Note: Descriptions are shown in the official language in which they were submitted.
CA 02783392 2012-06-06
OIL-GAS WELL STRUCTURE FOR FACILITATING EXTRACTING A
DOWNHOLE FILTER STRING AND METHOD FOR EXTRACTING THE
STRING
Technical Field
The present invention relates to the oil exploitation field, and specifically
relates
to an oil-gas well structure for facilitating extracting a downhole filter
string and
a method for extracting the downhole filter string from the oil-gas well. The
oil-gas well here refers to a production well in a broader sense in oil-gas
field
development, which includes an oil well, a gas well, a natural gas well, an
injection well, etc.
Background Art
The completion structure of most mechanically sand control oil-gas wells
comprises an oil-gas well and a downhole filter string run into the oil-gas
well,
and the oil-gas well includes a vertical well, a deviated well, a highly-
deviated
well and a horizontal well. As shown in Figure 1, the reference sign 1 in
Figure
1 indicates a borehole wall of an oil-gas well, the reference sign 2 indicates
a
downhole filter string, the reference sign 3 indicates an annulus between the
downhole filter string and the borehole wall, the reference sign 4 indicates a
packer for hanging the downhole filter string. The downhole filter string here
is
a downhole filter string in a broader sense and has a plurality of forms, for
instance, in a first circumstance there is a downhole filter string having no
flow-restrict function which at this same is only a sand control filter, which
is
also called as a sand control screen. In a second circumstance, there is a
filter
having a flow-control function, i.e. a flow-control filter string, which is
also
called as a flow-control screen. The flow-control filter has a flow-control
function, and at the same time has a filtering function, which function is
sometimes to prevent anti-channeling particle medium outside the flow-control
filter from entering a wellbore and also has the function of preventing
formation
sand from entering a wellbore for a sand production well. The flow-control
function of the flow-control filter embodies a flow-restrict function as well.
The downhole filter string refers to a string formed by connecting one or more
downhole filters in series. For example, a sand control screen with a total
length
of 300 meters which is placed into a horizontal well is formed by connecting
30
sand control screens of about 10 meters in series.
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In an oil-gas well containing the downhole filter string, there exist the
following
two circumstances outside the downhole filter string: one circumstance in
which outside the downhole filter string there are artificially filled with
gravels
which include quartz sands or ceramsites; the other circumstance in which
outside the downhole filter string there are no fillers, if there are no
fillers
outside the downhole filter string, after a period of production by a sand
production well, the produced formation sand may also fill up the annulus
between the downhole filter string and the borehole wall, as shown in Figure
1,
the reference sign 5 in Figure 1 represents formation sands or artificially
filled
gravels accumulated outside the downhole filter string. Both naturally filled
formation sands and artificially filled gravels produce a great resistance for
pulling a downhole filter string such that it is difficult to extract a
downhole filter
string in an oil-gas well, in particular a well having a long downhole filter
string,
such as a highly-deviated well and a horizontal well, in which it is almost
impossible to extract a downhole filter string.
However, it is necessary to extract a downhole filter string under a number of
circumstances, such as the following several circumstances:
1. It is necessary to repair a damaged downhole filter string, or to replace a
downhole filter string;
2. It is necessary to recycle extracted downhole filter strings so as to save
much
expenditure.
3. When a flow-control filter string is used, the extraction of a flow-control
filter
string in the production process may facilitate conveniently regulating the
flow-control parameters of the flow-control filter string such as to adapt to
the
flow requirements of different exploitation stages and improve the production
efficiency of an oil-gas well.
At present, there is still no oil-gas well structure facilitating extracting a
downhole filter string and a particularly effective method for extracting a
downhole filter string from an oil-gas well.
Summary of the Invention
The technical problem required to be solved by the present invention is to
provide an oil-gas well structure facilitating extracting a downhole filter
string
and a method for extracting a downhole filter string from the oil-gas well.
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In order to solve the aforementioned problem, the present invention uses the
following technical solution:
The oil-gas well structure for facilitating extracting a downhole filter
string of
the present invention comprises a borehole wall and a downhole filter string
run
into the oil-gas well, one end of the downhole filter string close to the
wellhead
being an upper end of the filter string which end is fixedly connected with
the
borehole wall, an annulus being formed between the downhole filter string and
the borehole wall; the annulus between the downhole filter string and the
borehole wall is filled with ultra light particles, wherein the density of the
ultra
light particles approaches or is equal to the density of a carrier fluid for
carrying
the ultra light particles, the carrier fluid for carrying the ultra light
particles is a
liquid for carrying and conveying the ultra light particles into the annulus
or
backwashing and conveying the ultra light particles out of the annulus.
The ultra light particles and the carrier fluid for the ultra light particles
have a
density difference within a range of from -0.35 to +0.35, which range contains
two endpoint values.
Preferably, the ultra light particles and the carrier fluid for the ultra
light
particles have a density difference within a range of from -0.3 to +0.3, which
range contains two endpoint values.
The ultra light particles are particles which have an average particle
diameter of
0.05-1.2 mm, and a real density of 0.7-1.3 g/cm3.
Preferably, the ultra light particles are particles which have an average
particle
diameter of 0.05-0.8 mm, and a real density of 0.94-1.08 g/cm3.
Preferably, the ultra light particles are macromolecule polymer particles.
Preferably, the ultra light particles are high density polyethylene particles
which
have an average particle diameter of 0.05-0.8 mm, and a real density of
0.90-0.98 g/cm3.
Or, the ultra light particles are polypropylene and PVC macromolecule polymer
particles which have an average particle diameter of 0.05-0.8 mm, and a real
density of 0.7-1.3 g/cm3.
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Or, the ultra light particles are styrene and divinylbenzene cross-linked
copolymer particles which have an average particle diameter of 0.05-0.8 mm,
and a real density of 0.94-1.08 g/cm3.
The present invention also discloses a method for extracting a downhole filter
string from the oil-gas well structure for facilitating extracting a downhole
filter
string, which method includes the following steps:
1) Establishing channels: opening an annulus between an upper end of a
downhole filter string and a borehole wall;
2) Removing ultra light particles by a carrier fluid for backwashing:
injecting a
carrier fluid for ultra light particles into the downhole filter string in
order to
backwash and carry the ultra light particles away from the annulus;
3) Extracting the downhole filter string.
When the downhole filter string is a flow-control filter string, the step of
removing ultra light particles by a carrier fluid for backwashing is in way
such as
to connect a fluid injection pipe with the downhole filter string and directly
inject the carrier fluid for ultra light particles into the flow-control
filter string,
due to a flow-control effect of the flow-control filter string, the injection
fluid is
uniformly injected into ultra light particles from various segments of the
flow-control filter string, and ultra light particles accumulated outside the
downhole filter string are removed by means of an upper fluid flow passage of
the downhole filter string.
When the downhole filter string is a flow-control filter string, the step of
removing ultra light particles by a carrier fluid for backwashing is in a way
such
as to run a fluid injection pipe into the downhole filter string, said fluid
injection
pipe performs fluid injection; a lower portion of the fluid injection pipe has
an
opening an upper portion of which is provided with a seal ring having an
outside
diameter substantially identical to an inside diameter of the downhole filter
string, the fluid injection being in a sectional manner; the fluid injection
pipe is
gradually run into a bottom of the downhole filter string for sectional fluid
injection and sectional removal of ultra light particles outside the downhole
filter string from the top of the downhole filter string, when ultra light
particles
outside an anterior segment of the downhole filter string close to a wellhead
are
removed, the fluid injection pipe is penetrated into the downhole filter
string for
another segment until those outside the downhole filter string are completely
removed; or it is possible to continuously move the fluid injection pipe to
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perform fluid injection until ultra light particles outside the downhole
filter
string are removed.
When the downhole filter string is a downhole filter string having no
flow-restrict function, the step of removing ultra light particles by a
carrier fluid
for backwashing is in a way such as to run a fluid injection pipe into the
downhole filter string, said fluid injection pipe performs fluid injection; a
lower
portion of the fluid injection pipe has an opening an upper portion of which
is
provided with a seal ring having an outside diameter substantially identical
to
an inside diameter of the downhole filter string, the fluid injection being in
a
sectional manner; the fluid injection pipe is gradually penetrated into a
bottom
of the downhole filter string for sectional fluid injection and sectional
removal of
ultra light particles outside the downhole filter string from the top of the
downhole filter string, when ultra light particles outside an anterior segment
of
the downhole filter string close to the wellhead are removed, the fluid
injection
pipe is penetrated into the downhole filter string for another segment until
those outside the downhole filter string are completely removed. The fluid
injection pipe may be moved in a manner such as to continuously move the
fluid injection pipe to perform fluid injection until ultra light particles
outside the
downhole filter string are removed.
Preferably, the carrier fluid for ultra light particles as defined in the
present
invention is water or water solution.
The present invention utilizes a carrier fluid for ultra light particles
having a
density of about 1 g/cm3 and chooses ultra light particles having a real
density
very close to that of a carrier fluid so that the carrier fluid may easily
carry the
ultra light particles for filling into an annulus between the downhole filter
string
and the borehole wall, filling in and filling up the annulus between the
downhole
filter string and the borehole wall, a part of the carrier fluid enters the
downhole
filter string and returns to the ground surface and a further part of the
carrier
fluid penetrates into the formation through the borehole wall; and finally
form
a completion structure which fill up ultra light particles in the annulus
between
the downhole filter string and the borehole wall.
At the same time, the ultra light particles occupy the space of the annulus
between the downhole filter string and the borehole wall, and also obstruct a
accumulating of the formation sand in the space of the annulus between the
downhole filter string and the borehole wall.
CA 02783392 2012-06-06
The present invention chooses particles having an average particle diameter of
0.05-1.2 mm, and a real density of 0.7-1.3 g/cm3 as ultra light particles for
filling the annulus between the downhole filter string and the borehole wall,
when it is necessary to extract the downhole filter string, it is possible to
easily
remove ultra light particles accumulated outside the downhole filter string,
and
as the density of the ultra light particles is very close to that of the
carrier fluid,
the carrier fluid circulating in a low speed may conveniently take the ultra
light
particles to the ground and remove the ultra light particles in the annulus
outside the downhole filter string so that the downhole filter string may be
conveniently extracted from the oil well. The requirements for extracting a
downhole filter string are satisfied.
The method as defined in the present invention, which is easy to carry out,
overcomes the difficulties in extracting a downhole filter string in an oil
well and
thus facilitates the production, and moreover, the removed ultra light
particles
may be recycled, thereby greatly reducing the production cost.
Description of the Drawings
Figure 1 is a view of the completion structure as defined in the Background
Art.
Figure 2 is a view of the completion structure as defined in the embodiment 1
of
the present invention.
Figure 3 is a view of a flow path of the carrier fluid for backwashing and
removing ultra light particles outside the filter string as defined in the
embodiment 2 of the present invention.
Figure 4 is a view of a flow path of the carrier fluid for backwashing and
removing ultra light particles outside the filter string as defined in the
embodiment 3 of the present invention.
Figure 5 is a view of a flow path of the carrier fluid for backwashing and
removing ultra light particles outside the filter string as defined in the
embodiment 4 of the present invention.
Figure 6 is a view of the oil-gas well structure after removing ultra light
particles
as defined in the present invention.
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Detailed description of the preferable embodiments
Embodiment 1
As shown in Figure 2, an oil-gas well structure for facilitating extracting a
downhole filter string as defined in the present invention comprises an oil-
gas
well borehole wall 1 and a downhole filter string 2 run into the oil-gas well,
a
packer 4 for hanging the downhole filter string is provided between one end of
the downhole filter string close to the wellhead and the borehole wall, an
annulus is formed between the downhole filter string and the borehole wall;
the
annulus between the downhole filter string and the borehole wall is filled
with
ultra light particles 6.
Embodiment 2 A method for extracting a control-flow filter string
In the completion structure as shown in Figure 2 and as defined in the
embodiment 1, the ultra light particles are polypropylene and PVC
macromolecule polymer particles which have an average particle diameter of
0.05-0.8 mm, and a real density of 0.7-1.3 g/cm3.
As shown in Figure 3, the downhole filter string, which is a flow-control
string
filter 2, is provided with a flow-control filter 2-1; the method for
extracting the
downhole filter string is as follows:
1) Opening a packer for hanging the downhole filter string: for a packer unset
by pulling, the opening method is in a way such that the packer is unset
automatically when the packer is pulled. For a packer unset by rotating, the
packer is unset automatically when the packer is rotated. Between the unset
packer and the borehole wall there exists a gap which becomes a fluid
circulating passage.
2) Removing ultra light particles by a carrier fluid for backwashing: connect
a
fluid injection pipe with the downhole filter string and directly inject the
carrier
fluid for ultra light particles into the flow-control filter string, due to a
flow-control effect of the flow-control filter string, the injection fluid is
uniformly
injected into ultra light particles from various segments of the flow-control
filter
string; in Figure 3, the arrow direction indicates a flow method of the
carrier
fluid.
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3) Removing: ultra light particles are taken out of the well by the carrier
fluid
until the ultra light particles accumulated outside the downhole filter string
are
removed; the structure of oil-gas well after removal is as shown in Figure 6.
4) Extracting the downhole filter string.
Embodiment 3 A method for extracting a control-flow filter string
In the completion structure as shown in Figure 2 and as defined in the
embodiment 1, the ultra light particles are styrene and divinylbenzene
cross-linked copolymer particles which have an average particle diameter of
0.05-0.8 mm, and a real density of 0.94-1.08 g/cm3.
As shown in Figure 4, the downhole filter string, which is a flow-control
string
filter 2, is provided with a flow-control filter 2-1; the method for
extracting the
downhole filter string is as follows:
1) Opening a packer for hanging the downhole filter string: for a packer unset
by pulling, the opening method is in a way such that the packer is unset
automatically when the packer is pulled. For a packer unset by rotating, the
packer is unset automatically when the packer is rotated. Between the unset
packer and the borehole wall there exists a gap which becomes a fluid
circulating passage.
2) Removing ultra light particles by a carrier fluid for backwashing: running
a
fluid injection pipe 7 into the downhole filter string, said fluid injection
pipe 7
performs fluid injection; a lower portion of the fluid injection pipe has an
opening an upper portion of which is provided with a seal ring 8 having an
outside diameter substantially identical to an inside diameter of the downhole
filter string, the fluid injection being in a sectional manner; the fluid
injection
pipe is gradually penetrated into a bottom of the downhole filter string for
sectional fluid injection and sectional removal of ultra light particles
outside the
downhole filter string from a top of the downhole filter string, due to an
effect
of the seal ring, the seal ring may block the carrier fluid injected into the
downhole filter string by the fluid injection pipe at a lower side of the seal
ring
and concentrate the carrier fluid to impact parts deposited with ultra light
particles, when ultra light particles outside an anterior segment of the
downhole filter string close to a wellhead are removed, the fluid injection
pipe
is penetrated into the downhole filter string for one further segment until
those
outside the downhole filter string are completely removed; such also avoids
that the carrier fluid does not produce the effect of the deposited ultra
light
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particles and saves much carrier fluid. The arrow direction in Figure 4
indicates
a flow direction of the carrier fluid. The dotted line in Figure 4 presents
that the
fluid injection pipe is gradually penetrated into the downhole filter string
for
sectional fluid injection. The fluid injection pipe may be penetrated into the
downhole filter string in a continually uniform-speed penetrating manner. As
the continually uniform-speed moving injection pipe gradually injects fluid,
the
depth after ultra light particles are removed gradually increases until the
ultra
light particles outside the downhole filter string are completely removed. The
arrow direction in Figure 4 indicates a flow method of the carrier fluid.
3) Removing: ultra light particles are taken out of the well by the carrier
fluid
until the ultra light particles accumulated outside the downhole filter string
are
removed; the structure of oil-gas well after removal is as shown in Figure 6.
4) Extracting the downhole filter string.
Embodiment 4 A method for extracting a downhole filter string having no
flow-restrict function
In the completion structure as shown in Figure 2 and as defined in the
embodiment 1, the ultra light particles are high density polyethylene
particles
which have an average particle diameter of 0.1-0.5 mm, and a real density of
0.94 g/cm3.
As shown in Figure 5, the downhole filter string is a downhole filter string 2
having no flow-restrict function, and the method for extracting the downhole
filter string is as follows:
1) Opening the annulus between one end of the downhole filter string close to
the wellhead and the borehole wall, establishing a fluid circulating passage
at
an upper portion of the annulus between one end of the downhole filter string
close to the wellhead and the borehole wall: for a packer unset by pulling,
the
opening method is in a way such that the packer is unset automatically when
the packer is pulled. For a packer unset by rotating, the packer is unset
automatically when the packer is rotated. Between the unset packer and the
borehole wall there exists a gap which becomes a fluid circulating passage.
2) Removing ultra light particles by a carrier fluid for backwashing: running
a
fluid injection pipe 7 into the downhole filter string, said fluid injection
pipe 7
performs fluid injection; at the end of the fluid injection pipe there is
provided
with a seal ring 8 having an outside diameter substantially identical to an
inside
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diameter of the downhole filter string, a fluid outlet 9 of the fluid
injection pipe
is at a position slightly lower than the seal ring of the fluid injection
pipe, the
fluid injection being in a sectional manner; the fluid injection pipe is
gradually
penetrated into a bottom of the downhole filter string for sectional fluid
injection and sectional removal of ultra light particles outside the downhole
filter string from the top of the downhole filter string, due to an effect of
the seal
ring, the seal ring may block the carrier fluid injected into the downhole
filter
string by the fluid injection pipe at a lower side of the seal ring inside the
downhole filter string so that it is difficult for the carrier fluid to enter
the upper
side of the seal ring and thus at places where the ultra light particles are
removed at an upper side there are no more carrier fluid entering from the
filter
string, and concentrate the carrier fluid to remove ultra light particles that
are
required to be removed, when ultra light particles outside an anterior segment
of the downhole filter string close to a wellhead are removed, the fluid
injection
pipe is penetrated into the downhole filter string for another segment until
those outside the downhole filter string are completely removed; such also
avoids the run-up of the carrier fluid and thus saves much carrier fluid and
maintains a higher flow speed of impacting ultra light particles. The arrow
direction in Figure 5 indicates a flow direction of the carrier fluid. The
dotted line
in the figure presents that the fluid injection pipe is gradually penetrated
into
the downhole filter string for sectional fluid injection. The fluid injection
pipe
may be penetrated into the downhole filter string in an intermittently
penetrating manner. The intermittently moving injection pipe gradually injects
fluid until the ultra light particles outside the downhole filter string are
completely removed.
3) Removing: ultra light particles are taken out of the well by the carrier
fluid
until the ultra light particles accumulated outside the downhole filter string
are
removed; the structure of oil-gas well after removal is as shown in Figure 6.
4) Extracting the downhole filter string.
The carrier fluid as defined in the embodiments 2-4 may be water or a water
solution added with common additives for an oil field.
The method as defined in the present invention, which is easy to carry out,
overcomes the difficulties in extracting a downhole filter string in an oil
well and
thus facilitates the production, and moreover, the removed ultra light
particles
may be recycled, thereby greatly reducing the production cost.
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The density of the particles in the present patent refers to a real density of
particles.
The present patent also contains a circumstance in which a thinner downhole
filter string is secondarily run into an initial downhole filter string of a
well that
is already present with a downhole filter string. It contains circumstances in
which a filter string is run into a casing perforated well, a well with a
porous
pipe and an open-hole well.
Finally, it is imperative to explicate that: apparently, the aforementioned
embodiments only pertain to exemplifications made to clearly present the
present invention rather than definitions on the embodiments. On the basis of
said descriptions, a person skilled in the art may also make changes or
variations of other different forms. Hereby, it is unnecessary and impossible
to
list all the embodiments. However, the obvious changes or variations deriving
therefrom still fall into the protection scope of the present invention.
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