Note: Descriptions are shown in the official language in which they were submitted.
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System and method for recompletion of old wells
The present invention relates to a system and method for recompletion of old
wells.
More specifically the invention relates to a system and a method as disclosed
in the
preamble of claim 1 and 7, respectively.
In a preferred embodiment of the invention a plurality of autonomous valves or
flow
control devices are substantially as those described in WO 2008/0048745 Al,
belonging
to the applicant of the present application.
Devices for recovering of oil and gas from long, horizontal and vertical wells
are known
from US patent publications Nos. 4,821,801, 4,858,691, 4,577,691 and GB patent
publication No. 2169018. These known devices comprise a perforated drainage
pipe
with, for example, a filter for control of sand around the pipe. A
considerable
disadvantage with the known devices for oil/and or gas production in highly
permeable
geological formations is that the pressure in the drainage pipe increases
exponentially in
the upstream direction as a result of the flow friction in the pipe. Because
the
differential pressure between the reservoir and the drainage pipe will
decrease upstream
as a result, the quantity of oil and/or gas flowing from the reservoir into
the drainage
pipe will decrease correspondingly. The total oil and /or gas produced by this
means
will therefore be low. With thin oil zones and highly permeable geological
formations,
there is further a high risk that of coning, i. e. flow of unwanted water or
gas into the
drainage pipe downstream, where the velocity of the oil flow from the
reservoir to the
pipe is the greatest.
From World Oil, vol. 212, N. 11 (11/91), pages 73 - 80, is previously known to
divide a
drainage pipe into sections with one or more inflow restriction devices such
as sliding
sleeves or throttling devices. However, this reference is mainly dealing with
the use of
inflow control to limit the inflow rate for up hole zones and thereby avoid or
reduce
coning of water and or gas.
WO-A-9208875 describes a horizontal production pipe comprising a plurality of
production sections connected by mixing chambers having a larger internal
diameter
than the production sections. The production sections comprise an external
slotted liner
which can be considered as performing a filtering action. However, the
sequence of
sections, of different diameter creates flow turbulence and prevent the
running of work-
over tools.
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US 5.435.393 describes a production pipe with a lover drainage pipe divided
into
sections and with one or more inflow restriction devices which controls the
flow of oil
or gas from the reservoir into the drainage pipe based on the precalculated
loss of
friction pressure along the drainage pipe, the precalculated production
profile of the
reservoir and the precalculated inflow of gas or water. This publication does
thus not
relate to recompletion of old wells, nor to the use of autonomous flow control
devices in
said recompletion.
When extracting oil and or gas from geological production formations, fluids
of
different qualities, i.e. oil, gas, water (and sand) is produced in different
amounts and
mixtures depending on the property or quality of the formation. None of the
above-
mentioned, known devices are able to distinguish between and control the
inflow of oil,
gas or water on the basis of their relative composition and/or quality.
With the autonomous valve as described in WO 2008/0048745 Al is provided an
inflow control device which is self adjusting or autonomous and can easily be
fitted in
the wall of a production pipe and which therefore provide for the use of work-
over
tools. The device is designed to "distinguish" between the oil and/or gas
and/or water
and is able to control the flow or inflow of oil or gas, depending on which of
these
fluids such flow control is required.
The device as disclosed in WO 2008/0048745 Al is robust, can withstand large
forces
and high temperatures, needs no energy supply, can withstand sand production,
is
reliable, but is still simple and very cheap.
A problem with the prior art is that the well, with or without inflow control
devices, has
to be abandoned since the well is not able to produce anymore due to gas
and/or water
breakthrough.
In existing wells large quantities of oil will remain along the path of the
well due to
"short-circuit" effects, i.e. that only parts of the well are producing oil.
As shown in the
enclosed figure 9 a section of the well path adjoins a high permeability zone
in which
substantially all the inflow occurs. In such high permeability zones gas
and/or water
will enter at a faster rate than in other zones of the well. If gas
experiences a break-
through in such high permeability zones the gas will flow even easier than the
oil (gas
has a higher mobility than oil) such that this zone will increase its
proportion of the total
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inflow compared with a situation in which oil was present there. If water
experiences a
breakthrough, water will also flow easier that oil. The importance of this
will be
increasing with a higher difference in viscosity between oil and water. These
effects
reduse the drainage rate.
Short-circuit effects might also appear in low oil zones with zones comprising
gas
and/or water above or below them.
The system and method according to the invention seeks to reduce or eliminate
the
above and other problems or disadvantages by iserting a pipe with a at least
one, and
preferably a plurality of autonomous valves into an existing well, and thus
increase oil
recovery with limited investments. The invention might thus be regarded as an
improvement of an existing stinger solution in which an impervious pipe
section having
solid walls are arranged on a location in the well in which gas breakthrough
previously
has been experienced.
The system and method according to the invention are characterized by the the
features
as disclosed in the characterizing clause of claim 1 and 7, respectively.
Advantageous embodiments are set forth in the dependent claims.
The present invention will be further described in the following by means of
examples
and with reference to the drawings, where:
Fig. 1 shows a schematic view of a production pipe with a control device
according to WO 2008/0048745 Al,
Fig. 2 a) shows, in larger scale, a cross section of the control device
according
to WO 2008/0048745 Al, b) shows the same device in a top view.
Fig. 3 is a diagram showing the flow volume through a control device
according to the invention vs. the differential pressure in comparison
with a fixed inflow device,
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Fig. 4 shows the device shown in Fig. 2, but with the indication of different
pressure zones influencing the design of the device for different
applications.
Fig. 5 shows a principal sketch of another embodiment of the control device
according to WO 2008/0048745 Al,
Fig. 6 shows a principal sketch of a third embodiment of the control device
according to WO 2008/0048745 Al,
Fig. 7 shows a principal sketch of a fourth embodiment of the control device
according to WO 2008/0048745 Al.
Fig. 8 shows a principal sketch of a fifth embodiment of WO 2008/0048745
Al where the control device is an integral part of a flow arrangement.
Fig. 9 shows a principal view of a prior art well intersecting a high
permeability
zone of a reservoir.
Fig. 10 shows a principal view of the well in fig. 9, which, in accordance
with
the invention, is recompleted with a new pipe with autonomous valves
inserted into the well, causing a substantially uniform inflow into the
well.
Fig. 11 a shows a principal view of a lateral well in accordance with the
invention,
e.g. the well in fig. 10, and
Fig. I lb shows an enlarged principal view of the part of fig. I la
constricted by a
circle.
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Fig. 1 shows, as stated above, a section of a production pipe 1 in which a
control device
2, according to WO 2008/0048745 Al is provided. The control device 2 is
preferably of
circular, relatively flat shape and may be provided with external threads 3
(see Fig. 2) to
be screwed into a circular hole with corresponding internal threads in the
pipe or an
5 injector. By controlling the thickness, the device 2, maybe adapted to the
thickness of
the pipe or injector and fit within its outer and inner periphery.
Fig. 2 a) and b) shows the prior control device 2 of WO 2008/0048745 Al in
larger
scale. The device consists of a first disc-shaped housing body 4 with an outer
cylindrical
segment 5 and inner cylindrical segment 6 and with a central hole or aperture
10, and a
second disc-shaped holder body 7 with an outer cylindrical segment 8, as well
as a
preferably flat disc or freely movable body 9 provided in an open space 14
formed
between the first 4 and second 7 disc-shaped housing and holder bodies. The
body 9
may for particular applications and adjustments depart from the flat shape and
have a
partly conical or semicircular shape (for instance towards the aperture 10.)
As can be
seen from the figure, the cylindrical segment 8 of the second disc-shaped
holder body 7
fits within and protrudes in the opposite direction of the outer cylindrical
segment 5 of
the first disc-shaped housing body 4 thereby forming a flow path as shown by
the
arrows 11, where the fluid enters the control device through the central hole
or aperture
(inlet) 10 and flows towards and radially along the disc 9 before flowing
through the
annular opening 12 formed between the cylindrical segments 8 and 6 and further
out
through the annular opening 13 formed between the cylindrical segments 8 and
5. The
two disc-shaped housing and holder bodies 4, 7 are attached to one another by
a screw
connection, welding or other means (not further shown in the figures) at a
connection
area 15 as shown in Fig 2b).
The present invention exploits the effect of Bernoulli teaching that the sum
of static
pressure, dynamic pressure and friction is constant along a flow line:
1 z
pstatic + 2 pv + Apf6~tio.
When subjecting the disc 9 to a fluid flow, which is the case with the present
invention,
the pressure difference over the disc 9 can be expressed as follows:
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_ 11_ 1 2
hover [Pover(P4) Punder(f(pi P2 p3) J- 2 PV
Due to lower viscosity, a fluid such as gas will "make the turn later" and
follow further
along the disc towards its outer end (indicated by reference number 14). This
makes a
higher stagnation pressure in the area 16 at the end of the disc 9, which in
turn makes a
higher pressure over the disc. And the disc 9, which is freely movable within
the space
between the disc-shaped bodies 4, 7, will move downwards and thereby narrow
the flow
path between the disc 9 and inner cylindrical segment 6. Thus, the disc 9
moves dawn-
wards or up-wards depending on the viscosity of the fluid flowing through,
whereby
this principle can be used to control (close/open) the flow of fluid through
of the device.
Further, the pressure drop through a traditional inflow control device (ICD)
with fixed
geometry will be proportional to the dynamic pressure:
Ap=K. pv2
where the constant, K is mainly a function of the geometry and less dependent
on the
Reynolds number. In the control device according to the present invention the
flow area
will decrease when the differential pressure increases, such that the volume
flow
through the control device will not, or nearly not, increase when the pressure
drop
increases. A comparison between a control device according to the present
invention
with movable disc and a control device with fixed flow-through opening is
shown in
Fig. 3, and as can be seen from the figure, the flow-through volume for the
present
invention is constant above a given differential pressure.
This represents a major advantage with the present invention as it can be used
to ensure
the same volume flowing through each section for the entire horizontal well,
which is
not possible with fixed inflow control devices.
When producing oil and gas the control device according to the invention may
have two
different applications: Using it as inflow control device to reduce inflow of
water, or
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using it to reduce inflow of gas at gas break through situations. When
designing the
control device according to the invention for the different application such
as water or
gas, as mentioned above, the different areas and pressure zones, as shown in
Fig. 4, will
have impact on the efficiency and flow through properties of the device.
Referring to
Fig. 4, the different area/pressure zones may be divided into:
- A1, P1 is the inflow area and pressure respectively. The force (P1=A1)
generated by this
pressure will strive to open the control device (move the disc or body 9
upwards).
- A2, P2 is the area and pressure in the zone where the velocity will be
largest and hence
represents a dynamic pressure source. The resulting force of the dynamic
pressure will
strive to close the control device (move the disc or body 9 downwards as the
flow
velocity increases).
- A3, P3 is the area and pressure at the outlet. This should be the same as
the well
pressure (inlet pressure).
- A4, P4 is the area and pressure (stagnation pressure) behind the movable
disc or body 9.
The stagnation pressure, at position 16 (Fig. 2), creates the pressure and the
force
behind the body. This will strive to close the control device (move the body
downwards).
Fluids with different viscosities will provide different forces in each zone
depending on
the design of these zones. In order to optimize the efficiency and flow
through
properties of the control device, the design of the areas will be different
for different
applications, e.g. gas/oil or oil/water flow. Hence, for each application the
areas needs
to be carefully balanced and optimally designed taking into account the
properties and
physical conditions (viscosity, temperature, pressure etc.) for each design
situation.
Fig. 5 shows a principal sketch of another embodiment of the control device
according
to WO 2008/0048745 Al, which is of a more simple design than the version shown
in
Fig. 2. The control device 2 consists, as with the version shown in Fig. 2, of
a first disc-
shaped housing body 4 with an outer cylindrical segment 5 and with a central
hole or
aperture 10, and a second disc-shaped holder body 17 attached to the segment 5
of the
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housing body 4, as well as a preferably flat disc 9 provided in an open space
14 formed
between the first and second disc-shaped housing and holder bodies 4, 17.
However,
since the second disc-shaped holder body 17 is inwardly open (through a hole
or holes
23, etc.) and is now only holding the'disc in place, and since the cylindrical
segment 5 is
shorter with a different flow path than what is shown in Fig.2, there is no
build up of
stagnation pressure (P4) on the back side of the disc 9 as explained above in
conjunction
with Fig. 4. With this solution without stagnation pressure the building
thickness for the
device is lower and may withstand a larger amount of particles contained in
the fluid.
Fig. 6 shows a third embodiment according to WO 2008/0048745 Al where the
design
is the same as with the example shown in Fig. 2, but where a spring element
18, in the
form of a spiral or other suitable spring device, is provided on either side
of the disc and
connects the disc with the holder 7, 22, recess 21 or housing 4.
The spring element 18 is used to balance and control the inflow area between
the disc 9
and the inlet 10, or rather the surrounding edge or seat 19 of the inlet 10.
Thus,
depending on the spring constant and thereby the spring force, the opening
between the
disc 9 and edge 19 will be larger or smaller, and with a suitable selected
spring constant,
depending on the inflow and pressure conditions at the selected place where
the control
device is provided, constant mass flow through the device may be obtained.
Fig. 7 shows a fourth embodiment according to WO 2008/0048745 Al, where the
design is the same as with the example in Fig. 6 above, but where the disc 9
is, on the
side facing the inlet opening 10, provided with a thermally responsive device
such as
bi-metallic element 20.
When producing oil and/or gas the conditions may rapidly change from a
situation
where only or mostly oil is produced to a situation where only or mostly gas
is produced
(gas breakthrough or gas coning). With for instance a pressure drop of 16 bar
from 100
bar the temperature drop would correspond to approximately 20 C. By providing
the
disc 9 with a thermally responsive element such as a bi-metallic element as
shown in
Fig. 7, the disc will bend upwards or be moved upwards by the element 20
abutting the
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holder shaped body 7 and thereby narrowing the opening between the disc and
the inlet
or fully closing said inlet.
The above examples of a control device as shown in Figs. 1 and 2 and 4 - 7 are
all
5 related to solutions where the control device as such is a separate unit or
device to be
provided in conjunction with a fluid flow situation or arrangement such as the
wall of a
production pipe in connection with the production of oil and gas. However, the
control
device may, as shown in Fig. 8, be an integral part of the fluid flow
arrangement,
whereby the movable body 9 may be provided in a recess 21 facing the outlet of
an
10 aperture or hole 10 of for instance a wall of a pipe 1 as shown in Fig. 1
instead of being
provided in a separate housing body 4. Further, the movable body 9 may be held
in
place in the recess by means of a holder device such as inwardly protruding
spikes, a
circular ring 22 or the like being connected to the outer opening of the
recess by means
of screwing, welding or the like.
Fig. 9 shows a principal view of a well 24 intersecting a high permeability
zone 25 of a
reservoir 26. As indicated by the size of the arrows the inflow into the well
24 is non-
uniform, and with a breakthrough in the zone 25 in which substantially all of
the inflow
occurs.
Fig. 10 shows a principal view of the well in fig. 9, which, in accordance
with the
invention, is recompleted with a new pipe 27 with autonomous valves (not shown
in this
figure) inserted into the well, causing a substantially uniform inflow into
the well. A
plurality of constrictors or swell packers 29 are arranged along the well to
seal between
the inserted pipe 27 and the existing well 24.
Figs. 11 a and 1 lb respectively show a principal view of a lateral well in
accordance
with the invention, e.g. the well shown in fig. 10, and an enlarged principal
view of the
part of fig. 11 a constricted by a circle. In fig l lb the existing or old
well 24 is indicated
by dotted lines and the new pipe 27 with autonomous valves 2 (of which only
one is
shown for clarity) is indicated by solid lines. Preferably a plurality of
autonomous
valves 2 are arranged along the length of the inserted pipe 27, and preferably
at least
one valve 2 in each pipe section defined between two successive constrictors
or swell
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packers 29, in order to create a substantially uniform inflow into the
recompleted well
24, 27 and thus an increased oil recovery.
An embodiment of a method according to the invention preferably comprises the
s following steps (not necessarily in said order) :
Providing an old well 24,
Providing a new pipe 27 comprising a plurality of autonomous valves 2 arranged
along the length of the pipe 27,
passing said pipe 27 into said old well 24 for recompleting the old well 24,
10 providing a plurality of swell packers or constrictors 29 along the well to
seal
between the inserted pipe 27 and the old well 24 and to define a plurality of
well
sections between two successive constrictors or swell packers 29 in each of
which
sections at least one autonomous valve 2 is to be located,
in order to create a substantially uniform inflow into the recompleted well
24, 27
and thus an increased oil recovery.
Further, the inserted pipe 27 preferably covers substantially the whole length
of the old
well 24.
In a most basic embodiment according to the invention, the pipe 27 just covers
a limited
length to be arranged at a very distinct location in the well 24 in which
breakthrough is
to be prevented, i.e. a distinct fraction in the formation or reservoir 26
intersectied by
the well 24. This location will then be isolated by providing one constrictor
or swell
packer 29 on each side of said fraction, and with just one autonomous valve 2
arranged
in such a single isolated section of the well.
With the valve or control device described in WO 2008/0048745 Al, due to the
constant volume rate, a much better drainage of the reservoir is thus
achieved. This
result in significant larger production of that reservoir.
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Even though the well 24 shown in figs. 9 -11 is a horizontal or lateral well,
it should be
emphazized that wells of any inclination, including vertical wells, are within
the scope
of the present invention as stated in the appended claims.
As also mentioned in the introductionary part of the description, the
autonomous valves
2 preferably are those described in WO 2008/0048745 Al and above, but any type
of
autonomous valve (e.g. electronically operated) is conceivable within the
context of the
invention.
