FIELD OF INVENTION
This invention relates to method and system for magnetic ranging and
geosteering, relates generally to downhole ranging and, more specifically, to a
ranging system utilizing a magnetic beacon to guide one wellbore toward
5 another wellbore.
BACKGROUND TECHNICAL INFORAMTION
As the easy-to-access and easy-to-produce hydrocarbon resources have
been depleted over the last century, more and more difficult wells remain.
Also, as global hydrocarbon demand is continuously growing, meeting this
10 demand requires development of more advanced recovery procedures, often
referred to in industry as complex recovery completions and production
techniques. These techniques include, for example, Steam Assisted Gravity
Drainage ("SAGD"), Thermal Assisted Gravity Drainage ("TAGD"), Toe to
Heel Air Injection ("THAI"), Vaporized Hydrocarbon Solvent ("VAPEX")
15 production and Fire Flooding. Such techniques address the mobility problem of
the heavy oil wells by thermally and/or chemically altering the viscosity of the
bitumen to allow for easy extraction.
While each of the complex completion techniques offer a solution to the
issue of heavy oil extraction, they all rely on a common challenge facing
20 well bore construction - the precise placement of adjacent local.cased well bores.
With SAGO and TAGD, injector wells must be precisely placed within a few
meters of the production well, with the injector well being placed a few meters
on top of the producer. Traditionally, this has been accomplished by placing
both the injeCtor and producer wellhead within a few meters at surface. The
25 second well drilled in the well pair subsequently "follows" the in-situ cased
wellbore using some magnetic ranging method.
However, due to issues such as location footprint constraints, infield
drilling requirements and producer well replacement, it is often desired that a
new producer or injector well be re-drilled from a separate location. This
-2-
IPfr D~LKI R2-R5-2B16
location is .. often selected so that the end of the lateral insitu well is approached
by a new drilling well from the opposite direction. However, due to the
increased wellhead to wellhead distance and the uncertainty associated with
traditional surveying based on gravity and earth's magnetic fields, the precise
5 distance between the two wells cannot be achieved. Also, in the case of the
THAI method, it is required that the toe of the horizontal cased wellbore be
intersected with a directional well, a requirement which cannot be met using
traditional surveying techniques alone.
To address the precision wellbore placement requirement of these
10 "opposite approach azimuth" complex completion methods, industry standard
magnetic ranging tools have been deployed, such as the Magnetic Guidance
Tool ("MGT") and Rotating Magnetic Ranging Service ("RMRS"). However,
these techniques are not optimal, as the accuracy of the system at the range
required for the particular application is limited. This limitation translates into
15 operational inefficiency in practice, as sidetracks are often necessary to deliver
the intersection or precise separation that is required. These operational
inefficiencies can also translate into inefficiency in the completion and
production ofthe well, as the well separation and/or intersection point are less
than optimal.
20 In some complex wellbore construction projects, the primary objective
is not hydrocarbon production, but rather hydrocarbon transportation. In
hydrocarbon transportation projects, two wellbores drilled from opposite
directions are often intersected to produce a common wellbore. This 'utube"
comm1:1nication between wellbores allows the deep subterranean borehole to be
25 completed with a common casing string and used as a pipeline for hydrocarbon
transportation. While similar projects have been completed in the past with
conventional magnetic ranging techniques, the same inefficiencies associated
with these techniques as described above has led to cost overruns and general
operational efficiency.
- 3-
IFD D~LKT n2-B5-2816
Accordingly, there is a need in the art for improved downhole ranging
. · techniques to overcome these and other shortcomings in conventional
approaches.
5 BRIEF DESCRIPTION OF THE DRAWINGS
10
15
20
FIG. IA illustrates a ranging system, according to certain illustrative
embodiments ofthe present disclosure;
FIG. IB illustrates alternative approach scenarios of a drilling assembly,
according to cer:tain illustrative embodiments of the present invention;
FIG. I C illustrates the "approach zone" of a drilling assembly, according
to certain illus~rative embodiments ofthe present invention;
FIG: 2A illustrates the magnetic fields at a cross-section from a beacon
that is oriented horizontally along axis A, according to certain illustrative
embodiments of the present disclosure;
FIG. 2B illustrates a beacon oriented at a 45 degree angle along axis B,
according to certain illustrative embodiments of the present disclosure;
FIG. 3 illustrates a variety of beacon/receiver dipole configurations of
ranging systems, according to alternative embodiments of the present
disclosure;
FIG. 4 is a block diagram of system circuitry for a beacon, according to
certain illustrative embodiments of the present disclosure;
FIG. 5 is a block diagram of system circuitry used for a receiver dipole,
according to certain illustrative embodiments of the present disclosure;
FIG. 6 is a flow chart of a generalized ranging method utilized to
25 determine the relative position of a first and second wellbore, according to
30
certain illustrative methods of the present disclosure; and
FIGS. 7, 8 and 9 are flow charts of.alternative methods to determine the
relative position of a first and second wellbore, according to certain illustrative
methods ofthe present disclosure.
-4-
IPD DELHT ~2-G5-291~ 17;55
DESCRIPTION OF INVENTION w.r.t. DRAWINGS
Illustrative embodiments and related methodologies of the present ·
disclosure are described below as they might be employed in a ranging system
and method utilizing a magnetic dipole beacon to guide one wellbore toward
5 another wellbore. In the interest of clarity, not all features of an actual
implementation or methodology are described in this specification. It will of ·
course be appreciated that in the development of any such actual embodiment,
numerous implementation-specific decisions must be .made to achieve the
developt?rs' specific goals, such as compliance with system-related and
10 business-related constraints, which will vary from one implementation to
another. Moreover, it will be appreciated that such a development effort might
be complex and time-consuming, but would nevertheless be a routine
undertaking for those of ordinary skill in the art having the benefit of this
disclosure. Further aspects and advantages of the various embodiments and
15 related methodologies of the disclosure will become apparent from
consideration ofthe following description and drawings.
As described herein, the present disclosure describes illustrative ranging
methods and systems that utilize a magnetic dipole beacon to guide one
wellbore towards another wellbore. In a generalized embodiment, the beacon
20 induces low frequency magnetic fields into the formation from a first wellbore,
which are then sensed by one or more dipoles (acting as receiver(s)) in a second
wellbore. The beacon and/or receiving dipoles are magnetic dipoles, and in
certain embodiments one or both may be a triaxial magnetic dipole.
Nevertheless, in either embodiment, the magnetic fields that are emitted from
25 the beacon form a natural path of approach to the first well bore. As a result, the
second wellbore can be steered to align with the magnetic field direction, which
will automatically establish the ideal approach towards the first wellbore.
FIGS. 1 A-1 C are provided to illustrate this generalized summary of the
present disclosure. FIG. IA illustrates an illustrative ranging system 100 ofthe
30 present disclosure that can be utilized in, for example, a SAGD application.
- 5-
IPD DELHI 02-85-281~ 17;55
Here, a first well 10 (e.g., producer wellbore) has been drilled using any suitable
drilling technique, and a bottomhole assembly 11 is deployed downhole via a
wireline 13, tor example. Bottom hole assembly 11 includes a magnetic dipole
17 serving as the beacon. Beacon 17 may take a variety of forms, including for
5 example, a solenoid or magnetometer. In this embodiment, dipole 17 is a
triaxial magnetic dipole positioned near the toe of first well 10. A second well
12 (e.g., injector wellbore) is then drilled using drilling assembly 14 which may
be, for example, a logging-while drilling ("L WD") assembly, measurementwhile
drilling assembly ("MWD") or other desired drilling assembly. In this
10 exemplary embodiment, drilling assembly 14 includes a bottom hole assembly
having a triaxial magnetic dipole 16 serving as the receiver. Note, however,
that dipoles 16 and 17 may serve as a beacon or receiver, and may take the form
of other dipole realizations other than triaxial.
As will be described in greater detail below, during an exemplary
15 drilling operation using relative positioning system 100, beacon 17 emits low
frequency magnetic fields 18 which propagate toward second wellbore 12.
Magnetic fields 18 form a natural path of approach which are utilized by
drilling assembly 14 to geosteer second well 12 as desired. To achieve this,
local or remote processing circuitry calculates the direction of magnetic fields
20 18 and uses this data to determine the distance and direction to beacon 17
within first well 10. Once the relative position is determined, the circuitry
generates signals necessary to steer the drilling assembly 14 in the direction
needed to intersect or avoid first well 10 as desired.
To further summarize the intent of this disclosure, FIG. 1 B shows
25 alternative approach scenarios of drilling assembly 14, while FIG. 1 C shows the
"approach zone" of drilling assembly 14. First well 10 is not illustrated for
simplicity. As shown in FIG. 1B, in each approach Sl:t!nario 1-3, drilling
assembly 14 steers second well 12 towards direction H of magnetic fields 18
which naturally meets the two wells. If such intersection is not desired, other
30 illustrative embodiments of the present disclosure utilize magnetic field
- 6 -
~PD D~LHT R2-85-2BlS 1T"SS
gradients to determine the distance and direction to beacon 17 once the wells
get close enough to each other, and the wells can be steered along the ideal
approach (such as a injector/producer configuration of SAGD). In other
illustrative embodiments, orientation of beacon 17 can be adjusted based on the
5 desired approach angle, thus allowing an ideal approach in the approach zone,
as shown in FIG. lC.
Although the present disclosure is described in the context of a SAGD
application, it may be utilized in a variety of other applications that accurately
and reliably position a well being drilled with respect to a nearby well. Such
10 applications may include, for example, the drilling of relief wells and/or well
avoidance operations. In a well avoidance application, a well is drilled utilizing
the positioning system described herein, which actively searches for the
magnetic fields emitted by the beacon in the drilling path. If such wells or
structures are detected, the positioning system alters the drill path accordingly.
15 In relief operations, the first well bore may be a blow out well, while the second
wellbore is an intersecting well utilized to stop a hydrocarbon spill emitting
from the first well. Here, the intersecting well may be substantially
perpendicular to the other well. In yet other embodiments, the second well may
be drilled such that its end intersects with the toe of the first wellbore to create a
20 utube.
The operation of an illustrative magnetic beacon will now be described.
FIGS. 2A and 2B illustrate the operation of a magnetic beacon oriented at 0
degrees and 45 degrees, respectively, according to illustrative embodiments of
the present disclosure. Magnetic. field, H, from a magnetic dipole (emitted from
25 beacon 17 or receiver 16, e.g.) at low frequency is independent ofthe resistivity
of the formations, and it can be written as:
H = (114n)(3r(r · u)- u)(llr3
)
Eq.(l),
- 7 -
TOn rr_~_r..~.~ .T 82-95-2016 ..;;....r ~ ----
where f is the unit vector pointing from the beacon to the antenna in the other
well, and it is the unit vector in the direction of the magnetic field measurement.
FIG. 2A shows the magnetic fields at a cross-section from a beacon 17
that is oriented horizontally along axis A, while FIG. 2B shows beac.on 17
5 oriented at a 45 degree ·angle along axis B. As it can be seen, magnetic fields 18
propagate from one pole to the other in a roughly circular pattern, where each
magnetic field line originates and terminates at the magnetic dipole position.
The fields 18 that are around the magnetic dipole 17 (in· roughly radial
direction) show a mainly circular pattern in the volume of operation. As a
10 result, they cannot be used effectively for guiding bottom hole assembly 14.
However, the fields 18 that are roughly in axial direction (adjacent axis A,B)
from the dipole beacon 17 follow a linear or curved pattern, which marks a
smooth approach to the beacon position. Each beacon orientation allows a
smooth approach from a. certain approach zone, as shown in FIG. 1C. If
15 approach from a different approach zone is required, beacon orientation can be
altered to point to that zone as shown in FIG. 2B.
There are a variety of ways in which to alter the orientation of the
beacon. For example, alteration of the beacon orientation may be performed
mechanically by rotating the antenna physically in the desired direction. It can
20 .also be accomplished synthetically by adjusting relative strengths of multiple
antennas that make up the beacon, in the case of a b~acon implementation with
multiple antennas that are pointing in different directions.
In certain illustrative embodiments of the present disclosure, the angle of.
beacon 17 can be varied with respect to time to optimize the well path of
25 approach. In one embodiment, the adjustment can be performed manually or
automatically by an electrical system that determines the ideal angle based on
the absolute and relative position of wells. In other embodiments, the
orientation can also be adjusted to find or maintain the minimum or the
maximum signal at the receiver in the other well. In yet other embodiments, the
JO beacon orientation at which the maximum axial or total received fields are
- 8 -
XPD DPLH~ B2-B5-2816
5
obtained can be maintained to optimize the guidance operation. The beacon
orientation can also be used along with the survey infonnation from the second
well to triangulate or locate the second well with respect to the first well, where
the location information can be used to optimize a well path.
In other embodiments, multiple beacon orientations can be established at
the same position along a borehole by placing multiple collocated or staggered
magnetic dipoles, and by varying the signal levels of such dipoles to establish
different magnetic dipole orientations. As an example, a tri-axial beacon can be
used to synthesize any arbitrary beacon orientation from a weighted
10 combination of all three. Also, different frequencies can be used by different
beacons to allow multiple measurements to be made simultaneously in the other
wellbore. When multiple beacons are used at the same position, they can allow
multiple choices in the angle of approach.
As described above, preferably the beacon is placed at or near the toe of
15 the well. However, depending on the operational need, it can also be placed at
different positions along the well as desired. For example, if the well needs to
be intersected in the middle of a horizontal section, the beacon can be placed at
the point of desired intersection. In such cases, the beacon may be removed
immediately before the intersection, after the intersection path is set with high·
20 confidence. In other illustrative embodiments, multiple beacons can be placed
at different positions along the wellbore, and steering decision can be made
collectively based on all of the beacons. For example, a toe beacon can be used
in the approach, but after the approach is complete, the beacon can be moved to
a new location in the first well to allow ideal SAGD placement.
25 The beacon may be positioned downhole in a variety of ways. For
example, the beacon may be deployed along a wireline (solenoid on a wire, e.g.)
as shown in FIG. lA. Alternatively, for example, the beacon may be deployt::d
along a wireline logging tool, a production tool along a cased wellbore, as part
of a L WD tool, or may even be permanently deployed in a cased well bore.
30 When permanently deployed, the beacons may be made out of a high friction
- 9 -
IPD O~LH~ ~2-95-2916 17;55
housing material which prevents 'it from sliding along the wellbore.
Alternatively, the beacon may simply be positioned along a horizontal portion
of the wellbore, thus using gravity to maintain its position. In yet other
embodiments, the housing may be a magnetic housing which adheres it to the
5 casing or some other metallic downhole structure. · In case the casing is
composed of magnetic material, a direct current signal can be used to turn the
beacon into an electromagnet which can simultaneously be excited with the
alternating current that operates the beacon.
In yet other illustrative embodiments of the present disclosure, the
10 magnetic beacons may also be placed at the surface or at the bottom of the sea
floor in an offshore application. In such applications, depending on the desired
well path, magnetic field lines can be utilized directly to steer the well.
FlG. 3 is a simplified illustration of a variety of beacon/receiver dipole
configurations of ranging systems 300A-E, according to alternative
15 embodiments of the present disclosure. The beacons dipoles 17 are shown on
the left-hand side and the receiver dipoles 16 are shown on the right-hand side.
Although the described application is based on L WD measurements for the
receiver(s) dipole 16, it is also possible to utilize a wireline tool to make such
measurements, as previously described. Such a wireline tool can be deployed
20 inside the bottom hole assembly 14, for example, or it can replace it completely.
In some embodiments, receiver dipoles 16 are placed as close as possible to the
drill bit 19, however, dut: to presence of drill motor and difficulties in routing
power and communication through the motor section, it may be more feasible to
have the receivers 16 above the bit 19 and drill motor. Note that in alternate
25 embodiments, dipoles 16,17 may act as a beacon or receiver.
Still referring to FIG. 3, in certain embodiments, beacon(s) 17 may be
comprised of a single magnetic dipole that is oriented in the desired direction
mechanicaHy or by design. In such cases, the dipole may be oriented in the
axial (z-) direction (as is one of the beacons 17 of system 3000). However, it is
30 more advantageous to have a tri-axial beacon . configuration with three
- 10-
collocated magnetic dipoles that are ideally placed orthogonal to each other.
Such beacons are shown in ranging systems 300A, B, C (two triaxial beacons),
0 (single triaxial beacon and one single-axis beacon), and E (two triaxial
beacons). The triaxial configuration allows orientation of the beacon m any
s desired direction without any mechanical manipulation.
In yet ~ther embodiments, beacons J 7 may be comprised of multiple
beacon dipoles ·at different positions along the wellbore (or a downhole
tool/assembly), such as shown in ranging systems 300C, D and E. Such
embodiments allow the acquisition of gradient measurements, which is the
10 difference of magnetic fields between two closely spaced receivers 16. The
orientation of the gradient may be arbitrary, however, a z-directed gradient
(such as that shown in system 300C, D, and E) is ideal for an horizontal
approach. In other illustrative embodiments, however, other gradient directions
(such as x- or y- gradients) may also be acquired.
15 In those embodiments utilizing multiple beacons, for example, the
beacons may be referred to as a first and third magnetic dipole. Here, the first
magnetic dipole may be utilized to acquire a first magnetic field measurement,
while the third magnetic dipole is utilized to acquire a second magnetic field
measurement. The directions of the first and/or second magnetic field
20 measurement may then be utilized for ranging/steering determinations· as
described herein.
The magnetic dipoles can be realized with, for example, tiltt:d or non- .
tilted coils, solenoids, flux-gate magnetometers, atomic magnetometers, or any
other type of device that can measure magnetic fields. The sensitivity and
25 signal to noise ratio ofthe dipole receiver determines the range and accuracy of
the measurement. As understood in the art, the gradient measurement requires
much higher signal to noise in the magnetic field, compared to an absolute
measurement for achieving the same percentage accuracy.
Still referring to FIG. 3, the receiver(s) 16 that are shown in right-hand
30 side of the figure are also magnetic dipoles and they are of tri-axial
- 11 - .
TPO D~tHI n2-B5-2BlS
configuration. However, one of the receivers 16 of system 300B is a single-axis
dipole receiver. Nevertheless, in those embodiments using triaxial designs, the
triaxial receivers may be realized by a one or more single or dual axis receivers,
thereby taking advantage of the multiple measurements at different rotation
5 angles that are naturally available during the rotation phase of the drilling
process. · In such embodiments, a triaxial measurement is synthetically
constructed from multiple single or dual axial measurements at different
rotation angles by combining all measurements with appropriate weights. Such
manipulation of measurement coordinate systems is based on linear algebra and
10 vector manipulation. Similar to what was described above for the beacon, the
receivers in certain embodiments can also perform a gradient measurement for
calculation of distance or orientation. The gradient orientation can be the axial .
(z-) direction for a horizontal approach, however, alternate direction could also
be acquired. Each magnetic dipole that makes of one of the three axes, may be
15 collocated or staggered along the borehole axis with respect to each other.
The design of bottom hole assembly 14 may take a variety of forms. In
one illustrative embodiment, the receiving dipole(s) may be placed in grooves
on the bottom hole assembly with a protective cover. In others, the receiving
dipole(s) are positioned along the bottom hole assembly within a non-magnetic
20 collar which does not interfere with operation of the dipoles. It is noted here
that what is described herein for the transmitting or receiving dipoles is not
considered to be limiting and alternative configurations with more and less
number of dipoles are possible.
FIG. 4 is a block diagram of system circuitry 400 for the beacon dipole,
25 according to certain illustrative embodiments of the present disclosure .. A
system control center 402 activates the signal generator 404 to thereby produce
a signal that is routed to different beacons as necessary. A de-multiplexer 406
can be ·used to select which beacon 17 is operated, however multiple beacons
can also be operated at the same time as mentioned above. In certain
JO embodiments, the system can be operated as narrow band at a substantially
- 12-
T_-c~~~ ·0.·~- -·· ;n....,:::c;..-. t~ ~~ : T-:::- A-2- -RS--- -291S
~------------------------------------------------------------------------
fixed frequency, or it can be operated with a time-domain pulse with wide-band
excitation. For the wide-band excitation, the maximum frequency of operation
can be limited to minimize the formation resistivity effects which may
complicate the fields and interpretation. Yet, a wide band of low frequencies in
5 the range 0.0 I - I 00 Hz, for example, can be used also partially dependent on
the desired range of operation. Furthermore, the excitation may be dynamically
optimized based on the estimated range between the transmitting and receiving
dipoles. Again, as previously mentioned, the beacon magnetic dipoles may be
transmitting and drilling well magnetic dipoles may be receiving. Alternatively,
10 the beacon magnetic dipoles may be receiving and drilling well magnetic
dipoles may be transmitting.
Although this embodiment of circuitry 400 forms part of beacon I7, in
other illustrative embodiments, one or more components of circuitry 400 may
be located at a remote location from beacon 17 (surface, e.g.). In such
15 embodiments, beacon 17 would include the necessary communications circuitry
for wired or wireless communications.
FIG. 5 is a block diagram of system circuitry 500 used for the receiver
dipole(s), according to certain illustrative embodiments of the present
disclosure. A system control center 502 receives the magnetic field
20 measurement signals from a multitude of receivers I6 at the same of different
positions along the wellbore. In this embodiment, the received data is stored in
a data buffer 504 and then communicated to the surface via
processing/communications unit 506 for further processing. In certain other
embodiments, some or all ofthe processing may be performed downhole, which
25 may provide savings in telemetry bandwidth. The acquisition unit 508 may
make measurements as a function. of time and the measurement may be
converted to frequency domain via Fourier transform. The magnetic field
measured data may be analyzed in complex Phasor domain at individual
frequencies with real and imaginary parts, or with associated phase or amplitude
30 information. Due to the low frequency nature of the excitation, the received
- I3 -
5
measurement signals will have substantially constant phase which is
independent of the formation properties. As a result, amplitude information is
expected to carry most of the desired data, and phase can be neglected from
communication and subsequent processing, in certain embodiments.
Although this embodiment of circuitry 500 forms part of drilling
assembly 14, in other illustrative embodiments, one or more components of
circuitry 500 may be located at a remote location from assembly 14 (surface,
e.g.). In such embodiments, drilling 14 would include the necessary
communications circuitry for wired or wireless communications to thereby
10 communicate data back uphole and/or to other assembly components (to steer a
drill bit forming part of assembly 14, for example).
In alternate embodiments, the circuitry 400,500 necessary to perform
one or more aspects of the techniques described herein may be located at a
remote location away from beacon 17/drilling assembly 14, such as the surface
15 or in a different wellbore. Although not shown, circuitry 400,500 may include
at least one processor and a non-transitory and computer-readable storage, all
interconnected via a system bus. Software instructions executable by the
processor for implementing the illustrative relative positioning methodologies
described herein in may be stored in locai storage or some other computer-
20 readable medium. It will also be recognized that the positioning software
instructions may also be loaded into the storage from a CD-ROM or other
appropriate storage media via wired or wireless methods.
Moreover, various aspects of the disclosure may be practiced with a
variety of computer-system configurations, including hand-held devices,
25 multiprocessor systems, microprocessor-based or programmable-consumer
electronics, minicomputers, mainframe computers, and the like. Any number of
computer-systems and computer networks are acceptable for use wilh the
present disclosure. The disclosure may be practiced in distributed-computing
environments where tasks are performed by remote-processing devices that are
30 linked through a communications network. In a distributed-computing
- 14-
environment, program modules may be located in both local and remote
computer-storage media including memory storage .devices. The present
disclosure may therefore, be implemented in connection with various hardware,
software or a combination thereof in a computer system or other processing
5 system.
In certain other illustrative embodiments, calibration of the
magnetometers and coils used as transmitting or receiving dipoles can be
performed via one of the standard and available surface or in-situ calibration
methods. Moreover, in certain embodiments, calibration may be performed as a
10 function of pressure and temperature, which reduces the errors in the calibration
application with varying environmental conditions.
As yreviously described, embodiments of the present disclosure analyze
the direction of magnetic fields to determine the direction to the beacon. As a
result, a drilling assembly may be steered along a desired well path. In certain
15 other embodiments, the distance to the beacon may also be determined. Here,
the distance calculations performed by system control center 502 will now be
described. With reference to FIGS. lA-5, provided that the second wellbore 12
is in the approach zone, the magnetic field can be approximated as the
following:
20
H = (112n)u(llu3
)
Eq.(2a),
Hu = 11(2nu3
)
Eq.(2b),
where u is the distance between the beacon and receiving dipoles and Hu is the
25 projection·· of H in the u direction. Hu = H • u, where • is inner product
operation. System control center 502 can then calculate the distance between
the beacon and the receiver based on Equations (2a,b) as follows:
u = 3.Y(l/(2nHu))
Eq.(3),
- 15 -
IPO nELHT n2-B5-2Bl6
------------
where 3
--./ r~fers to.the cube root.
Even though Equation (3) can be used to calculate the distance in certain
embodiments, it presents challenges because the exact strength of the beacon
·and gain of the receiver may not be known or accurately calibrated. Even
5 though calibration may have been performed individually to the beacon and the
receiver, after fabrication, combined gain of the beacon and receiver may have
drifted. As a result, the distance calculation of system control center 502 may
be skewed by such factor. In <_>rder to avoid such problem, certain embodiments
of the present disclosure perform a gradient measurement (derivative of the
10 field along direction u) as follows:
(8Hu)l(8u) =-3/(2mi)
Eq.(4).
When the ratio between the absolute measurement U.e., amplitude of the
measurem~nt) and gradient measurement are taken, distance between the
15 beacon and the receiver can be computed by system control center 502 m a
normalized fashion that is free of any gain errors as follows:
20
Huf((8Hu)l(8u)) = -(113)u
Eq.(5a),
u = -3 (Hui((8Hu)l(8u)))
Eq.(5b}.
It can be seen from Equations (5a,b) that distance can be calculateq as a
ratio of the absolute measurement to the gradient measurement times a factor of
3. This formula is valid only if the second well is in the approach zone of the
beacon, i.e. the second well is substantially aligned with the· beacon orientation.
25 As described above, the beacon cC:m be dynamically orientated in the direction
of the second well to achieve such condition.
FIG. 6. is a flow chart of a generalized ranging method 600 utilized to
determine the relative position of a first and second wellbore, according to
certain illustrative methods of the present disclosure. At block 602, a first
30 magnetic dipole is positioned along a first wellbore. At block 604, a triaxial
- 16-
r~D D~LKI R2-85-2Bl6
.---------------------------------------------------
magnetic dipole is positioned along a second well bore. The dipoles of the first
and second wellbores may be beacons or receivers, as previously described.
Thus, if the dipole of the first wellbore is a beacon, the dipole of the second
wellbore is a receiver - and vice versa. Nevertheless, in either embodiment, at
5 block 606 a magnetic field is propagated between the first and second wellbores
(emitted from one of the dipoles), where it is measured by the opposing dipole
in the other wellbore. At block 608, the system control center calculates the
direction of the first magnetic field measurement, which can be calculated from
the magnetic field measurements in three linearly independent directions using
10 simple linear algebra. In the case where the three directions are all
perpendicular to each other, the direction is simply the vector that is made from
each of the measurements. In the case where three directions are not
perpendicular to each other, a coordinate transformation can be applied.
Thereafter, at block 610, the directional data is processed by the system control
15 center to thereby steer the bottom hole assembly as desired based upon the
direction data. In one embodiment, the bottom hole assembly is aligned to be in
the direction of the first magnetic field measurement. In other embodiments,
however, ~he bottom hole assembly may be steered to avoid the beacon emitting
the dipole.
20 Method 600 may be implemented in a variety of ways. For example, as
illustrated in FIGS. 1A-3, the bottom hole assembly 14 may be positioned along
the second wellbore and comprise the triaxial magnetic dipole(s). In such an
embodiment, the magnetic field is transmitted from one or more first magnetic
dipoles (i.e., beacons) positioned in the first wellbore 10, and the first magnetic
25 field measurement is then acquired in the second wellbore using the triaxial
dipole(s). Alternatively, however, in this same embodiment, the magnetic field
may be transmitted using the triaxial magnetic dipole(s) (i.e., beacon) in the
second wellbore, and the first magnetic field measurement is obtained using the
magnetic dipole in the first wellbore.
- 17-
In yet another implementation of method 600, the bottom hole assembly
14 may be positioned along first well bore I 0 and comprise the first magnetic
dipole(s). Here, the magnetic field may then be propagated from the second
wellbore 12 using the triaxial magnetic dipole(s) (which may be positioned
5 along wellbore 12 using any of the methods described herein). The first
magnetic field measurements are then obtained using the first magnetic
dipole(s) of assembly 14 in the first well bore I 0. Alternatively, however, in this
same embodiment, the magnetic field may be transmitted using the first
magnetic dipole as the beacon, and then the first magnetic field measurement is
10 obtained using the triaxial magnetic dipole(s) in the second wellbore 12.
In yet other methods 600, at block 602, placement of the first magnetic
dipole in the first wellbore is accomplished by placing at least one magnetic
dipole in the first wellbore. It is also possible to synthetically generate a
magnetic dipole by using combinations of multiple secondary dipoles as shown
15 in systems 300C-E of FIG. 3. In certain embodiments, the secondary magnetic
dipoles are collocated, meaning that their electrical centers are at the same
position, where electrical center is the effective center of the equivalent
magnetic dipole. As· shown in systems 300C-E, three secondary magnetic
dipoles may be utilized to synthesize the first magnetic dipole. This &llows
20 changing the angle of the beacon electrically, without any physical alteration.
FIGS. 7, 8 and 9 are flow charts of more detailed methods to determine
the relative position of a first and second wellbore, according to certain
illustrative methods of the present disclosure. In method 700, the first magnetic
dipole(s) and triaxial magnetic dipole(s) are positioned in the wellbores as
25 previously described in method 600. At block 702, survey data is first used to
place the second wellbore 12 within the approach zone. Based on the survey
data, ideal drilling path and drilling direction of tht:: well are determined and
drilling is executed based on this information. At block 704, beacon 17 is
activated to propagate the magnetic ·field, and the system control center
30 (controlling the receiver dipole(s)), via receivers 16, obtains absolute magnetic
- 18-
field measurements as previously described. Thereafter, at block 706, the
system control center determines the direction and distance to the beacon and
steers the drilling assembly to align (or avoid) with the direction of the magnetic
field. The method can be terminated ifthe wells are deemed to be very close to
5 each other (if no intersection is desired) from the survey data.
In method 800, the first magnetic dipole(s) and triaxial magnetic
uipole(s) are positioned in the wellbores as previously described. At block 802,
survey data is first used to place the second wellbore within the approach zone.
At block 804, beacon 17 is then activated to propagate the magnetic field, and
10 the system control center, via the receiver(s) 16, obtains ~bsolute magnetic field
measurements. Using the measurements at block 806, the system control center
then calculates the distance and direction to the beacon 17 using the absolute
magnetic field measurement using Equation (3) described herein. At block 808,
the system control center then determines the optimal well path based on the
15 measured relative beacon position. At block 810, the drilling assembly is
steered along the optimal well path.
In method 900, the first magnetic dipole(s) and triaxial magnetic
dipole(s) are positioned in the wellbores as previously described. At block 902,
survey data is first used to place the second wellbore within the approach zone.
20 At block 904, beacon 17 is then activated to propagate the magnetic field, and
the system control center, via the receiver(s) .16, obtains absolute magnetic field
measurements. At block 906, the system control center, using two or more
receivers 16 and their measurements, obtains a magnetic field gradient
measurement. Using the absolute and gradient measurements at block 908, the
25 system control center then calculates the distance and/or direction to the beacon
17 using the using the Equations (3) and (5), respectively, described herein. At
block 910, the system control center then determines the optimal well path
based on the measured relative beacon position. At block 912, the drilling
assembly is steered along the optimal well path.
- 19-
IPD D~LKI n2-D5-2Dl6
Alternatively, using any of methods 700, 800 or 900, the system control
center may adjust the direction of the beacon before or after the first magnetic
field meas.urement is obtained. To do so, the system control center first
calculates the expected bit position and drilling orientation of the second
5 wellbore 12 based upon survey data. Then the system control center determines
an optimal well path based on drilling considerations such as mechanical
properties of layers. Thereafter, the direction of the beacon may be adjusted
based upon the optimal well path of the second wellbore. This can allow
execution of drilling in an optimal well path rather than a random one and it can
10 produce savings in drilling time, cost and enhance safety.
As previously described, in an alte~native application, the relative
positioning system and methods of this disclosure are also useful in well
avoidance operations. In such an application, a target well is not necessarily
present. Nevertheless, in one illustrative method, the relative positioning
15 system is deployed along a drilling assembly. During drilling, processing
circuitry on-board (or remote to) the system actively searches for other magnetic
fields emitted from beacons utilizing the various components and magnetic
field features described herein. Once the magnetic fields are measured and
analyzed, the positioning system alters the drill path accordingly.
20 Therefore, embodiments of the present disclosure described herein
-utilize the natural shape of magnetic fields for guidance and landing of
wellbores. Embodiments of the disclosure do not require any interpretation,
distance of direction calculation in the approach phase. As a result, the system
does not require any synchronization between the beacon and the receivers; and
25 it ca~ function even in the case of lower signal to noise ratios which translates
to larger range of operation. The system also allows landing of the wells on top
of each other from opposite directions, which could potentially decrease the
total time of the drilling operation in a SAGD operation (if both wells are
injectors, or both are producers). Furthermore, the disclosed systems can be
30 used to intersect the wells head-on, which can, again, be used for various
-20-
5
purposes, such as to reduce the time of drilling, or to be able to have two access
points to a well for optimized production.
Embodiments described herein further relate to any one or more of the
following paragraphs:

claims.
1. A method for downhole ranging, the method comprising placing
a first magnetic dipole in a first wellbore; placing a triaxial magnetic dipole in a
second well bore; obtaining a first measurement of a magnetic field propagating
between the first and second wellbores; calculating a direction of the first
magnetic field measurement; and steering a bottom hole assembly based upon
10 the direction of the first magnetic field measurement.
2. A method as defined in paragraph I, wherein the bottom hole
assembly is positioned along the second wellbore, the bottom hole assembly
comprising the triaxial magnetic dipole; and obtaining the first measurement
comprises: transmitting the magnetic field from the first wellbore using the first
15 magnetic dipole; and obtaining the first magnetic field measurement using the
triaxial magnetic dipole in the second wellbore.
3. A method as defined in any of paragraphs 1-2, wherein the
bottom hole assembly is positioned along the second wellbore, the bottom hole
assembly comprising the triaxial magnetic dipole; and obtaining the first
20 measurement comprises: transmitting the magnetic field from the second
wellbore using the triaxial magnetic dipole; and obtaining the first magnetic
field measurernt:nt using the first magnetic dipole in the first wellbore.
4. A method as defined in any of paragraphs 1-3, wherein the
bottom hole assembly is positioned along the first wellbore, the bottom hole
25 assembly comprising the first magnetic dipole; and obtaining the first
measurement comprises: transmitting the magnetic field from the second
wellbore using the triaxial magnetic dipole; and obtaining the first magnetic
field measurement using the firstmagnetic dipole in the first wellbore.
5. A method as defined in any of paragraphs 1-4, wherein the
30 bottom hole assembly is positioned along the first wellbore, the bottom hole
- 21 -
TPD DEIHT R2-R5-281S
5
assembly comprising the first magnetic dipole; and obtaining the first
measurement comprises: transmitting the magnetic field from the first wellbore
using the first magnetic magnetic dipole; and obtaining the first magnetic field
measurement using the triaxial magnetic dipole in the second wellbore.
6. A method as defined in any of paragraphs 1-5, wherein steering
the bottom hole assembly based upon the direction of the first magnetic field
measurement comprises aligning the bottom hole assembly to the direction of
the first magnetic field measurement.
7. A method as defined in any of paragraphs 1-6, wherein placing
10 the first magnetic dipole in the first wellbore comprises placing at least two
secondary magnetic dipoles in the first wellbore; and synthesizing the first
magnetic dipole using the at least two secondary dipoles.
15
8. A method as defined in any of paragraphs 1-7, wherein the at
least two secondary magnetic dipoles are collocated.
9. A method as defined in any of paragraphs 1-8, wherein the at
least two secondary magnetic dipoles comprise three secondary magnetic
dipoles.
10. A method as defined in any of paragraphs 1-9, further
comprising adjusting a direction of the first magnetic dipole after at least one
20 first magnetic field measurement is obtained.
11. A method as defined in any of paragraphs 1-10, wherein
adjusting the direction of the first magnetic dipole comprises analyzing survey
data of the second wellbore; calculating an expected well path of the second
wellbore based up·on the survey data; and adjusting the direction of the first
25 magnetic dipole based upon the expected well path of the second well bore.
12 ... A method as defined in any of paragraphs 1-1 1, further
comprising placing a third magnetic dipole along the first wellbore; utilizing the
third magnetic dipole to obtain a second measurement of the magnetic field
. .
propagating between the first and second wellbores; and.calculating a direction
30 of the second magnetic field measurement, wherein the directions of the first
- 22-
IPh DELHX G2-G5-2B1S 17;55
and second magnetic field measurements are utilized to steer the bottom hole
assembly.
13. A method as defined in any of paragraphs 1-12, further
comprising calculating a distance between the first and second wellbores based
5 upon an amplitude of the first magnetic field measurement.
14. A method as defined in any of paragraphs 1-13, wherein the
distance is calculated using: u = 3"(11(27tHu)).
15. A method as defined in any of paragraphs 1-14, further
comprising obtaining a magnetic field gradient measurement using the first and
10 second magnetic field measurements; and utilizing the magnetic field gradient
measurement to calculate a distance between the first and second wellbores.
16. A method as defined in any of paragraphs 1-15, wherein
obtaining the magnetic field gradient measurement further comprises
calculating an amplitude of the first magnetic field measurement; and
15 calculating the distance between the first and second wellbores further
comprises calculating a ratio of the amplitude of the first magnetic field
measuremt;:nt to the magnetic field gradient measurement.
20
1 7. A method as defined in· any of paragraphs 1-16, wherein the ratio
is expressed as:. u = -3 (Hu/((8Hu)/(8u))).
18. A method as defined in any of paragraphs. 1-18, wherein the first
wellbore is a producer well; and the second wellbore is an injector well,
wherein the method is utilized in a Steam Assisted Gravity Drainage operation.
19. A method as defined in any of paragraphs 1-18, wherein the first
wellbore is a blow out well; and the second wellbore is an intersecting well,
25 wherein the method is utilized to stop a hydrocarbon spill emitting from the
blow out well.
20. A method as defined in any of paragraphs 1-19, wherein the
method is utilized to intersect the first and second wellbores to create a single
well.
- 23-
5
10
21. A method as defined in any of paragraphs 1-20, wherein the first
·well bore is intersected with an end of the second well bore.
22. A method as defined in any of paragraphs l-2l, wherein the first
wellbore is intersected substantially perpendicularly with the second wellbore.
23. A method as defined in any of paragraphs 1-22, wherein the
method is utilized in a well avoidance operation.
24. A method as defined in any of paragraphs 1-23, wherein the
bottom hole assembly is a drilling assembly, logging assembly or wireline
assembly.
25. A downhole ranging system comprising processing circuitry to
implement any of the methods of claims 1-24.
Moreover, the methodologies described herein may be embodied within
a computer-program product comprising instructions which, when executed by
at least one processor, causes the processor to perform any of the methods
15 described herein.
Although various embodiments and methodologies have been shown
and described, the disclosure is not limited to such embodiments and
methodologies and will be understood to include all modifications and
variations... Therefore, it should be understood that the disclosure is not
20 intended to be limited to the particular forms disclosed. Rather, the intention is
to cover all modifications, equivalents and alternatives falling within the spirit
and scope of the disclosure as defined by the appended claims.