Field oflnvention
This invention relates to ranging using current profiling and generally to
apparatus and methods associated with measurements related to oil and gas
5 exploration.
Background Technical Information
As the easy-to-access and easy-to-produce hydrocarbon resources have been
·depleted over the last century, more and more difficult wells remain. Moreover, the
10 world's hydrocarbon demand is continuously growing. Meeting this demand ·
requires development of more advanced recovery procedures, one of which is the
steam assisted gravity drainage (SAGD) application. SAGD addresses the mobility
problem of the heavy oil wells by injection of high pressure and high temperature
steam, which reduces viscosity ofthe oil and allows easy extraction. This injection
15 is performed from a wellbore (injector) that is drilled in parallel to the producing
well (producer) at a distance in the order of a few meters from each other. The
placement of the injector needs to be achieved with very small margin in distance,
since getting it too close would expose the producing well to very high pressure and
temperature, and getting it too far would reduce efficiency of the process. It is well
20 known that traditional surveying techniques suffer from a widening cone of
uncertainty as the well gets longer and they caimot achieve the precision in
placement that is required.
. 25
Brief Description of the Drawings
Figures lA-lB are schematic representations of an example surfaceexcitation
single well ranging system with respect to current profiling and with
respect to distance provided from absolute measurement, in accordance with various
embodiments.
Figure 2 is a schematic representation of an example of voltage profiling, in
30 accordance with various embodiments.
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17 52
Figures 3A-3C are schematic representations of examples of impedance
profiling, in accordance with various embodiments.
Figure 4 is a schematic representation of an absolute measurement principle
with respect to a target pipe, in accordance with various embodiments.
5 Figure 5 is a flow diagram of features of an example system ranging
operation, in accordance with vc:uiuus t::tuuuc.limtmts.
Figure 6 is a flow diagram of features of an example method ofranging, in
accordance with various embodiments.
Figure 7 is a schematiC representation of features of an example system
10 operable to conduct ranging operations to a production well, in accordance with
various embodiments.
Figure 8 is a block diagram of features of an example system operable to
conduct ranging operations, in accordance with various embodiments.
15 Description of Invention w.r.t. Drawings
The following detailed description refers to the accompanying drawings that
show, by way of illustration and not limitation, various embodiments in which the
invention may be practiced. These embodiments are described in sufficient detail to
enable those skilled in the art to practice tfl.ese and other embodiments, Other
20 embodiments may be utilized, and structural, logical, and electrical changes may be
made to these embodiments. The various embodiments are not necessarily mutually
exclusive, as some embodiments can be combined with one or more other .
embodiments to form new embodiments. The following detailed description is,
therefore, not to be taken in a limiting sense.
25 In a recent approach, a single well solution provides currents that are
· injected from the surface. However, this' method requires a gradient measutement
for accurate distance calculation, which t:equires a very sensitive magnetic field
measurement and very large currents to be injected from the surface.
Herein, a producing well may be referred to as a production well, a producer
30 well, or a producer. An injecting well may be referred to as an injection well, an
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IPD DELHI B2-B5-2~1B 17"52
injector well, or an injector.
In various embodiments, ranging techniques may include generating a
current profile for a target well, acquiring magnetic signals at a second well, and
determining ranging to the target well with respect to the second well using the .
5 magnetic signals and the current profile. A production well can be a target well for
which distance and direotion from another \veil, :mch as an injection 'vvcll, i3 to be
determined. In various embodiments, an apparatus and process, as taught herein,
can utilize a wireline production tool with electrodes that can measure voltages due
to surface excitation and can inject currents to a producer well to measure pipe
10 resistance along the well. This procedure allows accurate distance calculation from
absolute measurements, which has significantly larger range compared to a gradient
measurement. This ranging operation may be separated into four parts: (i) profiling
of surface excitation voltages in a producer; (ii) profiling of impedances along the
producer; (iii) calculation of currents on the producer; and (iv) calculation of
15 distance from the currents.
With respect to voltage profiling, the surface excitation can be setup and
activated exactly the same way it will be in the regular operation (same electrode
locations, same frequencies). Ideally, this is performed after the producer is drilled;
however it is also possible to the setup and activation after most of the electrically
20 active sections are· drilled. It is also preferred to do/repeat this operation after
injector is drilled since inclusion of a new BHA or casing sections in the injector as
part of drilling may affect the voltages. If the voltage profiling is performed before
the injector is drilled, a correction on the profiled voltages can be performed to take
into account the effect of inclusion of injector casing or BHA. This will be
25 explained in more detailed in discussions to follow.
The source can be either voltage controlled or current controlled and can
alternate with very low frequencies in the order of 0.02-250 Hz. In some
applications, higher frequencies on the order of250 Hz to 10 GHz may also be used.
In suc_h high frequency applications, measurements may be made during drilling due
30 to relatively small interference of the influence of earth's magnetic fields. However,
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IPO nELHI R2-85-28~~ 17 52
5
high frequencies can result in significantly large current leaks on the pipe and they
cannot be used with deep applications unless an insulated excitation line is brought
downhole. The source can be located at the surface and can be connected to the .
well via an insulated cable that is clamped to a fixed location in the well.
·'
Figures lA-lB are schematic representations of an example surfaceexcitation
single v\tell raugiug systt!rn with respect to current protiling and with
respect to distance provided from absolute measurement. Figure lA shows n
producer 1 02-A in which a pipe 1 08-A is disposed, where the producer 1 02-A is
separated from an injectdes, to
control generation of currents from selected electrodes of the plurality of electrodes
and collection ofvoltages based on the generation ofthe currents, and to control
acquisition of a measured magnetic field from the magnetic sensor; and
a processing unit operatively coupled to the contt:ol unit and arranged to
25 generate, from interaction with the control unit, a voltage profile, an impedance ·
profile, and a current profile using the voltage profile and the impedance profile, the
processing unit to perform a ranging operation to the first well with respect to the
second well using the current profile with ameasured magnetic field.
30 28. · A system as claimed in claim 27, wherein the first well is a production well.
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IPG nELHT A2-B5-28~~ 17"53
29. ·: A .system as claimed in claim 28, wherein the second well is an injector well
in a steam assisted gravity drainage (SAGD) application.
5 30. A system as claime~ in claim i7, wherein the emitter is disposed at a surface
from which the first well was formed.
10
15
20·
31. A system as claimed in claim 27, wherein the emitter is disposed in the first
well.
32. A system as claimed in claim 27, wherein the control unit is arranged to
activate the emitter using voltage controlled or current controlled activation at
frequencies in the range from about 0.02 Hz to about 250 Hz.
A system as claimed in claim 27, wherein the processing unit is arranged to
generate the voltage profile from determination of voltage differences between pairs
of locations along the pipe of the first well for current injected at a well head of the
first well with a current return at location on a surface from which the first well was
formed.
34. A systetn as claimed in claim 27, wherein the processing unit is arranged to
generate the impedance profile from injection of current from one electrode of the
plurality of electrodes to another electrode of the plurality of electrodes and
determination of voltage differences between pairs of locations along the pipe
25 between or at locations of the electrodes injecting and receiving the current.
35. A system as claimed in any one of claims 27-34, wherein the control unit
and the processing unit are arranged to perform a ranging operation with respect to
the second well after drilling a portion of the second well and after stopping the
30. drilling.
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IPQ nELHT B2-B5-2B16 17 53
36. A system as claimed in any one of claims 27-34, wherein the processing unit
is arranged to determine distance and direction to the ·second well using a
relationship between distance and a ratio of current to measured magnetic field at a
5 depth, the current at the depth taken from the current profile at the depth for current
iujt::~o:lt::u ala wt!ll head of the first well with a current return at location on a surface
from which the first well was formed.
37. A system as claimed in any one of claims 27-34, wherein the processing unit
10 and the control unit are arranged· to repeat generation of a voltage profile, generation
of an impedance profile, and generation of a current profile after further drilling of
the second well.
38. A system as claimed in any one of claims 27-34, wherein the second well is
15 a production well.
20
25
39. A system as claimed in any one of claims 27-34, wherein the control unit
and the processing unit are arranged to perform a ranging operation with respect to
one or more wells that are different from the first and second wells.