence value, of natural
gas, gas leaks have become a very significant issue. For environmental and
other
reasons it is therefore desirable to find an affordable and safe way to
control the
migration of gas to the surface even in wells that are no longer producing on
a
commercial scale.
Previous attempts by the gas production industry to address the
problem have concentrated on variations of a one-piece solution to sealing the
annular gap. In one example, well owners attempted to weld steel plates onto
the surface casing stub to seal the gap to the production casing.
Disadvantageously, not all of the production casings were centered in the
surface
casing, so the solution would not work on all wells. Such an approach also
presented significant safety issues. For instance, if a welder accidentally
burned a
hole in the production casing, then there could be an uncontrolled escape of
gas
leading to injuries and/or death. Further, since some of these wells are
already
venting natural gas up the annulus between the casings - welding is not an
option
at all.
Another example was to suspend production at the well, pull the
production tubing, set a bridge plug, remove the production tubing spool,
install a
surface casing spool with a vent, then reinstall everything else. The cost of
this
was typically $25,000 to $35,000 per well. Such is a prohibitively costly
approach,
particularly for wells that are no longer producing on a commercial scale.
Accordingly it is desirable to identify a way to seal and vent well-heads,
which is
both safe and cost-effective.
Devices sometimes known as "mud cans" were used while pulling
tubing or drill pipes still filled with fluid. The mud can would be wrapped
around
the joint between 2 lengths of production tubing or drill pipe and then quick-
latched
to hold the device in place while breaking the joint to disconnect the pipes
so that
the fluid could drain through a port and out to a vacuum truck. Mud cans were
not
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built to hold pressure, they were more like a funnel for redirecting drilling
fluid while
disassembling a drill string. The mud cans had the same size opening at each
end
and were always open to the vacuum truck, but the mud cans still leaked fluid
around the edges. While mud cans appear similar in structure to some
embodiments of the structures disclosed in the detailed description herein,
the
similarities are superficial and mud cans must not be confused with such
structures. Mud cans are for use in a very different application and have very
different operational specifications. Basically, the so-called mud can is for
a
temporary, non-sealing application and is small in volume and light-gauge in
construction ¨ such that it is completely unsuitable for the current
application.
BRIEF SUMMARY
An apparatus to prevent uncontrolled escape of annular gas from
well-heads may be summarized as including an elongate pressure vessel
consisting of at least two mating shell portions, configured to be assembled
around
an upper-most point of intersection between a surface casing and a production
casing installed at a well-head, the production casing positioned
concentrically
within the surface casing, to thereby form an annulus between the surface and
the
production casings, each of the shell portions respectively having a lower end
and
an upper end, each of the upper and the lower ends having a cover portion to
enclose a cavity when the shell portions are matingly coupled to one another,
each
of the cover portions proximate the upper end of each shell portion having a
respective portion of an upper opening that when the shell portions are
assembled
is sized to closely be received around the production casing, and each of the
cover
portions proximate the lower end of each shell portion having a respective
portion
of a lower opening that when the shell portions are assembled is sized to
closely
be received around the surface casing; a respective mating flange around a
mating
perimeter of each the shell portions to provide a surface to releaseably
fasten the
shell portions to one another to assemble the pressure vessel; a number of
mating
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flange seals coupled to the mating flanges; a number of opening seals coupled
to
a perimeter of each of the first and the second openings; and a number of
fasteners to selectively couple the flange on each shell portion to one
another so
as to sealingly assemble the elongate pressure vessel around the point of
intersection with the cavity in fluid communication with the annulus.
The apparatus may further include a vent outlet through either mating
shell portions; and a venting fluidly coupled to the cavity, and operable to
control
escape of accumulated annular gas from the pressure vessel. The pressure
vessel may be a cylindrical tank when assembled. There may be more than two
mating shell portions. One of the mating flanges may have a groove and the
other
one of the mating flanges may have a ridge sized to be sealingly received in
the
groove. The mating flange seal may include at least one of a PTFE joint-
sealant
tape. The number of fasteners may include a number of bolts and nuts.
The apparatus may further include an upper opening flange portion
welded about a respective portion of the upper opening of each of the shell
portions; and a lower opening flange portion welded about a respective portion
of
the lower opening of each of the shell portions. The respective shell portions
may
each include an upper opening flange portion and a lower opening flange
portion
which are unitary single piece constructions of the shell portions positioned
about a
respective portion of the upper and the lower openings of each of the shell
portions.
A method of preventing the uncontrolled escape of annular gas from
a well-head, the well-head having an annulus at the upper-most point of
intersection between a surface casing and a production casing positioned
concentrically within the surface casing thereby forming the annulus between
the
surface and production casings may be summarized as including installing at
least
a first seal around an exterior of the production casing above the point of
intersection; installing at least a second seal around an exterior of the
surface
casing below the point of intersection; assembling a pressure vessel around
the
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point of intersection, the pressure vessel forming an enclosed sealed cavity
between the first seal around the exterior of the production casing and the
second
seal around the exterior of the surface casing; and allowing annular gas to
collect
inside the sealed cavity.
The method may further include controllably venting the collected
annular gas from the pressure vessel; and measuring a flow of the annular gas
vented so as to eliminate sustained casing pressure from the well-head.
An apparatus to prevent uncontrolled escape of annular gas from
well-heads may be summarized as including an elongate pressure vessel
consisting of at least two mating shell portions, configured to be assembled
around
an upper-most point of intersection between a surface casing and a production
casing installed at a well-head, the production casing positioned
concentrically
within the surface casing, to form an annulus between the surface and the
production casings, each of the shell portions respectively having a lower end
and
an upper end, each of the lower and the upper ends respectively having a cover
portion to enclose a cavity when the shell portions are matingly coupled to
one
another; a mating flange around a mating perimeter of each the shell portions
to
allow fastening of the shell portions to one another to assemble the pressure
vessel at the well-site; a TEADIT 24B PTFE joint-sealant tape positioned
between
opposing ones of the mating flanges when the shell portions are assembled to
one
another; a production casing receiving flange through each cover portion at
the
upper end of each shell portion, the production casing receiving flange having
an
inner radius of about 2.25 inches (114.3/2 mm), for assembly around a
production
casing installed at the well-head; a surface casing receiving flange through
each
cover portion at the lower end of each shell portion, the surface casing
receiving
flange having an inner radius of 3.5 inches (177.8/2 mm) , for assembly around
a
surface casing installed at the well-head; a number of pieces of TEADIT 24B
PTFE
joint-sealant tape positionable between the production and the surface casing
receiving flanges and the production and surface casings, respectively; and a
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number of fasteners to selectively fasten the mating flanges on each shell
portion
to adjacent ones of the shell portions to sealingly assemble the elongate
pressure
vessel around the point of intersection such that the cavity is in fluid
communication with the annulus.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
In the drawings, identical reference numbers identify similar elements
or acts. The sizes and relative positions of elements in the drawings are not
necessarily drawn to scale. For example, the shapes of various elements and
angles are not drawn to scale, and some of these elements are arbitrarily
enlarged
and positioned to improve drawing legibility. Further, the particular shapes
of the
elements as drawn, are not intended to convey any information regarding the
actual shape of the particular elements, and have been solely selected for
ease of
recognition in the drawings.
Figure 1 is a top, front, right side isometric view of a well-casing
annular gas pressure seal and venting apparatus, according to one illustrated
embodiment.
Figure 2 is a front elevational view the well-casing annular gas
pressure seal and venting apparatus of Figure 1.
Figure 3 is a partial cross-sectional view of the well-casing annular
gas pressure seal and venting apparatus of Figure 2, taken along a section
line 3-3
in Figure 2.
Figure 4 is top plan view of the well-casing annular gas pressure seal
and venting apparatus of Figure 1.
Figure 5 is an isometric view of an well-casing annular gas pressure
seal and venting apparatus installed at a well-site, according to one
illustrated
embodiment.
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DETAILED DESCRIPTION
In the following description, certain specific details are set forth in
order to provide a thorough understanding of various disclosed embodiments.
However, one skilled in the relevant art will recognize that embodiments may
be
practiced without one or more of these specific details, or with other
methods,
components, materials, etc. In other instances, well-known structures
associated
with well-sites have not been shown or described in detail to avoid
unnecessarily
obscuring descriptions of the embodiments.
Unless the context requires otherwise, throughout the specification
and claims which follow, the word "comprise" and variations thereof, such as,
"comprises" and "comprising" are to be construed in an open, inclusive sense,
that
is as "including, but not limited to."
Reference throughout this specification to "one embodiment" or "an
embodiment" means that a particular feature, structure or characteristic
described
in connection with the embodiment is included in at least one embodiment.
Thus,
the appearances of the phrases "in one embodiment" or "in an embodiment" in
various places throughout this specification are not necessarily all referring
to the
same embodiment. Further more, the particular features, structures, or
characteristics may be combined in any suitable manner in one or more
embodiments.
As used in this specification and the appended claims, the singular
forms "a," "an," and "the" include plural referents unless the content clearly
dictates
otherwise. It should also be noted that the term "or" is generally employed in
its
sense including "and/or" unless the content clearly dictates otherwise.
The headings and Abstract of the Disclosure provided herein are for
convenience only and do not interpret the scope or meaning of the embodiments.
Figure 1 shows a well-casing annular gas pressure seal and venting
apparatus denoted generally as 100, according to one illustrated embodiment.
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The well-casing annular gas pressure seal and venting apparatus
includes a number of mating shell portions, for example mating half-shells 110
and
111 that are securely fastenable to one another by any suitable fasteners. As
shown, first half-shell 110 is coupled (typically welded) to mating flange 140
having
a series of holes 146 (not shown) through which bolts 145 may be inserted to
mate
mating flange 140 to mating flange 141 of second half-shell 111. It is
contemplated
that other forms of fastener, such as rivets or suitable clamps and/or hinges
may
be used in place of the illustrated bolts. Each half-shell also has two
opening
flanges, (e.g., semi-circular flanges), one on each end of the half-shell 110,
111,
projecting through top and bottom end cover portions (e.g., half-covers) 120,
122
respectively, of half-shell 110 and top and bottom end cover portions (e.g.,
half-
covers 121, 123) (Figure 3) respectively, of half-shell 111.
A corresponding pair of opening or semi-circular flanges 130, 131
with an associated seal 134, and pair of opening or semi-circular flanges 132,
133
with an associated seal 135 (Figure 3), are constructed to sealingly engage
well-
casings (see Figure 5) of different sizes. The pair of opening or semi-
circular
flanges 130, 131 are each sized to closely accommodate OCTG standard
production casing when the semi-circular flanges 130, 131 are mated together.
Thus the flanges 130,131 may be denominated as production casing receiving
flanges. The pair of opening or semi-circular flanges 132, 133 are sized to
closely
accommodate OCTG standard surface casing when the semi-circular flanges 132,
133 are mated together. Thus, the flanges 132, 133 may be denominated as
surface casing receiving flanges.
When semi-circular flanges 130 and 131 are mated to one another,
they form a toroid that seals the upper end of apparatus 100 tightly around
the
production casing so as to prevent annular gas from escaping apparatus 100
except through vent outlet 160. At a lower end of apparatus 100, semi-circular
flanges 132 and 133 mate to form a toroid that seals the bottom of apparatus
100
tightly around a surface casing to prevent annular gas escape. Half-shells 110
and
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111 are illustrated in a cylindrical profile, but it is understood that
apparatus 100
will function substantially the same using other profiles such as rectangular,
hexagonal, or elliptical.
Figure 2 shows a half-shell assembly 200.
The half-shell assembly 200 is comprised of half-shell 110 physically
coupled to flange 140, end half-covers 120, 122, and semi-circular flanges
130,
132, which are all visible together in Figure 2 along with half-cavity 201,
from which
gas may be vented via vent outlet 160. The face 142 of the flange 140 may have
any suitable number of holes 146 through which to apply mechanical fasteners
to
fasten half-shell 110 to half-shell 111. The half-cavity 201 surrounds the
point of
intersection of the casings when installed. According to an alternate
embodiment
of apparatus 100, half-shells 110, 111 may be constructed with end half-covers
120, 122, 121, 123, respectively, sufficiently thick to act as flanges.
Openings
may be machined in the end half-covers 120, 122, having the same inner
diameter
as semi-circular flanges 130 and 132 respectively. Openings may be machined in
the end half-covers 121, 123 having the same inner diameter as semi-circular
flanges 132, 133. The end half-covers may integrally form the flanges as an
integral one piece construction, requiring no welding or other coupling acts.
Such
may eliminate the need to install any semi-circular flanges into the four end
half-
covers 120, 121, 122, 123 of apparatus 100.
To enhance the sealing effect of flanges 140, 141, as well as the
toroids formed by the pairs of the semi-circular flange pairs 130, 131 and
132, 133,
seals 155, 134 and 135, respectively, may comprise any suitable material such
as
a gasket compound capable of conforming to complex or rough or pitted surfaces
typically encountered on weather aged tubular elements at well-sites.
According to
one embodiment, seal 155 is a joint sealant such as that manufactured by W.L.
Gore & Associates, Inc. Another suitable sealing product, manufactured by
TALuft, is sold as TEADIT 24B, which is a PTFE joint-sealant tape capable of
withstanding relatively high pressures (4200 kPa or 600 PSI) SCP without
failure.
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Whether in the form of a tape, a gel compound, a pre-shaped sheet gasket, a
form-in-place gasket, or any similar treatment or combination of the
foregoing, the
seal 155 applies to face 142 of planar flange 140 so as to prevent pressurized
gas
escape between flanges 140 and 141. Similarly, seals 134 and 135 prevent
pressurized gas escape between a production casing and pair of semi-circular
end
flanges 130, 131, and, a surface casing and pair of semi-circular end flanges
132,
133, respectively.
Flange 140 as illustrated is shown with face 142 having a simple
planar design to which any suitable seal 155 may be applied to prevent annular
gas leakage from shells 110, 111 to whatever pressure level the local
authorities
specify. However, it is contemplated that flange 140 may be manufactured with
interlocking elements such that there is a groove (not shown) on one half-
shell and
a corresponding ridge (not shown) on the other half-shell. Such may
accommodate very high pressure applications. Such may be implemented with
narrower flanges.
Figure 3 shows the apparatus 100 in a partially cut-away side view.
In particular, a planar butt joint 305 between semi-circular flanges
130, 131 is visible, as well as a butt joint 306 between semi-circular flanges
132,
133. However, it is similarly contemplated that joint configurations other
than a
planar joint may be employed. For example, either the semi-circular flanges or
the
openings in the half-shells may be manufactured with interlocking elements,
such
that there is a groove on one and a corresponding ridge on the other half-
shell
assembly, if needed or desired for any reason. Regardless of the particular
sealing structure employed for a particular embodiment and installation, once
sealed around the casings, apparatus 100 accumulates and contains annular gas
in half-cavities 201 and 301 until vented. Also visible in Figure 3 is a point
315
(vertical level) where surface casing 310 intersects production casing 320
inside
the cavity formed by combining half-cavities 201, 301. Seals 135, 134 are
visible
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surrounding an exterior of surface casing 310 and production casing 320,
respectively.
Figure 4 shows half-shells 110, 111 fastened together using
fasteners such as bolts 145.
In particular, top seal 134 is visible along the inner circumference of
the toroid formed by semi-circular flanges 130 & 131.
In operation, apparatus 100 is installed over the well-site casings at
the level, earlier identified by point 315, where the surface and production
casings
begin to overlap at the top end of the surface casing. Apparatus 100 may be
manufactured in any suitable length(s), but is typically approximately 2 feet
long
such that bottom semi-circular flanges 132, 133 engage surface casing 310
approximately one foot below the upper end of the surface casing 310 at point
315,
while top semi-circular flanges 130, 131 engage production casing 320
approximately one foot above that same level at point 315. Such results in the
"joint" being roughly vertically centered inside half-shells 110, 111. Prior
to
fastening half-shells 110, 111 into position at any suitable level proximal
point 315,
apparatus 100 may be adjusted vertically up or down to ensure that all semi-
circular flanges are positioned over straight segments of undamaged exterior
face
on their respective casings. Such permits an effective gas tight seal of
annular gas
inside cavity 201, 301. At a site where either or both casings are damaged
over a
vertical span sufficient to prevent sealing a standard length version of
apparatus
100, it is to be understood that an extended custom length apparatus 100
(working
in the same manner) can be manufactured so as to reach far enough along the
casings to permit the installer to seal around undamaged segments of each
casing.
Figure 5 shows the apparatus 100 installed at a typical well-site 500,
according to one illustrated embodiment.
The apparatus 100 enclosing point 315 being at the level of
intersection (not visible) between surface casing 310 and production casing
320
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through which casing, production tubing (not shown) delivers a hydrocarbon
flow to
any suitable valve assembly 520. Vent assembly 510 is fluidly coupled to vent
outlet 160 to permit a well operator to periodically monitor, measure flow
rates, and
divert annular gas accumulated in apparatus 100, so as to release any
sustained
pressure therein. Conventional monitor or measuring equipment, for example gas
flow meters may be employed.
The above description of illustrated embodiments, including what is
described in the Abstract, is not intended to be exhaustive or to limit the
embodiments to the precise forms disclosed. Although specific embodiments of
and examples are described herein for illustrative purposes, various
equivalent
modifications can be made without departing from the spirit and scope of the
disclosure, as will be recognized by those skilled in the art of gas flow
control. The
teachings provided herein of the various embodiments can be applied to other
apparatus that control gas flow at well sites, not necessarily the exemplary
well-
casing annular gas pressure seal and venting apparatus generally described
above.
For example, while illustrated as two mating halves, the apparatus
may include more than two portions which mate together in a similar fashion to
the
two mating halves. Also for example, while illustrated as employing a circular
cross-section, other geometric shapes may be employed.
The various embodiments described above can be combined to
provide further embodiments. To the extent that they are not inconsistent with
the
specific teachings and definitions herein, all commonly assigned U.S. patents,
U.S.
patent application publications, U.S. patent applications, referred to in this
specification and/or listed in the Application Data Sheet are incorporated
herein by
reference, in their entirety. Aspects of the embodiments can be modified, if
necessary, to employ structures and concepts of the various patents and
applications to provide yet further embodiments.
These and other changes can be made to the embodiments in light
of the above-detailed description. In general, in the following claims, the
terms
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used should not be construed to limit the claims to the specific embodiments
disclosed in the specification and the claims, but should be construed to
include all
possible embodiments along with the full scope of equivalents to which such
claims are entitled. Accordingly, the claims are not limited by the
disclosure.
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