COMBINATION BURST-DISC SUBASSEMBLY FOR HORIZONTAL AND VERTICAL WELL COMPLETIONS

SOUS-ENSEMBLE COMBINE A DISQUE DE RUPTURE POUR LA COMPLETION DE PUITS HORIZONTAUX ET VERTICAUX

English Abstract

A combination profile and burst-disc subassembly is provided for use in directional, horizontal or deviated or vertical wells during snubbing , bridge plug retrieval or zone separation operations in combination with packers and/or completion strings; the sub provides an plug for non-vertical situations which can be opened without wireline, while providing a landing for a wireline plug which may be required for vertical well sections during related operations.

French Abstract

Un sous-ensemble de profil de combinaison et de disque de rupture est fourni afin d'être utilisé dans des puits directionnels, horizontaux ou déviés ou verticaux lors du curage sous pression, de la récupération du bouchon de support ou d'opérations de séparation de zone en combinaison avec des garnitures d'étanchéité ou des colonnes d'achèvement; le sous-ensemble fournit un bouchon pour les situations non verticales qui peut être ouvert sans câble métallique, tout en fournissant un accrochage pour bouchon de câble métallique qui peut être nécessaire pour des sections de puits verticales pendant les opérations connexes.

Claims

WHAT IS CLAIMED IS:
1. A subassembly for horizontal and vertical wellbore completions with at
least two
pressure sealing mechanisms, comprising (i) a burst disc and (ii) a fitting
for a profile plug.
2. A method for unsealing a tubing string after installation into a wellbore
comprising
bursting a burst disc within a combination burst disc-profile fitting
subassembly by injection of
fluid under pressure higher than the burst pressure of the burst disc, and
then resealing the
tubing string for removal or other operational reasons by landing and seating
and sealing a
profile plug into the included profile fitting in the subassembly attached to
the tubing.
3. The method of claim 2 where the tubing string is first sealed with an
intact burst disc
and is also sealed with a plug seated and sealed into a plug receiving profile
fitting.
4. The method of claim 3 where the plus is removed and the tubing string is
sealed with
an intact burst disc alone.
5. The method of claim 4 where, after the burst disc is burst the tubing
string is later
resealed with a plug seated into a plug receiving profile fitting alone.

Description

CA 02762730 2011-12-23
COMBINATION BURST-DISC SUBASSEMBLY FOR HORIZONTAL AND
VERTICAL WELL COMPLETIONS
FIELD OF THE INVENTION
The present invention relates generally to a subassembly for a
completion/drilling string use in directional, horizontal, deviated or
vertical wells
during snubbing, bridge plug retrieval or zone separation operations in
combination
with packers and/or completion strings; the sub provides a plug for non-
vertical
situations which can be opened without wireline, while providing a landing for
a
1o wireline plug which may be required for vertical well sections during
related
operations.
BACKGROUND OF THE INVENTION
In drilling, completion or service operations in a deviated well, it is
sometimes important to be able to seal the tubing string mid-way to isolate
production
or other pressurized zones of the wellbore from surface.
In the_ past, tubing end-plugs have been used during injection of tubing
into such a well, the plugs generally being a metallic or aluminum disc
attached to the
bottom of the tubing string prior to injection, and then the destruction of
the metallic
disc when the tubing string is located at bottom hole. This has the
undesirable effect
of leaving metal fragments at the bottom workface of the wellbore which is
difficult or
expensive to remove. These devices have only been run at the bottom of a
tubing
string, and cannot provide for dual sealing for tripping out of the wellbore.
Another mechanism sometimes seen is the use of an Otis nipple,
consisting of multiple profiles to receive a variety of plug devices via
wireline delivery
downhole. These mechanisms provide for a single plug, and while unpiuggable
and
repluggable, are constrained by the plug delivery mechanism - that is,
wireline plugs
may be difficult to retrieve from deep deviated or horizontal wellbores, and
may be
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impossible to inject and refit in non-vertical orientations. Additionally, if
such a plug
fitting fails during injection, the wireline plug may become a projectile, and
two
wireline plugs cannot or cannot easily be installed for the injection
operations.
Similarly, multi-profile landing nipples to receive a variety of plugs are
manufactured
under the Baker trade name.
Frangible pressure seals such as disclosed in US5,924,696 are also
known, but have not been deployed providing dual barriers during injection,
nor do
these devices themselves provide plug fittings, and have required the use of
additional nipples or landings.
Thus, there is a need for a device to overcome the limitations of the
prior art, in particular for use in deviated or non-vertical or horizontal
wellbore
situations.
SUMMARY OF THE INVENTION
To mitigate some of the problems with the prior art, this system
provides for in a first aspect, a subassembly with at least two pressure
sealing
mechanisms, comprising (i) a burst disc and (ii) a fitting for a profile plug.
In a second
aspect, the invention provides a 'method of sealing a tubing string during
injection into
a wellbore by providing a subassembly within the tubing string sealed by an
intact
burst disc. In a further embodiment, the invention provides that method where
the
tubing string is also sealed with a plug seated and sealed into a plug
receiving profile
fitting. In another embodiment, the invention provides a method of unsealing a
tubing
string after installation into a wellbore comprising bursting a burst disc
within a
combination burst disc - profile fitting subassembly by injection of fluid
under
pressure higher than the burst pressure of the burst disc, and then resealing
the
tubing string for removal or other operational reasons by landing and seating
and
sealing a profile plug into the included profile fitting in the subassembly
attached to
the tubing.
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CA 02762730 2011-12-23
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of
example only, with reference to the attached Figure, wherein:
Fig. 1 is a longitudinal cross-section of an exemplary subassembly of
the invention with an intact burst-disc installed, lower end toward the right
hand side
of the figure.
DETAILED DESCRIPTION
Generally, the present invention provides a subassembly 1 with at least
two pressure sealing mechanisms, comprising (i) a burst disc 4 and (ii) a
fitting for a
1o profile plug 6. The burst disc 4 is generally deployed below the profile
plug fitting 6
when the subassembly 1 is used, and the inner passage of the subassembly 1
when
sealed by either an intact burst disc 4 or a plug in the profile plug fitting
6, or both,
does not permit fluid flow from tubing attached below the subassembly 1
through the
subassembly 1 to tubing or the wellbore above the subassembly (or packing
between
the wellbore and the tubing, wherever located).
The burst disc 4, most typically made of breakable ceramic or similar
substance, is designed to be breakable/broken by exertion of force from above
the
disc 4, such as by increasing fluid pressure within the conduit of attached
wellbore
tubing above the subassembly 1, while remaining unbroken/unbreakable by
pressure
exerted on the burst disc 4 from below the disk. Thus, the tubing string into
which the
subassembly 1 is assembled (not shown, above and below the subassembly 1) can
be sealed by the burst disc 4 when it is intact or opened when the burst disc
4 is
broken. The burst disc may be broken by exertion of increased pressure from
uphole
equipment, and the tubing below the subassembly can later be resealed by use
of a
plug in the profile plug fitting 6 by wireline. If a plug is fitted at the
plug fitting 6 and if
the burst disc 4 is unbroken, the subassembly provides a redundant double plug
to
the tubing string, enhancing reliability and safety.
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This selective sealing functionality provides new and non-obvious utility
to drilling, completion and other operations, in particular in situations
where the lower
portion of the wellbore is deviated, non-vertical, or horizontal making the
use of
wireline plugs impractical. The unitization of the two sealing mechanisms
provides a
subassembly of short length which does not require additional assembly steps
while
making or breaking the tubing string.
The subassembly can be deployed for injecting or removing tubing into
a wellbore, in particular a well-bore having a vertical part from surface
downward and
a connected deviated or horizontal or non-vertical part below the vertical
part of the
1o wellbore. This way, the tubing can be sealed from formation pressures by
the burst
disc during injection of the tubing into the well, and so the burst disc 4 can
be in place
at a point in the non-vertical part of the wellbore until the bottom end of
the tubing
string is placed were desired by the operator, at which stage the burst disc 4
can be
broken by application of pressure down the tubing's inner conduit, thus
opening the
tubing's bottom end. In that setting, wireline plugs cannot be deployed
because
gravity alone will not provide sufficient force to inject the plugged tubing
beyond a
certain point of travel in a non-vertical direction due to frictional forces
between the
tubing's outside walls and the wellbore, among other forces. For similar
reasons a
wireline removal of a plug from a profile fitting in a non-vertical
orientation may be
difficult or impossible. In an embodiment, the subassembly 1 will be placed at
a point
on the tubing string such that when the tubing string is placed where the
operator
wants it, the subassembly is at or above the point where the wellbore changes
from
vertical to non-vertical directions, although placement of the subassembly
will depend
upon where the tubing needs to be sealed during removal, which may be
dependent
upon a number of factors such as tubing length and size, location of packers,
location
of production zones, location of perforations, pressures and other downhole
conditions.
When removing tubing from such a wellbore, a standard wireline-
deployed plug may be set at or near the bottom of the vertical part of the
wellbore,
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CA 02762730 2011-12-23
and the tubing removed. When the subassembly 1 reaches the bottom of the
substantially vertical part of the wellbore, it will be capable of receiving a
wireline
deployed plug to mechanically seat and seal within the profile fitting 6 of
the
subassembly 1, and thus seal the tubing during its trip out of the wellbore to
surface.
The subassembly 1 can be run into the wellbore with the burst disc 4
and plug seated and sealed to the profile plug fitting 6 to create a dual
barrier. Even
though the burst disc 4 could be in position above the plug profile fitting 6,
it is more
advantageous in operation to place the burst disc 4 below.
A shaved or slim-hole or special combination burst disc subassembly 1
1o with smaller diameter, for example 2 7/8" O.D. may be used, such that two
small
diameter tools or strings can be worked through a 4 '/2" liner or wellbore,
while
standard (non-shaved or slim-hole) 2 78" O.D. assemblies could not.
It will be apparent to those knowledgeable about drilling, completion,
workover and snubbing operations in the oilfield that the use of this
invention can be
applicable to other oilfield situations, and yet retains its novelty.
The above-described embodiments of the invention are intended to be
examples only. Alterations, modifications and variations can be effected to
the
particular embodiments by those of skill in the art without departing from the
scope of
the invention, which is defined solely by the claims appended hereto
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Representative Drawing