Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM FOR SEALING AN ANNULAR SPACE IN A WELLBORE
The present invention relates to a system for sealing
an annular space between a tubular element extending into
a wellbore and a cylindrical wall surrounding the tubular
element, wherein a control line for controlling a
downhole device extends in longitudinal direction along
the tubular element. In the field of hydrocarbon fluid
production from a wellbore it is generally required to
seal the annular space formed between a production
conduit extending into the wellbore and a surrounding
casing or liner, or between the casing or liner and the
wellbore wall. In such applications many times one or
more control lines for power transmission or signal
transmission extend through the annular space. Various
packers have been applied to provide such sealing
functionality. Some of these have terminal connections at
either end for connecting the control lines to the
packers. Although such packers may provide adequate
sealing capability, it has been experienced that assembly
of the packers and control lines to the tubular element
at a well site can be difficult.
US patent No. 6,173,788 discloses a packer for
sealing an annular space between a tubular element
extending into a wellbore and a wellbore casing, wherein
a control line for controlling a downhole device extends
in longitudinal direction through a recess formed in the
outer surface of the packer. It is a drawback of the
known system that the control line needs to involve bends
at both ends of the packer since the recess is radially
displaced from the outer surface of the tubular element.
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Another drawback of the known system occurs if the
tubular element is provided with a plurality of the known
packers mutually spaced along the tubular element.
Generally such packers are pre-assembled to respective
portions of the tubular element, termed "subs", which are
to be connected to adjacent portions of the tubular
element by threaded connections. As a result, upon
assembly of the tubular element, it may occur that the
recesses of the respective packers become non-aligned.
It is an object of the invention to provide an
improved system for sealing an annular space between a
tubular element extending into a wellbore and a
cylindrical wall surrounding the tubular element, which
system overcomes the drawbacks of the prior art.
In accordance with the invention there is provided a
system for sealing an annular space between a tubular
element extending into a wellbore and a cylindrical wall
surrounding the tubular element, wherein a control line
for controlling a downhole device extends in longitudinal
direction along the tubular element, the system
comprising an annular seal layer extending around the
tubular element, the seal layer having an inner surface
provided with a recess for radially receiving the control
line, the seal layer being provided with a longitudinal
slit defining a pair of opposite longitudinal edges which
are movable relative to each other between an open
position wherein the seal layer can be radially applied
to the tubular element, and a closed position wherein the
seal layer extends around the tubular element.
It is thereby achieved that the control line can be
extended along the tubular element before the seal layer
is radially applied to the tubular element thereby
obviating the need to include bends in the control line.
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In case the tubular element is provided with a plurality
of seal layers, it is furthermore achieved that the seal
layers can be assembled to the tubular element such that
the recesses of the respective seal layers are suitably
aligned with the control line.
It is to be understood that the control line can
function to transmit signals to or from the downhole
device, for example to actively control the downhole
device or to transmit measured signals, or to transmit
power to or from the downhole device.
Preferably the system further comprises fastening
means for fastening the seal layer in the closed position
thereof to the tubular element.
The system of the invention can suitably be applied
in combination with an inflow control device for
controlling inflow of fluid from the earth formation into
the tubular element, wherein the control line is arranged
to control the inflow control device.
Suitably each seal layer includes a material
susceptible of swelling upon contact with a selected
fluid. Thus the seal layer is activated by contact with
the selected fluid (for example water or hydrocarbon
fluid), which implies that it is no longer required to
activate the seal layer by mechanical or hydraulic means.
This is an important advantage since such swelling seat
layers can be made significantly longer than conventional
packers.
In a preferred embodiment the system of the invention
includes a plurality of said seal layers and a plurality
of said inflow control devices, the seal layers and the
inflow control devices being arranged in alternating
order along the tubular element. The annular space is
thereby divided into a number of compartments whereby
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cross-flow of fluid between different compartments is
substantially prevented, and inflow of formation fluid
from each compartment into the tubular element is
controlled by the respective inflow control device in
communication with the compartment.
In order to prevent or reduce formation water
bypassing each seal layer through the rock formation
opposite the seal layer, it is preferred that the seal
layer is significantly longer than a conventional packer.
For example, in a preferred embodiment the length of the
seal layer substantially corresponds to the length of the
respective tubular joint to which the seal layer is
applied. In this respect it is to be understood that the
seal layer suitably is assembled from a plurality of
short seal layer sections positioned adjacent each other
along the tubular joint. Seal layer sections having a
length of between 0.5 - 2.0 meter, for example about 1
meter, allow convenient handling on the drilling rig
floor.
The invention will be described in more detail
hereinafter by way of example, with reference to the
accompanying drawings in which:
Fig. 1 schematically shows a wellbore in which an
embodiment of a conduit and seal layer used in the method
~5 of the invention is applied;
Fig. 2A schematically shows a cross-sectional view of
the conduit of Fig. 1;
Fig. 2B schematically shows the seal layer before
application to the conduit:
Fig. 3 schematically shows a longitudinal section of
the seal layer when applied to the conduit
Fig. 4 schematically shows a longitudinal section of
seal layer when applied to the conduit; and
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Fig. 5 schematically shows detail A of Fig. 4.
In the drawings like reference numerals relate to
like components.
Referring to Fig. 1 there is shown a wellbore 1
formed in an earth formation 2 for the production of
hydrocarbon fluid, the wellbore 1 having a substantially
vertical upper section 1a and a substantially horizontal
lower section 1b extending into a zone 3 of the earth
formation from which hydrocarbon fluid is to be produced.
The earth formation zone 3 is fractured whereby there is
a risk that water from other formation zones (not shown)
enters the lower wellbore section 1b via fractures in
formation zone 3. The upper wellbore section 1a is
provided with a casing 4 cemented in the wellbore by a
layer of cement 5, and a wellhead 6 is arranged on top of
the wellbore 1 at surface 7. A production liner 7 extends
from the lower end part of the casing 4 into the
substantially horizontal wellbore section 1b. A
production tubing 9 provides fluid communication between
the wellhead 6 and the production liner 7, the production
tubing 9 being suitably sealed to the production liner 7
by packer 10.
The production liner 7 is provided with a plurality
of inflow control devices in the farm of inflow control
valves ~12, 13, 14, 15 spaced along the length of the
liner 7. Each inflow control valve 12, 13, 14, 15 is
electrically connected to a control center 16 at surface
via a set of control lines 18 extending along the outer
surface of the production liner 7 and the inner surface
of the casing 4, so as to allow each inflow control
valve 12, 13, 14, 15 to be opened or closed from the
control center 16.
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A plurality of seal layers 20, 22, 24, 26 is arranged
in the annular space 28 between the production liner 7
and the wall of wellbore section 1b, wherein the seal
layers 20, 22, 24, 26 and the inflow control valves 12,
13, 14, 15 are arranged in alternating order along the
production liner 7. Each seal layer 20, 22, 24, 26
includes a material susceptible of swelling upon contact
with water from a water-bearing layer of the earth
formation 2, such material preferably being HNBR
elastomer.
Referring to Figs. 2A and 2B there is shown a cross-
section of the production liner 7 and the seal layer 20
before application of the seal layer to the production
liner 7. The set of control lines 18 is enclosed by a
cover member 30 which is fastened to the outer surface of
the production liner 7 by suitable fastening means (not
shown). The seal layer 20 has a longitudinal slit 31
defining a pair of opposite longitudinal edges 32, 34
allowing the seal layer 20 to be movable between an open
position (as shown in Fig. 2) in which said edges 32, 34
are displaced from each other so as to allow the seal
layer 20 to be radially applied in the direction of
arrow 35 to the production liner 7, and a closed position
(as shown in Fig. 3) in which said edges 32, 34 are
located adjacent each other so as to allow the seal
layer 20 to substantially enclose the production liner 7.
Furthermore, the seal layer 20 is provided with pairs of
bores 36, 38 spaced at regular longitudinal distances
along the seal layer 20. The bores 36, 38 of each pair
are formed at the respective longitudinal edges 32, 34,
and are formed so as to allow a bolt (referred to
hereinafter) to be extended through the aligned bores 36,
38 in order to fasten the seal layer 20 to the production
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liner 7. The seal layer 20 is provided with a
longitudinal recess 40 formed at the inner surface
thereof for accommodating the set of control lines 18 and
the cover member 30.
In Fig. 3 are shown the production liner 7 and the
seal layer 20 after the seal layer 20 has been radially
applied to the production liner 7 so as to enclose the
production liner 7. The seal layer 20 is clamped to the
conduit by a plurality of bolt/nut assemblies 42, each
bolt/nut assembly 42 extending through a corresponding
pair of the bores 36, 38.
Referring to Figs. 4 and 5 there is shown the seal
layer 20 and the production liner 7 in longitudinal
section. The production liner 7 is assembled from a
number of tubular joints 44 having a standard length of
about 10 m (30 ft), whereby each seal layer 20, 22, 24,
26 extends substantially the full length of the
respective tubular joint 44 to which the seal layer 20 is
applied. Each such joint 44 is provided with respective
connector portions 48 at opposite ends thereof for
interconnecting the various joints 44. The outer surface
of the annular seal layer 20 is provided with a plurality
of annular recesses 46 regularly spaced along. the length
of the seal layer 20.
During normal operation, the production liner 7 is
assembled from the respective tubular joints 44 and from
respective short sections of tubular element (termed
"subs"; not shown) which include the respective control
valves 12, 13, 14, 15. Assembly occurs at the well site
in progression with lowering of the production liner 7
into the wellbore 1. The set of control lines 18 together
with the cover member 30 is fed to the production
liner 7, and fixedly connected thereto, simultaneously
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with lowering of the production liner 7 into the
wellbore 1. Each seal layer 20, 22, 24, 26 is then
radially applied to the production liner 7 at the desired
location thereof in a manner that the recess 40 encloses
the cover member 30 (and hence the control lines 18). The
seal layer 20 is then moved to its closed position so as
to enclose the tubular joint 44, and fixed to the tubular
joint 20 by fastening the bolt/nut assemblies 42
extending through the respective pairs of bores 36, 38.
The other seal layers 22, 24, 26 are assembled to the
respective tubular joints 44 in a similar manner. The
production liner 7 is installed in the wellbore 1 such
that the seal layers 20, 22; 24, 26 and the inflow
control valves 12, 13, 14, 15 are located in the earth
formation zone 3 containing hydrocarbon fluid.
After the wellbore 1 has been suitably completed,
hydrocarbon fluid is allowed to flow from earth formation
zone 3 into the wellbore section 1a and from there via
the inflow control valves 12, 13, 14, 15 into the
production liner 7 and the production tubing 9. In the
event that formation water enters the annular space
between the production liner 7 and the wellbore wall, one
or more of the seal layers 20, 22, 24, 26 which become
into contact with the formation water will swell until
further swelling is prevented by the wellbore wall. The
annular recesses 46 enlarge the contact area of the seal
layers with formation water, thereby promoting swelling
of the seal layers. Once the swollen seal layers 20, 22,
24, 26 become compressed between the production liner 7
and the wellbore wall, further migration of the formation
water through the annular space is prevented. In order to
determine the location of water inflow, a test is carried
by successively opening and/or closing the inflow control
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valves 12, 13, 14, 15 and simultaneously measuring the
inflow of formation water. The location of inflow is
determined from an observed reduced (or eliminated)
inflow of formation water as a result of closing of one
or more specific inflow control valves 12, 13, 14, 15.
Once the location of water inflow has been determined,
one or more of the inflow control valves) 12, 13, 14, 15
at the location of inflow are closed so that inflow of
formation water into the production liner 7 is thereby
eliminated.
Swelling of each seal layer 20, 22, 24, 26 also
results in adequate sealing of the seal layer against the
production liner 7 and the cover member 30 so as to.
prevent fluid migration between the seal layer and the
production liner or the cover member 30.
Instead of allowing the seal layer to swell by virtue
of contact with water from the earth formation, such
swelling can be triggered by bringing the seal layer into
contact with water-base wellbore fluid pumped into the
wellbore.
Furthermore, the seal layer can be made of a material
susceptible of swelling upon contact with hydrocarbon
-. fluid, such as crude oil or diesel. In such application
the seal layer can be induced to swell upon contact with
hydrocarbon fluid produced from the wellbore.
Alternatively the seal layer can be induced to swell by
pumping hydrocarbon fluid, such as diesel or crude oil,
into the wellbore. The latter procedure has the advantage
that premature swelling of the seal layer during lowering
of the tubular element into the wellbore, is prevented.
Also, a hybrid system can be applied including seal
layer sections susceptible of swelling upon contact with
hydrocarbon fluid, and seal layer sections susceptible of
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swelling upon contact with water from the earth
formation.
