Note: Descriptions are shown in the official language in which they were submitted.
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MONITORING FORMATION PROPERTIES
Field of Invention
The present invention relates to a method and apparatus
for monitoring properties in a formation traversed by at
least one wellbore.
Background
In the oil and gas industry, the sampling of fluids and
measuring formation pressure in the porous strata of the
formation being drilled can provide valuable information
about the formation and its ability to yield oil and/or gas.
Formation pressure is one of the key properties that
engineers, geologists, and petrophysicists use to
characterize the mobility of oil and gas formations and
estimate reserves. Formation pressure data can be collected
at specific times throughout the life of the well or it can
be monitored on a long-telm basis. Ideally, operators would
like to be able to obtain a real time pressure profile of the
well over its lifetime to aid in optimization of production.
Formation pressures can be measured using a variety of
methods. The most common method involves running a wireline
formation pressure tester (FPT) in either an open or cased
hole completion. This method requires drilling into the
formation or shooting a hole in the casing. The FPT method
works well in permeable formations; however, it is limited to
one data point for pressure at a specified time. Obtaining
multiple data points is desirable because it is difficult to
determine whether a pressure measurement reflects the virgin
formation pressure or pressure after depletion. In addition,
having a number of measurements over an extended period of
time allows for identification of depletion even if the
actual virgin formation pressure is unknown.
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In tighter, less permeable formations, the traditional
FPT method has limits because it takes a long time to build
up to the formation pressure. In addition, the method is less
accurate in formations prone to a phenomenon known as
supercharging. Supercharging is the increase of formation
pressure around the wellbore as a result of exposure to the
higher pressure from the mud used in the drilling process. In
supercharged reservoirs, the mudcake fails to adequately hold
the drilling fluid in the wellbore, causing drilling fluid to
penetrate the formation and create a high-pressure or "super-
charged" zone. Using the FPT method under these conditions
may require extrapolation or yield an inaccurate data point
for pressure that is between the mud pressure and the
formation pressure.
Another method used in tighter formations is the
diagnostic formation injection test (DFIT). In this method,
the formation is pressured up, a fracture is created beyond
the supercharged area and the pressure fall off back to the
formation pressure is monitored. Usually pressure is measured
at the surface and the accuracy is within hundredths of psi.
A gauge may also be placed downhole to obtain a more accurate
measurement; however, in tight formations, it is still a
challenge to get an accurate measurement within 100 psi.
Long-term build-up is another method for measuring
formation pressure. Here the well is shut in for an extended
period (weeks or months) and the pressure is measured as it
builds back up to the current formation pressure. As with the
DFIT method, measuring can be performed at the surface or
downhole, but both methods require that the well be shut in
with no production. The long-term build-up method
traditionally yields one data point representing the pressure
for the whole well. In principle, a profile could be obtained
by placing a number of gauges between bridge plugs in the
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casing, but doing so may force the operator to abandon the
well or rely on retrievable bridge plugs. The long-term
build-up method will also likely damage the casing integrity
because the casing has to be perforated in order to have
communication between the gauge and the formation.
US Patent 5,467,823 discloses a method and apparatus of
monitoring subsurface formations containing at least one
fluid reservoir and traversed by at least one well. The
method includes lowering a sensor to a depth level
corresponding to the reservoir, positioning the sensor at
this depth while isolating the section of the well where the
sensor is located from the rest of the well and providing
fluid communication between the sensor and the reservoir.
Because this system requires isolating the section of the
well where the sensor is located from the rest of the well,
this could not serve as a long-term pressure measurement
option. In addition, the chances of maintaining pressure
isolation while achieving communication to surface over the
wireline with multiple sensors are remote.
Summary of the Invention
The present inventions include a method for monitoring
pressure in a formation traversed by at least one wellbore
comprising providing a tubular element having an outside
surface, attaching a perforating gun oriented in such a way
that when fired, the perforating gun does not damage the
tubular element, connecting a sensor to the perforating gun
in close proximity to the perforating gun wherein the sensor
is exposed to the wellbore, inserting the tubular element
into the wellbore, securing the tubular element in the
wellbore, firing the perforating gun to penetrate the
formation, exposing the sensor to the formation pressure, and
monitoring the pressure in the formation with the sensor to
obtain pressure data.
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The present inventions also include an apparatus for
monitoring pressure in a formation traversed by at least one
wellbore lined with casing comprising a wireless communications
module mounted on the outside of the casing, a perforating gun
oriented away from the casing mounted on the outside of the
casing, and a sensor mounted on the outside of the casing
wherein the sensor is not protected from overpressure.
The present inventions also include an apparatus for
monitoring pressure in a formation traversed by at least one
wellbore comprising a tubular element having an outside
surface, a wireless communications module mounted on the
outside surface of the tubular element, a perforating gun
oriented away from the tubular element mounted on the outside
surface of the tubular element, and a sensor mounted on the
outside surface of the tubular element wherein the sensor is
not protected from overpressure.
According to a further aspect of the present
invention, there is provided a method for monitoring pressure
in a formation in a wellbore comprising: providing a tubular
element having an outside surface; attaching a perforating gun
to said outside surface; connecting a sensor to the perforating
gun; inserting the tubular element into the wellbore; securing
the tubular element in the wellbore; firing the perforating gun
to penetrate the formation; wherein the sensor is a pressure
gauge mounted in close proximity to the perforating gun, the
perforating gun comprising shaped charges that are oriented at
an angle of about 45 relative to a tangent line at the
circumference of the tubular element to penetrate the cement
and formation according to mutually substantially orthogonal
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paths such that when fired, the perforating gun does not damage
the tubular element and exposes the pressure gauge to the
formation pressure; and monitoring the pressure in the
formation using data obtained from the pressure gauge.
According to another aspect of the present invention,
there is provided an apparatus for monitoring pressure in a
formation in a wellbore lined with casing comprising: a
wireless communications module mounted on the outside of the
casing; a perforating gun mounted on the outside of the casing;
and a sensor mounted on the outside of the casing, and wherein
the sensor is a pressure gauge mounted in close proximity to
the perforating gun, the perforating gun comprising shaped
charges that are oriented at an angle of about 45 relative to
a tangent line at the circumference of the tubular element to
penetrate the cement and formation according to mutually
substantially orthogonal paths such that when fired, the
perforating gun does not damage the tubular element and exposes
the pressure gauge to the formation pressure.
According to still another aspect of the present
invention, there is provided an apparatus for monitoring
pressure in a formation traversed by at least one wellbore
comprising: a tubular element having an outside surface; a
wireless communications module mounted on the outside surface
of the tubular element; a perforating gun mounted on the
outside surface of the tubular element; and a sensor mounted on
the outside surface of the tubular element wherein the sensor
is not protected from overpressure and wherein the sensor is a
pressure gauge mounted in close proximity to the perforating
gun, the perforating gun comprising shaped charges that are
oriented at an angle of about 45 relative to a tangent line at
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the circumference of the tubular element to penetrate the
cement and formation according to mutually substantially
orthogonal paths such that when fired, the perforating gun does
not damage the tubular element and exposes the pressure gauge
to the formation pressure.
Brief Description of the Drawings
The present invention is better understood by reading
the following description of non-limitative embodiments with
reference to the attached drawings, wherein like parts of each
of the figures are identified by the same reference characters,
and which are briefly described as follows:
Figure 1 illustrates a perspective view of one
embodiment of the pressure monitoring apparatus.
Figure 2 illustrates a side view of one embodiment of
the pressure monitoring apparatus installed in a wellbore.
Figure 3 shows a top view of the wellbore
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illustrating the direction of the perforations.
Figure 4 illustrates a side view of another
embodiment of the pressure monitoring apparatus installed in a
wellbore.
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Detailed Description of the Invention
Figure 1 shows one embodiment of an apparatus for
monitoring formation properties. In this embodiment, tubular
element 101 is a section of casing, liner, or other material
used to maintain the integrity of the wellbore. Tubular
element 101 may also be a section of tubing, cement stinger,
or other device used to lower equipment into a wellbore.
Perforating gun 102 and sensor 103 are mounted on the outside
of tubular element 101 in close proximity to one another.
Perforating gun 102 and sensor 103 may be connected either
directly or via additional tubulars or hoses.
Any type of perforating gun may be used; however the
direction of the perforations must point away from the casing
(tubular element 101) so that when fired, the perforating gun
does not damage the casing. In a wireless embodiment of the
invention, perforation gun 102 may be fired by pressuring up
the casing using conventional methods of wireless
perforating. In an alternative embodiment, a wire may be
attached to perforating gun 102 and used for firing. In this
embodiment, a conventional casing conveyed wireless
perforating gun with the inward facing shaped charges removed
is shown.
Any type of sensor may be used including, for example,
strain gauges, quartz gages, and other conventional sensing
devices. The embodiments in this application discuss using a
pressure sensor; however, sensors that measure other well
properties could be employed.
Wireless communications module 104 is shown connected to
tubular element 101. Wireless telemetry technology is known
in the industry and may be used to transmit data gathered
downhole to surface production facilities. In this case,
wireless communications module 104 transmits the pressure
data gathered from sensor 103 real time to the surface.
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Figure 2 depicts the apparatus shown in Figure 1
installed in wellbore 201. A section of wellbore 201 is shown
traversing formation 202 with tubular element 101 lowered
inside. As in Figure 1, perforating gun 102, sensor 103, and
wireless communications module 104 are mounted on the outside
of tubular element 101. In Figure 2 only one section of the
wellbore is shown. Because the transmission system is
wireless, an operator may install numerous sensors and
perforating guns in a single wellbore to obtain the desired
data.
In operation, once tubular element 103 is lowered to its
desired position in wellbore 201, cement 203 is optionally
pumped through annulus 204, securing tubular element 101 in
place. Then the casing is pressured up and perforating gun
102 is activated. Figure 3 depicts the top view of the
apparatus in the wellbore to indicate the direction of the
perforations. Shape charges 301 are shown connected to
perforating gun 102. When fired, shaped charges 301 penetrate
cement 203 and formation 202 according to paths 302 thereby
exposing sensor 103 to the formation pressure. During the
perforating operation, tubular element 101 remains intact and
sensor 103 is not damaged even though it is in direct
pressure communication with the gun and not protected from
the pressure shock generated by the firing of the gun
(referred to as "overpressure" in the industry). Sensor 103
gathers data, which is transmitted to surface unit 205 by
wireless communication module 104, thus providing pressure
data without the need to drill a dedicated observation well
or compromise casing integrity.
Another embodiment of the invention uses a hard-wired
connection to transmit the pressure data gathered downhole.
Figure 4 depicts a hard-wired embodiment that is installed on
the outside of a section of casing. Wellbore 401 is shown
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traversing formation 402. First apparatUs 403 and second
apparatus 404 are shown mounted on the outside of casing 405.
First apparatus 403 and second apparatus 404 are connected by
wire 406, which extends to the surface (not shown). First
apparatus 403 and second apparatus 404 consist of perforating
guns (407 and 410), sensors (408 and 411), and communications
modules (409 and 412). The entire apparatus is secured in the
wellbore using cement 413. In this embodiment, the data
collected by sensors 408 and 411 is transmitted using wire
406 to the surface (not shown). Transmission with a wire may
be less reliable than using wireless communication because
the wire might be damaged during placement in the hole or
when zones are perforated for production. However, hard-wired
transmission systems are advantageous because they provide
higher frequency data, can transmit data for longer periods,
and enable deeper measurements to be contained. Furthermore
the wire may also be used to fire the perforating guns.
Although the system of some embodiments of the present
invention was developed for tight, low permeability
reservoirs, some embodiments of the invention may also be
useful in high permeability reservoirs. In many areas,
multiple reservoirs penetrated by a single wellbore are
produced and managed separately because of legal or reservoir
management requirements. Some embodiments of the present
invention enable the operator to have a single well produce
one horizon, while acting as a pressure observation well for
one or more other reservoirs, thus obviating the need to
drill dedicated pressure observers.
Advantages of the embodiments of the invention include
one or more of the following:
(i) Provides accurate pressure measurement in tight low
permeability formations
(ii) Maintains casing integrity
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(iii) Allows for simultaneous production and monitoring
(iv) Avoids need to drill separate observation well
(v) May be used in high permeability formations in which
multiple reservoirs are penetrated by single wellbore
(vi) Uses multiple bullets, improving the chance of
establishing pressure communication with formation.
Those of skill in the art will appreciate that many
modifications and variations are possible in terms of the
disclosed embodiments, configurations, materials, and methods
without departing from their scope. Accordingly,
the scope of the claims appended hereafter and their
functional equivalents should not be limited by particular
embodiments described and illustrated herein, as these are
merely exemplary in nature.
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