Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEMS AND METHODS FOR GUIDING THE DRILLING OF A
HORIZONTAL WELL
FIELD OF THE INVENTION
The invention relates generally to systems and methods for guiding the
drilling of a
horizontal well and, more specifically, to systems and methods for guiding the
drilling
of a horizontal well into an intersection with a vertical well.
BACKGROUND OF THE INVENTION
Directional drilling, or slant drilling, is typically utilized to drill non-
vertical wells.
Directional drilling is utilized in a wide variety of applications, including
oil drilling,
utility installation drilling, and in-seam drilling. In some applications,
directional
drilling is utilized to intersect an existing vertical well with a horizontal
well. Various
techniques and methods are typically utilized in an attempt to accurately
intersect the
vertical well with the horizontal well that is being drilled.
One conventional technique that is utilized is to rely on directional surveys
in an
attempt to place the horizontal well in close proximity to a vertical target
well.
However, this technique may often be ineffective due to errors in the
surveying of the
two wells and the land survey at the surface.
Other conventional techniques utilize various sensors that are intended to
assist in the
guiding of the intersection of the horizontal well with a vertical well. The
sensors
may be situated either in the drilling assembly of the horizontal well with a
signal
source in the existing vertical well or, alternatively, in the existing
vertical well with a
signal source in the drilling assembly of the horizontal well. However, many
of these
conventional techniques may also include small but inherent errors in
determining the
intersection of the vertical and horizontal wells. Errors in estimating the
positions of
both the vertical and horizontal wells can accumulate as drilling and
surveying
progresses. Eventually, the additive errors impacting the path or trajectory
may be so
large as to prevent a desired near intersection of the two wells.
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Additionally, it can be difficult to accurately determine a range or distance
between a
horizontal well that is being drilled and a target vertical well utilizing the
prior art
techniques. A failure to accurately determine the range or distance often
leads to
failed intersections or poor intersections between the two wells. A poor
determination
of range or distance may prevent a driller that is guiding the drilling of the
horizontal
well from being able to plan and take corrective maneuvers in steering the
drilling of
the horizontal well. Thus, without an accurate determination of range or
distance, a
driller may not be able to correct the direction of the drilling of the
horizontal well in
order to intersect a vertical well.
Accordingly, there is a need for improved systems and methods for guiding the
drilling of a horizontal well in order to intersect a vertical well.
BRIEF DESCRIPTION OF THE INVENTION
According to one aspect of the invention, a method is provided for guiding the
drilling
of a horizontal well. A current is provided in at least one conductor
positioned in a
target vertical well. A magnetic field generated by the current is measured at
a
drilling assembly that is drilling the horizontal well. A direction from the
drilling
assembly towards the target vertical well is determined based at least in part
on the
measured magnetic field. A distance from the drilling assembly to the target
vertical
well is determined based at least in part on the measured magnetic field. The
determination of the distance also includes at least one gradient.
According to another aspect of the invention, a system is provided for guiding
the
drilling of a horizontal well. The system can include at least one conductor,
one or
more sensors, and a control unit. The at least one conductor is positioned in
a target
vertical well. The at least one conductor carries a current signal. The one or
more
sensors are associated with a drilling assembly that is drilling the
horizontal well. The
one or more sensors measure the intensity of a magnetic field generated by the
current
signal. The control unit receives the intensity measurements from the one or
more
sensors. The control unit determines a direction from the drilling assembly
towards
the target vertical well based at least in part on the received intensity
measurements.
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The control unit determines a distance from the drilling assembly to the
target vertical
well based at least in part on the received intensity measurements. At least
one
gradient calculation is utilized to determine the distance from the drilling
assembly to
the target vertical well.
Other aspects of the invention will become apparent from the following
description
taken in conjunction with the following drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
Having thus described the invention in general terms, reference will now be
made to
the accompanying drawings, which are not necessarily drawn to scale, and
wherein:
FIG. 1 is a schematic diagram of an exemplary intersection of a vertical well
by a
horizontal well in accordance with an illustrative aspect of the invention.
FIG. 2 is a schematic diagram of a target vertical well, according to an
illustrative
aspect of the invention.
FIG. 3 is a schematic diagram of an exemplary drilling assembly that is
utilized to
detect a target vertical well, according to an illustrative aspect of the
invention.
FIG. 4 is a schematic diagram that depicts the current direction of the
drilling
assembly and the target direction to the target vertical well, according to an
illustrative aspect of the invention.
FIG. 5A is a top view schematic diagram of the drilling of a horizontal well
to form
an intersection or near-intersection with a vertical well, according to an
illustrative
aspect of the invention.
FIG. 5B is a cross sectional view taken along the line A to A' of the drilling
of a
horizontal well to form an intersection or near-intersection with a vertical
well,
according to an illustrative aspect of the invention.
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FIG. 6 is a top view schematic diagram of exemplary adjustments that are made
during the drilling of a horizontal well to form an intersection or near-
intersection
with a target vertical well, according to an illustrative aspect of the
invention.
FIG. 7 is a block diagram of an exemplary control unit that is utilized in
accordance
with certain aspects of the invention.
FIG. 8 is an exemplary flowchart of the general operation of the control unit
of FIG.
7, according to an illustrative aspect of the invention.
FIG. 9 is a graphical representation of one example of falloff rates for two
different
alternating current magnetic fields having different intensities, in
accordance with an
illustrative aspect of the invention.
FIG. l0A is an exemplary flowchart depicting the operations that can be taken
by the
control unit of FIG. 7 to determine a distance or range to a target vertical
well, in
accordance with an illustrative aspect of the invention.
FIG. lOB is a graphical representation of the distances and values that can be
measured and/or determined by utilizing the exemplary operations depicted in
FIG. 10A, in accordance with an illustrative aspect of the invention.
FIG. 11 is an exemplary flowchart depicting the operations that can be taken
by the
control unit of FIG. 7 to determine a direction to a target vertical well, in
accordance
with an illustrative aspect of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Illustrative aspects of the inventions now will be described more fully
hereinafter with
reference to the accompanying drawings, in which some, but not all aspects of
the
inventions are shown. Indeed, the invention may be embodied in many different
forms and should not be construed as limited to the aspects set forth herein;
rather,
these aspects are provided so that this disclosure will satisfy applicable
legal
requirements. Like numbers refer to like elements throughout the description
and
drawings.
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The invention is described below with reference to block diagrams of systems,
methods, apparatuses and computer program products according to an aspect of
the
invention. It will be understood that each block of the block diagrams, and
combinations of blocks in the block diagrams, respectively, can be implemented
by
computer program instructions. These computer program instructions may be
loaded
onto a general purpose computer, special purpose computer, or other
programmable
data processing apparatus to produce a machine, such that the instructions
which
execute on the computer or other programmable data processing apparatus create
means for implementing the functionality of each block of the block diagrams,
or
combinations of blocks in the block diagrams discussed in detail in the
descriptions
below.
These computer program instructions may also be stored in a computer-readable
memory that can direct a computer or other programmable data processing
apparatus
to function in a particular manner, such that the instructions stored in the
computer-
readable memory produce an article of manufacture including instructions that
implement the function specified in the block or blocks. The computer program
instructions may also be loaded onto a computer or other programmable data
processing apparatus to cause a series of operational steps to be performed on
the
computer or other programmable apparatus to produce a computer implemented
process such that the instructions that execute on the computer or other
programmable
apparatus provide steps for implementing the functions specified in the block
or blocks.
Accordingly, blocks of the block diagrams support combinations of ways to
perform
the specified functions, combinations of steps for performing the specified
functions
and program instruction for performing the specified functions. It will also
be
understood that each block of the block diagrams, and combinations of blocks
in the
block diagrams, can be implemented by special purpose hardware-based computer
systems that perform the specified functions or steps, or combinations of
special
purpose hardware and computer instructions.
The invention may be implemented through an application program running on an
operating system of a computer. The invention also may be practiced with other
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computer system configurations, including hand-held devices, multiprocessor
systems, microprocessor based or programmable consumer electronics, mini-
computers, mainframe computers, etc.
Application programs that are components of the invention may include
routines,
programs, components, data structures, etc. that implement certain abstract
data types,
perform certain tasks, actions, or tasks. In a distributed computing
environment, the
application program (in whole or in part) may be located in local memory, or
in other
storage. In addition, or in the alternative, the application program (in whole
or in
part) may be located in remote memory or in storage to allow for the practice
of the
inventions where tasks are performed by remote processing devices linked
through a
communications network. Exemplary aspects of the invention will be described
with
reference to the figures, in which like numerals indicate like elements
throughout the
several drawings.
Disclosed are aspects of systems and methods for guiding or controlling the
drilling of
a horizontal well or hole so as to intersect or very nearly intersect an
existing vertical
well or a series of vertical wells. As used herein, the term "horizontal"
means parallel
to or approximately parallel to level ground or the plane of the horizon. As
used
herein, the term "vertical" means being in a position or direction that is
perpendicular
to or approximately perpendicular to the plane of the horizon. The vertical
wells to be
intersected may be disposed more or less in a straight line; however, it will
be
appreciated that the horizontal well may be utilized to intersect other
vertical well
arrangements.
A signal may be transmitted, injected, or otherwise communicated into an
existing
vertical well that is a target for the intersection or near intersection by a
horizontal
well that is to intersect the vertical well. The drilling assembly utilized in
the drilling
of the horizontal well may include or contain sensing components that are
capable of
identifying the signal in the vertical well. Once the signal in the vertical
well has been
identified, the location of the vertical well in relation to the drilling
assembly may be
accurately determined.
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Both a direction from the drilling assembly to the vertical well and a range
or distance
between the drilling assembly and vertical well may be determined. Based at
least in
part on these determinations, the steered path, course, or trajectory of the
horizontal
well may be controlled so as to bring about an intersection or near-
intersection of the
horizontal well and the target vertical well. Other target vertical wells may
then be
located and intersected by the horizontal well by utilizing the same
technique.
Accordingly, a single horizontal well may intersect a second well or multiple
vertical
wells.
FIG. 1 is a schematic diagram of an exemplary application 100 in which a
vertical
well 105 is intersected by a horizontal well 110 in accordance with an
illustrative
aspect of the invention. It will be appreciated that the systems, methods, and
techniques described in aspects of the invention may be utilized in a wide
variety of
applications. For example, aspects of the invention may be utilized in the
drilling of
horizontal wells in conjunction with collecting hydrocarbon products.
Certain hydrocarbon products such as gases, for example, methane often found
captured in relatively shallow coal deposits (also referred to as coal bed
methane, or
CBM) are usually held in place by the hydrostatic pressure of water. In order
to
collect these gases or other hydrocarbon products, the partial pressure of the
water can
be reduced by a suitable "dewatering" process. The "dewatering" process
removes a
critical amount of water in order to release the gases and induce a flow of
the gases
toward the wellbore of a nearby well, such as, for example, the vertical well
105 of
FIG. 1. The gases or other hydrocarbon products are then extracted from the
well,
compressed, and piped to market. In order to complete the "dewatering," a
vertical
well 105 can be underreamed within a coal seam or coal seams.
The underreaming functions to enlarge a section 115 of the wellbore which is
within a
coal seam past its original drilled size. The wellbore can be enlarged to any
size such
as, for example, to a diameter of several feet. The enlarged wellbore section
115 acts
as a reservoir or sump for collection of the water, thereby allowing a more
efficient
removal of water in order to collect the gases. A horizontal well 110 that is
being
drilled is steered into an intersection or near-intersection with the vertical
well 110
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near the enlarged section 115 of the wellbore in order to remove the water and
later to
produce the methane gas flowing into the enlarged section 115.
An extension of this method utilizes a steered horizontal well 110 to
interconnect
multiple vertical wells, thereby further increasing efficiency in collecting
gases. A
further extension of the method is to drill a complex pattern of horizontal
wells and
interconnected passages between strategically placed vertical wells. Such a
configuration of horizontal and vertical wells reduces the number of surface
locations
needed to facilitate drilling and collection of gases. Accordingly, such a
configuration
may be more efficient and may reduce the environmental impact caused at the
surface.
According to aspects of the invention, at least one vertical well 105 is
intersected or
nearly intersected by a horizontal well 110. The drilling of the horizontal
well 110
can be precisely or accurately guided utilizing a measurement while drilling
(MWD)
system, technique, and/or method. Although aspects of the invention are
described
herein as utilizing a measurement while drilling (MWD) system or technique, it
will
be appreciated that other tools, systems, techniques and/or methods can be
utilized in
accordance with aspects of the invention. A directional driller (not shown)
that is
directing or guiding the drilling of the horizontal well 110 is supplied with
data or
information that will assist in completing the intersection or near-
intersection. The
directional driller can be an individual, entity and/or a system or system
component
that is guiding the drilling of the horizontal well 110. The directional
driller can be
located at or associated with a surface location 117 at which the drilling of
the
horizontal well 110 is commenced. The directional driller guides a steerable
drilling
assembly 120 that is utilized to drill the horizontal well. The data provided
to the
directional driller can include information associated with a direction from
the drilling
assembly 120 to the target vertical well 105 and information associated with a
distance from the drilling assembly to the target vertical well 105. The data
allows
the directional driller to orient the drilling assembly 120 and control the
placement
and drilling of the horizontal well 110. Additionally, the data allows an
accurate
intersection or near-intersection between the horizontal well 110 and the
enlarged
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section 115 of the vertical well 105. The accurate intersection or near-
intersection
achieved by utilizing the data allows a reduction of the size needed for the
enlarged
section 115 of the vertical well 105. By increasing the accuracy in guiding
the
drilling assembly 120 to the target vertical well 105, both the size of the
enlarged
section 115 and the time needed to underream and clean the vertical well 105
can be
reduced.
With continued reference to FIG. 1, the drilling assembly 120 includes at
least one
motor 125 and at least one drill bit 130. The drilling assembly 120 also
includes one
or more sensors 135 that are utilized to locate the target vertical well 105.
A wide
variety of techniques, methods, or systems can be utilized to locate the
target vertical
well 105. According to an aspect of the invention, the one or more sensors 135
are
sensors that are capable of detecting a magnetic field such as, for example, a
magnetic
field that is generated or created by an alternating current. One or more
conductors
140 are positioned in the vertical well 105 or near the vertical well 105. The
one or
more conductors 140 are utilized to carry a current through at least a portion
of the
length of the vertical well 105. The current is supplied to the one or more
conductors
140 by an appropriate current generation source such as, for example, a
suitable
alternating current generation source 145.
The alternating current generation source 145 is connected to one end of the
one or
more conductors 140. An alternating current is driven through the one or more
conductors 140 in order to generate alternating current magnetic fields that
can be
detected by the one or more sensors 135 in the drilling assembly 120. The one
or
more conductors 140 are also connected to or tenninated at a ground 150 such
as, for
example, to earth ground. The one or more conductors 140 are terminated at a
ground
150, such as earth ground, at their distal ends. By connecting the one or more
conductors 140 to a ground 150, the one or more conductors 140 create a
discrete
source for detection by the one or more sensors 135, as explained in greater
detail
below with reference to FIG. 2.
Additionally, at least a portion of the vertical well 105 may include an
appropriate
casing 155, as will be understood by those skilled in the art. The casing 155
can be
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any suitable well casing or combination of well casings. Similarly, at least a
portion
of the horizontal well 110 may include an appropriate casing 160. The casing
160 can
be any suitable well casing or combination of well casings.
FIG. 2 is a schematic diagram of a target vertical well 105, according to an
illustrative
aspect of the invention. One or more conductors, similar to 140 in FIG. 1, are
lowered into the target vertical well 105. The one or more conductors, such as
140,
make up a wireline 205. The wireline 205 is lowered into the target vertical
well 105
by a suitable wireline lowering device 207. The wireline 205 is extended from
the
surface through the target vertical well 105, and the wireline 205 is
terminated to a
ground, similar to 150 in FIG. 1, at its distal end. The wireline 205 includes
a
grounding electrode 210 that forms a suitable connection to earth ground.
The grounding electrode 210 is any suitable contact electrode that forms a
connection
to earth ground, as will be understood by those of skill in the art. At the
surface, one
side of an alternating current generation source, shown as 145 and similar to
that
shown in FIG. 1, is connected to the wireline 205, and the alternating current
generation source, such as 145, drives an alternating current into the
wireline 205.
The opposite side of the alternating current generation source, such as 145,
is
connected to a ground, such as 150, for example, to earth ground. Accordingly,
an
alternating current is driven through the wireline 205 and allowed to return
to the
alternating current generation source, such as 145, through the earth. The
alternating
current that is communicated onto or present in the wireline 205 creates or
generates
one or more alternating current magnetic fields or lines of magnetic flux,
such as 215.
Given an elongated wireline 205, the alternating current magnetic fields
propagate in
perpendicular or substantially perpendicular manner from the wireline 205. At
the
end of the wireline 205, the grounding electrode 210 functions to diffuse the
alternating current into the earth. The alternating current magnetic field may
have
many different intensities and/or frequencies. For example, the alternating
current
magnetic field may be a low-frequency field.
In the horizontal well, shown as 110 in FIG. 2, in progress, the drilling
assembly, such
as 120, includes one or more sensors, such as 135, that detect the alternating
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magnetic fields that are produced as a result of the current in the wireline
205. The
one or more sensors, such as 135, can include any number of sensors that are
capable
of detecting the alternating current magnetic fields such as, for example, an
orthogonal triad of alternating current sensors. According to an aspect of the
invention, the one or more sensors 135 have a sensitivity of approximately 0.3
nanoteslas; however, it will be appreciated that sensors with other
sensitivities may be
utilized as desired. For example, sensors with a sensitivity of approximately
0.1
nanoteslas can be utilized. Additionally, the one or more sensors 135 are
capable of
detecting very low intensities of low-frequency alternating current magnetic
fields. It
will be appreciated that the magnitude of the current signal within the
wireline 205
can be controlled so that the alternating current magnetic fields propagated
from the
wireline 205 have intensities that fall within the sensitivity range of the
one or more
sensors 13 5.
FIG. 3 is a schematic diagram of an exemplary drilling assembly 120 that is be
utilized to detect a target vertical well, such as 105, according to an
illustrative aspect
of the invention. The one or more sensors, such as 135, in the drilling
assembly 120
detect the alternating current magnetic field that is produced by the wireline
205. The
field vector at the one or more sensors 135 is at a right angle to a target
direction to
the target vertical well 105. Additionally, the field vector at the one or
more sensors
135 is at a tangent to the concentric lines of magnetic flux that are
propagating from
the wireline 205.
The alternating current magnetic field is detected and measured by the one or
more
sensors 135. The one or more sensors 135 then communicate the measurements to
one or more control units that process the measurements. The information can
be
communicated via any appropriate communication technique(s) or device(s) such
as,
for example, a mud pulse system, a steering tool probe, a wired connection, a
wireless
connection, a cellular connection, and/or a radio connection. A first control
unit 305
can be included in or associated with the drilling assembly 120. The first
control unit
305 can process the measurements and communicate or transmit to a directional
driller information associated with a distance and/or a direction from the
drilling
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assembly 120 to the target vertical well 105. The communicated information can
be
further processed by at least one control unit (not shown) associated with the
directional driller.
Information associated with the direction and distance to the target vertical
well 105
can be communicated or provided to the directional driller in an appropriate
form that
allows the directional driller to guide the drilling of the horizontal well
110 to achieve
an intersection or near-intersection with the target vertical well 105. With
the
provided information, the directional driller can adjust the path of the
drilling
assembly 120 as needed to achieve the intersection or near-intersection within
acceptable limits of curvature, or "dogleg" in the horizontal well 110. Small
amounts
of dogleg in the horizontal well 110 may be acceptable. The acceptable dogleg
may
vary depending on the application, and the acceptable dogleg can be expressed
in any
appropriate form such as, for example, in degrees per 100 feet or in degrees
per 30
meters. Relatively larger amounts of dogleg or curvature of the hole may cause
problems in the continuation of the drilling and/or in the later installation
of pipe in
the horizontal well 110.
FIGS. 4-6 are schematic diagrams depicting the guidance of the drilling of a
horizontal well 110 to create an intersection or near-intersection with a
target vertical
well 105, according to an illustrative aspect of the invention. FIG. 4 is a
schematic
diagram that depicts the current direction 405 of the drilling assembly, shown
in
FIGS. 1-3 as 120, and the target direction 420 to the target vertical well
105. As
shown in FIG. 4, the target direction 425 to the target vertical well 105
forms
approximately a right angle with a line 410 that is approximately tangential
to the arc
of the alternating current magnetic field 415 that is emitted from the
wireline 205. An
approximate angle 0 425 represents the difference between the current
direction 405
and the target direction 420 if such a difference exists.
FIG. 5A is a top view schematic diagram of the drilling of a horizontal well,
shown in
FIG. 1 as 110, to form an intersection or near-intersection with a vertical
well, shown
in FIG. 1 as 105, according to an illustrative aspect of the invention.
Similarly, FIG.
5B is a cross sectional view taken along the line A to A' of FIG. 5A and
depicting the
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drilling of a horizontal well 110 to form an intersection or near-intersection
with a
vertical well 105, according to an illustrative aspect of the invention. FIG.
5B is a
view along the path taken by the horizontal well 110 in progress, and FIG. 5B
depicts
the formation of the intersection or near-intersection between the horizontal
well 110
and the vertical well 105 at an enlarged section 115 of the vertical well 105.
FIG. 6 is a top or plan view schematic diagram of adjustments that may be made
during the drilling of a horizontal well 110 to form an intersection or near-
intersection
with a target vertical well 105. In other words, FIG. 6 illustrates how a
directional
driller utilizes the capability for determining range and/or direction in
order to guide
the drilling of the horizontal well 110. With reference to FIG. 6, from a
starting
location 600 of the drilling assembly 120, the current direction 405 of the
drilling
assembly 120 is shown. The current direction 405 can be the direction from the
drilling assembly 120 to a target position 610 of the vertical well 105 that
is based on
a survey taken at the surface or on some other estimated location of the
vertical well
105. Also shown in FIG. 6 is the target direction 420 towards the target
vertical well
105. A directional driller that is guiding the drilling assembly 120 can
follow or
approximately follow the current direction 405 until the drilling assembly 120
reaches
a distance 605 from the vertical well 105 at which the one or more sensors 135
may
detect the alternating current magnetic field.
The distance 605 may be referred to as the detection range of the one or more
sensors
135. The detection range 605 of the one or more sensors is dependent upon the
type
or types of sensors that are utilized. The approximate detection range 605 is
typically
a known value that is associated with one or more of the sensors; however, the
detection range 605 may be determined and/or verified by any suitable method
or
technique. Additionally, it will be appreciated that the detection range 605
may vary
according to a variety of factors such as, for example, the density of the
earth and/or
other materials that are situated between the drilling assembly 120 and the
target
vertical well 105.
Once the drilling assembly 120 reaches or is within the detection range 605,
the
directional driller can adjust the path of the drilling assembly based on the
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measurements taken by the one or more sensors 135. The directional driller can
adjust the path in order to form an intersection or near-intersection between
the
horizontal well 110 and the vertical well 105. An enlarged section 115 of the
vertical
well 105 may be situated at the intersection or near-intersection. As shown in
FIG. 6,
the drilling of the horizontal well 110 can be guided along an adjusted path
615 based
at least in part on the measurements taken by the one or more sensors 135 in
order to
form the intersection or near-intersection.
According to an aspect of the invention, the measurements taken by the one or
more
sensors 135 are processed by one or more control units, similar to 305 in FIG.
7, in
order to provide the directional driller with appropriate information
associated with an
accurate direction and an accurate distance or range from the drilling
assembly 120 to
the target vertical well 105. The processed measurements and/or data can be
provided
to the directional driller in an appropriate format that facilitates the
guiding of the
drilling assembly 120 by the directional driller.
FIG. 7 depicts a block diagram of an exemplary control unit 305 utilized in
accordance with the invention in order to determine the direction and distance
from
the drilling assembly, such as 120, to a target vertical well, such as 105.
The control
unit 305 can be a control unit associated with the drilling assembly 120. A
similar
control unit can be associated with the directional driller at the surface. It
will be
appreciated that aspects of the invention may utilize any number of control
units. For
example, certain aspects may utilize a single control unit.
The control unit 305 of FIG. 7 includes a memory 705 and a processor 710. The
memory 705 stores programmed logic 715 (e.g., software) in accordance with the
invention. One example of software or a computer-readable medium is program
code
or a set of instructions operable to receive and process measurements data in
order to
determine a distance and/or direction from the drilling assembly, such as 120,
to a
target vertical well, such as 105. The memory 705 also includes data 720
utilized in
the operation of the aspect of the invention, and also includes an operating
system
725. The data 720 can include measurements data taken by the one or more
sensors,
such as 135, in the drilling assembly 120. The processor 710 utilizes the
operating
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system 725 to execute the programmed logic 715, and in doing so, may also
utilize the
data 720. A data bus 730 provides communication between the memory 705 and the
processor 710. Users can interface with the control unit 305 via one or more
user
interface device(s) 735 such as a keyboard, mouse, control panel, or any other
devices
capable of communicating digital data to or from the control unit 305.
The control unit 305 can communicate with external devices such as, for
example, the
one or more sensors 135, via one or more appropriate interface devices 740.
The one
or more interface devices 740 can also facilitate the output of data by the
control unit
305 to one or more suitable output devices such as, for example, a display,
and/or to
one or more other system components or external devices. It will be
appreciated that
communication with external devices may be facilitated with any suitable data
communication technique such as, for example, communication via a direct
connection, communication via a wired network connection, communication via a
wireless network connection and/or communication via a cellular network
connection.
Further the control unit 305 and the programmed logic 715 implemented thereby
may
comprise software, hardware, firmware or any combination thereof.
FIG. 8 is an exemplary flowchart of example general operations taken by a
control
unit, such as 305, in accordance with an illustrative aspect of the invention.
It will be
appreciated that some or all operations described herein can be achieved by a
single
control unit or by a combination of control units utilized in accordance with
the
invention. Once the control unit, such as 305, commences operations, the
control unit
305 goes to block 805 and receive measurements from the one or more sensors,
such
as 135, in the drilling assembly, such as 120. The received measurements can
be
associated with the alternating current magnetic field that is generated by
the wireline,
such as 205, in the vertical well, such as 105. For example, the received
measurements can be associated with a strength of the alternating current
magnetic
field.
At block 810, the control unit 305 determines a distance from the drilling
assembly
120 to the target vertical well 105. At block 815, the control unit 305
determines a
direction from the drilling assembly 120 to the target vertical well 105. The
path of
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the drilling assembly can be adjusted based at least in part on the determined
direction
and distance or range in order to facilitate an intersection or near-
intersection between
the horizontal well 110 and the target vertical well 105.
At block 820, the distance and/or direction determinations can optionally be
adjusted.
The adjustments can place the determinations in a more appropriate form for
subsequent processing or actions that may be taken based upon the
determinations.
For example, if the directional driller is an individual and the distance
determinations
are made using metric units (e.g., meters), then the distance determinations
can be
adjusted to standard units (e.g., feet) before they are communicated and/or
displayed
to the directional driller. As another example, if the directional driller is
an
individual, then the direction determination can be adjusted or corrected to
magnetic
north prior to being communicated and/or displayed to the directional driller.
For example, the direction determination includes an approximate angle 0 425
representing the difference between the current direction 405 of the drilling
assembly
120 and the target direction 420 to the vertical well 105. The angle 0 can be
corrected
to magnetic north in order to provide the directional driller with a desired
heading for
the drilling of the horizontal well 110 in order to achieve an intersection or
near-
intersection with the target vertical well 105. It will be understood that any
adjustments made to the distance and/or direction determinations are optional
and
may not be necessary. For example, if the path of the drilling assembly 120 is
automatically controlled by a suitable device or system such as, for example,
a
computerized guidance system, then adjustments to the distance and/or
direction
determinations may not be necessary.
At block 825, the direction and/or the distance determinations can optionally
be
communicated to the directional driller. The communication to the directional
driller
can include a communication to a control unit associated with the directional
driller
from another control unit such as, for example, a control unit associated with
the
drilling assembly 120. The communication can also include a communication to
an
appropriate output device associated with the directional driller such as, for
example,
a display associated with the directional driller.
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The operations described in FIG. 8 can be performed continuously or
periodically as
the horizontal well 110 is drilled. With reference to FIG. 8, the operations
of the
control unit 305 continue at block 805 following the determination of a
direction and
a distance to a target vertical well 105, and the optional adjustment and
communication of these determinations. At block 805, the control unit 305
receives
new measurements from the one or more sensors 135, and the control unit 305
utilizes
these new measurements to determine a new or updated direction and/or distance
to a
target vertical well 105. As shown in FIG. 8, the operations of the control
unit 305
are performed continuously; however, it will be appreciated that the
operations of the
control unit 305 can be performed periodically.
For example, the control unit 305 can receive and process measurements at
predetermined time intervals such as, for example, every ten seconds. Many
different
predetermined time intervals may be utilized in accordance with aspects of the
invention, as will be understood by those of skill in the art. Additionally,
it will be
understood that the control unit 305 can direct the storage of any number of
received
measurements, determined values, and/or adjusted values. For example, the
control
unit 305 can store a measurement or a value in the memory 705 of the control
unit
305. As another example, the control unit 305 can direct an associated memory
device to store a measurement or a value.
It will be appreciated that the operations described above with reference to
FIG. 8 do
not necessarily have to be performed in the order set forth in FIG. 8, but
instead can
be performed in any suitable order. Additionally, it will be understood that,
in certain
aspects of the invention, the control unit 305 can perform more or less than
all of the
operations set forth in FIG. 8. It will also be appreciated that the
operations set forth
in FIG. 8 can be performed by any appropriate control unit or combination of
control
units such as, for example, a control unit associated with the drilling
assembly and/or
a control unit associated with the directional driller.
According to an aspect of the invention, a distance or range between the
drilling
assembly, such as 120 shown in FIG. 1, and the target vertical well, such as
105
shown in FIG. 1, is determined. The distance or range is determined utilizing
one or
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more measurements that are taken by the one or more sensors, such as 135 shown
in
FIG. 1, of the drilling assembly, such as 120 shown in FIG. 1. In some aspects
of the
invention, the one or more sensors 135 include three sensors that measure the
intensity of an alternating current magnetic field that is generated by a
wireline 205 in
the target vertical well 105; however, it will be understood that the drilling
assembly
120 may include or be associated with any number of sensors that are
configured to
measure the intensity of the alternating current magnetic field.
The three sensors respectively measure the intensity of the alternating
current
magnetic field in three directions or dimensions. For example, a first sensor
measures
the intensity of the alternating current magnetic field in a direction that
roughly
corresponds to the current path of the drilling assembly 120, which can be
referred to
as the Z direction. As discussed earlier with reference to FIG. 4, the Z
direction forms
an approximate right angle with a line 410 that is approximately tangential to
the arc
of the alternating current magnetic field 415 that is emitted from the
wireline 205.
The second and third sensors measure the intensity of the alternating current
magnetic
field in respective directions that are perpendicular to the current path of
the drilling
assembly 120, which can be referred to respectively as the X direction and the
Y
direction. The X direction and the Y direction are additionally perpendicular
to one
another. The three sensors can take scalar and/or vector measurements of the
alternating current magnetic field.
Once the intensity of the alternating current magnetic field has been
determined by the
three sensors, a single intensity measurement or value of the intensity is
determined or
calculated based on a combination of the thee intensity measurements, as will
be
understood by those of skill in the art. It will be appreciated that other
suitable
determinations of the intensity of the alternating current magnetic field can
be utilized
in accordance with aspects of the invention.
The distance or range is then determined or calculated based on one or more
intensity
measurements. Many different methods can be utilized in order to determine the
distance or range, as will be appreciated by those of skill in the art. A few
methods
are discussed herein by way of example only. A first exemplary method assumes
a
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relatively simple model of the alternating current magnetic field. The first
exemplary
method assumes a model in which there is no loss or very little loss of the
current
present on the wireline 205 into the surrounding vertical well 105 (i.e., the
current
producing the field is precisely known), and for which the grounding electrode
210
has a low termination resistance value, which creates a resistive path to
ground with
little or no current loss. In other words, the first exemplary model assumes a
relatively ideal or ideal, straight current-carrying wire.
In the first exemplary method, the relationship between the value of the
alternating
current carried by the wireline 205, the generated field intensity, and the
distance or
range is given by the following equation:
H = P I (1)
2;r = rn
where "H" represents the generated field intensity, "I" represents the value
of the
alternating current carried by the wireline 205, "r" represents the distance
or range,
"n" represents the falloff rate of the magnetic field, and " o" is a constant
of
47E * 10-7 T- m/A, or the permeability of free space. Equation (1) represents
a special
case of the Biot-Savart Law for the magnetic field intensity due to a current
in a thin,
infinitely long straight conductor. The value of "n" can be assumed to be
equal to 1;
however, it will be appreciated that other values for "n" may be utilized. For
example, the value of "n" can change as the one or more sensors 135 approach
the
wireline 205 and the diffuse currents become more concentrated as the distance
or
range decreases. Simplifying equation (1) yields:
H _ 2 I=10-' or
rn
H = KnI (2)
r
where "K" is a constant of 2 x 10 -7. Solving for distance or range yields:
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K=I
r" = or
H
r=(KII" (3)
H J
This equation can be used to calculate range, and the current and the field
intensity
should be known (or closely estimated).
If a low loss wire model is assumed, then equation (3) can be utilized to
determine or
calculate the distance or range between the drilling assembly 120 and a target
vertical
well 105 if the current in the wireline 205 is known and the intensity of the
alternating
current magnetic field is known, accurately measured, and/or closely
approximated.
It will be appreciated that a value for the current can be assumed for the
calculation
based upon a current that is supplied to the wireline 205 by the alternating
current
generation source 145. Alternatively, the current can be measured in the
wireline 205
by an appropriate current measuring device such as, for example, an ammeter or
a
current sensing transformer, and the current measurement can be communicated
to a
control unit such as, for example, the control unit 305 associated with the
drilling
assembly 120.
The second exemplary method for determining a distance between a drilling
assembly
120 and a target vertical well 105 makes no or limited assumptions about the
loss of
current from the wireline 205 to the surrounding vertical well 105 and/or
earth.
Additionally, the second exemplary method does not assume that the amplitude
of the
alternating current in the wireline 205 is a known amplitude; however, the
second
exemplary method can assume that the alternating current in the wireline 205
has a
constant or approximately constant amplitude. For certain applications, such
as for
example, the CBM application 100 depicted in FIG. 1, the wireline 205 may not
have
a current with an exactly known amplitude flowing through it. For example, as
the
wireline 205 approaches the grounding electrode 210, the amplitude of the
current
may not be exactly known at or near the terminal end of the wireline 205
connected to
the grounding electrode 210. It will be appreciated that at least a portion of
the
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current may be lost to the surrounding vertical well 105 and/or that at least
a portion
of the current may be diffused into the earth.
FIG. 9 is a graphical representation of one example of falloff rates for two
different
alternating current magnetic fields having different intensities. The falloff
rates
depicted in FIG. 9 represent the falloff rates of magnetic field intensity
over distance
as the magnetic fields propagate away from a source such as, for example, the
wireline 205. With reference to FIG. 9, the field intensity versus distance is
illustrated
for the two magnetic fields 905, 910. The first magnetic field 905 represents
a
magnetic field that is generated by a lower amplitude of current in the
wireline 205
relative to the current that generated the second magnetic field 910.
At a distance "r," from the source (e.g., the wireline 205), the intensity of
the first
magnetic field 905 is "Hal" and the intensity of the second magnetic field 910
is
"Hbl". The slope or gradient of the first magnetic field 905 at "rl" is A Hal/
A rl, and
the slope or gradient of the second magnetic field 910 at "r," is A Hbl/ A rl.
The
falloff rate is expressed as an exponential "n" in the denominator. The
falloff rate of
intensity over distance for each field is approximately the same and may be
given by:
FalloffOverDist = 1 (4)
r
Thus, the distance or range "rl" is independent of the strength of the source
and of the
attenuation effect.
According to an aspect of the invention, the second exemplary method for
determining a distance or range can make use of one or more gradient
calculations.
For example, the second exemplary method can make use of the measurements of
the
intensity of the alternating current magnetic field to calculate one or more
gradients.
A method that utilizes one or more gradients to determine a distance or range
can also
be referred to as gradient ranging. Differentiating equation (2) above
provides a rate
of change of the alternating current magnetic field intensity as the distance
changes
given a value of the current in the wireline 205. Differentiating equation (2)
leads to
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the derivative of the filed intensity with respect to distance, which can be
referred to
as the field gradient. The field gradient is given by:
dH -n=K=I
dr y,,,+i (5)
where "K" is a constant of 2 x 10 "7 . The derivative can be utilized with the
intensity
value at a location to determine or calculate the distance or range to the
target vertical
well 105. Taking the ratio of the intensity to the gradient results in an
expression for
the distance or range "r" and the falloff rate "n", given as:
H (K = I) (rn+') r (6)
(dH -r" (-n=K=I) n
dr )
From equation (6), "r" is determined as:
-r=n= ~ (7)
dr
In equation (7), the constant "K" and the current "I" are no longer used.
Further, a
close approximation for dH/dr can be given by AH/Ar. Accordingly, the rate of
change of the measured intensity over a change in distance can be utilized in
a
determination of a distance between the drilling assembly 120 and a target
vertical
well 105. In a situation in which a single set of sensors 135 is included in
the drilling
assembly 120, the gradient can be measured and/or approximated by utilizing
the
sensors 135 in at least two positions. At each position, the intensity of the
alternating
current magnetic field is measured, and a determination of the distance or
range to the
target vertical well 105 is made based at least in part on the intensity
measurements at
each position. Each measured intensity can be the total intensity of the
alternating
current magnetic field that is measured at each position. Additionally, at
each
position, a depth of the drilling assembly 120 from the surface can be
inputted and/or
measured. The value of "n" can also be inputted and/or entered. It will be
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appreciated that a predetermined value for "n" can be inputted such as, for
example, a
default value of one.
According to an aspect of the invention, the measurements can be made in many
different modes of operation for the drilling assembly 120 such as, for
example, a
drilling mode, pushing on the bit, or in a pulling-back or off-bottom mode.
One or
more sets of data can be taken to improve the accuracy of the distance or
range
determination. One or more sets of data can be taken at one or more locations
or
positions of the drilling assembly 120. It will be appreciated that a
plurality of
determinations based on a plurality of data sets can be averaged together to
improve
the accuracy of the determinations.
FIG. l0A is an exemplary flowchart depicting exemplary operations taken by the
control unit, such as 305 of FIG. 7, to determine a distance or range to a
target vertical
well 105, in accordance with an illustrative aspect of the invention. The
operations
depicted in FIG. l0A utilize a drilling assembly 120 that is operating in a
pulling-back
or off-bottom mode. At block 1005, the drilling assembly 120 is located or
stopped at
a first position "Pa". Point "Pa" is a point that is situated at a desired
depth. At point
"Pa", the drill bit 130 is pulled off the bottom by an appropriate distance
such as, for
example, by one or two foot. At point "Pa", the distance or range to the
target vertical
well 105 is given as "ra". At block 1010, data is acquired from the one or
more
sensors 135 and the total magnetic field intensity "Ha" is determined by the
control
unit 305. The data and/or the field intensity "Ha" is stored for later use at
block 1015.
At block 1020, the drilling assembly 120 is moved to a different position "Pb"
in the
horizontal well 110. For example, the drilling assembly 120 is moved forward
in the
horizontal well 110 by a predetermined distance "Arl". The predetermined
distance
"Orl" can be any appropriate distance such as, for example, a distance that is
much
smaller than the distance or range from the drilling assembly 120 to the
target vertical
well 105. At position "Pb", the distance or range to the target vertical well
105 is
given as "rb". At block 1025, data is acquired from the one or more sensors
135 and
the total magnetic field intensity "Hb" is determined by the control unit 305.
The data
and/or the field intensity "Hb" is stored for later use at block 1030.
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At block 1035, the drilling assembly 120 is moved to a different position "P,"
in the
horizontal well 110. For example, the drilling assembly 120 is moved forward
in the
horizontal well 110 by a predetermined distance "Ar2". The predetermined
distance
"Ar2" can be any appropriate distance such as, for example, a distance that is
much
smaller than the distance or range from the drilling assembly 120 to the
target vertical
well 105. The predetermined distance "Ar2" can be approximately equal to the
distance "Orl"; however, it will be understood that "Ar2" may be a different
distance
than "Orl". At position "P.", the distance or range to the target vertical
well 105 is
given as "rc". At block 1040, data is acquired from the one or more sensors
135 and
the total magnetic field intensity "H," is determined by the control unit 305.
The data
and/or the field intensity "H," is stored for later use at block 1045.
At block 1045, several data values are stored by the control unit 305 for
later use. For
example, values for "Pa", "Pb", and "Pc" are stored. The corresponding depths
at "Pa",
"Pb", and "Pc" can respectively be "r,", "r2", and "r3". Additionally, the
values can be
referenced to the same point such as, for example, to the drill bit 130 of the
drilling
assembly 120. Values for "n" and "K" can also be stored by the control unit
305.
The value for "n" can be set to a default value such as, for example, to 1Ø
The value
of "K" can be 2 x 10 -7. It will be appreciated that other values can be
stored by the
control unit 305. These other values may include values utilized in
calculations other
than those for gradient ranging. These other values may include for example, a
value
of the current "I" that is present in the wireline 205.
At block 1050, values for the average intensity between two positions and the
difference in intensity for two positions is calculated by the control unit
305 according
to the following equations:
(Ha + Hb )
Havx, = 2 OH, = Hh - Ha
Hav~2 = 2 OHZ = H, - Hn (8)
(Hb + H~~ )
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At block 1055, one or more gradient ranging calculations are determined by the
control unit 305 according to the following equations:
HavK, Orl
Rangeg.ad, = n' AH, - 2
Or,
Hovgz Ar2 RangeKra~rz = n ' (9)
AHz 2
Arz
The determined gradient range values are referenced to position "Pa".
Additionally,
the values can be corrected to the depth of the drilling assembly 120.
At block 1060, the two gradient range values are averaged by the control unit
305
according to the following equation:
Ran e _ (Rangeg,ad, + Rangexrad2 (10)
g avg - )
2
The determined value for Rangea~g represents the distance or range from the
drilling
assembly 120 to the target vertical well 105.
It will be appreciated that the operations described above with reference to
FIG. I OA
do not necessarily have to be performed in the order set forth in FIG. 10A,
but instead
may be performed in any suitable order. Additionally, it will be understood
that, in
certain aspects of the invention, the control unit 305 can perform more or
less than all
of the operations set forth in FIG. 10A. It will also be appreciated that the
operations
set forth in FIG. l0A can be performed by any appropriate control unit or
combination
of control units such as, for example, a control unit associated with the
drilling
assembly and/or a control unit associated with the directional driller.
FIG. I OB is a graphical representation of exemplary distances and values that
can be
measured and/or determined by utilizing the exemplary operations depicted in
FIG. 10A.
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According to another aspect of the invention, a direction from the drilling
assembly
120 to the target vertical well 105 is determined. The one or more sensors 135
are
utilized to measure the components of the alternating current magnetic field.
The
measured components of the alternating current magnetic field are utilized to
determine or calculate a relative direction angle "0" 425 between the current
path of
the drilling assembly 120 and the actual direction to the target vertical well
105.
According to an aspect of the invention, the components of the alternating
current
magnetic field are measured in three directions. A sensor "k" measures the
component
of the field in the Z direction, a sensor "i" measures the component of the
field in the X
direction, and a sensor "j" measures the component of the field in the Y
direction.
The values measured by the "i" and "j" sensors can be resolved into a "radial"
value.
The radial value is a vector that lies in a plane that is situated at a right
angle to the
direction of the borehole of the horizontal well 110. The radial value is
given by:
radial = (i2 + jz) (11)
The value measured by the "k" sensor can be referred to as an "axial" value.
The
value measured by the "k" sensor is a value that is aligned with the borehole
or the
current path of the drilling assembly 120. The direction to the target "0" 425
is
determined by the following equation:
axial
6=tan' (12)
radial
In the event that the current path of the drilling assembly 120 coincides or
very nearly
coincides with the direction "0" 425 to the target vertical well 105, the
tangent field
will form a right angle with the axial sensor "k" and the output of the sensor
"k" will
be zero. Additionally, the phase of the axial sensors can change 180 degrees
as the
axial null orientation is passed in rotating the current path of the drilling
assembly 120
from left side of "0" 425 to the right side of "0" 425, or vice versa.
The determined value of "0" 425 can be a value that is relative to the current
path of
the drilling assembly 120. According to an aspect of the invention, the value
of "0"
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425 can be adjusted. For example, the value of "0" 425 can be corrected to
magnetic
north so that a directional driller may be presented with familiar terminology
while
steering the drilling of the horizontal well 110.
FIG. 11 is an exemplary flowchart depicting exemplary operations taken by a
control
unit, such as 305 in FIG. 7, at block 815 of FIG. 8 to determine a direction
to a target
vertical well 105, in accordance with an illustrative aspect of the invention.
At block
1105, the components of the alternating current magnetic field are measured by
one or
more sensors 135 and communicated to the control unit 305. At block 1110, the
measurements are stored by the control unit 305. At block 1115, the control
unit 305
determines a radial value according to equation (11) above. At block 1120, the
control unit 305 determines an axial value in the direction of the current
path of the
drilling assembly 120. At block 1125, the control unit 305 determines the
direction to
the target vertical well 105, or "0" 425, based at least in part on the radial
value and
the axial value.
It will be appreciated that the operations described above with reference to
FIG. 11 do
not necessarily have to be performed in the order set forth in FIG. 11, but
instead can
be performed in any suitable order. Additionally, it will be understood that,
in certain
aspects of the invention, the control unit 305 can perform more or less than
all of the
operations set forth in FIG. 11. It will also be appreciated that the
operations set forth
in FIG. 11 can be performed by any appropriate control unit or combination of
control
units such as, for example, a control unit associated with the drilling
assembly and/or
a control unit associated with the directional driller.
Many modifications and other aspects of the invention set forth herein will
come to
mind to one skilled in the art to which the invention pertains having the
benefit of the
teachings presented in the foregoing descriptions and the associated drawings.
Therefore, it is to be understood that the invention is not to be limited to
the specific
aspects disclosed and that modifications and other aspects are intended to be
included
within the scope of the appended claims. Although specific terms are employed
herein, they are used in a generic and descriptive sense only and not for
purposes of
limitation.
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