Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND APPARATUS FOR WELL COMPLETION INSTALLATION
MONTTORING AND CONTROL
The present invention relates to methods and apparatus having application in
the field
of well construction, completion, monitoring and control. In particular, the
invention
provides methods and apparatus that are particularly useful in oil or gas
wells situated
in weakly consolidated or unconsolidated formations requiring screen
completions.
Traditional methods of completing hydrocarbon wells involve cementing a casing
or
liner (typically made of steel) into the well and then forming perforations at
locations
in the well believed to be situated in producing formations extending through
the
casing and cement into the formation to provide paths along which fluids can
flow
into the well. These flow paths can often be improved by fracturing or other
stimulation methods well known in the industry. Once the well has been
completed, it
is relatively easy to re-enter the well with measurement tools and make
measurements
near the regions in which there are perforations to determine the nature and
characteristics of the fluids flowing into the well from the formation at that
point.
Also, it is possible to seal off the perforations if it is discovered that
undesirable fluids
flow is encountered, for example high volume fractions or flow rates of water
entering
the well at that point. All of these are generally possible because the
perforations
constitute a relatively small extent of the well and the presence of the
otherwise solid
casing allows portions of the well to be sealed while well treatments are
taking place.
However, there are certain, well-known situations in which this traditional
approach
to well completion cannot be used, in particular when the producing formation
is
weakly consolidated or unconsolidated, such as sand, or where the producing
section
of the well has been drilled in a long reach horizontal section. In the first
case, the
formation is too weak to allow casing to be installed, or for permanent
perforations
tunnels into the formation to be formed. The only effective manner to allow
fluids to
pass into the well is to provide a highly perforated or apertured liner, often
called a
"screen" or "sand screen" or "gravel pack" to be placed in the well in the
formation of
interest. In the past, such wells have often been left without any form of
liner,
sometimes called "barefoot completion" or have had slotted liners or screens
inserted
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into the well but not secured by cement, similar to the approach to that used
in
unconsolidated formations as described above.
One known form of screen useful in unconsolidated formations or long reach
horizontal wells is shown in Figures l and 2. The screen is formed in sections
having
a base tube 12 which is provided with holes 14 along its length and around its
circumference. The screen itself is formed by a triangular section wire 16
(base
outermost) that is wound around the outside of the base tube 12 between small
collar
sections 18 provided at each end of the base tube 12 and separated from the
outer
surface of the base tube by longitudinal splines 22 secured to the outer
surface of the
base tube so as to define an axially segmented annular chamber 24 around the
base
tube 12. The wire screen 16 is wound in such a way that a small space is left
between
adjacent windings that is small enough to prevent small particles such as sand
entering the chamber 24 or base tube 12 yet not so small as to inhibit the
flow of
fluids into the well. While this construction allows flow in the radial
direction (i.e.
into the base tube, it also allows axial flow inside and outside the screen
with little or
no restriction. This can bring certain problems when it comes to monitoring
the
production in the well or treating the well or formation with treatment
fluids. In the
case of monitoring or measurement, since there can be flow into the well at
almost
any point and since there can be flow outside the base tube in axial
directions (i.e. in
the chamber 24), it is very difficult to relate a measurement made at any
particular
point in the well to the behaviour of a specific region of the formation
outside the
well. In the case of well treatment, pumping a fluid inside the base tube
cannot
guarantee placement in a zone of interest since there is nothing to force the
fluid into
that zone. Even the use of coiled tubing to deliver treatment fluids cannot
guarantee
proper placement or treatment.
Various forms of screen-type completions are known. US 5,435,393 describes one
particular form in which the completion is divided into sections, each of
which is
provided with a controllable restriction in a passage communicating between
the
annular chamber and the inside of the base pipe. This restriction is used to
control the
pressure difference between the formation and the inside of the base pipe so
as to
maintain a given pressure drop along the completion.
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Long horizontal producing sections are often found in offshore wells, either
singly or
in mufti-lateral completions. Offshore wells can be completed as subsea (i.e.
the
wellhead is located on the sea bed) or platform (i.e. the wellhead is located
on a
platform at the sea surface. Subsea wells are a significantly less expensive
method of
developing oil and gas fields than using platforms, because the platform
itself is a
significant portion of the total cost. However a disadvantage of subsea
wellheads is
that it is very expensive to gain access to the well once it is completed. For
dry
wellheads on land or on platforms, interventions are made to acquire data
about the
reservoir and producing fluids, and about the completion itself. The data
obtained is
new data not known at the time of the original well design, and can be used to
plan
further interventions to modify the flow of fluids from the reservoir, for
example
shutting zones which produce water. The huge expense and operational risk of
performing equivalent interventions in subsea wells means they are rarely
done.
There are alternative methods of changing the flow of fluids from a reservoir
without
a physical intervention. Chemical treatments can be injected along the subsea
flowline down the well, or along permanently installed subsea chemical
injection
lines. This utilizes the flowline linking the hydrocarbon gathering point and
the
reservoir. However, the absence of data on the reservoir identifying the
specific zones
needing treatment means reservoir treatments in subsea wells are also rarely
done. It
is also difficult to position a chemical treatment accurately in any
particular zone.
This limits most subsea chemical treatments to fluids which have a preference
for any
zone producing a specific unwanted fluid, however such indiscriminate chemical
treatments risk reducing the productivity of all zones. Other chemical
treatments are
intended to treat the entire completion, for example scale treatments. However
it is
not currently possible to verify whether these chemical treatments have
reached the
entire completion. The lack of interventions to log, and the difficulty in
verifying the
placement of chemical treatments in subsea wells results in a much lower
ultimate
recovery than a comparable field developed from a platform.
One recent development in the field of monitoring wells after completion and
during
production is that of permanent monitoring using sensors foxed at locations in
the
well to provide continuous or repeated measurements. However, if it is desired
to
obtain accurate information about the contribution of each part of the
completion to
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the overall production from the well, it is currently necessary to provide
multiple
measurements in each part of the well to allow accurate determination of which
part
of the well is responsible for significant changes in its production, which
can be
expensive and difficult to achieve given the power and space constraints of
the
downhole environment.
The present invention attempts to provide solutions for some or all of the
problems
identified above in relation to the construction, installation and monitoring
of
completions and the conducting of well treatment operations.
In accordance with a first aspect of the invention, there is provided a method
of
monitoring fluid production in a well, comprising:
measuring over time local parameters at a series of locations along the well,
each local measurement being responsive to changes in the parameters in the
region in
which it is made;
measuring fluid properties in the well over time downstream from the series of
locations; and
,determining changes in the local measurements and in the measured fluid
properties; and
identifying locations of the formation contributing to the changes in the
measured fluid properties by determining corresponding changes in the local
measurements.
By combining a distributed measurement made within the formation and a
measurement of the fluids in the well downstream of the producing formation,
it is
possible to identify the location in the well at which a change has occurred
in the
produced fluids.
It is preferred that each local measurement corresponds to a discrete location
at which
formation fluids enter the well.
The local parameter measurement can be any parameter that is affected by
changes in
the fluids flowing between the formation and the well at this location. For
example,
resistivity, conductance, temperature, pressure or chemical composition
parameters
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might be measured. The sampling rate of the local measurements is preferably
relatively high, particularly with respect to the flow rate of fluids in the
well, such that
the time at which a change is measured at a specific location can be'
identified relative
to corresponding measurements at other locations.
The fluids properties measured downstream of the local measurements are
typically
flow rates, preferably volumetric flow rates. The flow rates measured at the
downstream location are used to quantify change of flow into the well whose
particular location has been identified by the local measurement. Also, by
determining
the physical location of a local sensor and determining the time between a
change
being measured at the local sensor and a measured at the downstream location,
the
flow rate determined at the downstream location can be confirmed or
calibrated.
In accordance with a second aspect of the invention, there is provided
apparatus for
completing a well, comprising:
an base pipe; and
an permeable screen surrounding the base pipe and defining a chamber outside
the base pipe and inside the screen;
wherein the base pipe is provided with an apertured portion of limited axial
extent
providing fluid communication between the chamber and the inside of the base
pipe
such that fluid entering the chamber through the permeable screen passes into
the base
pipe only via the apertured portion; and, in use, the screen and apertured
portion cause
a relatively low pressure drop between the outside of the apparatus and the
inside of
the base pipe.
In accordance with a third aspect of the invention, there is provided a method
of
completing a well, comprising:
installing a series of tubular members in the well connected in an end-to-end
arrangement, each tubular member comprising an elongate base pipe and an
elongate
screen surrounding the base pipe and provided with multiple apertures
distributed
along its length, the screen and the base pipe together defining an annular
chamber
between them,
wherein the base pipe is provided with an apertured portion of limited axial
extent
providing fluid communication between the chamber and the inside of the base
pipe
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such that fluid entering the chamber through the permeable screen passes into
the base
pipe only via the apertured portion.
Preferably, the base pipe has a series of longitudinal splines formed around
its outer
surface, the splines acting to segment the chamber into a series of axial
segments.
These splines can be formed by wires fixed to the outer surface of the base
pipe, for
example.
It is particularly preferred that a collar section is provided on the base
pipe near to the
apertured portion, the collar defining a manifold that communicates with the
annular
chamber and the apertured portion such that fluid flowing from the annular
chamber
into the base pipe flows through the manifold. In one embodiment, the collar
is
located at one end of the base pipe and a simple collar is located at the
other end, the
two collars defining the ends of the permeable screen and annular chamber.
The collar can also include a sensor system and/or a sealing system for
closing off
flow through the apertured portion. The sensor system and/or sealing system
can be
provided with connections for a data and power network.
In on particular embodiment, the apertured portion of the base pipe is located
in a part
connecting two screen sections, the collar is located at the end of one of the
two
screens and is connected to the connecting part by the manifold.
The collar can be provided with ports between the annular chamber and the
manifold
and the base pipe provided with one or more apertures connecting to the
manifold.
In accordance with a fourth aspect of the invention, there is provided a
method of
treating a well that has been completed as described above, comprising pumping
a
treatment fluid from the surface into the well while measuring local
parameters in
each tubular member; detecting the arrival of the treatment fluid from the
measurement of local parameters; and ceasing pumping so as to leave the
treatment
fluid in a region of the well to be treated.
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In accordance with a fifth aspect of the invention, there is provided a
completion
system, comprising:
a tubular member for location in a well, the member including at least on
opening allowing communication between the interior and exterior of the
member;
and
a closure system located adjacent the or each opening and including a source
of stored energy which, on activation, operates to close the or each opening.
It is preferred that the openings in the tubular member are confined to a
region of
limited axial extent. It is particularly preferred that the openings are near
a collar on
the outside of the tubular member. In one such arrangement, the closure system
can be
located in or on a manifold.
The closure system can comprise a reservoir of expandable fluid and an
activator. On
operation, the activator ruptures the reservoir and allows the fluid to enter
the
manifold where it expands to prevent fluid flowing therethrough.
Alternatively, the
closure system can comprise a heating system for activating a sealing fluid
pumped
into the manifold from the surface.
It is particularly preferred that the closure system is reversible to allow
reopening
The present application will now be described by way of example, with
reference to
the accompanying drawings, in which:
Figure 1 shows a prior art sand screen;
Figure 2 shows a detail of the screen shown in Figure 1;
Figure 3 shows a sand screen incorporating embodiments of the invention;
Figures 4 a - c show cross sections of the screen of Figure 3;
Figure 5 shows a schematic view of a well completed using the sand screen
shown in
Figure 3;
Figure 6 shows an alternative form of well completion to that shown in Figure
5;
Figure 7 shows plots of measurements made over time for a well completed as
shown
in Figure S;
Figure 8 shows schematically a method of well treatment according to an
embodiment
of the invention; and
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Figure 9 shows a sealing system according to an embodiment of the invention.
Referring now.to the drawings, the sand screen shown in part in Figure 3 is
similar to
that of Figures 1 and 2 and corresponding parts are given corresponding
reference
numbers in the 100 series. The screen 110 shown in Figure 3 is also formed in
two
sections: a base pipe 112 and a wire screen 116 extending between collar
sections 118
on the outside of the base pipe 112 defining a chamber 124 (Figure 4a). The
collar
section 118' is formed on a connector section 112' of the base pipe 112 and is
provided with an end plate 130 having ports 132 which connect the chamber 124
to a
manifold 134 within the collar (Figure 4b). The ports 132 are provided between
the
wires or splines 122 supporting the screen 116. The other end of the screen
116 is
connected to a simple end plate (not shown).
The manifold 134 is in the form of a shroud which encircles the base tube 112'
(Figure 4 c) and directs the fluids into a delivery pipe 136 which is
connected to an
aperture 138 in the base pipe 112' such that the only fluid communication path
between the chamber 124 and the inside of the base pipe 112' is via the ports
132,
manifold 134 and aperture 138.
The ports 132, manifold 134 and aperture 138 are dimensioned such that there
is
essentially no restriction of flow of fluids from the screen 116 into the base
pipe 112,
i.e. there is essentially no pressure drop between the screen 116 and the
inside of the
pipe 112', the inner diameter of the base pipe 112 being the only significant
restriction to flow from the formation into the well.
The collar is also provided with a sensor package and associated electronics
140
which are connected to a power and data communication system 142 running along
the well from the surface. The sensor can be any one of a number of permanent
or
long term sensors that can be installed in a well and which are responsive to
fluid or
other environmental parameters such as pressure or temperature, chemical
composition, conductivity or dielectric, or electrodes responsive to
resistivity or
inductance either in the formation itself or the fluids entering the screen.
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The manifold 134 also includes a sealing system 144 that is connected to the
same
data and power network 142 as the sensor system 140. The operation of the
sealing
system 144 is described in more detail below.
Figure 5 shows an example of a well completed using screens of the type shown
in
Figure 3. The well shown in Figure 5 is an offshore, subsea well (well head
located on
sea bed). The well extends vertically downwardly 154 from the well head 150
and the
proceeds in a substantially horizontal section 156 through the producing
reservoir
158. The vertical section of the well is completed in a conventional manner
with steel
casing 160 cemented into the borehole. The horizontal section 158 is completed
using
a series of screens 110 of the type described above connected in an end to end
manner. The sensors 140 and sealing systems 144 are connected to a network 148
running through the well and connected to a power and data acquisition unit
162 at
the well head 150. The effect of installing the screens described above is to
divide the
well into a series of finite producing elements as all of the fluids entering
a given
screen enter the base pipe at a single location, that of the aperture
connecting to the
manifold. Thus each screen has the effect of focussing the production in that
region
into a specific point in the well.
A
A flow measurement device 164 is positioned in the well downstream of the
horizontal section 158. This device can be any suitable flow meter such as a
venturi
device, spinner, electromagnetic device or combination of these. One
particularly
preferred form of meter is the EWM Electric Watercut Meter of Schlumberger
that
comprises a capacitive measurement system and an electromagnetic measurement
system downstream of a venturi. Such a meter can measure flow rates for
mixtures of
0 - 100% water.
A similar completion with an alternative form of sensor system is shown in
Figure 6.
In this case, instead of the discrete sensors in each collar, the system
comprises a
distributed continuous sensor 166, particularly a distributed fibre optic
temperature
sensor which is installed in a U tube extending along the well. Such a system
is
available from Sensa of UK and is operated from the well head without the need
to be
connected to the data and power network 148 downhole. Such a system can be
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operated to give discrete measurements at any given location in the well, in a
similar
manner to a series of discrete sensors.
In use, the flow meter 164 measures the total flow rate of the fluids produced
from the
well. Any changes in production are reflected in this flow rate measurement.
However, from this measurement alone, it is not possible to identify where the
event
causing the change in production has taken place and so is not useful for
identifying
selective treatment options if the change is an undesirable one, such as water
breakthrough. Clearly a change in production of fluids for a given screen or
screens
will be reflected in the measurements made by the associated sensors 140
located in
the collars (or the associated discrete measurement is a distributed sensor is
used) but
in view of the restrictions on space and power, it is typically not possible
to provide a
full multiphase flow sensor in each collar and so it is essentially impossible
to obtain
accurate quantitative measurements in each collar to identify the particular
change in
production that is detected by the flow meter downstream. Most of the sensors
that
can be installed in the screen are essentially non-quantitative in respect of
flow, or are
of unreliable or unknown accuracy and therefore very difficult to interpret.
However,
each sensor will be sensitive to the fact that a change in production is
occurring and
therefore the locations) of the changing production can be identified by
correlating a
detected change in the sensors) one or more screens with a measured change in
the
production from the well as measured by the flow meter.
By simultaneously measuring the local parameters in the reservoir on the
screens and
the fluid properties downstream, it is possible to use the qualitative local
measurement
to identify the location of the change of fluid flow into the well.
Because it is possible to identify the location of the change in production to
within
one or two screen lengths, it is possible to design well treatment actions
that address
only this region rather than all regions as has been the case in the past.
Where a well
includes multilateral completions from a main well, a flow meter can be
installed in
each completion to provide the benefits outlined above.
In Figure 7, there is shown a plot of the reading from the downstream flow
meter in
terms of % water (W%) in the flowing fluids vs. time (T). An array of
instrumented
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screens of the type described above (S, - S,4) is monitored over the same time
period
with respect to the resistivity measured at each screen. What is monitored
over time
for the array is. the change 0 in the measurement rather than the absolute
measurement
itself. At time T,, the flow meter shows an increase in water cut of the
produced
fluids. An examination of the screen measurements for the same time period
shows
that the readings from screen S4 changed during that time period indicating
that water
influx started in the region of screen S4. At time T2, the flow meter
indicated an
increase in water cut. In this case, the sensor at screen S7 showed a change,
indicating
the location of new water influx. A further change in water cut occurred at
time T3
and is indicated on screen sensor S,2. In each case, it is a change 0 in the
measurement from a screen sensor that is needed to identify the location of
the event
causing the change, not the absolute measurement from that sensor. At all
other times
or other locations, the sensors have a substantially constant reading
suggesting that
there has been no change in the fluids produced.
In the case described above, the increase in water cut after times T, and TZ
might still
be sufficiently low that remedial action in the well is not justified, but
with the
increase at T~ might then increase the water cut to a degree that it will be
worthwhile
performing a well treatment to shut off the water influxes and allow the well
to
continue at low water cut production. Knowing the location of the water
breakthrough
allows a treatment to be designed which only addresses these locations and
allows the
other parts of the well to continue production unchanged.
While the example given above uses the example of increased water production
as the
change detected, it could be any change in production, for example a change in
the
type of oil produced at a given screen might also be detected. This can be
important in
flow assurance, especially for wells with long subsea tie-backs.
The construction of the screens described above also allows treatments to be
provided
at the level of each individual screen because flow into the base pipe is all
focused
through the chamber. Thus it is possible to exercise effective control at the
individual
screen level to modify flow from the formation into the well. For example, in
the case
described above, water breakthrough only occurs at screens S4, S7 and S,Z.
Therefore,
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shutting off those screens will allow the well to continue producing oil only
(and
hence avoid the need for separators or the like) while only reducing the
production
from the well marginally. This can be repeated each time water breakthrough
occurs
until the reduction in overall production is sufficient to justify
installation of
separators and producing the well as a mixture of oil and water (often
involving
opening the shut off screens as well).
The local sensors in each screen can also be used to monitor the progress of
treatment
fluids pumped through the well. In a typical subsea completion, the only way
previously to ensure accurate placement of a well treatment has been to locate
a vessel
over the well head and perform a well intervention using a coiled tubing
deployed into
the reservoir. This is a very expensive and time consuming operation. Using a
completion of the type described above, it is possible to pump a well
treatment fluid
down the well from the surface and monitor its progress in real time using the
local
sensors in each screen. Figure 8 shows such a process in a schematic form. The
well
in question is a subsea well having a well head 250 on the sea bed 252 which
is
connected to a production platform 254 by means of a pipeline 256 running
along the
sea bed 252. The well 'extends down from the well head 250 in to the producing
reservoir 258 where it runs in an essentially horizontal path and is completed
with
instrumented screens 260 as described above. Although only one well is shown
here,
there may be multiple wells connected to a single well head which will have
valves
allowing individual wells to be isolated from the others.
In order to conduct well treatments, fluids are pumped into the well from the
platform
254. This can be done from a treatment skid or the like located on the
platform 254,
or, as is shown here, from a support boat 262 which connects to the pipeline
256 via
the platform 254. A slug of treatment fluid 264 is injected into the pipeline
from the
boat 262 and is pumped down the well using a suitable fluid as is known in the
art.
For example, the treatment in question can be an annular chemical packer which
includes a highly conductive chemical additive as a marker. As the slug 264
passes
each screen 260, a portion of the fluid enters the manifold 266 where its
presence
causes a change in the reading from the sensor 268. Thus, by monitoring the
measurements from the screens 260, the progress of the slug 264 through the
well can
be determined. This data can be represented in graphical form on a display
unit 270
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on the platform 254 or support boat 262 from which pumping is controlled. When
the
sensors 268 indicate that the slug 264 has reached the screen identified in
the previous
monitoring step, pumping can be stopped or the pump rate can be increased to
shear
the fluid so as to decrease its viscosity and enable it to be pumped from the
base pipe
into the chamber and screen. The fluid then sets and seal off production from
the or
each particular screen.
An alternative form of control of flow through a screen can be obtained using
the
sealing system installed in the chamber of each screen. One example of a
sealing
system in accordance with an embodiment of the invention is shown in Figure 9.
The
sealing system is located in the manifold 300 near to the point where the flow
enters
the base pipe 302 and comprises a reservoir 304 containing a sealing fluid and
a
heating coil 306 around the manifold 300 at that point that is connected to
the data
and power network. In use, when it is desired to shut off a given screen, a
signal is
sent to the relevant sealing system to cause an expandable sealing fluid to be
released
from the reservoir 304. This can be done using a small detonator cap,
electromagnetic
device or even by heating using the coil 306. This serves to rupture the
reservoir
which releases the sealing fluid into the chamber where it expands. The
heating coil
306 can then be used to set the fluid and prevent flow through the manifold
300.
While the objective is that the expanded sealing fluid should fill the chamber
and
prevent fluid flow into the base pipe, it is often enough that the expanded
fluid
provide sufficient flow restriction in the chamber that the pressure drop is
too great
for fluid to flow. The pressure drop required for this is relatively small in
many cases.
It is also possible to use the heating coil 306 to break the seal by raising
the
temperature even higher provided that a suitable breakable sealing fluid is
used. This
allows screens to be reopened in the future. Alternatively, a mechanical
system for
reopening can be used.
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