Fiber Optic Current Monitoring for Electromagnetic Ranging
Field of the Invention
The invention relates to borehole drilling operations, and more particularly to
methods and systems for tracking the drilling of multiple boreholes relative to one another.
Most particularly, the invention relates to methods and systems for determining the relative
location of a target well from a borehole being drilled utilizing a fiber optic sensor
positioned in the target well.
Background of the Invention
As easy-to-access and easy-to-produce hydrocarbon resources are depleted, there is
an increased demand for more advanced recovery procedures. One such procedure is
15 steam assisted gravity drainage (SAGD), a procedure that utilizes steam in conjunction
with two spaced apart wellbores. Specifically, SAGD addresses the mobility problem of
heavy oil in a formation through the injection of high pressure, high temperature steam into
the formation. This high pressure, high temperature steam reduces the viscosity of the
heavy oil in order to enhance extraction. The injection of steam into the formation occurs
20 from a first wellbore (injector) that is drilled above and parallel to a second wellbore
(producer). As the viscosity of the heavy oil in the formation around the first well bore is
reduced, the heavy oil drains into the lower second wellbore, from which the oil is
extracted. Commonly, the two wellbores are drilled at a distance of only a few meters
from one other. The placement of the injector wellbore needs to be achieved with very
25 small margin in distance. If the injector wellbore is positioned too close to the producer
wellbore, the producing well would be exposed to very high pressure and temperature. If
the injector well bore is positioned too far from the producer well bore, the efficiency of the
SAGD process is reduced.
30 It is well known that traditional surveymg techniques, often referred to as
"ranging", utilized to evaluate the distance between two wellbores suffer from a widening
cone ofuncertainty as the wellbores become longer, making it more difficult to achieve the
precision in placement that is required in SAGD applications. Electromagnetic (EM)
systems and methods have been employed in ranging to determine direction and distance
35 between two wellbores.
1
wo 2015/094202 PCT/US2013/075908
In EM ranging systems, one of the wellbores is cased in a conductive metal
(typically steel). This wellbore is typically referred to as the "target" wellbore and usually
represents the SAGO injector wellbore. In any event, a current is applied to the target
wellbore casing by a low-frequency current source. Currents flow along the wellbore
5 casing and leak into the formation. The currents result in an EM field around the target
wellbore. The EM fields from the currents on the target wellbore casing are measured
using an electromagnetic field sensor system disposed in the other wellbore, which is
typically the wellbore in the process of being drilled. This second wellbore usually
represents the SAGO producer wellbore. Although it may be deployed on wireline, tubing
10 or the like, in many cases, the electromagnetic field sensor system is carried by a drill
string and represents a logging-while-drilling ("L WO") system.
The distance and direction from the L WD device to the target well bore can be
determined if the magnitude of the current on the target wellbore is known. However,
15 while it is generally understood that the magnitude of current decreases along the length of
the target wellbore and that current will leak into the formation, typically, the actual
magnitude of the current, and particularly the distribution of the current along the target
wellbore, is unknown. Thus, it is common practice to simply estimate the magnitude of the
current in a target wellbore in order to yield ranging results. Otherwise, without knowing
20 the current, the ratio of EM fields and/or their gradients can approximate the distance and
direction from the L WO device to the target well. To improve upon L WO ranging, it
would be advantageous to know the magnitude and distribution of current along the target
well bore.
25 Brief Description of the Drawings
Various embodiments of the present disclosure will be understood more fully from
the detailed description given below and from the accompanying drawings of various
embodiments of the disclosure. In the drawings, like reference numbers may indicate
30 identical or functionally similar elements. The drawing in which an element first appears
is generally indicated by the left-most digit in the corresponding reference number.
35
FIG. 1 illustrates EM ranging in a SAGO drilling system having fiber optic current
sensors distributed along a target well bore.
2
5
wo 2015/094202 PCT/US2013/075908
FIG. 2 illustrates EM ranging in a relief well operation having fiber optic current
sensors distributed along a target wellbore.
FIG. 3 illustrates a fiber optic current sensor disposed adjacent a casing section.
FIG. 4 illustrates an embodiment of a fiber optic current sensor formed of a
magnetically permeable body.
FIG. 5 illustrates an embodiment of a fiber optic current sensor formed of a
10 magnetostrictive body.
15
20
FIG. 6 illustrates an embodiment of a fiber optic current sensor formed of an
electrostrictive body.
FIG. 7 shows a flow chart of one method for electromagnetic ranging utilizing fiber
optic current sensors.
Detailed Description of the Invention
The foregoing disclosure may repeat reference numerals and/or letters in the
various examples. This repetition is for the purpose of simplicity and clarity and does not
in itself dictate a relationship between the various embodiments and/or configurations
discussed. Further, spatially relative terms, such as "beneath," "below," "lower," "above,"
"upper," "uphole," "downhole," "upstream," "downstream," and the like, may be used
25 herein for ease of description to describe one element or feature's relationship to another
element(s) or feature(s) as illustrated in the FIGS. The spatially relative terms are intended
to encompass different orientations of the apparatus in use or operation in addition to the
orientation depicted in the FIGS.. For example, if the apparatus in the FIGS. is turned
over, elements described as being "below" or "beneath" other elements or features would
30 then be oriented "above" the other elements or features. Thus, the exemplary term "below"
can encompass both an orientation of above and below. The apparatus may be otherwise
oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors
used herein may likewise be interpreted accordingly.
3
wo 2015/094202 PCT/US2013/075908
Referring initially to Figures 1 and 2, a first well bore 10 extends through the
various earth strata including formation 12. First wellbore 10 includes a fiber optic current
sensor system 14 installed therein, which sensor system 14 includes an optical fiber 16
having at least one fiber optic sensor 18 disposed along optical fiber 16. In some
5 embodiments, a plurality of fiber optic sensors 18 may be disposed along an optical fiber
16 to form at least a one-dimensional array of fiber optic sensors 18. In this same vein,
fiber optic current sensor system 14 may comprise a plurality of optical fibers 16 disposed
within wellbore 10, each of the optical fibers having a plurality of fiber optic sensors 18
disposed along its length. The plurality of optical fibers may be spaced apart around
10 wellbore 10 to form a two-dimensional array. In some embodiments, multiple fiber optic
current sensors can be placed at different azimuths about wellbore 10 to obtain an
azimuthal estimate ofvariations in the current along wellbore 10.
Disposed within well bore 10 along at least a portion of its length is an elongated
15 conductive member 20 which is generally oriented within wellbore 10 to be axially aligned
therewith. Wellbore 10 may be cased or uncased. To the extent wellbore 10 is cased, in
some embodiments, conductive member 20 may be the casing disposed within wellbore 10.
For either cased or uncased wellbores, in some embodiments, conductive member 20 may
be a wire deployed along well bore 10 or tubing, a pipe string or tool string disposed within
20 wellbore 10. In any event, conductive member 20 is disposed to conduct a current along
at least a portion of the length of well bore 10 to be surveyed utilizing fiber optic current
sensor system 14. Moreover, conductive member 20 is generally disposed within wellbore
10 to radiate a magnetic field radially outward from well bore 10.
25 An electric current source 22 is utilized to define a current waveform and excite
current flow in conductive member 20. The current may be an alternating current having a
low frequency, such as approximately 1 to 30 hertz. The particular manner in which
current source 22 excites a current in conductive member 20 is not intended to be a
limitation. In some embodiments, electric current source 22 may be a current generator
30 directly connected to conductive member 20, such as at a casing head 24, and located on
the surface of formation 12. In some embodiments, electric current source 22 may be
disposed on the surface of formation 12 a distance removed from casing head 24, whereby
a current is injected into the ground by a conductor and travels through formation 12 to
conductive member 20. In some embodiments, electric current source 22 may be carried
4
wo 2015/094202 PCT/US2013/075908
on a wireline, cable, tubing string or drill string disposed in another wellbore, as discussed
in more detail below. As used herein, "current source" refers to any source use to generate
an electric current and any electrical conductors, connections or equipment utilized to
inject or otherwise deliver the current to conductive member 16. Thus, a current source
5 may include an electric generator positioned at the surface of a wellbore and conductors
positioned within a wellbore to inject current into the formation. Likewise, an electric
generator may be a mud motor or similar power generation or power storage device
positioned within a wellbore.
10 A fiber optic interrogation system 26 is disposed in optical communication with
optical fiber 16. The disclosure is not limited to any particular type of fiber optic
interrogation system, but may be selected based on the optical response for the particular
survey system with which it is utilized. For example, the optical fiber 16 may be
positioned in well bore 1 0 for purposes in addition to the ranging system described herein
15 and the fiber optic interrogation system 26 may be selected accordingly. In this regard, in
some embodiments, other types of fiber optic sensors may be disposed along an optical
fiber, including but not limited to acoustic, temperature, pressure, chemical and
electromagnetic sensors. For example, the optical fiber cable can be interrogated m
different manners for distributed temperature and/or distributed acoustic sensing.
20
In any event, at least a portion of the fiber optic current sensor system 14, namely
sensor(s) 18, is positioned about the conductive member 20. In embodiments that utilize a
casing as the conductive member 20, sensor(s) 18 are placed outside the casing. For
example, sensor(s) 18 may be placed outside the casing and cemented into place. Sensor(s)
25 18 may be attached to the exterior of the casing. Likewise, if the conductive member 20 is
tubing, a pipe string or tool string, sensor(s) 18 would be positioned on the exterior of the
foregoing, such as by attachment, or otherwise radially spaced apart in the well bore 10
from such conductive member 20. However, in such case, in one or more embodiments,
this spacing or standoff distance be as small as possible. In some embodiments, therefore,
30 a ranging tool may generally include a conductive member 20 (other than the well bore
casing) carrying a fiber optic sensor system 14. The ranging tool could be lowered into
cased or uncased wellbores for ranging purposes. The ranging tool therefore, would
conduct a current, propagate a magnetic field into the formation, and utilize an optic sensor
system to measure the current along the tool.
5
wo 2015/094202 PCT/US2013/075908
With ongoing reference to Figures 1 and 2, there is shown a second wellbore 28. A
drilling system 30 is generally shown associated therewith. Drilling system 30 may
include a drilling platform 32 positioned over formation 12, and a wellhead installation 34,
5 including blowout preventers 36. Platform 32 may be disposed for raising and lowering a
conveyance mechanism 48.
Attached to the end of conveyance mechanism 48 is an electromagnetic (EM)
sensor 50. The disclosure is not limited to any particular type of electromagnetic sensor
10 50. In some embodiments, the electromagnetic sensor 50 can measure at least one
component of the magnetic field or the gradient of the magnetic field. In some
embodiments, the electromagnetic sensor 50 can measure at least one component of the
electric field or the gradient of the electric field.
15 With respect to Figure 1, to the extent drilling system 30 is being utilized to
actively drill second wellbore 28, conveyance mechanism 48 may be a tubing string or drill
string, having a bottomhole assembly 52 attached to the end of string 48. Bottomhole
assembly 52 includes electromagnetic sensor 50 and a drill bit 54. Bottomhole assembly
may also include a power system 56, such as a mud motor, a directional steering system
20 58, a control system 60, a current injector system 61, and other sensors and instrumentation
62. As will be appreciated by persons of skill in the art, the bottom hole assembly 52
illustrated in Figure 1 may be a measurement-while-drilling or logging-while-drilling
system in which electromagnetic ranging can be utilized while a drill string is deployed in
wellbore 28.
25
30
With respect to Figure 2, conveyance system 48 may be a wireline, slickline, cable
or the like and used to lower electromagnetic sensor 50 into wellbore 28. Power and
communications to electromagnetic sensor 50 may be carried locally by appropriate
modules 64 or may be transmitted via conveyance system 48.
The fiber optic current sensor system 14 as described herein may be deployed on
land or may deployed offshore.
6
wo 2015/094202 PCT/US2013/075908
Moreover, fiber optic current sensor system 14 is not limited to any particular
orientation of the first and second well bores. As depicted in Figure 1, first and second
well bores 10, 28, respectively are substantially horizontal well bores. In such case, fiber
optic current sensor system 14 may be particularly useful in ranging for SAGD operations.
5 Alternatively, as depicted in Figure 2, first and second wellbores 10, 28, respectively are
substantially vertical wellbores. Thus, fiber optic current sensor system 14 may be used in
drilling relief wells or intersecting wells, such as when it is desirable to establish direct
fluid communication between two wells. This may be particularly useful in well
intervention operations, for example.
10
FIG. 3 shows a fiber optic sensor 18 disposed adjacent a conductive member 20,
such as the illustrated casing section. In certain embodiments, fiber optic sensor 18 is
generally formed of a magnetically or electrically responsive core or body 72. As shown,
fiber optic sensor 18 is positioned along an optical fiber 16 that generally runs parallel with
15 conductive member 20. Electrical current transmitted by conductive member 20 generally
flows axially along conductive member 20 as illustrated by current lines 74 (although there
may be some current leakage into the formation), resulting in a radially emanating
magnetic field induced about conductive member 20, such as illustrated by magnetic field
lines 76.
20
In embodiments where responsive core 72 is formed of a magnetically responsive
body, fiber optic sensor 18 is disposed adjacent conductive member 20 so that magnetically
responsive body 72 is within the magnetic field 76. As such, magnetic field 72 causes a
reaction in magnetically responsive body 72. The reaction results in an optical change to
25 optical fiber 16. The optical change in optical fiber 16 is dependent upon the strength of
the magnetic field, which in tum is proportional to the current in conductive member 20
adjacent the fiber optic sensor 18.
In embodiments where responsive core 72 is formed of an electrically responsive
30 body, the core may be an electrostrictive body.
The invention is exemplified in the following theoretical example which is not
intended to limit the scope of the disclosure.
7
5
wo 2015/094202 PCTIUS2013/075908
The target wellbore is defined by the coordinate system r = {x, y, z} and can be
approximated by an infinitely long current source oriented in the z direction in a
homogeneous geological formation of conductivity a, such that the electric current along
the target wellbore casing can be approximated as:
J(r) = Io(r)o(z)uz, (1)
The current I has a frequency dependence and is injected at the wellbore-in one
ore more embodiments, at the wellhead--and conducted along the wellbore's elongated
conductive member, i.e., the metal casing. Given the finite resistivity of the formation
10 about the conductive member, current is leaked into the formation. Given the radial
symmetry about the target wellbore, the electromagnetic fields can be described in
cylindrical coordinates r = (z, p, 8) about the z axis. Note that the cylindrical coordinates
r = (z, p, 8) can be transformed to Cartesian coordinates r = (x, y, z), and vice versa.
15 Of particular interest to electromagnetic rangmg is the distance to the target
wellbore from the electromagnetic field sensing unit in the second wellbore, p =
.J x 2 + y 2 , and the direction (angle) to the target well bore from the electromagnetic field
sensing unit in the second well bore, 8. The orientation of the target well bore relative to the
electromagnetic field sensing unit in the second wellbore can be also be retrieved.
20 The frequency-domain magnetic field excited about the target wellbore only has a 8-
directed tangential component:
(2)
where k = .J iWJla is the wavenumber, p is the radial distance between the two wellbores
in the xy-plane, and K1 is the modified Bessel function of the second kind of order one. At
25 low frequencies used for and small distances typically encountered in EM ranging, the
modified Bessel function in equations (2) can be approximated by:
30
such that the magnetic fields (2) can be expressed as:
H8 (r,w) = --
1-u8 ,
2np
(3)
(4)
The current I, which has heretofore been unknown in pnor art methods, IS
measured along the conductive member in the target wellbore using fiber optic current
8
wo 2015/094202 PCT IUS20 13/075908
sensors. Hence, the distance from the electromagnetic field sensing unit in the second
well bore to the conductive member in the target well bore can be approximated by:
I p = - 2rcHo(r,w)" (5)
5 The direction from the electromagnetic field sensing unit in the second wellbore to
the conductive member in the target well bore is simply given by the direction orthogonal to
both H8 (r, w) and the z axis of the second wellbore. Hence, the relative distance, direction
and angle between two wellbores can be determined and drilling trajectory, whether for
purposes of intercepting the wellbores or drilling the wellbores in a parallel or other
10 relationship, can be accordingly adjusted.
Turning to Figure 4, one embodiment of a fiber optic sensor 18 is illustrated. In
this embodiment, responsive core or body 72 is magnetically responsive and shown as a
magnetically permeable core 78 with a portion of optical fiber 16 forming at least one, and
15 in one or more embodiments, a plurality of loops around core 78 in the form of an optical
fiber coil 79. Although not a limitation, core 78 may have a round cross-section shape. In
other embodiments, the cross-sectional shape may be square or some other polygonal
shape. Core 78 may be solid or hollow. In one or more embodiments, core 78 is elongated
and disposed along a primary axis A. In these embodiments, the fiber optic current sensor
20 18 exploits the Faraday rotation effect in a fiber coil, whereby the polarization of light in
an optical fiber is rotated with the propagation of light along a magnetic field line. In some
embodiments, the magnetically permeable core is a thin ferrite shaft or tube. This
essentially emulates a ferrite-cored solenoid. This fiber coil measures the magnetic fields
induced about casing, from which the current can be estimated, or other transfer functions
25 derived with respect to the BHA system.
30
It should be noted that in some embodiments of the disclosure where an optical
fiber coil 79 is formed, the electrically conductive body 20 can function as the
magnetically responsive body.
Turning to Figure 5, another embodiment of a fiber optic sensor 18 is illustrated. In
this embodiment, responsive core or body 72 is magnetically responsive and shown as a
magnetostrictive body 80. The magnetostrictive body 80 may be formed of cobalt,
9
wo 2015/094202 PCT/US2013/075908
TbxDYI-xFez, such as Terfenol-D, or Fes1Sb.sB13.sCz, such as Metglas, in some
embodiments. The body 80 is not limited in shape. However, in one or more
embodiments, the body 80 may be elongated and disposed along an axis A. For example,
the body 80 may have a round cross-sectional shape. In other embodiments, the cross-
5 sectional shape of the body 18 may be square or some other polygonal shape. Body 80
may be solid or hollow. Optical fiber 16 is rigidly attached to or otherwise bonded to at
least a portion of body 80, such as at bond line 82. Thus, changes in the shape of body 80
will result in strain, and hence an optical change, in optical fiber 16. The strain can be
measured using a fiber laser strain sensor interrogation system from which the current can
10 be estimated, or other transfer functions derived with respect to the BHA system.
Turning to Figure 6, another embodiment of a fiber optic sensor 18 is illustrated. In
this embodiment, responsive core or body 72 is electrostrictive, formed of a dielectric
material and shown as electrostrictive body 84. Without limiting the foregoing, such
15 electrostrictive material may include engineered ceramics, or relaxor ferroelectrics, such as
lead magnesium niobate (PMN), lead magnesium niobate-lead titanate (PMN-PT) or lead
lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT) or lithium niobate. The
current in conductive member 20 may be derived from measurement of the electric field,
which itself is measured from the potential difference between two electrodes. In some
20 embodiments, the electrodes 86, 88 are in contact with the conductive member 20, such as
the metal casing, to measure an axial potential difference. In other embodiments, one
electrode is in contact with the conductive member 20 and the other electrode is in contact
with the formation to measure a radial potential difference. Regardless of the electrode
configuration, the potential difference across the electrodes drives electrostrictive body 84.
25 The body 84 is not limited in shape. However, in one or more embodiments, the body 84
may be elongated and disposed along an axis. For example, the body 84 may have a round
cross-sectional shape. In other embodiments, the cross-sectional shape of the body 18 may
be square or some other polygonal shape. Body 84 may be solid or hollow. Optical fiber
16 is rigidly attached to or otherwise bonded to at least a portion of body 84, such as at
30 bond line 90. Thus, changes in the shape of body 84 will result in strain, and hence an
optical change, in optical fiber 16. The strain can be measured using a fiber laser strain
sensor interrogation system from which the current can be estimated, or other transfer
functions derived with respect to the BHA system.
10
wo 2015/094202 PCT/US2013/075908
Figure 7 is a flowchart illustrating embodiments of the ranging method utilizing
optical sensors. The ranging method 700 includes methods for utilizing an optical sensor,
methods for measuring current along a conductive body. In some embodiments, the
ranging method may be utilized in SAGD operations or for intersecting wellbores, such as
5 in well intervention operations. In any event, in a first step 710, a current is generated by
an electrical source, and the wave form of the current is defined. In this regard, the
magnitude and frequency of the current may be selected. The current is typically an
alternating current. In step 720, the current is applied or injected to a conductive member
disposed in a first wellbore, such as, for example, the metal casing of a target wellbore.
10 The current may be applied by directly connecting an electrical source to the conductive
member. For example, if the conductive member is the metal casing within the first
well bore, electrical leads may be attached to the wellhead or casing hanger at the top of the
casing string. Alternatively, the current may be applied by injecting the current into a
formation adjacent the first wellbore so that the current travels through the formation to the
15 conductive member. In this regard, the current may be injected at the surface of a wellbore
or may be injected from a second wellbore in the formation. The current may be injected
as part of logging-while-drilling or measurement-while-drilling operations in the second
well bore.
20 In step 730, a fiber optic current sensor is utilized to measure the current on the
conductive member. The fiber optic current sensor may be a single sensor or incorporated
in an array of fiber optic current sensors as describe above. The fiber optic current sensor
includes a core that is responsive to magnetic or electric changes resulting from the current
in the conductive member. In some embodiments, a magnetic field generated by the
25 current within the conductive member will result in a change in the physical shape of the
core, such as a magnetostrictive core, which change causes a strain on an optical fiber. The
strain on the optical fiber results in a change of the fiber's optical response and may be
utilized to calculate the magnitude of the current in the conductive member at that point.
In other embodiments, the electrical current at a particular location along the length of the
30 conductive member may be applied to a sensor core. The electric current will result in a
change in the physical shape of the core, such as an electrostrictive core, which change
causes a strain on an optical fiber. The strain on the optical fiber results in a change of the
fiber's optical response and may be utilized to calculate the magnitude of the current in the
conductive member at that point. In other embodiments, the optical fiber may be looped or
11
wo 2015/094202 PCT/US2013/075908
coiled around a magnetically permeable core. The magnetically permeable core enhances
the magnetic field induced by the current in the conductive member, which enhanced
magnetic field will alter the optical response of the fiber coil. The altered optical response
can be utilized to calculate the magnitude of the current in the conductive member at that
5 point. In other embodiments, a plurality of sensors disposed along the length of the
conductive member may be used to determine current loss along the conductive member,
such as loss of magnitude or leakage into the formation.
In step 740, an electromagnetic field sensing instrument is utilized to measure the
10 electromagnetic field propagating from the conductive member. In some embodiments, the
electromagnetic field sensing instrument is deployed in the second wellbore. To the extent
deployed in the second wellbore, the electromagnetic field sensing instrument may be
carried on a wireline, slickline, cable, tubing, pipe string, tool string or drill string, as a
particular operation dictates. To the extend carried on a drillstring, the electromagnetic
15 field sensing instrument may be included as part of a bottom hole assembly (BHA) utilized
during drilling operations. In some embodiments, drilling operations may be suspended
while the electromagnetic fields are measured. While not necessary, in some
embodiments, steps 730 and 740 may be practiced simultaneously, while in other
embodiments the order of the steps may be reversed.
20
In step 750, the measured electromagnetic field and the measured current are
utilized to determine or calculate a range between the first and second wellbores as
described above. The calculated range may include distance, direction and angle of the
second wellbore, and in particular, the electromagnetic field sensing instrument, to the first
25 wellbore.
In step 760, once the range has been calculated, to the extend the ranging is utilized
in directional drilling operations, the actual trajectory of the second wellbore may be
verified against a desired trajectory. To the extent there is a discrepancy between the
30 actual trajectory and the desired trajectory, the actual trajectory of the second wellbore may
be altered or adjusted based on the calculated range in order to ensure the second wellbore
is drilled as desired relative to the first wellbore. If a desired trajectory is based on a
predetermined drilling plan and the acutal trajecory has deviated from the desired
trajectory, then the trajecotry may be altered to achieve the desired trajectory. In this
12
wo 2015/094202 PCT/US2013/075908
regard, to alter or adjust the trajectory of the well bore, the drill bit may be repositioned or
reoriented. Thus, results of the ranging may be utilized to guide a drill bit during
directional drilling, such as in SAGD operations or wellbore intersect or intervention
operations. In step 770, once the measurements have been obtained, and corrections to the
5 trajectory of the second wellbore or orientation of the drill bit have been implemented,
drilling of the second wellbore is continued along the correct trajectory.
To the extent the foregoing method is utilized in SAGD operations, once the second
well bore has been drilled, steam is injected into one of the well bores to cause hydrocarbons
10 in the formation to migrate to the other wellbore, after which, the hydrocarbons are
recovered from the other wellbore.
Moreover, the methods described herein may be embodied within a system
comprising processing circuitry to implement any of the methods, or a in a computer-
15 program product comprising instructions which, when executed by at least one processor,
causes the processor to perform any of the methods described herein.
One benefit to the system and method disclosed herein is that the fiber optic current
measurement sensors are rotationally invariant to the orientation of the electromagnetic
20 sensors, meaning that the sensors can be deployed from a rotated BHA device, or a
wireline device, without needing orientation information about the BHA or wireline
device. Furthermore, the methods can be practiced in real time. Thus, ranging can be
determined on the fly and adjustments to drilling trajectories made without a delay in
drilling.
25
Thus, a wellbore ranging system for surveying a target wellbore from a second
well bore has been described. Embodiments of the well bore ranging system may generally
have an electromagnetic field sensing instrument disposed in the second wellbore; an
elongated conductive member in the target wellbore, the conductive member oriented
30 along an axis that is substantially parallel with the target wellbore; an electric current
source exciting current flow in the conductive member of the target well bore; and a fiber
optic sensor disposed adjacent the conductive member of the target wellbore. In other
embodiments, a wellbore ranging system may generally have a bottom hole assembly
carried at the distal end of a drill string disposed in the second wellbore, the bottom hole
13
wo 2015/094202 PCT/US2013/075908
assembly comprising an electromagnetic field sensmg instrument and a drill bit; an
elongated conductive member in the target wellbore, the conductive member oriented
along an axis that is substantially parallel with the target wellbore; an electric current
source exciting current flow in the conductive member of the target wellbore; and a fiber
5 optic sensor system, the fiber optic sensor system comprising a plurality of spaced apart
fiber optic sensors, each sensor having a core formed of material selected from the group
consisting of magnetically responsive material and electrically responsive material; a fiber
optic interrogation system; an optical fiber extending from the fiber optic interrogation
system to the cores, wherein a portion of the optical fiber is disposed adjacent to each core.
10 Likewise, an optical sensor for measurement of an electric current has been described.
Embodiments of the optical sensor may generally have a core formed of material selected
from the group consisting of magnetically responsive material and electrically responsive
material; and an optical fiber disposed adjacent said core. For any of the foregoing
embodiments, the system or sensor may include any one of the following elements, alone
15 or in combination with each other:
20
25
30
The fiber optic sensor comprises a core formed of material selected from the
group consisting of magnetically responsive material and electrically responsive
material; and an optical fiber disposed adjacent said core.
A sensor core is formed of a magnetostrictive material and the optical fiber
is bonded to the core.
A sensor core is formed of a magnetically permeable material and the
optical fiber forms at least one loop around the core.
A sensor the core is formed of an electrostrictive material and the optical
fiber is bonded to the core.
A sensor core is comprised of an elongated body disposed along an axis and
the sensor is positioned adjacent the conductive member so that the elongated axis
of the core is substantially perpendicular to the axis of the conductive member.
14
5
10
15
20
25
30
35
wo 2015/094202 PCT /US20 13/075908
A fiber optic interrogation system in optical communication with the fiber
optic sensor.
An optical fiber extending from the fiber optic interrogation system to the
fiber optic sensor.
A plurality of optic sensors disposed along at least a portion of the length of
the conductive member to form a sensor array.
The conductive member is casing.
The conductive member is a tubular positioned within the target wellbore.
The electric current source is in direct electrical communication with the
conductive member.
A drill string in the second wellbore, the drill string having multiple drill
pipe sections with a drill bit disposed on an end of the drill string, wherein the
electromagnetic sensor is carried by the drill string.
The conductive member is an electrically conductive casing disposed within
the target wellbore and wherein the electric current source is in direct electrical
communication with the conductive member, the bottom hole assembly further
comprising a power system disposed to provide power to the electromagnetic field
sensing instrument and a directional steering system disposed to steer the drill bit.
The fiber optic sensor comprises a magnetically responsive core and an
optical fiber.
An optical fiber is bonded to a core.
An optical fiber is bonded to a magnetically responsive core.
An optical fiber forms at least one complete loop around a magnetically
responsive core.
15
5
10
15
20
25
30
wo 2015/094202 PCT/US2013/075908
The fiber optic sensor compnses an electrically responsive core and an
optical fiber.
A optical fiber is bonded to an electrically responsive core.
A sensor core is comprised of an elongated body disposed along an axis.
An elongated core body is a solid shaft.
An elongated core body is a hollow tube.
An elongated core elongated body has a round cross-sectional shape.
An elongated core body is square in cross-section.
An elongated core body is formed of ferrite.
An optical fiber forms a plurality of loops around a sensor core.
An optical fiber forms a coil disposed around a sensor core.
A sensor core is an elongated metal body disposed along an axis and the
optical fiber forms a plurality of loops extending axially along at least a portion of
the length of an elongated core body.
The axis of an elongated core body is substantially perpendicular to the axis
of the conductive member.
A plurality of optic sensors.
A plurality of sensors forms an array.
16
5
10
15
20
25
30
wo 2015/094202 PCT/US2013/075908
A plurality of optic sensors are spaced apart along at least a portion of the
length of the conductive member.
A plurality of sensors are radially spaced apart about the ax1s of the
conductive member.
The conductive member is a wire disposed within the target wellbore.
A fiber optic interrogation system.
An optical fiber extending from a fiber optic interrogation system to the
fiber optic sensor.
The electromagnetic field sensing instrument is a magnetometer.
The electromagnetic field sensing instrument is a gradiometer.
The electric current source is a time varying current source.
A time varying current source is a low frequency alternating current source.
The target wellbore comprises a wellhead and the electric current source is
disposed adjacent the wellhead.
The electric current source is in direct electrical communication with the
conductive member.
The electric current source is carried by the drill string m the second
borehole.
A drill string in the second wellbore, the drill string having multiple drill
pipe sections with a drill bit disposed on an end of the drill string, wherein the
electromagnetic sensor is carried by the drill string.
17
5
10
15
wo 2015/094202 PCTIUS2013/075908
A wireline extending into the second wellbore, wherein the electromagnetic
sensor is carried by the wireline.
Tubing extending into the second wellbore, wherein the electromagnetic
sensor is carried by the tubing.
A magnetically responsive material is a magnetostrictive material.
A magnetostrictive material is selected from the group consisting of cobalt,
TbxDY1-xFe2, and Fes1ShsB13.sC2.
A core is formed of electrostrictive material.
An electrostrictive material is selected from the group consisting of lead
magnesium niobate (PMN), lead magnesium niobate-lead titanate (PMN-PT) or
lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT) and lithium
niobate.
A method for electromagnetic ranging has been described. Embodiments of the
ranging method may include positioning an optical fiber in a target wellbore having a
20 conductive member disposed therein; applying a current flow to the conductive member;
and utilizing the optical fiber to measure the current flow on the conductive member.
Likewise, a method for performing steam assisted gravity drainage to recover
hydrocarbons from a formation has been described. Embodiments of the hydrocarbon
recovery method include producing an alternating current flow in a target wellbore;
25 measuring the current in the target wellbore utilizing an optical fiber; measuring from a
wellbore being drilled the electromagnetic field emanating from the current flow; injecting
steam in one of the wellbores to cause hydrocarbons in the formation to migrate to the
other wellbore; and recovering hydrocarbons from the other wellbore. Likewise, a method
for measuring current along a conductive body has been described. Embodiments of the
30 current measurement method may include positioning an optical fiber adjacent a
conductive member; applying a current flow to the conductive member; and utilizing the
optical fiber to measure the current flow on the conductive member. Likewise, a method
for utilizing an optical sensor has been described. Embodiments of utilizing an optical
sensor may include providing an optical sensor having a core formed of material selected
18
5
10
15
20
25
30
wo 2015/094202 PCTIUS2013/075908
from the group consisting of magnetically responsive material and electrically responsive
material; and an optical fiber disposed adjacent said core; and utilizing the core to alter the
optical response of the optical fiber. For any of the foregoing embodiments, the method
may include any one of the following steps, alone or in combination with each other:
The magnitude of the current flow at at least one location along the
conductive member is measured.
The intensity of the current flow along the conductive member is measured.
Positioning a magnetically responsive material adjacent the optical fiber.
Altering an optical response of the optical fiber utilizing the magnetically
responsive material.
Altering a property of the magnetically responsive material by positioning
the magnetically responsive material in a magnetic field produced by the current
flow in the conductive member.
Generating an alternating current and causing the alternating current to flow
along the conductive member.
Injecting a current into the formation in which the target wellbore extends
from a second wellbore in the formation.
Utilizing an electromagnetic field sensing instrument disposed in a second
wellbore to measure a magnetic field emanating from the conductive member; and
determining a range of the target wellbore from the second wellbore utilizing the
measured magnetic field and measured current flow.
Measuring the magnetic field while conducting drilling operations.
Utilizing the range to guide a drill bit.
19
5
10
15
20
25
30
wo 2015/094202 PCT/US2013/075908
The alternating current is a low frequency.
The frequency is between approximately 1 to 30 Hertz.
Initiating drilling of the second well; and, interrupting drilling during the
step of taking measurements.
Drilling the wellbore being drilled; suspending drilling and measuring the
electromagnetic field; and continuing drilling based on the measured
electromagnetic field and current.
Altering an optical response of the optical fiber utilizing the magnetically
responsive material.
Altering a property of the magnetically responsive material by positioning
the magnetically responsive material in a magnetic field produced by the current
flow in the conductive member.
Generating an alternating current and causing the alternating current to flow
along the conductive member.
Utilizing the magnetic field to generating a strain on the optical fiber.
Identifying a current magnitude based on the strain on the optical fiber.
Measuring a property based on an altered optical response.
Placing a sensor core in a magnetic field and altering the core utilizing the
magnetic field.
Inducing a strain on an optical fiber based on an altered core.
Utilizing a magnetic field to alter the optical response of an optical fiber.
20
wo 2015/094202 PCTIUS2013/075908
Utilizing the magnetic field to generate a strain on an optical fiber.
Identifying a property magnitude based on the strain on an optical fiber.
5 A measured property magnitude is electrical current magnitude.
Measuring electrical current based on an altered optical response.
Although various embodiments and methods have been shown and described, the
10 disclosure is not limited to such embodiments and methodologies and will be understood to
include all modifications and variations as would be apparent to one skilled in the art.
Therefore, it should be understood that the disclosure is not 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
15 appended claims.
21
5
wo 2015/094202 PCT/US2013/075908

Claims
1. A wellbore ranging system for surveying a target wellbore from a second wellbore,
said system comprising:
an electromagnetic field sensing instrument disposed in the second well bore;
an elongated conductive member disposed in the target wellbore, the conductive
member oriented along an axis that is substantially parallel with the target wellbore;
an electric current source exciting current flow in the conductive member of the
target well bore; and
a fiber optic sensor disposed adjacent the conductive member of the target
10 wellbore.
2. The system of claim 1 wherein said fiber optic sensor comprises an optical fiber
and a core formed of material selected from the group consisting of magnetically
responsive material and electrically responsive material; wherein the optical fiber is
15 disposed adjacent said core.
3. The sensor of claim 2, wherein the core is formed of a magnetostrictive material
and the optical fiber is bonded to the core.
20 4. The sensor of claim 2, wherein the core is formed of a magnetically permeable
25
30
material and the optical fiber forms at least one loop around the core.
5. The sensor of claim 2, wherein the core is formed of an electrostrictive material and
the optical fiber is bonded to the core.
6. The sensor of claim 2 wherein said core is comprised of an elongated body
disposed along an axis and the sensor is positioned adjacent the conductive member so that
the elongated axis of the core is substantially perpendicular to the axis of the conductive
member.
7. The sensor of claim 1, further comprising a fiber optic interrogation system in
optical communication with the fiber optic sensor.
22
wo 2015/094202 PCT/US2013/075908
8. The system of claim 7, further comprising an optical fiber extending from the fiber
optic interrogation system to the fiber optic sensor.
9. The system of claim 1, further comprising a plurality of optic sensors disposed
5 along at least a portion of the length of the conductive member to form a sensor array.
10. The system of claim 1, wherein the conductive member is casing.
11. The system of claim 1, wherein the conductive member is a tubular positioned
10 within the target wellbore.
15
12. The system of claim 1, wherein the electric current source is in direct electrical
communication with the conductive member.
13. The system of claim 1, further comprising a drill string in the second well bore, the
drill string having multiple drill pipe sections with a drill bit disposed on an end of the drill
string, wherein the electromagnetic sensor is carried by the drill string.
14. A wellbore ranging system for surveying a target wellbore from a second wellbore,
20 said system comprising:
a bottom hole assembly carried at the distal end of a drill string disposed in the
second wellbore, the bottom hole assembly comprising an electromagnetic field sensing
instrument and a drill bit;
an elongated conductive member disposed in the target wellbore, the conductive
25 member oriented along an axis that is substantially parallel with the target wellbore;
30
an electric current source exciting current flow in the conductive member of the
target wellbore; and
a fiber optic sensor system, the fiber optic sensor system comprising:
a plurality of spaced apart fiber optic sensors, each sensor having a core
formed of material selected from the group consisting of magnetically responsive
material and electrically responsive material;
a fiber optic interrogation system; and
an optical fiber extending from the fiber optic interrogation system to the
cores, wherein a portion of the optical fiber is disposed adjacent to each core.
23
wo 2015/094202 PCT/US2013/075908
15. The system of claim 14, wherein the conductive member is an electrically
conductive casing disposed within the target wellbore and wherein the electric current
source is in direct electrical communication with the conductive member, the bottom hole
5 assembly further comprising a power system disposed to provide power to the
electromagnetic field sensing instrument and a directional steering system disposed to steer
the drill bit.
16. A method for electromagnetic ranging comprising:
10 positioning an optical fiber in a target wellbore having a conductive member
disposed therein;
applying a current flow to the conductive member; and
utilizing the optical fiber to measure the current flow on the conductive member.
15 17. The method of claim 16, wherein the magnitude of the current flow at at least one
location along the conductive member is measured.
18. The method of claim 16, wherein the intensity of the current flow along the
conductive member is measured.
20
19. The method of claim 16, further comprising positioning a magnetically responsive
material adjacent the optical fiber.
20. The method of claim 19, further comprising altering an optical response of the
25 optical fiber utilizing the magnetically responsive material.
30
21. The method of claim 20, further comprising altering a property of the magnetically
responsive material by positioning the magnetically responsive material in a magnetic field
produced by the current flow in the conductive member.
22. The method of claim 16, further comprising:
utilizing an electromagnetic field sensing instrument disposed in a second wellbore
to measure a magnetic field emanating from the conductive member; and
24
5
10
15
WO 201!'/U942ltl
determining a range ofthe target \Vcllborc from the second wcllborc utilizing the
rneusun:d rnagn;;tic tidd and measured current t1uw.
::D. Tbc method of claim 22, further comprising utilizing the range to guide a dr1ll bit.
~4. The method of daim 1(1. further comprising:
drilling the wcllborc being drilled;
suspending drilling and measuring the electromagnetic field: and
continuing drilling based on the measured electromagnetic field and current
25. 'fbc encthod ofdai.m I 6, further comprising:
providing an optic•d sensor having an optical fiber disposed adjacent a sensor core
tbrrned ofnmtcrial selected from the group consisting of magnetically responsive material
ami electrically respon~ive matc·rial~ and
utilizing the core to alter the optical response of the optical fiber.
:26. Tbc method uf claim 25, further comprising, mea,o;;uring a property basc.d on the
altered optical rc1>ponsc.
20 27. The method <>f claim 25, further comprising, indudng a strain on the optical fiber
based on the altered core.
28. ·rhc method of claim 25, further comprising utilizing a magnetic field to alter the
optical n.,~pon;S.c of the optical fiber.
29. The n1elhod ofdairn 22. further comprising:
injecting steam in one of the wcllbores to cause hydrocarbons in the fonuation to
migrate to the otlK~r wdlborc; and
recovering hydl'ocarbons from the ot.her wcllbore.