Note: Descriptions are shown in the official language in which they were submitted.
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TUBULAR SLUG REDUCER
Field of the InverLtion
This invention relates to devices and techniques for reducing or eliminating
slugs in a tubular string within a well, such as liquid slugs in a gas well,
or gas slugs
in a liquid well or pipeline. More particularly, the device of the present
invention is
highly reliable and does not interfere with the passage of various tools
through the
tubular or pipeline.
8ackaround of.th~s Invention
Various types of devices have been designed for reducing or eliminating
slugs in a flow line. Slugs in a flaw line may cause serious problems to
to downstream epuipment, such as blow-out preventers, flow controt valves, and
sensors. Most slug prevention devices are positioned within the bore of the
tubular
string, and thereby substantially interfere with the passage of wireline
tools, coiled
tubing tools, pigs, or other devices intended to pass through the tubular
string or
pipeline.
U.S. Patent No. 5,698,014 discloses a spiral or auger type separator
particularly intended for well production fluid flow. U.S. Patent No.
5,431,228
discloses another version of a liquid-gas separator for use in downhole
producing
wells. An early version of an air-water separator is disclosed in U.S. Patent
No.
4,762,176. U.S. Patent No. 5,570,744 discloses another version of a separator
far
well production fluids, including a spiral baffle.
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The disadvantages of the prior art are overcome by the present invention,
and an improved slug reducer for use along a flow line is hereinafter
disclosed.
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Summay o_fhe Invention
According to a preferred embodiment, a flow line for reducing axial
separation of different density fluids passing through the flow line includes
one or
more grooves in a wall of the flow line and radially outward of a generally
cylindrical
hare of the flow line. Each of the one or more grooves forms a spiral along an
axial
length of the flow line, thereby swirling fluid passing through the flow line
and
causing lighter fluid to move toward a center of the flow line due to a
created vortex
and heavier fluid to move toward a radiaily outer portion of the flow line.
In anotherembodiment, atubularfor reducing axial separation of liquid slugs
IO and gas slugs passing through the tubular in a well includes one or more
grooves
in the tubular, with the one or more grooves each forming a spiral along the
axial
length of the tubular, Swirling fluid passing through the tubular in the well
causes
gas to move toward a center of the tubular due to the created vortex and
liquid to
move toward a radially outer portion of the tubular.
I S According to the method of the invention, axial separation of different
density
fluids passing through a flow line having a generally cylindrical bore is
reduced by
forming one or more grooves in a wall of a flow line and radially outward of
the
generally cylindrical bore of the flow line. The recesses may be formed by one
or
more radially outward projections on a mandrel, such that when the flow line
moves
20 axially over the mandrel while rotating, the one or more grooves are formed
in the
flow line.
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~fhese and other features and advantages of the invention will become
apparent from the following detailed description, wherein reference is made to
the
figures in the accompanying drawings,
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Brief Description of the Drawin4s
Figure 1 is a cross-sectional view of ~ portion of a tubular and a portion of
a
coupling threadedly connected to the tubular, with a single spiral groove
provided
in both the tubular and the coupling.
Figure 2 is a cross-sectional end view of another embodiment of a tubular
with three circumferentially spaced grooves in the tubular.
Figure 3 is a detailed view of a portion of the groove shown in Figure 2.
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Detailed Descriiption of Preferred_E bodimenis
Figure 1 illustrates a flow line, such as an oil field tubular 10, threadedly
connected to a coupling 12 by threads 14. The flow line 10 is provided with a
single
spiraling groove 16, and the coupling 12 is provided with a similar spiraling
groove
18. It should be noted that the grooves 16, 18 may be on different spiral
pitches,
and is not critical that the end of the groove in one tubular be aligned with
the
beginning of the groove in the next tubular. It is a particular feature of the
invention
to provide grooves along a coupling, and in some embodiments couplings of an
axial length of several feet or more may be used, such that the couplings
interconnect tubular lengths and swirl the fluids to provide the axial
separation.
Figure 2 is a cross-sectional view of a tubular 30, such as a production
tubing
or drill pipe, which has three circumferentially spaced grooves, 32, 34 and
3B, with
the grooves spaced equal above the circumference above the tubular. In many
embodiments, two or more circumferential grooves will be provided along a
length
of the tubular to achieve the desired effect.
Figure 3 is a more detailed view of one of the grooves in a suitable tubular.
As shown in Figure 3, the groove has a radial depth 40, which a preferred
embodiment is from 2% to 25°% of a wall thickness of the flow line, and
in many
embodiments will be from 7% to 12% of the wall thickness of the flew tine.
Figure
2o 3 also illustrates that the groove has there circumfet'ential width 44
which is from 2%
to 50% of the bore internal diameter 46 of the flow line, and in many
applications is
from 5°% to 25% of the bore internal diameter. ~ Each of the grooves is
thus formed
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along a substantial portion of an axial length of one or more interconnected
tubular
members, and/or is formed along a substantial portion of an axial length of
one or
more couplings each interconnecting two tubular members.
Figure 3 also illustrates that each of the groov~s preferably has radially
inner
S edge 48 and radially outer edge 50 which each have a radius of from 10% to
40%
of a radial depth 40 of the groove. This feature reduces stress in the tubular
due
to the grooves, and decreases the likelihood of paraffins, waxes, and other
materials will build up adjacent the edges of the groove.
The size of the grooves in the pitch of the spiraling grooves which are
preferred will depend to some extent upon the velocity of the fluid moving
through
the flow line. Higher velocity fluids will require Isss groove depth. In a
preferred
embodiment, the tubular may be of the type having a verified thickness, such
as the
thickness 42 of the tubular wail normally greater than conventional thickness
of the
tubular. In other applications, an increased wall thickness tubular may be
utilized
t5 to maintain the desired strength of the tubular while still providing the
spiraling
grooves along the tubular.
According to a method of the invention, the grooves in the tubular may be
formed by a machining operation. In a preferred application, however, the
grooves
may be formed when initially extruding the tubular. For this application, a
mandrel
may be provided with radially outward projections forming the grooves in the
inner
wall of the tubular. The tubular thus passes over the mandrel and is rotated
at the
desired rate to achieve the spiral pitch intended.
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A flow line with a generally cylindrical bore having a bore internal diameter
includes one or more grooves in the wall of the flow line according to a
preferred
embodiment of the invention. The grooves are thus radially outward of the
generally
cylindrical bore, with each groove forming a spiral along the axial length of
the flow
s line, thereby causing fluid to swirl as it passes through the flow line and
causing
lighter fluid to move toward a radial center of the flow line due to the
created vortex
and heavier fluid to move toward a radially outer portion of the flow line.
The
improved flow line thus reduces axial separation of different density fluids,
which in
one embodiment may be liquid slugs or gas slugs passing though the flow line,
and
to in another embodiment may be different density liquids. 'The grooves cause
spiraling of the fluids passing through the flow line, and reduce axial
separation of
one type fluid from another type fluid. A slug of one fluid upstream of the
spiral
grooves which occupies al) or substantial portion of the cross-section of the
bore
may thus be stretched by the spiral grooves, so that this fluid reaches a
downstream
15 facility and constitutes only a portion of the bore of the same diameter
flow line.
This axial stretching or separation of the fluid thus reduces the damage to
the
downstream equipment normally caused by a slug of one type fluid. In a
preferred
embodiment, two or more grooves are circumferentially spaced at substantially
uniform circumferential spacing about the flow line. This spiraling of fluid
in the flow
20 line also has the potential benefit of improved separation efficiency for
downstream
equipment, since separation of, for example, the liquid and the gas passing
through
the flow line prior to arrival at the downstream facility may assist
significantly in
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downstream separation, since substantially only liquid will be in the radially
outer
portion of the flow line, and substantially only gas will be in the radially
inner portion
of the flow line.
Although specific embodiments of the invention have been described herein
in some detail, this has been done solely for the purposes of explaining the
various
aspects of the invention, and is not intended to limit the scope of the
invention as
defined in the claims which follow. Those skilled in the art will understand
that the
embodiment shown and described is exemplary, and various other substitutions,
alterations and modifications, including but not limited to those design
alternatives
specifically discussed herein, may be made in the practice of the invention
without
departing from its scope.
