Note: Descriptions are shown in the official language in which they were submitted.
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TS 6166 PCT
PRODUCTION VALVE
The present invention relates to a wellbore system
comprising a main wellbore and a plurality'of branch
wellbores formed in an earth.formation. Such wellbore
system is generally referred to as a branched weilbore
system, or a multilateral wellboze system. It is to be
understood that in the context of the present invention
the welibore section extending from surface to the first
wellbore junction below surface is referred to as the
main wellbore, and the other wellbore sections are
referred to as branch-wellbores. For example, if the
wellbore system consists of a vertical wellbore extending
into-a reservoir and one branch extending from a junction
at the main wellbore into another reservoir, the part of
the vertical weilbore below the junction is referred to
as a branch weilbore, and the part of the vertical
wellbore above the junction is referred to as the main
wellbore.
In conventional multilateral weilbore systems it has
been tried to control fluid production by means of a
production valve at the wellhead located on top of the
main welibore. However.a problem inherent to the use of a
production valve at the wellhead is that selective
production from the different reservoirs is impossible.
Another problem occurs if one of the reservoirs is at a
= higher fluid pressure than another reservoir, whereby
hydrocarbon fluid flows from the high pressure reservoir
into the low pressure reservoir instead of to the
wellhead.
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A known wellbore system is described in
International patent application WO 96/30625. In the known
system valves are arranged at the branch points of a
multilateral well. If the fluid pressures in various well
branches are different some of the valves have to be
maintained in a half open position during an extensive
period of time, which causes high wear and erosion of the
valve. International patent application WO 97/37102
discloses another controllable downhole valve which is
subject to high wear if the valve is maintained half open
during a long period of time.
Accordingly, it is an object of some embodiments
of the invention to provide an improved wellbore system
which overcomes the problems of the prior art.
In accordance with a broad aspect of the
invention, there is provided a wellbore system formed in an
earth formation including at least one hydrocarbon fluid
reservoir, the wellbore system comprising a main wellbore
and a plurality of branch wellbores, each branch wellbore
extending from the main wellbore into the earth formation
and providing fluid communication between said at least one
hydrocarbon fluid reservoir and the main wellbore, each
branch wellbore being provided with a controllable
production valve for varying the flow rate of the stream of
hydrocarbon fluid, the valve comprising anchoring means for
fixedly anchoring the production valve in the branch
wellbore and control means for controlling the flow rate of
a stream of hydrocarbon fluid flowing from said at least one
reservoir via the branch wellbore into the main wellbore;
wherein the valve further comprises a critical flow choke
arranged in a flow passage so that the stream flows
therethrough and a closure member movable in a selected
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direction relative to the flow passage so as to at least
partially close the flow passage.
By the arrangement of the production valves
according to the invention in the branch wellbores it is
achieved that the flow rate of hydrocarbon fluid produced
from the different branch wellbores can be individually
controlled. Furthermore, the pressure drop across each
production valve can be controlled in a manner that the
pressure of the stream of fluid in the corresponding branch
wellbore downstream the production valve is such that flow
from one reservoir into another reservoir is prevented.
The invention will be described hereinafter in
more detail and by way of example with reference to the
accompanying drawings in which
Fig. 1 schematically shows an embodiment of a
production valve applied in the wellbore system according to
the invention;
Fig. 2 schematically shows a first detail of the
embodiment of Fig. 1;
Fig. 3 schematically shows a second detail of the
embodiment of Fig. 1;
Fig. 4 schematically shows a third detail of the
embodiment of Fig. 1;
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Fig. 5 schematically shows a detail of an alternative
power generator for use in a modified version of the
embodiment of Fig. 1; and
Fig. 6 schematically shows cross-section 6-6 of
Fig. 5.
In Fig. 1 is shown a production valve 1 fixedly
arranged within a casing 2 of a wellbore (not shown) by
means of a lock mandrel 4 which seals the production
valve 1 to the casing 2 and which is suitable to transmit
acoustic signals from the casing 2 to the production
valve 1. The wellbore forms one of a plurality of
wellbore branches of a branched wellbore system for the
production of natural gas. The branched wellbore system
is formed of a main wellbore and a plurality of branch
wellbores, each branch wellbore extending from the main
wellbore into a natural gas reservoir, whereby the
different reservoirs have mutually different fluid
pressures. The main wellbore is provided with a main
casing, and each branch wellbore is provided with a
branch casing similar to casing 2, each branch casing
being sealed to, and in metallic contact with, the main
casing.
The production valve 1 includes a tubular housing 6
provided with a controllable valve A, a valve actuation
module B, and a power generator C.
Fig. 2 shows in more detail the controllable valve A
having axis of symmetry 8, whereby at the upper side of
axis 8 the controllable valve A is shown in an open mode
thereof, and at the lower side of axis 8 the controllable
valve is shown in a closed mode thereof. The controllable
valve A includes a flow passage 10 and a closure
member 12 which is movable in axial direction relative to
the flow passage 10 between an open position in which the
closure member 12 leaves the flow passage open and a
closed position in which the closure member 12 closes the
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flow passage 10,. To'this end the closure member 12 is
provided with a frustoconical surface portion 14 which,
when the closure niember is in the closed position, is in
sealing contact with a correspondingly shaped seat
surface 16 surrounding the flow passage 10. The flow
passage is in fluid comnunicatiori with two inlet
openings 18 and an outlet 19', the inlet openings 18 being
arranged such that these are gradually covered by the
closure member 12 as the latter moves from the.open
position to the closed position thereof. A slotted
tube 20 is at one end thereof connected to the end of the
closure member 12 opposite the surface portion-14, which
tube 20 is at the other end thereof provided with an
annular shoulder 22. The housing is internally provided
with a stop ring 24 arranged so that the annular
shoulder'22 of the tube 20 contacts the stop ring 24 when
the frustoconical surface portion 14 of the closure
member 12 is only a very short distance away from the
seat surface 16. Thus, when the closure member 12 is
pushed against the seat surface 16, the tube 20 exerts a
tensile force to the closure member 12 and thereby acts
as a spring. An annular choke 26 is arranged in the flow
passage 10 such that fluid entering the housing 6 via the
inlet openings 18 flows via the annular choke 26 to the
outlet 19. A lock ring threadedly connected to the
housing locks the choke 26 in place.
Referring further to rig. 3 there is shown in more
detail the actuation module B which includes an electric
stepper motor 30 having a drive shaft 32 provided with a
first gear-wheel 34 driving a second gear-wheel 36. A
tubular spindle 38 extends in axial direction through the
second gear-wheel 36, the spindle 38 and the second gear-
wheel 36 having co-operating threads (not shown) by so
that when the second gear-wheel 36 is rotated, the
spi.ndle 38 moves in axial direction. A guide pin 40 is
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fixedly arranged in the housing by a fixing disc 42 such
that the guide pin extends in axial direction through the
tubular spindle 38 so as to guide the spindle 38 during
axial movement thereof. The end of the spindle 38 remote
from the fixing disc 42 is connected to the closure
member 12 by suitable connecting means (not shown). The
actuation module B furthermore includes a control
system 44 provided with a battery (not shown) for driving
the electric motor and a microprocessor (not shown)
having an acoustic sensor. The microprocessor has been
programmed to control operation of the stepper motor in
dependence of coded acoustic signals received by the
acoustic sensor. The various parts of the drive
assembly B are locked in the housing 6 by means of four
lock rings 46a, 46b, 46c, 46d.
Referring further to Fig. 4, the power generator C
includes a turbine having a housing member 48 fixedly
connected to the tubular housing 6 by thread
connection 50. A shaft 52 extends concentrically through
the housing member 48, which shaft is rotatably arranged
in a ceramic bearing 53 and is provided with an
impeller 54 arranged at the end of the shaft 52 opposite
the actuation module B. The other end of the shaft 52 is
provided with a thrust bearing 56 preventing axial
movement of the shaft 6 relative to the tubular
housing 6. A plurality of magnets 58 are fixedly
connected to the shaft 52 at regular angular intervals
along the circumference of the shaft 52. A glass sealed
coil 60 is fixedly arranged in the housing member 48 and
extends around the magnets 58, the coil being
electrically connected to the control system in a manner
that the coil 60 charges the battery when the shaft 52
rotates.
In Figs. 5 and 6 is shown an alternative power
generator 60 for incorporation in the production valve of
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Fig. 1 instead of the power generator C. The alternative
power generator 60 forms a fluidic electrical generator
comprising a generator body 62 including an outer body
part 62a and an inner body part 62b fixedly arranged in
the outer body part 62a. The outer body part 62a is
provided with a thread connection 64 for screwing the
power generator 60 into the housing 6 and with a fluid
chamber 66 having a fluid inlet 68 and two fluid
outlets 70, 72 extending in diverging directions. A
magnetic oscillator 74 is arranged in the fluid
chamber 66, the oscillator 74 being provided with two
supports 76 of triangular cross-sectional shape, each
support having an edge resting in a groove (not shown)
provided in the inner body part 62b in a manner allowing
angular oscillation of the oscillator 74 relative to said
edge. Thus the oscillator divides the fluid chamber 66 in
two fluid passages 66a, 66b along opposite sides of the
oscillator 74. A feed-back conduit 79 provides fluid
communication between the fluid passages 66a, 66b. Two
electric coils 80, 82 are arranged in the outer body
part 62a, which coils extend around the magnetic
oscillator 74 are provided with electric connections (not
shown) for connecting the coils 80, 82 to the control
system in a manner that the coils 80, 82 charge the
battery when the oscillator 74 oscillates in the fluid
chamber 66.
Each one of the branch wellbores is provided with a
production valve similar to the production valve 1,
except that the inner diameters of the annular chokes are
different for the different production valves. The
selection of said different inner diameters is discussed
hereinafter in relation to normal operation of the
production valve 1.
During normal operation of the embodiment of Fig. 1
natural gas is produced simultaneously from the different
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reservoirs, whereby for each reservoir a stream of
produced gas flows through the respective branch wellbore
into the main wellbore and from there to a production
facility (not shown) at surface. Thus the different
streams commingle in the main wellbore so as to form a
main stream of produced gas. The inner diameters of the
chokes 26 of the different production valves 1 are
selected such that, with each controllable valve A in the
open mode, the gas pressures in the different streams
downstream the respective chokes 26 are about equal. It
is thereby prevented that gas from a reservoir at a
relatively high pressure flows into a reservoir at a
relatively low pressure.
As long as it is desired to produce gas at a maximum
flow rate from the wellbore system, each controllable
valve A of a respective production valve 1 is kept in the
open mode. In this mode produced gas flows via the inlet
openings 18 into the flow passage 10 at maximum flow
rate. As the gas flows along the impeller 54 the latter
is rotated, resulting in rotation of the shaft 52 and the
magnets 58. An electric current is thereby generated in
the coil 60, which current flows via the control system
to the battery and thereby charges the battery. Since
critical flow of the gas does not occur at the location
of the closure member 12, but instead in the choke 26,
the closure member 12 is not subjected to enhanced
erosion as a result of gas flowing at critical flow rate
along the closure member.
When it is desired to decrease production of gas from
one or more of the branch wellbores a coded acoustic
signal representing an instruction to move the closure
member 12 a selected distance into the flow passage 10,
is generated in the main casing. This can be done, for
example, by inducing a sequence of metallic object
impacts on the main casing. The acoustic signal travels
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via the main casing, the branch casing 2 and the lock
mandrel 4 to the acoustic sensor which induces the
microprocessor to control the stepper motor 30 so as to
rotate the drive shaft 32 a selected number of
revolutions commensurate with the required movement of
the closure member 12. As a result the second gear-wheel
rotates and thereby moves the spindle 38 and the closure
member 12 over said selected distance into the flow
passage 10. The flow openings 18 are thereby partly
covered so that gas can only flow at a reduced flow rate
via the inlet openings 18 to the outlet 19.
When it is desired to stop production of gas from one
of the branch wellbores, the same procedure as described
with reference to decreasing production of gas is
followed, except that the coded acoustic signal now
represents an instruction to move the closure member 12
against the seat surface 16 of the housing 6. As a result
the closure member 12 is moved against the seat
surface 16 so that the controllable valve A is in the
closed mode. In this position the annular shoulder 22 of
the tube slotted 20 contacts the stop ring 24, and the
tube 20 exerts a tensile force to the closure member 12
biasing the closure member 12 away from the seat
surface 16.
When it is desired to bring the closure assembly back
to the open mode, a coded acoustic signal representing an
instruction to move the closure member 12 to the open
position thereof is generated in the main casing. Initial
movement of the closure member 12 from the closed
position to the open position thereof is promoted by the
tensile force from the slotted tube 20.
Normal operation of the modified version of the
embodiment of Fig. 1 is similar to normal operation of
the embodiment of Fig. 1, except that electric current is
generated by the alternative power generator 60 instead
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of the power generator C. Namely, gas which enters the
fluid chamber 66 via fluid inlet 68 flows through the
fluid passages 66a, 66b along the oscillator 74 and
further through the fluid outlets 70, 72. The feed-back
conduit 79 causes a Coanda effect to occur in the fluid
passages 66a, 66b causing flow of gas into the
outlets 70, 72 in an alternating manner. As a result
angular oscillation of the magnetic oscillator 74 occurs
around the support edges of the supports 76. An electric
current is thereby generated in the coils 80, 82, which
current flows via the control system to the battery and
thereby charges the battery.
