PRIORITY APPLICATION
[0001] This application claims the benefit of U.S. Provisional Application
Serial No. 62/062,333, filed on October 10, 2014 which application is
incorporated by reference herein in its entirety.
BACKGROUND
[0002] The present disclosure relates generally to methods and apparatus that
are used as part of ranging techniques, to determine distance and direction
between wells in geological formations.
[0003] With much of the world's easily obtainable oil having already been
produced, new techniques are being developed to extract less accessible
hydrocarbons. These techniques often involve drilling a borehole in close
proximity to one or more existing wells. Examples of directed drilling near an
existing well include well intersection for blowout control, multiple wells drilled
from an offshore platform, and closely spaced wells for geothermal energy
recovery. Another such technique is steam-assisted gravity drainage (SAGD)
that uses a pair of vertically-spaced, horizontal wells constructed along a
substantially parallel path, often less than ten meters apart. Careful control of the
spacing contributes to the effectiveness of the SAGD technique.
[0004] One way to construct a borehole in close proximity to an existing
well is "active ranging" in which an electromagnetic source is located in the
existing well and monitored via sensors on the drill string in the well under
construction. Another technique involves systems that locate both the source and
the sensor(s) on the drill string - these are sometimes called "passive ranging"
systems by those of ordinary skill in the art. Such ranging techniques are
sometimes limited in the degree of accuracy that can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a block diagram of a prior art well ranging system.
[0006] FIG. 2 is a block diagram of another prior art well ranging system.
[0007] FIG. 3 is a side, cut-away view of an apparatus according to various
embodiments of the invention.
[0008] FIG. 4 is a graph of current distribution along a wellbore, according
to a linear scale, comparing an embodiment of the invention with the prior art
using a nearby ground location.
[0009] FIG. 5 is a graph of the current distribution along a wellbore shown
in FIG. 4, according to a logarithmic scale.
[0010] FIG. 6 is a graph of current distribution along a wellbore, according
to a linear scale, comparing an embodiment of the invention with the prior art
using a distant ground location.
[0011] FIG. 7 is a graph of the current distribution along a wellbore shown
in FIG. 6, according to a logarithmic scale.
[0012] FIG. 8 is a block diagram of a logging system according to various
embodiments of the invention.
[0013] FIG. 9 is a flow diagram illustrating methods of constructing
apparatus, according to various embodiments of the invention.
[0014] FIG. 10 depicts an example system, according to various
embodiments of the invention.
DETAILED DESCRIPTION
[0015] Magnetic ranging has been widely used for various applications,
including well intersection, well avoidance, SAGD, and others. One excitation
method for magnetic ranging is surface excitation. Surface excitation is a
popular method of generating a ranging signal. It is relatively easy to implement,
without the need for complex cables and equipment. When surface excitation is
used, a current may be injected into the target well casing at the surface of the
well (e.g., at the well head). The current travels along the casing down-hole and
generates a magnetic field down-hole that can be measured at a distance (e.g., in
a drilling well) for ranging purposes. However, the excitation signal down-hole
may be very small when the distance beneath the surface is great, due to current
leakage into the formation. Consequently, sensor noise often affects magnetic
ranging accuracy at greater depths, leading to false signal measurements and
failures in well location.
[0016] For example, in ranging applications such as SAGD, excitation
current signals are injected via power cables from a power supply at the surface
into a target well. An electrical potential difference is created at two positions
such that a closed current loop path is enabled to generate current signals. To
achieve the potential difference, a voltage may be applied to the target well by
connecting the cables to the target well casing, whereas a ground stake is placed
at surface. Thus, the closed current loop path is provided via power cables, target
well casing, and formations.
[0017] Generally speaking, the ground stake should be placed far away from
the target well so that most of the injected current stays in the target well casing
at deeper depths, owing to less return current from the target well to the ground
stake position. The distance to the stake is usually about 200 m to 1000 m,
depending on the well depth. On the other hand, it can be challenging to locate
the stake at such a large distance, due to rig site conditions. For example, the rig
may be located in a forest, with trees and animals nearby. Safety issues may
prevent operators from running long distance ground positions. These
circumstances may persuade operators to locate the stake much closer to the
well, resulting in a relatively short path that increases the amount of leakage
current entering the formation, and reduces the amount of injection current and
downhole current available for inducing a magnetic ranging signal.
Consequently, the ranging signal performance at deeper depths will be poor.
[0018] Described herein are mechanisms that can be used to reduce leakage
current from the well where the ranging signal is injected. Instead of surface
excitation, downhole excitation is proposed, together with insulated gaps that
form part of the well casing. These mechanisms can significantly improve the
ranging signal strength at deep depth, even when the ground stake position is
close to the well head where the injection occurs. Thus, the various embodiments
described herein aim to improve down-hole current strength and thus, enhance
the available signal/noise ratio, for improved accuracy with respect to ranging
measurement technology. The details of various embodiments will now be
described.
[0019] FIG. 1 is a block diagram of a prior art well ranging system 100, with
surface excitation in a SAGD application. Here the power supply is connected to
the well head of a target well such that a current loop is enabled via cabling,
target well casing, the formation surrounding the casing, ground cabling, and the
power supply. Ranging based on surface excitation may fail if an insufficient
ranging signal is obtained at depth, due to excessive leakage current. Therefore,
to increase the current in the casing at depth by reducing the magnitude of the
leakage current, the ground point 110 should be placed far away from the target
well head location 120.
[0020] FIG. 2 is a block diagram of another prior art well ranging system
200, where the target well current at depth is increased using downhole
excitation. That is, instead of connecting the power supply cable to the well
head, one end of the cable 224 is dropped inside the target well to a selected
depth downhole, so that the injection point 230 is below the surface. This
enhances the target well current at deeper depths. However, due to some of the
injection current 234 flowing back via the well casing to the well head, a
significant amount of the injection current available from the power supply is not
flowing in the downhole direction at the injection point 230, as compared to
surface excitation (see FIG. 1). Indeed, about 30% - 60% of the injection current
234 flow back to the well head from the injection point 230, so that the
improvement obtained by using this technique is not as significant as might be
expected. For example, if one drops the cable end to locate the injection point
230 at 500 m below the surface of the Earth, the depth from which acceptable
ranging can be obtained might be expected to increase by 500 m as well. In
reality, this technique only increases the effective ranging depth by 200 m - 300
m.
[0021] FIG. 3 is a side, cut-away view of an apparatus 300 according to
various embodiments of the invention. Here the apparatus 300 includes a well
332 that has an outer casing 334 and an inner casing 336, surrounded by cement
338. These elements are arranged to enhance strength of the injected signal 340
at depth. As shown in FIG. 3, the downhole excitation injection terminal 344 is
located at 5 11 m below the surface 348 of the Earth, below an insulated gap 350
in the casing that spans the depth of 510m to 5 11 m below the surface 348 of the
Earth. Other parameters, such as formation resistivity, mud resistivity, cement
resistivity, casing conductivity, and casing permeability are also presented. The
values of these parameters represent typical SAGD field conditions.
[0022] The casing 336 is divided in the figure into two portions: an upper
portion 352, and a lower portion 354, which is at a lower depth than the upper
portion 352. The insulated gap 350 is used to minimize leakage current
amplitude at the injection terminal 344 into the upper portion 352, improving the
amplitude of the current at the injection terminal 344 in the lower portion 354.
Although such the gap 350 does not stop leakage current from flowing through
the surrounding formation 360s back to the upper portion 352 and the ground
point 362 at the surface 348, the gap 350 does operate to significantly improve
the strength of the injected signal 340 in the lower portion 354, when compared
to the prior art technique shown in FIG. 2.
[0023] Thus, an apparatus 300 may comprise two or more portions of
casing 336, joined by insulating gap 350 material, with an injection terminal 344
attached to the lowest one of the casing portions. In some embodiments, the
apparatus 300 may comprise a first well casing portion (e.g., the upper portion
352) and a second well casing portion (e.g., the lower portion 354) that has an
excitation signal injection terminal 344. The second well casing portion may be
joined to the first well casing portion by the insulating gap 350 material disposed
between the first well casing portion and the second well casing portion.
[0024] The insulating gap 350 may comprise a variety of materials. For
example, in some embodiments, the insulating gap 350 material comprises a
polymer, rubber, or glass. The insulating gap 350 may take the form of a gap sub
that attaches the lower portion 354 to the upper portion 352.
[0025] One or more of the portions of the casing 336 may be covered, at
least in part, by casing insulation material 364. Thus, in some embodiments, at
least one of the first well casing portion (e.g., the upper portion 352) or the
second well casing portion (e.g., the lower portion 354) comprises a conductive
metal at least partially surrounded by casing insulation material 364, to reduce
current leakage 368 into a geological formation 360 when current is injected into
the second well casing portion via the terminal 344.
[0026] The casing insulation material 364 may comprise a variety of
materials. For example, in some embodiments, the casing insulation material 364
comprises a polymer, rubber, or glass.
[0027] Some modeling studies were performed to compare the strength of
the injected down-hole signal 340 along the target well casing using the methods
shown in FIGs. 1-3: surface excitation (FIG. 1), downhole excitation (FIG. 2),
and downhole excitation with an insulated gap (FIG. 3). Each method was
studied using a ground point that was located 50 m away from the target well
head. This relatively small amount of separation is useful when rig site
conditions do not permit longer distances between the ground stake and the
target well head.
[0028] FIG. 4 is a graph 400 of current distribution along a wellbore,
according to a linear scale, comparing an embodiment of the invention with the
prior art using a nearby ground location. Here the current distribution is shown
along the target well casing at depth, as normalized by cable current from the
power supply for three different excitation methods: current injection at the well
head 410, current injected downhole 420, and current injected downhole, below
an insulating gap in the casing 430.
[0029] When injecting current at the wellhead 410, all current will be
injected from the power supply cable to the casing at the well head, and thus
100% of the current is shown to be present at a depth of zero meters in the
figure. For downhole excitation 420, 100% of the available current is not
flowing to portion of the casing below the injection point, since some current
(approximately 30% - 60% corresponding to different ground positions,
formation resistivities, etc.) will flow in the uphole direction - directly along the
casing toward the well head. Downhole excitation using an insulated gap 430
significantly improves the current distribution in the lower casing portion. As
shown in FIG. 4, around 98% of the injected current can be acquired at the
injection point, to flow in the downhole direction.
[0030] FIG. 5 is a graph 500 of the current distribution along a wellbore
shown in FIG. 4, according to a logarithmic scale. This graph 500 provides a
logarithmic scale for normalized current distribution, which makes it easier to
see that downhole excitation with an insulating gap 530 provides a significantly
higher current distribution downhole than injection at the well head 510 or
downhole injection 520 by itself, even though the ground point location is same
for all three cases.
[0031] Considering the same threshold of normalized current percentage in a
ranging requirement (e.g., 0.2%), surface excitation 510 may only provide
sufficient excitation of electromagnetic waves in the formation to enable ranging
applications at depths of up to about 1450 m. Downhole excitation 520 may only
provide sufficient excitation of electromagnetic waves in the formation to enable
ranging applications at depths of up to about up to depth of about 1650 m.
However, downhole excitation in combination with one or more insulating gaps
may provide sufficient excitation of electromagnetic waves in the formation to
enable ranging applications at depths of up to about 1720m.
[0032] FIG. 6 is a graph 600 of current distribution along a wellbore,
according to a linear scale, comparing an embodiment of the invention with the
prior art using a distant ground location. This figures details the outcome of
another study, where performance of the three different methods described with
respect to FIGs. 5-6 are compared when the ground point location for existing
methods (e.g., surface excitation 610 and downhole excitation 620 without an
insulating gap) is 1000 m away from the target well head, and where the
inventive method using downhole excitation with an insulating gap 630 has a
ground point location that is only 50 m away from the well head. Previous
modeling studies confirm that 1000 m (distant) ground location works well for a
typical SAGD application using surface excitation 610. Consequently, this
separation distance (D = 1000 m) between the ground point location (e.g., the
ground stake) and the well head have been used for the existing methods 610,
620, whereas a ground point location that is only 50 m away from the well head
(D = 50 m) is used for the inventive method 630 to verify a significant
improvement in injected current signal strength.
[0033] As shown in FIG. 6, at very deep depths (e.g., 1400 m to 1800 m) the
downhole excitation method with insulation gap and 50m ground position
(method 630) has very similar performance to the existing methods of injection
at the well head 610, and the downhole excitation 620 without an insulation gap
- even when a separation from the ground point of 1000 m is used.
[0034] FIG. 7 is a graph 700 of the current distribution along a wellbore
shown in FIG. 6, according to a logarithmic scale. Here it can be more clearly
seen that the even though the performance of injection downhole, combined with
an insulating gap 730 is not quite as good as downhole injection 720 without the
gap, this is mainly due to relative proximity of the ground point for the method
730 - which in many situations provides an advantage that is worth the slight
decrease in performance. And the method of injection downhole in conjunction
with an insulating gap 730 performs better than injection at the wellhead, even
when the method 710 is favored with a much greater separation between the well
head and the ground point.
[0035] Thus, it can be clearly understood by those of ordinary skill in the art,
after reading this disclosure, that the performance of downhole excitation can be
markedly improved by installing an insulating gap above the signal injection
point. When this occurs, the vast majority of the injection signal (e.g., current)
tends to travel downhole, instead of leaking into the formation, or traveling
uphole along the casing. In simple terms, if one or more gaps is located above
the injection point, which is lowered from the surface to approximately 500 m in
depth, an improvement in injection signal strength equivalent to 450m (90%)
occurs. This improvement in injected signal strength, which in turn improves the
strength of the electromagnetic ranging signals generated in the formation
thereby, comes with an additional advantage: similar or better performance is
obtained when the ground point is relatively close to the well head (e.g., less
than 100 m), versus a ground point that is relatively distant from the well head
(e.g., about 1000 m).
[0036] FIG. 8 is a block diagram of a ranging system 800 according to
various embodiments of the invention. Referring now to FIGs. 3 and 8, it can be
seen that the ranging system 800 can provide indications of electromagnetic field
strength in a formation that surrounds a drilling well 880, resulting from the
injection of a signal (e.g., current) into a target well 884. The ranging system 800
includes a receiver 804 operable outside of, or within a wellbore, and coupled to
a sensor S.
[0037] The processing unit 802 can be programmed to execute control
operations and couples to the receiver 804 to obtain measurements from the
sensor Sas described earlier herein. In some embodiments, a ranging system 800
comprises one or more of the receiver 804, as well as a housing (not shown in
FIG. 8; see FIG. 10) that can house the receiver 804 or other electronics. The
housing might take the form of a wireline tool body, or a downhole tool as
described in more detail below with reference to FIG. 10. The processing unit
802 may be part of a surface workstation or attached to a downhole tool housing.
In some embodiments, the processing unit 802 is packaged within the receiver
804.
[0038] The ranging system 800 can include a controller 825, other
electronic apparatus 865, and a communications unit 840. The controller 825 and
the processing unit 802 can be fabricated to operate the receiver 804 to acquire
measurement data, such as electromagnetic signal strength readings.
[0039] Electronic apparatus 865 (e.g., electromagnetic sensors, etc.) can
be used in conjunction with the controller 825 to perform tasks associated with
taking measurements downhole with the receiver 804. The communications unit
840 can include downhole communications in a drilling operation. Such
downhole communications can include a telemetry system.
[0040] The ranging system 800 can also include a bus 827 to provide
common electrical signal paths between the components of the ranging system
800. The bus 827 can include an address bus, a data bus, and a control bus, each
independently configured. The bus 827 can also use common conductive lines
for providing one or more of address, data, or control, the use of which can be
regulated by the controller 825.
[0041] The bus 827 can include instrumentality for a communication
network. The bus 827 can be configured such that the components of the ranging
system 800 are distributed. Such distribution can be arranged between downhole
components such as the receiver 804 and components that can be disposed on the
surface of a well, such as the power supply 875. Alternatively, several of these
components can be co-located, such as on one or more collars of a drill string or
on a wireline structure.
[0042] In various embodiments, the ranging system 800 includes
peripheral devices that can include displays 855, additional storage memory, or
other control devices that may operate in conjunction with the controller 825 or
the processing unit 802. The display 855 can display diagnostic and range
information (e.g., direction and/or distance) for measurements obtained by the
receiver 804 based on the injection of signals that induce magnetic fields in a
formation according to embodiments described above. The display 855 can also
be used to display one or more graphs, similar to what are shown in FIGs. 4-7.
[0043] In an embodiment, the controller 825 can be fabricated to include
one or more processors. The display 855 can be fabricated or programmed to
operate with instructions stored in the processing unit 802 (for example in the
memory 806) to implement a user interface to manage the operation of the
receiver 804 or components distributed within the ranging system 800. This type
of user interface can be operated in conjunction with the communications unit
840 and the bus 827. Various components of the ranging system 800 can be
integrated with the receiver 804 or associated housing such that processing
identical to or similar to the methods discussed with respect to various
embodiments herein can be performed downhole.
[0044] In various embodiments, a non-transitory machine-readable
storage device (e.g., memory 806) can comprise instructions stored thereon,
which, when performed by a machine, cause the machine to become a
customized, particular machine (e.g., the processing unit 802) that performs
operations comprising one or more features similar to or identical to those
described with respect to the methods and techniques described herein. A
machine-readable storage device is, herein, a physical device that stores
information (e.g., instructions, data), which when stored, alters the physical
structure of the device. Examples of machine-readable storage devices can
include, but are not limited to, memory 306 in the form of read only memory
(ROM), random access memory (RAM), a magnetic disk storage device, an
optical storage device, a flash memory, and other electronic, magnetic, or optical
memory devices, including combinations thereof.
[0045] The physical structure of instructions stored in the memory 806
may be operated on by one or more processors such as, for example, the
processing unit 802. Operating on these physical structures can cause the
machine to perform operations according to methods described herein. The
instructions can include instructions to cause the processing unit 802 to store
associated data or other data in the memory 806. The memory 806 can store the
results of measurements of formation parameters to include gain parameters,
calibration constants, identification data, etc. The memory 806 can store a log of
the electromagnetic signal strength data detected by the sensor(s) S. The memory
306 therefore may include a database, for example a relational database. Still
further embodiments may be realized.
[0046] For example, FIG. 9 is a flow diagram illustrating methods 9 11 of
constructing apparatus, according to various embodiments of the invention. In
some embodiments, a method 911 comprises installing a casing that has one or
more insulating gaps in a well at blocks 921 and 925, and attaching an insulated
conductor to one of the lower portions of the casing at block 929 (the lower
portion located in a lower region of the well, and being insulated by the gap from
one or more casing portions located in an upper region of the well). That is, the
injection point that is eventually coupled to the power supply by the insulated
conductor is disposed below the gap that exists between casing portions.
[0047] For example, a casing with insulating gaps can be effectively
installed even when a larger, outer, continuous casing (without insulating gaps)
has already been put in place. Thus, in some embodiments, a method 9 11
includes the activity at block 921, which comprises casing the well with an outer
casing that has an inner diameter that is larger than the expected outer diameter
of conductive casing, prior to casing the well with the conductive casing.
[0048] The method 911 may continue on to comprise casing the well
with the conductive casing separated by insulating gaps into at least two
portions, wherein the insulating gaps are less than one meter in length, at block
925. Of course, in some embodiments, the method 911 does not include the
installation of an outer casing; a single casing is used, and installed at block 925.
[0049] The method 911 may continue on to block 929 to comprise
attaching an insulated conductor to a lower one of the portions (of the conductive
casing) that is separated from an upper one of the portions by at least one of the
insulating gaps. Attaching the insulated conductor to the lower one of the
portions operates to form an excitation signal injection point that is not directly
electrically coupled to the upper one of the portions, wherein the upper one of
the portions is at a higher elevation of the well than the lower one of the
portions.
[0050] In some embodiments, a method 911 comprises coupling a power
supply to a ground point and a lower well casing that is separated from an upper
well casing by an insulating gap at block 933, and then injecting an excitation
signal into the lower casing at block 941. In some embodiments, the activity at
block 933 comprises coupling a power supply to a ground point associated with
a first well, and to a lower portion of a conductive casing disposed within the
first well, the lower portion of the conductive casing separated by an insulating
gap from an upper portion of the conductive casing, wherein the upper portion of
the conductive casing is at a higher elevation of the first well than the lower
portion of the conductive casing. ; and
[0051] In most embodiments, good ranging signal reception performance
can be achieved even when the ground point for the injection apparatus is
relatively close to the well head. Thus, the activity at block 933 may comprise
coupling the power supply to a ground point that is less than 100 m from an
opening of the first well in a surface of the Earth.
[0052] A casing with multiple insulating gaps can be installed, to permit
moving the excitation signal injection point from one location downhole, to
another. Thus, in some embodiments, the method 911 comprises moving the
excitation signal injection point from a first one of the lower one of the portions
to a second one of the lower one of the portions at block 937. In some
embodiments, the excitation signal injection point is stationary, and not
movable.
[0053] The method 911 may comprise, at block 941, injecting an
excitation signal into the lower portion of the conductive casing to induce a
magnetic field in a geological formation surrounding the first well.
[0054] The magnetic field arising from the excitation signal can be
detected by sensors in a second well (e.g., a drilling well) to determine the range,
such as the relative distance and direction, from the second well to the first well.
Thus, the method 9 11 may go on to block 949 to include receiving the ranging
signal corresponding to the magnetic field at a sensor disposed in a second well.
[0055] Injection and reception can occur in target and drilling wells,
respectively. Thus, the first well may be a target well, and the second well may
be a drilling well. Conversely, in some embodiments, injection may occur below
a gap in a drilling well casing, and reception may occur at the target well. Thus,
the first well may be a drilling well and the second well may be a target well.
[0056] As noted previously, sensors in the second well can provide
signals according to the strength of the magnetic field that has been induced by
the injected signal in the first well, and can be used to determine
direction/distance. Thus, the method 911 may include, at block 95 1, processing
the ranging signal to determine a distance or direction to the first well, from the
second well. In some embodiments, the method 911 includes repeating the
activities of blocks 937, 941, 949, and 951 one or more times, in a looped
fashion.
[0057] It should be noted that the methods described herein do not have
to be executed in the order described, or in any particular order. Moreover,
various activities described with respect to the methods identified herein can be
executed in iterative, serial, or parallel fashion. Information, including
parameters, commands, operands, and other data, can be sent and received in the
form of one or more carrier waves.
[0058] Upon reading and comprehending the content of this disclosure,
one of ordinary skill in the art will understand the manner in which a software
program can be launched from a computer-readable medium in a computerbased
system to execute the functions defined in the software program. One of
ordinary skill in the art will further understand the various programming
languages that may be employed to create one or more software programs
designed to implement and perform the methods disclosed herein. For example,
the programs may be structured in an object-orientated format using an objectoriented
language such as Java or C#. In another example, the programs can be
structured in a procedure-orientated format using a procedural language, such as
assembly or C. The software components may communicate using any of a
number of mechanisms well known to those of ordinary skill in the art, such as
application program interfaces or inter-process communication techniques,
including remote procedure calls. The teachings of various embodiments are not
limited to any particular programming language or environment. Thus, other
embodiments may be realized.
[0059] For example, FIG. 10 depicts an example system 1000, according
to various embodiments of the invention. This figure is presented to demonstrate
that the disclosed apparatus, systems, and methods are best understood in the
context of the larger systems in which they operate. Accordingly, FIG. 10
illustrates an example drilling environment in which a drilling platform 1002
supports a derrick 1004 having a traveling block 1006 for raising and lowering a
drill string 1008. A top drive 1010 supports and rotates the drill string 1008 as it
is lowered through the well-head 1012. A drill bit 1014 is driven by a downhole
motor and/or rotation of the drill string 1008. As the drill bit 1014 rotates, it
creates a borehole 1016 that passes through various formations. A pump 1018
circulates drilling fluid through a feed pipe 1020 to top drive 1010, downhole
through the interior of drill string 1008, through orifices in drill bit 1014, back to
the surface via the annulus around drill string 1008, and into a retention pit 1022.
The drilling fluid transports cuttings from the borehole 1016 into the retention
pit 1022 and aids in maintaining the borehole integrity.
[0060] The drill bit 1014 is just one piece of a bottom-hole assembly that
includes one or more drill collars (thick-walled steel pipe) to provide weight and
rigidity to aid the drilling process. Some of these drill collars include logging
instruments to gather measurements of various drilling parameters such as
position, orientation, weight-on-bit, borehole diameter, etc. The tool orientation
may be specified in terms of a tool face angle (a.k. a. rotational or azimuthal
orientation), an inclination angle (the slope), and a compass direction, each of
which can be derived from measurements by magnetometers, inclinometers,
and/or accelerometers, though other sensor types such as gyroscopes may also be
used. In one embodiment, the tool includes a three-axis fluxgate magnetometer
and a three-axis accelerometer. As is known in the art, the combination of those
two sensor systems enables the measurement of the tool face angle, inclination
angle, and compass direction. In some embodiments, the tool face and hole
inclination angles are calculated from the accelerometer sensor output. The
magnetometer sensor outputs are used to calculate the compass direction.
[0061] The bottom-hole assembly further includes a ranging tool 1024 to
receive electromagnetic ranging signals 1164 that result from a signal 1162 (e.g.,
current) injected by a surface power supply 1048 into the casing 1168 (at a
terminal point 1170, below an insulating gap 1172). These ranging signals 1164
can be processed to determine distance and direction to the well where the signal
1162 is injected, via the power supply 1048 and the insulated cable 1050.
[0062] Using the ranging signal 1164 measurements, in combination
with tool orientation measurements, the driller can, for example, steer the drill
bit 1014 along a desired path in the drilling well 1026 relative to the existing
well (e.g., target well) 1028 in the formation 1160 using any one of various
suitable directional drilling systems, including steering vanes, a bent sub, and a
rotary steerable system. The steering mechanism can be controlled from the
Earth' s surface, or downhole, with a downhole controller programmed to follow
the existing borehole 1028 at a predetermined distance 1030 and position (e.g.,
directly above or below the existing borehole, as determined by the strength and
direction of the received ranging signals 1164).
[0063] A telemetry sub 1032 coupled to the downhole tools (including
ranging tool 1024) transmits telemetry data to the surface via mud pulse
telemetry. A transmitter in the telemetry sub 1032 modulates a resistance to
drilling fluid flow to generate pressure pulses that propagate along the fluid
stream at the speed of sound to the surface. One or more pressure transducers
1034 convert the pressure signal into electrical signals for processing by a signal
digitizer 1036. Note that other forms of telemetry exist and may be used to
communicate signals from downhole to the digitizer. Such telemetry may
employ acoustic telemetry, electromagnetic telemetry, or telemetry via wired
drill pipe.
[0064] The digitizer 1036 supplies a digital form of the telemetry signals
via a communications link 1038 to a computer 1040 or some other form of a data
processing device. The computer 1040 operates in accordance with software
(which may be stored on information storage media 1042) and user input via an
input device 1044 to process and decode the received signals. The resulting
telemetry data may be further analyzed and processed by the computer 1040 to
generate a display of useful information on a computer monitor 1046 or some
other form of a display device. For example, a driller could employ this system
to obtain and monitor drilling parameters, formation properties, and the path of
the borehole relative to the existing borehole 1028 and any detected formation
boundaries. A downlink channel can then be used to transmit steering commands
from the surface to the bottom-hole assembly.
[0065] The power supply 1048 at the surface thus can be coupled to a
cable 1050 to inject current 1162 into target well casing 1152 and flowing to
down-hole so that magnetic fields that provide ranging signals 1164 can be
generated in the formation 1160 surrounding the target well 1028. Then sensors
in the ranging tool 1024 in the drilling well 1026 can determine the strength of
the magnetic fields that have been induced, so that distance and direction
between the target well 1028 and drilling well 1026 can be determined.
[0066] The target well 1028 often comprises a cased hole with cement
installed around the outside of the casing 1152. In the completion phase of oil
and gas wells, the cement serves to isolate the wellbore, prevents casing failure,
and keeps the wellbore fluids from contaminating freshwater aquifers. Thus,
many embodiments may be realized.
[0067] Referring now to FIGs. 3, 8, and 10, it can be seen that one form
of an apparatus 300 include a well 332 a well having a conductive casing 336
separated by at least one insulating gap 350 into at least two portions. The
apparatus 300 may further include an insulated conductor 372 directly
electrically coupled to a lower one of the portions 354 of the casing that is
separated from an upper one of the portions 352 of the casing by the at least one
insulating gap 350, to form an excitation signal injection point 344 that is not
directly electrically coupled to the upper one of the portions 352, wherein the
upper one of the portions 352 is at a higher elevation of the well 332 than the
lower one of the portions 354. The insulating gap 350 may be approximately 0.1
m in length, but may be larger or smaller. In most embodiments, it is less than 1
m in length.]
[0068] The apparatus 300 may include a ground point 362 that is
relatively close the well head 374. Thus, the apparatus 300 may comprise a
ground point 362 electrically coupled to a surface 348 of the Earth, wherein the
ground point 362 is less than 100m from an opening of the well (e.g., the well
head 374) on the surface 348 of the Earth.
[0069] A power supply may be coupled to the ground point and (a lower
portion of) the casing. Thus, the apparatus 300 may comprise a power supply
376 electrically coupled to the ground point 362 and to the lower one of the
portions 354.
[0070] An actuator, such as a reel, spool, or some other deployment
mechanism (e.g., a wireline tracker), may be used to change the location of the
current injection point to some desired position. Thus, in some embodiments, the
apparatus 300 comprises an actuator 380 (e.g., perhaps as one of the electronic
apparatus 865, or in some embodiments a separate hydraulic or
electromechanical apparatus coupled to and controlled by the controller 825) to
move the excitation signal injection point 344 from a first one of the lower one
of the portions 354', to a second one 354' ' of the lower one of the portions 354
(e.g., from the first injection terminal 344' to the second injection terminal
344").
[0071] A system may include two wells, at least one of which has a
casing divided into portions by insulating gaps, along with a signal injection
apparatus, and a signal receiver. Thus in some embodiments, a system 1000
comprises a first well 1028 having a conductive casing 1052 separated by at least
one insulating gap 1172 into at least two portions 1166, 1168, and an insulated
conductor 1050 directly electrically coupled to a lower one of the portions 1168
that is separated from an upper one of the portions 1166 by the at least one
insulating gap 1172, to form an excitation signal injection point (e.g., at one of
the terminals 1170) that is not directly electrically coupled to the upper one of
the portions 1166, wherein the upper one of the portions 1166 is at a higher
elevation of the well 1028 than the lower one of the portionsl 168.
[0072] The system 1000 may further comprise a second well 1026 that
includes a signal receiver 804, perhaps forming part of a ranging tool 1024. The
system 1000 may include a signal injection apparatus (e.g., a power supply 376,
1048; a cable 372, 1050; and/or a ground point 362, 1180), to inject an excitation
signal 340, 1162 directly into the lower one of the portions 1168 to induce a
magnetic field into a geological formation 1160 surrounding the lower one of the
portions 1168, to provide a ranging signal 1164 corresponding to the magnetic
field is to be received by the signal receiver 804.
[0073] The signal receiver may take a variety of forms. For example, the
receiver 804 may comprise any one or more of a magnetometer, a coil antenna,
or a telemetry receiver.
[0074] The well that includes the ranging signal receiver may comprise a
drilling well, and the other well (where the signal is injected) may have a ground
point located relatively closely to its well head. Thus, the second well 1126 may
comprise a drilling well, as shown in FIG. 10. In some embodiments, the well
locations are reversed with respect to what is shown in FIG. 10, so that signal
injection occurs at the drilling well 1126, and ranging signal reception occurs at
the target well 1128. The signal injection apparatus may comprise a power
supply 1050 coupled to a ground point 1180 that is less than 100 m from an
opening of the first well (e.g., the well 1128) in a surface of the Earth. In some
embodiments, the excitation signal 1162 comprises a current. In one or more
embodiments of the system 1000, and any of the various apparatus described
herein, there may be multiple gaps in a conductive well casing, for either a target
well or a drilling well, where the casing is separated into multiple portions. The
signal injection point may be selectively established at any of the lower portions,
including the lowest available portion of the casing.
[0075] In summary, using the apparatus, systems, and methods disclosed
herein may provide a significant improvement in the signal strength of a signal
injected into a well, perhaps as part of an SAGD application, even when the
ground point location is relatively close to the well head. The improved injected
signal strength, in turn, results in a greater magnitude of the ranging signals
arising from the electromagnetic signals induced in the formation. The disclosed
mechanism can be implemented at a low cost, to provide a practical alternative
to more conventional excitation methods, so that sensors in a drilling well can
accurately detect the ranging signal at depth, and thereby determine a relative
distance and direction to the target well. These advantages can significantly
enhance the value of the services provided by an operation/exploration company,
helping to reduce time-related costs. Additional examples are now discussed:
[0076] Example 1 is a method, comprising: coupling a power supply to a
ground point associated with a first well, and to a lower portion of a conductive
casing disposed within the first well, the lower portion of the conductive casing
separated by an insulating gap from an upper portion of the conductive casing,
wherein the upper portion of the conductive casing is at a higher elevation of the
first well than the lower portion of the conductive casing; and injecting an
excitation signal into the lower portion of the conductive casing to induce a
magnetic field in a geological formation surrounding the first well.
[0077] In Example 2, the subject matter of Example 1 may additionally
include receiving a ranging signal corresponding to the magnetic field at a sensor
disposed in a second well.
[0078] In Example 3, the subject matter of Examples 1-2 may
additionally include processing the ranging signal to determine a distance or
direction to the first well, from the second well.
[0079] In Example 4, the subject matter of Examples 1-3 may
additionally include wherein the first well is a target well and the second well is
a drilling well.
[0080] In Example 5, the subject matter of Examples 1-4 may
additionally include, wherein the first well is a drilling well and the second well
is a target well.
[0081] In Example 6, the subject matter of Examples 1-5 may
additionally include wherein the coupling comprises coupling the power supply
to a ground point that is less than 100 m from an opening of the first well in a
surface of the Earth.
[0082] Example 7 is a method, comprising: casing a well with a
conductive casing separated by insulating gaps into at least two portions; and
attaching an insulated conductor to a lower one of the portions that is separated
from an upper one of the portions by at least one of the insulating gaps, to form
an excitation signal injection point that is not directly electrically coupled to the
upper one of the portions, wherein the upper one of the portions is at a higher
elevation of the well than the lower one of the portions.
[0083] In Example 8, the subject matter of Example 7 may additionally
include prior to casing the well with the conductive casing, casing the well with
an outer casing that has an inner diameter that is larger than the outer diameter of
the conductive casing.
[0084] In Example 9, the subject matter of Examples 7-8 may
additionally include moving the excitation signal injection point from a first one
of the lower one of the portions to a second one of the lower one of the portions.
[0085] Example 10 is an apparatus, comprising: a well having a
conductive casing separated by at least one insulating gap into at least two
portions; and an insulated conductor directly electrically coupled to a lower one
of the portions that is separated from an upper one of the portions by the at least
one insulating gap, to form an excitation signal injection point that is not directly
electrically coupled to the upper one of the portions, wherein the upper one of
the portions is at a higher elevation of the well than the lower one of the
portions.
[0086] In Example 11, the subject matter of Example 10 may
additionally include wherein the at least one insulating gap is less than one meter
in length.
[0087] In Example 12, the subject matter of Examples 10-11 may
additionally include a ground point electrically coupled to a surface of the Earth,
wherein the ground point is less than 100m from an opening of the well on the
surface of the Earth.
[0088] In Example 13, the subject matter of Examples 10-12 may
additionally include a power supply electrically coupled to the ground point and
to the lower one of the portions.
[0089] In Example 14, the subject matter of Examples 10-13 may
additionally include an actuator to move the excitation signal injection point
from a first one of the lower one of the portions, to a second one of the lower one
of the portions.
[0090] Example 15 is an apparatus, comprising: an upper well casing
portion; and a lower well casing portion having an excitation signal injection
terminal, wherein the lower well casing portion is joined to the upper well casing
portion by insulating gap material disposed between the upper well casing
portion and the lower well casing portion.
[0091] In Example 16, the subject matter of Example 15 may
additionally include wherein the insulating gap material comprises a polymer,
rubber, or glass.
[0092] In Example 17, the subject matter of Examples 15-16 may
additionally include wherein at least one of the upper well casing portion or the
lower well casing portion comprises a conductive metal at least partially
surrounded by casing insulation material, to reduce current leakage into a
geological formation when current is injected into the lower well casing portion
via the terminal.
[0093] In Example 18, the subject matter of Examples 15-17 may
additionally include wherein the casing insulation material comprises a polymer,
rubber, or glass.
[0094] Example 19 is a system, comprising: a first well having a
conductive casing separated by at least one insulating gap into at least two
portions, and an insulated conductor directly electrically coupled to a lower one
of the portions that is separated from an upper one of the portions by the at least
one insulating gap, to form an excitation signal injection point that is not directly
electrically coupled to the upper one of the portions, wherein the upper one of
the portions is at a higher elevation of the well than the lower one of the
portions; a second well including a signal receiver; and a signal injection
apparatus, to inject an excitation signal directly into the lower one of the portions
to induce a magnetic field into a geological formation surrounding the lower one
of the portions, wherein a ranging signal corresponding to the magnetic field is
to be received by the signal receiver.
[0095] In Example 20, the subject matter of Example 19 may
additionally include wherein the signal receiver comprises a magnetometer, a
coil antenna, or a telemetry receiver.
[0096] In Example 2 1, the subject matter of Examples 19-20 may
additionally include wherein the second well comprises a drilling well, wherein
the signal injection apparatus comprises a power supply coupled to a ground
point that is less than 100 m from an opening of the first well in a surface of the
Earth, and wherein the excitation signal comprises a current.
[0097] The accompanying drawings that form a part hereof, show by
way of illustration, and not of limitation, specific embodiments in which the
subject matter may be practiced. The embodiments illustrated are described in
sufficient detail to enable those skilled in the art to practice the teachings
disclosed herein. Other embodiments may be utilized and derived therefrom,
such that structural and logical substitutions and changes may be made without
departing from the scope of this disclosure. This Detailed Description, therefore,
is not to be taken in a limiting sense, and the scope of various embodiments is
defined only by the appended claims, along with the full range of equivalents to
which such claims are entitled.
[0098] Such embodiments of the inventive subject matter may be
referred to herein, individually and/or collectively, by the term "invention"
merely for convenience and without intending to voluntarily limit the scope of
this application to any single invention or inventive concept if more than one is
in fact disclosed. Thus, although specific embodiments have been illustrated and
described herein, it should be appreciated that any arrangement calculated to
achieve the same purpose may be substituted for the specific embodiments
shown. This disclosure is intended to cover any and all adaptations or variations
of various embodiments. Combinations of the above embodiments, and other
embodiments not specifically described herein, will be apparent to those of skill
in the art upon reviewing the above description.
[0099] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill in the art that
any arrangement that is calculated to achieve the same purpose may be
substituted for the specific embodiments shown. Various embodiments use
permutations or combinations of embodiments described herein. It is to be
understood that the above description is intended to be illustrative, and not
restrictive, and that the phraseology or terminology employed herein is for the
purpose of description. Combinations of the above embodiments and other
embodiments will be apparent to those of ordinary skill in the art upon studying
the above description.

CLAIMS
What is claimed is:
1. A method, comprising:
coupling a power supply to a ground point associated with a first well,
and to
a lower portion of a conductive casing disposed within the first well, the lower
portion of the conductive casing separated by an insulating gap from an upper
portion of the conductive casing, wherein the upper portion of the conductive
casing is at a higher elevation of the first well than the lower portion of the
conductive casing; and
injecting an excitation signal into the lower portion of the conductive
casing to induce a magnetic field in a geological formation surrounding the first
well.
2. The method of claim 1, further comprising:
receiving a ranging signal corresponding to the magnetic field at a sensor
disposed in a second well.
3. The method of claim 2, further comprising:
processing the ranging signal to determine a distance or direction to the
first well, from the second well.
4. The method of claim 2, wherein the first well is a target well and the
second well is a drilling well.
5. The method of claim 2, wherein the first well is a drilling well and the
second well is a target well.
6. The method of claim 1, wherein the coupling comprises:
coupling the power supply to a ground point that is less than 100 m from
an opening of the first well in a surface of the Earth.
7. A method, comprising:
casing a well with a conductive casing separated by insulating gaps into
at least two portions; and
attaching an insulated conductor to a lower one of the portions that is
separated from an upper one of the portions by at least one of the insulating
gaps, to form an excitation signal injection point that is not directly electrically
coupled to the upper one of the portions, wherein the upper one of the portions is
at a higher elevation of the well than the lower one of the portions.
8. The method of claim 7, further comprising:
prior to casing the well with the conductive casing, casing the well with
an outer casing that has an inner diameter that is larger than the outer diameter of
the conductive casing.
9. The method of claim 7, further comprising:
moving the excitation signal injection point from a first one of the lower
one of the portions to a second one of the lower one of the portions.
10. An apparatus, comprising:
a well having a conductive casing separated by at least one insulating gap
into at least two portions; and
an insulated conductor directly electrically coupled to a lower one of the
portions that is separated from an upper one of the portions by the at least one
insulating gap, to form an excitation signal injection point that is not directly
electrically coupled to the upper one of the portions, wherein the upper one of
the portions is at a higher elevation of the well than the lower one of the
portions.
11. The apparatus of claim 10, wherein the at least one insulating gap is less
than one meter in length.
12. The apparatus of claim 10, further comprising:
a ground point electrically coupled to a surface of the Earth, wherein the
ground point is less than 100m from an opening of the well on the surface of the
Earth.
13. The apparatus of claim 12, further comprising:
a power supply electrically coupled to the ground point and to the lower
one of the portions.
14. The apparatus of claim 10, further comprising:
an actuator to move the excitation signal injection point from a first one
of the lower one of the portions, to a second one of the lower one of the portions.
15. An apparatus, comprising:
an upper well casing portion; and
a lower well casing portion having an excitation signal injection terminal,
wherein the lower well casing portion is joined to the upper well casing portion
by insulating gap material disposed between the upper well casing portion and
the lower well casing portion.
16. The apparatus of claim 15, wherein the insulating gap material comprises
a polymer, rubber, or glass.
17. The apparatus of claim 15, wherein at least one of the upper well casing
portion or the lower well casing portion comprises a conductive metal at least
partially surrounded by casing insulation material, to reduce current leakage into
a geological formation when current is injected into the lower well casing
portion via the terminal.
18. The apparatus of claim 17, wherein the casing insulation material
comprises a polymer, rubber, or glass.
19. A system, comprising:
a first well having a conductive casing separated by at least one
insulating gap into at least two portions, and an insulated conductor directly
electrically coupled to a lower one of the portions that is separated from an upper
one of the portions by the at least one insulating gap, to form an excitation signal
injection point that is not directly electrically coupled to the upper one of the
portions, wherein the upper one of the portions is at a higher elevation of the
well than the lower one of the portions;
a second well including a signal receiver; and
a signal injection apparatus, to inject an excitation signal directly into the
lower one of the portions to induce a magnetic field into a geological formation
surrounding the lower one of the portions, wherein a ranging signal
corresponding to the magnetic field is to be received by the signal receiver.
20. The system of claim 19, wherein the signal receiver comprises a
magnetometer, a coil antenna, or a telemetry receiver.
21. The system of claim 19, wherein the second well comprises a drilling
well, wherein the signal injection apparatus comprises a power supply coupled to
a ground point that is less than 100 m from an opening of the first well in a
surface of the Earth, and wherein the excitation signal comprises a current.