Note: Descriptions are shown in the official language in which they were submitted.
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EPS00494/EP/P1
Description
2D Well Testing with Smart Plug Sensors
Technical Field
[0001] This invention relates to an apparatus for characterising the
permeability of a formation surrounding a borehole well. In particular
permeability is determined by measuring the formation and borehole
pressure in oil, gas or similar wells.
Background Art
[0002] Once a well has been drilled, a well test is usually performed to
characterise the formation surrounding the borehole. Properties such
as skin, permeability, porosity of a reservoir, and production capacity
are some the properties used to characterise the formations. Knowing
how fluids flow through a reservoir is important for managing
hydrocarbons reserves. Fluid flow is governed by the permeability of
the formations.
[0003] A conventional well test can determine formation properties from
pressure measurements obtained by a drillstem test (DST) tool as
shown in Figure 1. In a conventional well test operation transient well
test conditions are applied to the well and the pressure below a tester
valve is measured. The valve is shut off causing a pressure build up
which is recorded. This build up is interpreted and can lead to the
determination of a series of well/formation parameters such as: skin,
permeability, reservoir pressure and distances to boundaries.
However often formations are not homogenous in quality and will
have layering features. In such cases the results obtained in terms of
reservoir properties from testing the whole thickness, h, is
representative of some average of the individual layer permeability
which is not really useful to a reservoir engineer for assessing the
potential of the well or the field under evaluation.
[0004] Such a test only provides a one dimensional characterization that is
only valid for perfectly homogenous medium. Because most
formations are not homogenous but rather show a layering structure,
a single pressure measurement does not sufficiently characterize
each individual layer component. In addition it is not possible to obtain
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a characterization of the vertical permeability from the results of a single
probe.
[0005] It is also known to measure the pressure of formation surrounding
the
borehole using sensors placed into the formation. US6693553 describes
deploying sensors into the formations as the wellbore is being drilled. An
antenna that can communicate with the sensor is located on the downhole
tool. US6070662 describes deploying sensors into the formations and placing
an antenna in the casing to communicate with the sensor.
[0006] However these methods only result in a single pressure measurement
and do
not simultaneously measure the pressure at different depths of the borehole
and therefore are not sufficient to characterise each individual layer
component of a formation in a single test.
[0007] W02006008172 describes a method for estimating the permeability
distribution of a formation surrounding a borehole. An acoustic emitter
located
either on the surface in the borehole excites a portion of the formation with
an
acoustic signal. An acoustic receiver located within the borehole measures
the acoustic response. This acoustic response can be used to assess a
formation pressure from which the permeability of the formation can be
estimated. Conventional well test pressure measurements can also be taken
to estimate the permeability of the formation.
[0008] It is the object of the invention to provide an apparatus to
characterise the
permeability of the formation around a borehole. The invention proposes an
apparatus and method for characterising the permeability of the formation in
two dimensions, horizontally and vertically, by directly measuring both the
borehole pressure and formation pressure.
Summary
[0009] A first aspect of the invention comprises an apparatus for
characterising the
permeability of a formation surrounding a wellbore, comprising; a drillstem
test (DST) tool comprising, a packer for isolating a zone of the wellbore, a
valve for controlling fluid into and out of the zone via a drill string of the
tool
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and, a pressure gauge for detecting the pressure in the zone; wherein the
apparatus further comprises an array of at least two antennas arranged on
the tool above the packer such that when in use each antenna of the array
aligns with a corresponding pressure sensor placed in the formation to obtain
pressure measurements and therefore allow horizontal and vertical
permeability to be determined.
[0010] The distance between each individual antenna of the array is
determined by
the placement of the sensors in the formation. Differing lengths of pipes
making up the drill string can be used to alter the distance between the
individual antennas.
[0011] The apparatus can further comprise an interrogating tool. The tool
scans the
array of antennas so that data obtained from each antenna is transmitted to
the interrogating tool which conveys the information up to the surface.
[0012] Preferably the array of antenna is mounted on the outside of the DST
tool.
[0013] Preferably the antennas can transmit and receive information from
the
sensors by wireless communication. The interrogating tool can also be used
to transfer power to the sensors via the antennas. The wireless
communication and the transfer of power can be based on electromagnetic
coupling or acoustic transmission.
[0014] A second aspect of the invention is a sensor system for
characterising the
permeability of a formation surrounding a wellbore in two dimensions,
comprising: at least two sensors in the formation surrounding the wellbore;
and an apparatus comprising, a drillstem test (DST) tool comprising, a packer
for isolating a zone of the wellbore, a pressure gauge for recording the
pressure in the zone, and a valve for controlling fluid into and out of the
zone
via a drillstring of the tool, and an array of at least two antennas arranged
on
the tool above the packer such that each antenna of the array aligns with a
corresponding pressure sensor in the formation.
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[0015] A third aspect of the invention comprises a method for characterising
the permeability of a formation surrounding a wellbore, comprising:
- inserting sensors into the formation surrounding the wellbore at
various depths;
- inserting an apparatus as described above in the wellbore;
- isolating a zone of the wellbore;
- changing the pressure in the zone by altering flow through the valve;
- measuring the pressure of the formation at the location of each
sensor and transmitting the data obtained to the array of antenna;
- measuring the pressure in the zone with the pressure gauge; and
- determining the horizontal and vertical permeability of the formation
using the pressure measurements obtained. The method may be
conducted in openhole or cased wells.
[0016] Preferably the spacing between the sensors is recorded as the
sensors are inserted into the formation.
[0017] Preferably method further comprises positioning the antennas along
the DST tool so that the spacing between the antennas is equal to the
spacing between the sensors in the formation, before inserting the
tool body down the wellbore.
[0018] The method can further comprise scanning the array of antennas with
an interrogating tool to transfer the information from the antenna to
the tool and to power the sensors.
[0019] Preferably the information from the interrogating tool is sent up-hole
for surface recording and further analysis.
[0020] Preferably transmitting the data between the sensors and antenna is
done by wireless mode. This can be electro-magnetic coupling or
acoustic transmission.
[0021] Preferably the method is preformed using the system described
above.
Brief description of the drawings
[0022] Figure 1 shows a conventional drillstem test tool arrangement.
[0023] Figure 2 shows a schematic of a two dimensional well test tool
arrangement.
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[0024] Figure 3 shows a schematic of a sensor plug used to detect the
pressure in the formation.
[0025] Figure 4 shows an arrangement for data transmission between the
sensor and array of antennas.
[0026] Figure 5 shows a schematic of the test well arrangement used to carry
out the example.
[0027] Figure 6 shows the results of the wellbore and layers pressure
responses of the test well.
Mode(s) for carrying out the invention
[0028] Referring to Figure 1 a conventional drill stem test tool 1 for
measuring the wellbore pressure comprises a pressure gauge 2, a
packer 3 and a tester valve 4. During a conventional well test, for
determining properties of a formation surrounding a wellbore 5, the
DST tool 1 is lowered down into a wellbore 5. The packer 3 is inflated
to isolate the zone of interest, h, of the wellbore. The valve 4 is initially
open and fluid can flow into the drillstring of the DST tool. The valve 4
is then closed to stop the fluid flow through the wellbore. A build up
occurs below the valve 4, and the pressure is monitored as a function
of time. The permeability of the reservoir is then estimated from the
well test measurement. As the whole thickness, h, of the formation
zone tested is often not homogenous in quality but instead comprises
layering features, with separate layers of medium quality sands 6 and
layers very good quality sands 7, surrounding the wellbore the result
obtained merely indicates an average of the zone and does not
characterise each individual layer component that may be present in
the reservoir. This conventional test only provides a one dimensional
horizontal characterisation of the permeability of the formation.
[0029] With reference to Figure 2 the DST tool 26 according to an
embodiment of the invention comprises an array of antennas 21
located on the outside of the drill string of the tool, a pressure gauge
23, a valve 27 and packer 28. Each of the antennas 21 comprising the
array are spaced apart to line up with a pressure sensor 24 in the
formation 25 to receive data from the sensor. The pressure gauge 23
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measures the pressure in the wellbore 22 in the perforated interval,
h1, as for a conventional DST well test.
[0030] The spacing between the pressure sensors 24 is recorded as the
sensors are inserted into the formation at predetermined depths such
that the spacing between each of the sensors 24 relative to each
other is known. The distance between the sensors is recorded by
differential measurements between the depths at which each sensor
is inserted into the formation. This information is used to ensure that
the antennas in the array are correctly spaced apart when preparing
the tool for inserting down the wellbore so that the spacing between
antennas on the array will be equal to the spacing between the
sensors. These sensors 24, located at different depths of the
formation, record the pressure within the formation at each of their
locations. The data obtained from these measurements at different
depths allows for the permeability of the formation to be characterised
along the wellbore axis.
[0031] When the measurements from the sensors 24 in the formation are
taken in combination with the pressure measurements obtained from
the conventional DST test preformed by the pressure gauge 23 a two
dimensional characterisation of the permeability of the formation, in
the horizontal and vertical direction, can be determined.
[0032] With reference to Figure 3 an example of a sensor plug 31, that can
be inserted in the formation comprises a sensing element 32, an
electronics plafform 33 inside a protective housing and a
communication element 34. The sensing element 32 senses the
pressure in the formation and the communication element 34, such as
an antenna, enables data to be received and transmitted from the
sensor. The antenna transmits the pressure data recorded by the
sensing element 32 to an antenna outside the formation located on
tool placed down the wellbore. The power supply for electronics
platform 33 is provided by embedded batteries or directly by antenna
34. To supply power via the antenna 34, the power is transferred from
the tool antenna towards antenna 34 by electro-magnetic coupling
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between the two antennae. Rechargeable batteries can be used and
recharged from the tool antenna. Energy harvesting techniques can
also be used to collect energy available at the reservoir level.
Vibrations induced by the downhole flow can be collected by electro-
acoustic sensors and converted to electrical energy to supply the
sensor electronics or recharge the battery cells. Further details of
suitable sensors can be found in W02006/005555.
[0033] With reference to Figure 4 each sensor 41 aligns with an antenna 42
of the array. The sensors 41 are inserted into the formation 44
through the casing 45 of the wellbore 46. The spacing of the sensors
41 is recorded during their insertion into the formation 44. The
sensors 41 are installed in a hole through the casing so that the
sensor extends between the inside and outside of the casing 45, with
the sensing elements in the formation 44 surrounding the well and the
communication antenna of the sensor able to communicate with the
antennas in the well. An array of antennas 42 and its associated
interrogating tool 47 are mounted on the outside of the drillstring 48 of
the DST tool. The antennas 42 are positioned along the drillstring 48
so that their spacing is equal to the spacing between each sensor 41.
The distance between each antenna 42 can be adjusted with pipes of
various lengths. The drillstring 48 is inserted down into the wellbore
46 until the array of antennas 42 is proximate to the sensor 41. When
the antennas 42 are aligned with their respective sensor 41, antenna
coupling 49 occurs between the antenna 42 of the array located on
the drillstring 48 and the antenna of the sensor 41. The sensors 41
may comprise a radioactive marker, such as a gamma ray pip-tag that
allows their location in the wellbore to be sensed by the DST tool.
[0034] Data is transmitted from the antenna in the sensor 41 to its
corresponding antenna 42 mounted on the outside of the drillstring 48
of the DST tool by wireless communication such as by electro-
magnetic coupling or acoustic transmission. The interrogating tool 47
scans the array of antennas 42 and all the data acquired by each
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antenna 42 is transferred to the interrogating tool 47. This allows the
data to be sent up-hole for surface recording and further analysis.
Example
[0035] A vertical test well penetrating a three layer formation as shown in
Figure 5 is constructed and pressure measurements are taken using
, the apparatus and method of the invention.
[0036] The welltest consists of flowing layer 3 at 2000 bl/d for 24 hours
followed by 48 hours of build up. The pressure response is recorded
at the wellbore by gauge 53 and within the formation layers 1 and 2 by
monitoring gauges 51 and 52 respectively.
[0037] An analytic model is built to have the characteristics shown in Table
1.
Layer # Thickness (ft) kr, (mD) kz (mD) Skin
1 35 70 10
2 20 35 4
3 50 150 20 0.5
Table 1 ¨ Forward model values of test well
[0038] The model is first run in a forward mode to simulate the pressure
responses in the well bore and at the two monitoring gauges. The
results are shown in Figure 6.
[0039] A non-linear regression routine is used to match the pressures
transient that are previously established and to recover the individual
layer permeabilities along the horizontal and vertical directions (kh, kz).
The results are shown in Table 2.
Layer # Thickness (ft) kh (mD) kz (mD) Skin
1 35 72 9
2 20 38 4
3 50 148 20 0.44
Table 2 ¨ Inverted values (in italics)
[0040] The results obtained with regards to horizontal and vertical
permeabilities and skin values compare well (within 10%) with the
forward model values of Table 1.
