WO2010059621A2 - Procédé et dispositif pour calibrer et corriger un bruit cohérent lors d'une détection dans un tubage - Google Patents

Procédé et dispositif pour calibrer et corriger un bruit cohérent lors d'une détection dans un tubage Download PDF

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Publication number
WO2010059621A2
WO2010059621A2 PCT/US2009/064780 US2009064780W WO2010059621A2 WO 2010059621 A2 WO2010059621 A2 WO 2010059621A2 US 2009064780 W US2009064780 W US 2009064780W WO 2010059621 A2 WO2010059621 A2 WO 2010059621A2
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WO
WIPO (PCT)
Prior art keywords
magnetic field
current
drill collar
measurement sub
magnetometer
Prior art date
Application number
PCT/US2009/064780
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English (en)
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WO2010059621A3 (fr
Inventor
Brian Clark
Mark Flaum
Jan Morley
Jaideva Goswami
Miguel Pabon
Original Assignee
Schlumberger Canada Limited
Schlumberger Technology B.V.
Prad Research And Development Limited
Services Petroliers Schlumberger
Schlumberger Holdings Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Schlumberger Canada Limited, Schlumberger Technology B.V., Prad Research And Development Limited, Services Petroliers Schlumberger, Schlumberger Holdings Limited filed Critical Schlumberger Canada Limited
Priority to US13/128,506 priority Critical patent/US9360581B2/en
Publication of WO2010059621A2 publication Critical patent/WO2010059621A2/fr
Publication of WO2010059621A3 publication Critical patent/WO2010059621A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
    • G01V3/26—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B47/00—Survey of boreholes or wells
    • E21B47/02—Determining slope or direction
    • E21B47/024—Determining slope or direction of devices in the borehole

Definitions

  • the present disclosure relates generally to well drilling operations involving magnetic ranging and, more particularly, to calibrating and correcting for noise that may arise during magnetic ranging.
  • two or more wells or boreholes may be drilled with a certain spatial relationship with respect to one another.
  • one borehole may be drilled such that it has a specific location relative to a previously drilled borehole.
  • heavy oil may be too viscous in its natural state to be produced from a conventional well, and, thus, an arrangement of cooperative wells and well features may be utilized to produce such oil.
  • SAGD Steam Assisted Gravity Drainage
  • X-SAGD Cross Well Steam Assisted Gravity Drainage
  • THAI Toe to Heel Air Injection
  • a voltage difference may be applied across an insulated gap in a BHA used to drill the new well.
  • a current may enter the surrounding formation and travel across the casing of the existing cased well, generating a magnetic field that may be measured by a magnetometer in the BHA. Based on the magnetic field measurements, the relative location of the existing cased well to the BHA may be determined. Noise in the measurement of the magnetic field, however, may impede this determination.
  • a system may include a borehole assembly and data processing circuitry.
  • the borehole assembly may include an electric current driving tool configured to cause a current to flow across a drill collar of the borehole assembly and an internal magnetometer disposed within the drill collar and between the insulated gap and an end of the borehole assembly, which may be configured to measure magnetic field signals that penetrate the drill collar.
  • the data processing circuitry may be configured to remove all or part of a noise component of the magnetic field signals that arises due to an eccentricity in the dnll collar.
  • a method for calibrating a measurement sub housing an internal magnetometer may include applying a current across a drill collar that surrounds an internal magnetometer, such that the current travels across the drill collar and along one or more other current paths to return to the drill collar, measuring magnetic fields that result while the drill collar is disposed at a first angle of rotation, rotating the drill collar to a second angle of rotation, measuring the magnetic fields that result while the drill collar is disposed at the second angle of rotation, and determining a relationship between the current across the drill collar and a portion measurable to the internal magnetometer of the magnetic field due to the current across the drill collar.
  • FIG 1 illustrates a well-drilling system for drilling a new well proximate to an existing cased well using magnetic ranging while drilling in accordance with an embodiment
  • FIG. 2 is a transverse cross-sectional schematic view of a measurement sub for calibration in accordance with an embodiment
  • FIG 3 is an axial cross-sectional schematic view of a measurement sub for calibration in accordance with an embodiment
  • FIG 4 is a cross-sectional schematic view of an eccentric drill collar of the measurement sub at the location of an internal three-axis magnetometer, in accordance with an embodiment
  • FIG. 5 is another cross-sectional schematic view of the eccentric drill collar of the measurement sub at the location of the internal three-axis magnetometer, in accordance with an embodiment
  • FIG. 6 illustrates a calibration system for calibrating a measurement sub with an eccentric drill collar in accordance with an embodiment
  • FIG. 7 is a flowchart describing a method for calibrating a measurement sub using the calibration system of FIG. 6, in accordance with an embodiment
  • FIGS. 8A-J are cross-sectional schematic views of an eccentric drill collar of a measurement sub at various angles of rotation, in accordance with an embodiment
  • FIGS. 9A-B are plots of simulated magnetic field measurements taken at the various angles of rotation of FIGS. 8A-J;
  • FIG. 10 is a flowchart describing another method for calibrating a measurement sub using the calibration system of FIG. 6, in accordance with an embodiment
  • FIG. 11 illustrates another calibration system for calibrating a measurement sub with an eccentric drill collar in accordance with an embodiment
  • FIG 12 is a flowchart describing a method for calibrating a measurement sub using the calibration system of FIG 11, in accordance with an embodiment
  • FIG 13 is a flowchart describing a method for determining the distance and direction to an existing cased well using a calibrated measurement sub, in accordance with an embodiment
  • FIG 14 is a flowchart describing a method for calibrating a measurement sub in situ m an earthen formation when the measurement sub includes an external magnetometer, in accordance with an embodiment
  • FIG. 15 is a flowchart describing a method for calibrating a measurement sub in situ m an earthen formation when the measurement sub does not include an external magnetometer, in accordance with an embodiment
  • FIG. 16 is a spectral plot of the simulated magnetic field measurements
  • FIG 17 is a plot of the gain and phase of the simulated magnetic field measurements against frequency
  • FIG. 18 is a flow diagram representing a manner of processing simulated magnetic field measurements, in accordance with an embodiment
  • FIGS. 19A-B are plots of simulated magnetic field measurements when the measurement sub is rotating at 60 RPM, in accordance with an embodiment
  • FIGS. 20 A-B are plots of simulated magnetic field measurements when the measurement sub is rotating at 30 RPM, in accordance with an embodiment
  • FIGS. 21 A-B are plots of the simulated magnetic field measurements of FIGS. 20 A-B when coherent magnetic signals have been removed, in accordance with an embodiment
  • FIG 22 is flowchart describing a method for calibrating a measurement sub in situ m an earthen formation while the measurement sub is rotating, in accordance with an embodiment
  • the terms “up” and “down,” “upper” and “lower,” and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements of the embodiments of the invention. These terms generally relate to a reference point at the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point, whether or not the drilled well continues in a true downward direction.
  • FIG 1 illustrates a well-drilling system 10 for drilling a new well proximate to an existing cased well using magnetic ranging while drilling techniques.
  • a variety of applications may involve drilling a new well proximate to an existing cased well, including drilling a Steam Assisted Gravity Drainage (SAGD) well pair or drilling a new well in a field having one or more preexisting cased wells
  • SAGD Steam Assisted Gravity Drainage
  • Such applications may be described in patent applications to Schlumberger Technology Corporation such as U.S. Patent Application No. 11/550,839, "METHOD AND APPARATUS FOR LOCATING WELL CASINGS FROM AN ADJACENT WELLBORE," filed
  • a new well 12 may be drilled in a formation 14 having an existing cased well 16 cased with a conductive casing
  • a borehole assembly (BHA) 18 may include, among other things, a diill bit 20 and a steerable system 22 to set the direction of the drill bit 20.
  • the steerable system 22 may be a rotary steerable system, such as PowerDnve®, which may receive downlinked commands and drill ahead in a specified trajectory of direction and inclination.
  • the steerable system 22 may be a mud motor with a bent sub; however, such an arrangement may be less efficient, as it may rely on manual orientations of the bent sub by a driller at the surface to control the direction and inclination of the drill bit 20.
  • the BHA 18 may include an electnc current driving tool 24, which may be a component of a measurement while drilling (MWD) tool, such as Schlumberger's E- Pulse or E-Pulse Express tool, or which may be a standalone tool.
  • the electric current driving tool 24 may apply a voltage difference (V 1 -V 2 ) across an insulated gap 26 in the drill collar of the BHA 18, causing an electric current 28 to flow across the drill collar of the BHA 18.
  • V 1 -V 2 a voltage difference across an insulated gap 26 in the drill collar of the BHA 18, causing an electric current 28 to flow across the drill collar of the BHA 18.
  • the electric current driving tool 24 may be any tool capable of generating the current 28 on the drill collai of the BHA 18
  • the voltage difference applied by the electric current driving tool 24 may be an alternating (AC) voltage operating at a preferred frequency range of 0.1 to 20 Hz.
  • the earth's magnetic field is significantly larger than the magnetic fields generated by the AC current, but can be removed from the signal by a high pass filter since it is constant in time.
  • the electric current 28 that is injected across the insulated gap, 7(0) can be measured locally and the amplitude of which may be transmitted to the surface by a MWD telemetry system, which may include the electric current driving tool 24 or which may be a separate MWD telemetry system.
  • part of the electric current 28 may also flow into the formation as an outflow formation current 30.
  • part of the outflow formation current 30 may travel across the existing cased well 16 as a casing current 32, as the casing on the existing cased well 16 may provide a path of low resistance.
  • the casing current 32 may return to the BHA 18 as inflow formation current 34.
  • the casing current 32 may be denoted as / ⁇ z ') , where z ' is the distance along the existing cased well 16 Though the casing current 32 may vary along the casing of the existing cased well 16, it may produce an azimuthal magnetic field Bi centered on the existing cased well 16.
  • a measurement sub 36 in the BHA 18 may measure the magnetic field Bi using an internal, three-axis magnetometer 38. By measunng the three orthogonal components of the magnetic field Bi , and with knowledge of the current 7(0) , it may be possible to determine the distance and direction from the internal magnetometer to the existing cased well 16. Specifically, the casing current 32 on the casing of the
  • the magnetic field Bi is proportional to / '(z ) and inversely proportional to the radial
  • the magnetic field Bo may be
  • the magnetic field Bo would not penetrate inside the drill collar of the measurement sub 36. Under such conditions, the internal three-axis
  • magnetometer 38 of the measurement sub 36 would not detect the magnetic field Bo .
  • one or more external magnetometers 40 may ser ⁇ e several purposes, three of which are explained in U S. Patent Application No. 11/781,704, "METHOD FOR OPTIMIZING MAGNETIC SIGNALS AND DETECTING CASING," filed July 23, 2007, and assigned to Schlumberger Technology Corporation, which is incorporated by reference in its entirety.
  • the one or more external magnetometers 40 can measure the external magnetic field Bo due to the current I(z) on the BHA 18, and hence determine the current I(z) via the above equation.
  • the current I(z) can then be used to provide a reference signal for lock-m detection for the internal three-axis magnetometer 38
  • the one or more external magnetometers 40 can also be used to estimate the resistivity of the formation 14, and can be used to improve the estimate of the casing current 32 on the casing of the existing cased well 16. A fourth use for the one or more external magnetometers 40 will be described further below
  • Measurements of the magnetic fields Bo and/or B ⁇ may be transmitted from the measurement sub 36 to the surface 42 for processing Specifically, the BHA 18 may communicate with a BHA control / MWD interface 44 using E-Pulse-based electric pulse telemetry, mud pulse telemetry, or any other telemetry system communication downlink.
  • the BHA control / MWD interface 44 may represent a stand-alone, special-purpose module associated with an MWD system of the BHA 18, or may represent an input device for a general processor-based system that may be employed for processing the measurements in accordance with the present techniques
  • a database 46 and data processing circuitry 48 may also represent components of such a general processor-based system
  • Such a processor-based system may be a general-purpose computer, such as a personal computer, configured to run a vanety of software, including software implementing all or part of the present technique.
  • the processor-based system may include, among other things, a mainframe computer, a distributed computing system, or an application-specific computer or workstation configured to implement all or part of the present technique based on specialized software and/or hardware provided as part of the system. Further, the processor-based system may include either a single processor or a plurality of processors to facilitate implementation of the presently disclosed functionality.
  • the processor-based system may encompass all or part of the BHA control / MWD interface 44, database 46, and/or data processing circuitry 48 may include a microcontroller or microprocessor, such as a central processing unit (CPU), which may execute various routines and processing functions.
  • the microprocessor may execute various operating system instructions as well as software routines configured to effect certain processes and stored m or provided by a manufacture including a computer readable-medium, such as a memory device (e.g., a random access memory (RAM) of a personal computer) or one or more mass storage devices (e g , an internal or external hard drive, a solid-state storage device, CD- ROM, DVD, or other storage device).
  • the microprocessor may process data provided as inputs for various routines or software programs, such as data provided as part of the present techniques in computer-based implementations.
  • Such data associated with the present techniques may be stored in, or provided by, the memory or mass storage device of the processor-based system that may encompass all or part of the BHA control / MWD interface 44, database 46, and/or data processing circuitry 48.
  • data may be provided to the microprocessor of the processor-based system via one or more input devices.
  • the BHA control / MWD interface 44 may represent one such input device; however, the input devices may also include manual input devices, such as a keyboard, a mouse, or the like.
  • the input devices may include a network device, such as a wired or wireless Ethernet card, a wireless network adapter, or any of various ports or devices configured to facilitate communication with other devices via any suitable communications network, such as a local area network or the Internet.
  • a network device such as a wired or wireless Ethernet card, a wireless network adapter, or any of various ports or devices configured to facilitate communication with other devices via any suitable communications network, such as a local area network or the Internet.
  • the processor-based system may exchange data and communicate with other networked electronic systems, whether proximate to or remote from the system
  • the network may include various components that facilitate communication, including switches, routers, servers or other computers, network adapters, communications cables, and so forth
  • Processing in accordance with techniques of the present disclosure may begin when the measurements of the magnetic fields Bo and/or Bi , obtained by the magnetometers 38 and 40, respectively, are received at the surface 42 by the BHA control / MWD interface 44. After receiving the measurements of the magnetic field
  • the BHA control / MWD interface 44 may store the measurements in the database 46, which may be accessible to the data processing circuitry 48.
  • the data processing circuitry 48 may employ the measurements of the magnetic field Bo and/or Bi to ascertain the relative location of the measurement sub 36 of the BHA 18 to the existing cased well 16.
  • the data processing circuitry 48 may diereafter output a relative location report 50, which may be stored in the database 46 or transmitted to the BHA control / MWD interface 44.
  • the relative location report 50 may indicate the location of the measurement sub 36 of the BHA 18 to the existing cased well 16 in the ( ⁇ ,y, z) coordinate system, as indicated in FIG. 1 Additionally or alternatively, the relative location report 50 may be provided to an operator via one or more output devices, such as an electronic display and/or a printer
  • the BHA control / MWD interface 44 may communicate with the BHA 18 using E-Pulse-based electric pulse telemetry, mud pulse telemetry, or any other telemetry system communication downlink Through the communication downlink, the BHA control / MWD interface 44 may control the BHA 18, as well as receive data obtained by the measurement sub 36. In the presently illustrated embodiment, the BHA control / MWD interface 44 may automatically steer the drill bit 20 based on the relative location report 50. Additionally or alternatively, an operator in control of the BHA control / MWD interface 44 may steer the drill bit 20 based on the printed or electronically displayed relative location report 50.
  • FIGS. 2 and 3 are schematic cross-sectional views of the measurement sub 36 of the BHA 18. Specifically, HG. 2 illustrates an axial cross-sectional view of the measurement sub 36 and FIG 3 illustrates a transverse cross-sectional view of the measurement sub 36.
  • the measurement sub 36 may include a cylindrical drill collar 52 having measurement tools in a pressure housing 54.
  • the pressure housing 54 may contain the three-axis magnetometer 38 as well as various power & control electronics 56, which may include a processor, memory, power supply, and so forth.
  • the measurement sub 36 may additionally include communication circuitry for communication with the surface 42 via another MWD tool in the BHA 18, as well as a three-axis inclinometer Measurements from the three-axis inclinometer may enable determination of the borehole orientation and rotational angle of the measurement sub 36 with respect to down, known quantitatively as the gravity tool face (GTF) Alternatively, the borehole direction, the borehole inclination, and the gra ⁇ ity tool face may be determined using a different sub of the BHA 18. Measurements from the three-axis magnetometer 38 in the measurement sub 36 may be used to determine the borehole direction with respect to magnetic North and/or the rotational angle of the measurement sub 36 with respect to magnetic North, known as the magnetic tool face (MTF)
  • MTF magnetic tool face
  • FIG. 4 illustrates a schematic cross- sectional view of the drill collar 52 of the measurement sub 36 at the location of the internal three-axis magnetometer 38 when the drill collar 52 is formed by a circular, eccentric bore 59.
  • the drill collar 52 may include a thin wall 60 and a thick wall 62.
  • Other "drill collar asymmetnes" in the drill collar 52 may arise, for example, based on non-uniform conductivity over a cross-section of the drill collar, a non-round bore 59, or a non-round collar outer diameter [0048]
  • a small magnetic field BDC due to the current I(z) may be detectable within the dnll collar 52. Because the
  • BDC has the same frequency and phase as the magnetic field Bl . Hence, it cannot be removed in the same manner as incoherent noise by simply averaging over time.
  • the drill collar 52 of the measurement sub 36 may have a scribe line 64 or other indicator that references its rotational orientation with respect to gravity tool face (GTF) or magnetic tool face (MTF).
  • Gravity tool face (GTF) is the angle ⁇ between the scribe line 64 and up.
  • K K I(z) (1), where K is a calibration constant pnmanly related to the geometry of the measurement sub 36. Both K and ⁇ are independent of temperature, pressure, and other downhole environmental effects. Once they are determined by calibration measurements, they can be used to correct the measurements of the internal three-axis magnetometer 38. [0051] Consider, for example, the exaggerated asymmetry of the drill collar 52 of the measurement sub 36 shown in FIG. 5, which illustrates a cross-sectional view of the drill collar 52 of the measurement sub 36 in an alternative coordinate system (x ', / ') .
  • the x ' axis is chosen to intersect the thinnest and thickest portions of the drill collar wall, forming an angle S with respect to the scribe line 64.
  • the inner diameter of the bore 59 of the drill collar 52 is 2 a
  • the outer diameter of the drill collar 52 is 2 b
  • the bore 59 is eccentric by an amount c.
  • the bore 59 and drill collar 52 outer diameter are otherwise perfect circles.
  • the unit vectors for the x ' and y ' axes are x ' and ⁇ ' .
  • the magnetic field inside the bore may be given by the following equation:
  • the magnetic field inside the bore 59 is constant in amplitude and direction and aligned with the direction normal to that of the eccentricity.
  • the calibration constant relating the internal field to the collar current may be given by the following equation:
  • the magnetic field Bi arising when the existing cased well 16 is 5 m distant may be measured as approximately 10 to 20 nTesla.
  • the magnetic field BDC mside the drill collar 52 of the measurement sub 36 may be similar in magnitude to the magnetic field Bi arising from the current I'(z ') on the existing cased well 16 as measured by realistic measurement subs 36.
  • the present disclosure descnbes various solutions for reducing or eliminating the internal magnetic field BDC from the signals measured by the magnetometer 38 of the measurement sub 36.
  • synchronous it is meant that BDC and Bi both have the same time dependence sin ⁇ t
  • Such solutions may involve various devices and techniques for calibrating the measurement sub 36 (e.g., obtaining K and ⁇ ) and/or for performing data acquisition procedures to reduce or eliminate effects of the internal magnetic field BDC .
  • FIG 6 illustrates an embodiment of a calibration system 66 for calibrating the measurement sub 36 and for obtaining K and ⁇ .
  • the calibration system 66 may be employed after manufacturing the measurement sub 36 or in a pre-job calibration performed in a field shop. There should be no magnetic materials or highly conductive materials in the area surrounding the calibration system 66.
  • the calibration system 66 includes a series of drill collars 68 having a similar configuration to the BHA 18, and may include the electnc current driving tool 24, the insulated gap 26, and the measurement sub 36 containing the internal three-axis magnetometer 38. Additionally, the measurement sub 36 may include the one or more external magnetometers 40.
  • the current 28 across the insulated gap 26 can be powered by downhole electronics or by a laboratory oscillator.
  • Two wire loops 70 and 72 of width L and height 2H may he m the plane of the measurement sub 36.
  • the two wire loops 70 and 72 may be identical in size and shape, and may be placed symmetrically with respect to the drill collar 68.
  • the two symmetric wire loops 70 and 72 may contain precision, matched resistors R1 and R2, respectively, and variable resistors VR1 and VR2, respectively.
  • the respective voltages V1 and V2 across the precision resistors R1 and R2 may be used to measure the currents /l and 12 that flow in the two loops 70 and 72, and the variable resistors VR 1 and VR2 may be used to control the two currents /l and /2.
  • variable resistors VR1 and VR2 can be used to null the sum of magnetic fields Bn and Bn due to the two wire loops 70 and 72 at the location of the measurement sub 36.
  • the sum of the two currents, /l + /2 flows on the drill collars 68, and results in a strong local azimuthal magnetic field Bo centered on the drill collars.
  • the internal three-axis magnetometer 38 of the measurement sub 36 is located at the center, i.e. at (0, 0, 0) , where the x and y directions are in the earth frame and perpendicular to the axis of the drill collar 68.
  • the x direction may be understood as vertically up
  • the y and z directions may be understood as horizontal, with the z direction aligned with the drill collars 68 axis.
  • the three-axis magnetometer 38 will have one sensor along the z direction, but the two transverse magnetometer sensors will not be aligned with the x and y axes in general. However, it is possible to compute the magnetic field in the geostationary frame from the two transverse magnetometer sensors.
  • FIG. 7 To calibrate the measurement sub 36 when the measurement sub 36 is not completely symmetric, a flowchart 74 is illustrated in FIG. 7.
  • the flowchart 74 may begin with a first step 76, in which current may be applied across the drill collars 68 using either downhole electronics or a laboratory oscillator. If the two rectangular wire loops 70 and 72 are symmetric, then the magnetic fields measurable by the three - axis magnetometer 38 located at (0,0,0) may be given by the following equation: M 0 (/2 - /1) yi+ ⁇ L/Hf +Jl + [LjHf (4)
  • ⁇ B ⁇ $ represents the magnetic field measurable by the interior three-axis magnetometer 38 of the measurement sub 36, where ⁇ is the angle between the scribe mark 64 and up (i e., the +x direction) of the measurement sub 36.
  • BL may be assumed to be relatively small after balancing the magnetic fields Bn and Bn of the two loops 70 and 72 in step 78.
  • the magnetic field B( ⁇ ) may be measured by the internal three-axis magnetometer 38 of the measurement sub 36.
  • ⁇ B( ⁇ ) is the magnetic field expressed in the earth frame (e.g., in x- y coordinates). If the direction of B( ⁇ ) rotates with the measurement sub 36. then it is due to the asymmetry of the drill collar 52 of the measurement sub 36. However, if the direction of B( ⁇ ) does not change with rotation, then it is most likely due to the magnetic field BL arising due to unbalanced wire loops 70 and 72.
  • B ⁇ may include a combination of both BDC and BL , SO that the magnetic field inside the drill collar can be written as follows:
  • B y ( ⁇ ) B DC cos( ⁇ - ⁇ ) + B Lj (5c).
  • step 82 after acquiring measurements of the magnetic fields B x ( ⁇ ) and
  • Equation (5b) and (5c) the data may be inverted, as illustrated by the following example.
  • measured quantities may be designated as ), By[P 1 ) ⁇ .
  • the angles do not have to have a uniform spacing, but there should be enough samples to fit the data to sine and cosine functions.
  • the following two quantities may be minimized with respect to B 1x , S , B ⁇ , and B ⁇ :
  • the data processing circuitry may determine the calibration constant K from
  • K B DC l(l ⁇ + 1 2 ) , where Z 1 and I 2 are measured using the precision resistors R1
  • FIGS. 9A-B illustrate how measured magnetic field B( ⁇ ) data may be employed in conjunction with Equations (5a)-(5c).
  • B 1x 5 nTesla
  • £ 40°
  • B L ⁇ 13 nTesla
  • B L 7.5
  • an ordinate 88 represents B x ( ⁇ ) magnetic field strength in units of nTesla and an abscissa 90 represents rotation angle ⁇ relative to the gravity tool face (GTF) in units of degrees.
  • an ordinate 102 represents B y ⁇ ) magnetic field strength in units of nTesla and an abscissa 104 represents rotation angle ⁇ relative to the gravity tool face (GTF) in units of degrees.
  • Individual BJ ⁇ ) data points 106 may fit a curve 108. Because the curve 108 represents the value
  • the calibration system 66 of FIG. 6 may employ the one or more external magnetometers 40 on the measurement sub 36 for determining the current 28 on the drill collar 52 of the measurement sub 36.
  • the current may be determined according to the following equation:
  • the calibration system 66 can be used to calibrate the one or more external magnetometers 40. That is, the calibration system 66 may relate the current 28 on the drill collar 52 of the measurement sub 36, which is equal to I 1 + I 2 , to the magnetic
  • the calibration system 66 of FIG. 6 may have a variety of configurations.
  • the wire loops 70 and 72 need not be rectangular, and could take any of a variety of shapes. Even a single wire loop may suffice in place of wire loops 70 and 72 if the size ( L and H) of the single wire loop is very large.
  • size of the single wire loop may be determined such that the magnetic field B 1 is not
  • the magnetic field B( ⁇ f>) may be measured.
  • step 120 the contribution to the magnetic field B ⁇ ) from the two loops 70 and 72 can be obtained from the averages of the measured components of the magnetic field B x ( ⁇ ) and B y ( ⁇ ) , according to the following equations:
  • the magnetic fields B 1x and B 1 can be obtained from the averages noted
  • the calibration angle S may be obtained by minimizing either of the following equations:
  • the calibration constant K may be determined from
  • FIG 11 illustrates an alternative calibration system 126 for calibrating the measurement sub 36.
  • the calibration system 126 of FIG. 11 may include the drill collars 68 having the electric current driving tool 24 for generating the current 28 across the insulated gap 26, as well as the measurement sub 36, which may include both the internal three-axis magnetometer 38 and the external magnetometer 40.
  • the drill collars 68 may be placed in a water- filled tank 128 with a simulated cased well 130 formed from, for example, casing or a metal pipe. It should be noted, however, that the presence of the simulated cased well 130 is not essential.
  • the current 28 may be generated across the insulated gap 26 with a known value /(0) .
  • a portion of the current 28 may flow out into water in the water- filled tank 128 as an outflow current 132.
  • Some of the outflow current 132 may flow across the simulated cased well 130 as casing current 134.
  • the casing current 134 and the remainder of the outflow current 132 may return to the drill collars 68 as an inflow current 136.
  • the water in the water-filled tank 128 and the simulated cased well 130 provide conductive paths for the current 28 to return to the drill collars 68 above the insulated gap 26.
  • a flowchart 138 illustrated in FIG. 12, describes a manner of calibrating the measurement sub 36 using the calibration system 126 illustrated in FIG. 11.
  • the current 28 may be applied across the insulated gap 26 using either downhole or laboratory electronics.
  • the three-axis magnetometer 38 may measure the magnetic field that penetrates the drill collars 68 at several angles
  • ⁇ j , i 1,2, 3,..., /2 ⁇ .
  • x and ⁇ coordinates are transverse to the
  • the magnetic field B L will not change as the angle ⁇ changes as the drill collars 68 rotate.
  • the magnetic field due to eccentricity B DC and the calibration angle ⁇ may be determined using, for example, the techniques described in the flowcharts 74 and 114.
  • the current 28 at the measurement sub 36, I(z) may be determined because the pnmary distinction between the calibration system 126 of FIG. 11 and the calibration system 66 of FIG 6 is that the current I(z) will vary along the length of the d ⁇ ll collars 68 in the calibration system 126, the current 28 at the insulated gap, /(0) , may be provided by the downhole electronics or laboratory electronics as a known quantity.
  • the current 28 at the measurement sub 36, I(z) may also be determined using Equation (7) above If the external magnetometer 40 is not present on the measurement sub 36, the current 28 at the measurement sub 36, I(z) , may be calculated using the known geometry of the drill collars 68, the water-filled tank 128, and the location and size of the simulated cased well 130.
  • an approximate answer may be obtained by assuming that the current 28 on the drill collars 68 decreases linearly above and below the insulated gap 26 For example, if the length of the drill collars 68 below the gap is L , then the current 28 measured at a distance z below the gap may be estimated using the following relationship: L-z
  • K B DC I I(z) .
  • a flowchart 150 describes a manner of employing the calibration angle ⁇ and the calibration constant K to reduce noise detected while performing techniques for magnetic ranging while drilling.
  • a current 32 may be caused to flow on the existing cased well 16.
  • the electric current driving tool 24 in the BHA 18 may produce the current 28 across the insulated gap 26, also denoted as the current I(z) m FIG. 1.
  • I(z) the current 28 across the insulated gap 26
  • I'(z ') • The current / ⁇ z ') produces
  • the magnetic field B 1 may be measured by the internal three-axis magnetometer 38 of the measurement sub 36 at various angles of BHA 18 rotation. While the three axes of magnetometer 38 will not coincide with the axes in the geostationary frame (x, y, z) , it is a simple matter to transform the three magnetometer axes readings into the geostationary frame. Thus, the magnetic field B j is not a function of the orientation of the measurement sub 36 (e.g., the gravity tool face (GTF) or magnetic tool face (MTF)). In the course of measuring the magnetic field ZJ 1 , the internal three-axis magnetometer 38 may additionally measure
  • the internal three-axis magnetometer 38 in the measurement sub 36 may detect a total magnetic field described by the following equation
  • Equation (14) differs from Equation (5a) in that it includes a magnetic field component in the axial, or z 5 direction. Normally, asymmetnes in the dnll collars of the BHA 18 produce very small magnetic fields in the axial direction and can be neglected.
  • the direction and distance from the BHA 18 to the existing cased well 16 are determined primarily based on the magnetic field components B, and B, , and B, is of lesser importance Hence, the presence of a small, uncorrected S 1 term is not problematic.
  • the transverse magnetic field components may be given by the following equations:
  • B y ( ⁇ ) B DC cos( ⁇ - ⁇ ) + B ly (15b).
  • the angle ⁇ may be
  • the measurements may be transmitted to the surface 42 for processing via the BHA control / MWD interface 44.
  • step 156 the data processing circuitry 48 may remove the magnetic field B DC due the collar asymmetry from the measurements obtained by the three-axis magnetometer 38 using the following equations:
  • step 158 once B, and B-, have been obtained by removing the portion of the measured magnetic field signals due to the magnetic field BDC , the distance and direction between the BHA 18 and the existing cased well 16 may be determined using methods described in the above-referenced patent applications
  • the measurement sub 36 may be calibrated using the calibration systems 66 or 126, as described above, the measurement sub 36 may also be calibrated in situ in a borehole when the measurement sub 36 is included in a BHA 18 such as the BHA 18 illustrated in FIG. 1.
  • a flowchart 160, illustrated in FIG. 14, describes a manner of calibrating the measurement sub 36 in situ Such a situation is similar to the calibration procedures described above with reference to the flowchart 138 of FIG. 12 involving the calibration system 126 of FIG. 11, except that the earth foimation 14 serves the same function as the water-filled tank 128 As in the techniques disclosed above, the existing cased well 16 need not be present to calibrate the measurement sub 36
  • a first step 162 the drilling may be halted at one depth.
  • the current 28 may be applied across the BHA 18 in step 164 using the electric current driving tool 24 and, in step 166, the three-axis magnetometer 38 may take several measurements of the resulting magnetic field components B x ( ⁇ ) and B y ( ⁇ ) , which represent
  • the measurement sub 36 includes components of those magnetic fields capable of penetrating the measurement sub 36 and thus measureable to the three-axis magnetometer 38.
  • the measurement sub 36 includes
  • the BHA 18 should be stationary [0085]
  • the external magnetometer 40 may be employed to determine the current 28 at the measurement sub 36 for each angle.
  • the magnetic field In step 170, the magnetic field
  • the calibration constant K may be determined, for example, using the techniques described above with reference to the flowcharts 74 and 114
  • In situ calibration may provide certain advantages, as additional coherent noise may be present in situ that may not otherwise be present in other settings.
  • elements of the drill bit 20 and the steerable system 22, which may include a mud motor and bent sub consisting of magnetic materials, may contribute a small magnetic signal under some circumstances. Because an in situ calibration calibrates the entire BHA 18, any such additional effects can be removed using the technique described in the flowchart 160 of FIG. 14.
  • Equations (16a) and (16b) may be applied to data obtained by the magnetometer 38 at subsequent depths. Only one angle for such measurements need be obtained at subsequent depths.
  • the method of the flowchart 174 of FIG. 15 may involve taking measurements of the magnetic field at a multiple angles. However, the flowchart 174 may additionally involve taking multiple measurements at varying depths to properly determine the current 28 on the BHA 18.
  • a first step 176 drilling may be halted at a first depth and, in step 178, the current 28 may be applied across the BHA 18 using the electric current driving tool 24
  • the three-axis magnetometer 38 may take several measurements of the resulting magnetic field components B x ( ⁇ ) and B y ( ⁇ ) , which represent
  • the measurement sub 36 includes components of those magnetic fields capable of penetrating the measurement sub 36 and thus measureable to the three-axis magnetometer 38.
  • the measurement sub 36 includes
  • the BHA 18 should be stationary
  • step 182 drilling may continue until, m step 184, drilling is halted at a second depth.
  • step 186 the current 28 may be applied across the BHA 18 and subsequently, in step 188, the three-axis magnetometer 38 may take several additional measurements of the resulting magnetic field components B x ( ⁇ ) and B y ( ⁇ )
  • the calibration constant K and calibration angle ⁇ may be determined in the manners described above.
  • a drawback to the methods described above in flowcharts 160 and 174 is the requirement to stop rotating the BHA, which may involve delaying the drilling process to acquire data.
  • An additional method where by the measurement can be performed while continuously rotating the BHA would be advantageous.
  • the magnetic field B ( ⁇ ) has two components, one
  • Equation (15) may be revised
  • the three-axis magnetometer 38 is related to a (x,y,z) coordinate system
  • Equations (20) and (21) express the transverse magnetic field components as measured by the three- axis magnetometer which is rotating at the angular frequency
  • the earth's magnetic field (A ) is modulated at frequency ⁇ Q
  • BDC field due to asymmetry
  • FIG 16 illustrates a plot 212 containing a spectrum of the measured magnetic
  • ordinate 214 represents the magnitude of the measured magnetic field B- .
  • abscissa 216 represents angular frequency.
  • the coherent noise BDC is observed at
  • the earth's magnetic field (A) is approximately 50,000 nanoTesla, whereas magnetic field Bi may be much smaller at approximately 10 to 100 nanoTesla.
  • the earth's magnetic field can be highly attenuated by a bandpass filter on the magnetometer output since ⁇ y Q is
  • FIG 17 is a plot 218 illustrating a typical frequency characteristic of a filter on the output of a magnetometer.
  • a first ordmate 220 represents the gain of the filter in units of decibels; a second ordinate 222 represents the phase in units of degrees, and an abscissa 224 represents frequency in units of Hertz on a logarithmic scale
  • a gam curve 226 low frequencies, such as the earth's magnetic field A , may be substantially attenuated.
  • a phase curve 228 illustrates the changes in phase of the received signals as frequency increases It should be noted that, while the earth's magnetic field may be fairly small, as shown in FIG. 16, measurements of A x and A 1 , can be used to determine the magnetic tool face (MTF) when combined with data from a three-axis accelerometer in the BHA 18.
  • MTF magnetic tool face
  • FIG. 18 illustrates a flow diagram for processing magnetic field signals obtained by the three-axis magnetometer 38 while the BHA 18 is rotating
  • data may be multiplied 230 with a signal from a local oscillator 232, before entering a low pass filter 234.
  • a sinusoidal reference signal may be multiplied 236 with the signal from the local oscillator 232, before entering a low pass filter 238.
  • the filtered data signal may be divided 240 by the filtered reference signal to produce a spectrum signal that may enable identification of the portion of the measured signals derived from the magnetic field Si from the current 32 on the existing cased well 16.
  • a peak-detection algorithm may subsequently identify the desired amplitudes and frequencies of the magnetic field Bi .
  • Such algorithms may be implemented m hardware at the surface 42, or the magnetic field signals may be digitized to be processed by the data processing circuitry 48 in a similar fashion.
  • FIGS. 19-21 represent simulated plots of data that may be obtained and/or processed to eliminate coherent noise in magnetic field signals detected by the three- axis magnetometer 38 during magnetic ranging while drilling.
  • the simulated data of FIGS. 19-21 are generated for 5 seconds at a sampling rate of 8031.37 Hz, and the magnetic field Bi arising from the current 32 on the existing cased well 16 occurs at 10 Hz.
  • the rotation of the BHA 18 is simulated to be 60 RPM
  • FIGS 20-21 the rotation of the BHA 18 is simulated to be 30 RPM.
  • FIG. 19 A a plot 242 illustrates a simulated magnetic field B-
  • An ordmate 252 represents the amplitude in units of nanoTesla, and an abscissa 254 represents frequency in units of Hertz.
  • Features apparent in the spectral plot 250 include a peak 256 representing the earth's magnetic field, two peaks 258 representing the primary signal attributable to the magnetic field Bi , and a peak 260 attributable to the coherent magnetic field
  • FIG. 2OA is a plot 262 illustrating a simulated magnetic field B- for a
  • plot 270 9 to 11 Hz is illustrated in plot 270, as shown in FIG. 2OB.
  • An ordinate 272 represents the amplitude in units of nanoTesla, and an abscissa 274 represents frequency in units of Hertz.
  • Features apparent in the spectrum 270 include a peak 276
  • the coherent noise (i.e BDC ) in spectrum 270 is approximately ten times greater than the desired signal (i.e. Bi ), and mask the expected peaks that should appear at 9.5 and 10 5 Hz.
  • FIG 21A is a plot 280 illustrating the simulated magnetic field B- 268 that has been processed to eliminate the coherent element of peak 276.
  • ordinate 282 represents the amplitude in units of nanoTesla
  • an abscissa 284 represents time in units of seconds
  • a curve 286 represents simulated magnetic field B y that has been processed to remove the coherent component located at approximately 10 Hz Suitable filtering algorithms may be found in the book, "Fundamentals of Wavelets", by J C Goswami and A. K. Chan, published by John Wiley & Sons, Inc. Refer to section 7.8 "Two Channel Perfect Reconstruction Filter Bank”.
  • the spectral view of the signal is illustrated m a plot 288, as shown in FIG. 21B.
  • An ordinate 290 represents the amplitude in units of nanoTesla
  • an abscissa 292 represents frequency in units of Hertz. With the coherent noise removed, features apparent in the spectral plot 288 include two peaks 294 representing the primary signal attributable to the magnetic field Bi .
  • FIG 22 is a flow chart 296 describing a manner of performing continuous calibration of the measurement sub 36 while the BHA 18 is rotating.
  • the electric current driving tool 24 may supply a current 28 across the BHA 18 and, in step 300, the time- varying magnetic field components B x ⁇ t, ⁇ G ) and
  • B (t, CO 0 ) may be measured using the three-axis magnetometer 38.
  • the measurements may be transmitted to the surface 42, where dedicated hardware and/or the data processing circuitry 48, in step 302, may demodulate and filter the measurements to extract the components of the magnetic field due to the current 32 on the existing cased well 16, Sl , in the manner described above.
  • the data processing circuitry 48 may employ the determination of the magnetic field Bi to ascertain the distance and direction between the BHA 18 and the existing cased well 16.
  • An alternative method may be used to remove the magnetic field BDC from the data acquired while the BHA is rotating. Referring to FIG. 23, the drill collar bore
  • the scribe mark 64 indicates
  • the angle between the x ' axis and the x is ⁇ .
  • earth frame is denoted by the x and y axes, and the angle between the x and x
  • the measured magnetic field components, B-(t) and _3-(r) can be
  • the coherent noise can be
  • angle ⁇ can be determined by the previously described calibration methods and the

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Abstract

L’invention divulgue des systèmes et des procédés pour l’acquisition améliorée de données de champ magnétique pour procéder à une mesure magnétique pendant un forage. Dans un mode de réalisation, un système de ce type peut comprendre un ensemble de trou de forage et un circuit de traitement de données. L’ensemble de trou de forage peut comprendre un outil d’entraînement de courant électrique qui est configuré pour entraîner un courant à s’écouler à travers une masse-tige de l’ensemble de trou de forage, et un magnétomètre interne disposé à l’intérieur de la masse-tige et entre l’espace isolé et une extrémité de l’ensemble de trou de forage, qui peut être configuré pour mesurer des signaux de champ magnétique qui pénètrent dans la masse-tige. Le circuit de traitement de données peut être configuré pour supprimer la totalité ou une partie d’une composante de bruit des signaux de champ magnétique qui est créée à cause de l’excentricité dans la masse-tige.
PCT/US2009/064780 2008-11-20 2009-11-17 Procédé et dispositif pour calibrer et corriger un bruit cohérent lors d'une détection dans un tubage WO2010059621A2 (fr)

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