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WO1996002733A1 - Procede permettant de corriger les composantes d'erreur presentes dans les donnees topographiques provenant d'un puits de forage - Google Patents

Procede permettant de corriger les composantes d'erreur presentes dans les donnees topographiques provenant d'un puits de forage Download PDF

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Publication number
WO1996002733A1
WO1996002733A1 PCT/GB1994/001523 GB9401523W WO9602733A1 WO 1996002733 A1 WO1996002733 A1 WO 1996002733A1 GB 9401523 W GB9401523 W GB 9401523W WO 9602733 A1 WO9602733 A1 WO 9602733A1
Authority
WO
WIPO (PCT)
Prior art keywords
magnetic field
component
earth
axial
borehole
Prior art date
Application number
PCT/GB1994/001523
Other languages
English (en)
Inventor
Andrew Goodwin Brooks
Original Assignee
Baker Hughes Incorporated
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 Baker Hughes Incorporated filed Critical Baker Hughes Incorporated
Priority to AU71902/94A priority Critical patent/AU7190294A/en
Priority to PCT/GB1994/001523 priority patent/WO1996002733A1/fr
Publication of WO1996002733A1 publication Critical patent/WO1996002733A1/fr

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Classifications

    • 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
    • E21B47/022—Determining slope or direction of the borehole, e.g. using geomagnetism

Definitions

  • the present invention relates to a method of determining the azimuth angle of a surveying instrument in a borehole in which the earth's magnetic field may be contaminated by an additional magnetic field due to drillstring magnetization. More particularly, the present invention relates to a method of computing azimuth without requiring accurate prior knowledge of the magnitude or direction of the earth's magnetic field and without requiring computation of the axial component of the earth's field. The present invention further relates to computing azimuth in steeply inclined boreholes which are oriented close to the east-west direction, wherein most prior methods become highly inaccurate.
  • Surveys are used to determine the position of a wellbore within the earth.
  • the orientation of the wellbore is determined at a particular depth by the deviation of the wellbore from a predetermined axis.
  • the deviations may be measured with respect to two reference vectors:
  • G is positive in the vertical downward direction
  • B is positive in the north direction and is inclined by a dip angle D below the horizon, as is shown in Figure 1.
  • the position of the wellbore relative to the earth's gravitational field vector G is identified as an inclination "I" angle, which is the angle between the longitudinal axis of the drillstring and the earth's gravitational field vector G.
  • the position of the wellbore relative to the earth's magnetic field vector B and the earth's gravitational field G is identified as a magnetic azimuth "A", which is the angle between the horizontal component of the longitudinal axis of the drillstring and the horizontal component of the earth's magnetic field vector B.
  • dip angle D is the complement of the angle between the earth's magnetic field vector B and the earth's gravitational field vector G (that is, 90 degrees less the angle between vectors B and G).
  • the dip angle D is available in look-up tables, computer programs, and charts for all latitudes and longitudes on the earth's surface.
  • accelerometers are utilized to measure the direction of the earth's gravitational field vector G
  • magnetometers are utilized to measure the earth's magnetic field vector B.
  • Each vector includes x-axis, y-axis, and z-axis components.
  • Figure 2 provides a view of the Cartesian coordinate system which is established relative to the bottomhole assembly of a drillstring.
  • the z-axis of the coordinate system is in alignment with longitudinal axis of the bottom hole assembly.
  • the x-axis and y-axis are perpendicular to the z-axis, and are fixed in position with respect to the bottom hole assembly. Therefore, rotation of the bottomhole assembly about the z-axis also rotates the x-axis and the y-axis by an amount measured in terms of tool face angle "T".
  • the inclination angle I provides a measure of the position of the bottomhole assembly of a drillstring relative to the gravity field vector G
  • the tool face angle T provides a measure of the angle in the xy-plane between the y-axis and the highside HS of the tool.
  • the three measured components of each field are subscripted x, y, and z.
  • the tool coordinate axes are shown in Figure 2.
  • the tool "orientation” is usually expressed in terms of the following three drilling angles: inclination I which is the angle between the z-direction and vertical; azimuth A which is the angle between the horizontal projections of the z-axis and the macfnetic north vector; and gravity tool face T which is the angle in the xy-plane between the high side HS of the tool and the y-axis.
  • Figure 3 shows these drilling angles.
  • a further useful drilling angle is the magnetic tool face angle M, defined here as the angle in the xy-plane between magnetic north N and the y-axis.
  • magnetometer readings are taken along the three axes to determine the magnetic field vector B components: these measurements are identified as B x , B y , and B z .
  • Accelerometer readings are taken along the three axes to determine the gravitational field vector G components: these measurements are identified as G x , G y , and G z . Since these vectors have both a direction and a magnitude, these tri-axial measurements will have to be scaled, or calibrated, to accurately reflect the magnitude of the vector they represent.
  • Survey tools utilize these x-y-z arrays of accelerometers and magnetometers to determine the directions and magnitudes of the B and G vectors in the x-y-z frame of reference. This information is used to determine the tool's "attitude", expressed by the inclination angle I, and the azimuth angle A and the tool face angle T.
  • the azimuth A, inclination I, and tool face angle T of the wellbore at that depth can be determined.
  • the value of the magnetic dip angle D can be calculated.
  • the three accelerometers are normally used to find I, T and G, the magnetometers are used to find B, and a combination of measurements from all sensors are required to calculate A and D.
  • An expected magnetic field strength B and dip angle D can be looked up in reference tables, computer programs, or charts based on the wellsite's longitude and latitude.
  • a directional map of the wellbore can be plotted. This directional map shows how far, and in what direction, the wellbore is deviated from the vertical and magnetic north, and ultimately where the well is bottomed.
  • the wellbore surveying tool is typically housed in a non-magnetic subassembly. Additionally, surrounding subassemblies may also be constructed of a non-magnetic material.
  • the drillstring can nonetheless become magnetized during drilling operations, to such an extent that the accuracy of the magnetic field measurements is severely impaired. Any magnetization of the bottomhole assembly in the vicinity of the surveying equipment will introduce a biasing error "e", which is an undesired error component contained in magnetometer readings due to the magnetization of the drillstring.
  • the biasing error includes the following two types of error components:
  • Patents 4,345,454, 4,709,486, and 5,103,177 all of these methods require accurate prior knowledge or external measurement of at least one component of the earth's magnetic field. Accuracy of the computed azimuth angle is then highly dependent on the accuracy with which these components are provided. In certain borehole attitudes, particularly those close to the horizontal east-west vector, accuracy of azimuth angles computed by these methods may be very poor.
  • U.S. Patent No. 4,345,454 to Brown describes a method and apparatus for measuring inclination and azimuth in a plurality of toolface attitudes. While this technique can effectively reduce the influence of small transverse magnetic anomalies associated with the drillstring, it cannot eliminate the effects of the axial anomalies which are generally much more significant and which are the subject of this invention.
  • U.S. Patent No. 4,709,486 to Walters describes a method for determining azimuth by taking measurements in a plurality of attitudes and using a pair of such measurements to solve for the uncontaminated axial magnetic component B z in each attitude.
  • a method for determining the azimuth angle of a surveying instrument in a borehole which includes the steps of: (1) measuring components of the earth's gravitational and magnetic fields at a plurality of non-parallel orientations within the borehole, (2) calculating the vertical component of the earth's magnetic field directly from such measurements, and (3) computing an azimuth angle for each orientation from the gravitational and magnetic field measurements and the calculated vertical component of the earth's field.
  • a further method is provided which is particularly advantageous in borehole attitudes close to the horizontal east-west vector, comprising computing the azimuth angle in a first orientation which is not close to horizontal east-west, computing the axial magnetic error component due to drillstring magnetization, applying a similar axial error component to the measured field in a second orientation, and computing azimuth in the second orientation.
  • Figure 1 is a simplified graphical depiction of the earth's field vectors
  • Figure 2 provides a view of the Cartesian coordinate system which is established with reference to the longitudinal axis of a drillstring disposed within a wellbore;
  • Figure 3 provides a graphical view of the azimuth, inclination, and tool face angles relative to the coordinate system
  • Figure 4 is a depiction of a survey instrument located within a drillstring and subject to the influence of drillstring magnetization
  • Figure 5 is a graph illustrating the relationship between those possible values of the squared horizontal component and the vertical component of the earth's magnetic field which are consistent with a set of gravitational and transverse magnetic measurements;
  • Figure 6 is a graph illustrating the relationship between those possible values of the horizontal and vertical components of the earth's magnetic field which are consistent with a set of gravitational and transverse magnetic measurements
  • Figure 7 is a graph illustrating the two possible values of the horizontal and vertical components of the earth's magnetic field which are consistent with two sets of gravitational and transverse magnetic measurements
  • Figure 8 is a graph illustrating the possible relationships between the horizontal and vertical components of the earth's magnetic field which are consistent with a plurality of sets of gravitational and transverse magnetic measurements.
  • Borehole directional surveying is normally accomplished by means of instruments which measure three orthogonal components of the earth's gravitational field G and the earth's magnetic field B at a plurality of survey stations spaced along the borehole. These six measurements are made with respect to an instrument- fixed set of axes in which the z-axis is parallel to the drillstring and the x-axis and y-axis make up a right- handed triad.
  • the six measured quantities G x , G y , G z , B x , B y and B z are related to the local gravitational field G, the horizontal component B h and the vertical component B v of the local geomagnetic field, and to the inclination I, azimuth A, and toolface attitude T of the instrument by the following equations:
  • A tan -1 [G* (B x *G y - B y *G x )/ ⁇ G z *(B x *G x + B y *G y ) + B z *(G x 2 + G y 2 ) ⁇ ]
  • the surveying instrument is typically housed in a non-magnetic subassembly within the ferromagnetic drillstring. Magnetization of the drillstring at each end of the subassembly may introduce an axial magnetic error component e z in addition to the axial component B z of the earth's field, as shown in Figure 4. While equations (7) through (9) may still be used to derive G, I and T from the accelerometer measurements, the computed values of B v , B h , and A may be corrupted by the error component e z if they are determined using equations (10) through (12).
  • Equations (1), (2), (4) and (5), defining the transverse components of the gravitational and magnetic fields, may be combined as follows :
  • equations (13) and (14) can be used to determine the azimuth A :
  • A tan -1 [(B x *G y - B y *G x )/ ⁇ (B x *G x + B y *G y + B v *G*sin 2 I)/cosI ⁇ ]
  • equations (13) and (14) can instead be combined in the following manner to eliminate A :
  • Equation (16) represents B h 2 as a quadratic function of B v , which is graphed in Figure 5.
  • the parabolic curve results from the single degree of freedom introduced by discarding equation (6), and it represents all combinations of B v and B h 2 which are consistent with the measured values of B x , B y , G x , G y and G z , and with equations (1) through (5). It is apparent from the form of this curve that the relationship between possible values of B h and B v can be represented by another curve which is of somewhat similar shape, as depicted in Figure 6; Figure 5 plots the square of the horizontal component of the magnetic field (B h 2 ) while Figure 6 plots B h versus B v .
  • this invention provides a means for determining B v , B h and A without the need for accurate external estimates of B v , B h , B or D.
  • intersections can be found algebraically by simultaneously solving the following equations
  • B x1 B h *cosI 1 *cosA 1 *sinT 1 + B h *sinA 1 *cosT 1 - B v *sinI 1 *sinT 1
  • B y1 B h *cosI 1 *cosA 1 *sinT 1 - B h *sinA 1 *sinT 1 - B v *sinI 1 *cosT 1
  • B x2 B h *cosI 2 *cosA 2 *sinT 2 + B h *sinA 2 *cosT 2 - B v *sinI 2 *sinT 2
  • Equation (16) may then be used to determine B h uniquely, since B h is always positive, while the two azimuth angles can be found from equation (15).
  • an alternate method for discriminating between the two possible roots consists of calculating the axial magnetization error field "e z " in each of the two orientations and selecting whichever root indicates the smallest change in magnetization error field.
  • One means of computing these axial magnetization error fields requires first computing the apparent values of the vertical component of the earth's magnetic field :
  • root B va may be assumed to be the correct root, otherwise root B vb is used.
  • this invention uses the components of the earth's field and the measured value of B z in a first attitude relatively remote from horizontal east-west, said components and attitude being found by the methods described above or by other methods, then determines the axial magnetization error field by the equation:
  • this same magnetization error can be used to determine a corrected axial field strength in a second attitude which may be close to horizontal east-west, as follows :

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  • Geology (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geophysics (AREA)
  • Fluid Mechanics (AREA)
  • Geochemistry & Mineralogy (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Measuring Magnetic Variables (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Detection And Prevention Of Errors In Transmission (AREA)
  • Detection And Correction Of Errors (AREA)

Abstract

L'invention concerne un procédé de détermination de l'angle de gisement d'un instrument topographique situé dans un puits à partir de mesures des composantes de champs magnétiques et de gravitation terrestres. Les angles de gisement sont calculés à partir de relevés concernant un minimum de deux trous de forage d'orientation différente. Les rélevés pris deux par deux permettent de résoudre une équation quadratique déterminante de la composante verticale du champ magnétique terrestre. L'invention se rapporte par ailleurs à une méthode de résolution graphique faisant appel à un minimum de trois relevés. Une autre méthode est utilisée pour des orientations est-ouest quasiment horizontales permettant de déterminer la composante axiale pour une deuxième orientation à partir de la composante axiale du champ magnétique terrestre mesurée pour une première orientation, en partant du principe que la composante d'erreur axiale due au champ magnétique crée par le train de tiges varie à une vitesse faible ou nulle.
PCT/GB1994/001523 1994-07-14 1994-07-14 Procede permettant de corriger les composantes d'erreur presentes dans les donnees topographiques provenant d'un puits de forage WO1996002733A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU71902/94A AU7190294A (en) 1994-07-14 1994-07-14 Method of correcting for error components in wellbore survey data
PCT/GB1994/001523 WO1996002733A1 (fr) 1994-07-14 1994-07-14 Procede permettant de corriger les composantes d'erreur presentes dans les donnees topographiques provenant d'un puits de forage

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/GB1994/001523 WO1996002733A1 (fr) 1994-07-14 1994-07-14 Procede permettant de corriger les composantes d'erreur presentes dans les donnees topographiques provenant d'un puits de forage

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WO1996002733A1 true WO1996002733A1 (fr) 1996-02-01

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998021448A1 (fr) * 1996-11-08 1998-05-22 Baker Hughes Incorporated Procede de correction des erreurs d'un magnetometre dans un puits de forage
WO1999066173A1 (fr) * 1998-06-18 1999-12-23 Shell Internationale Research Maatschappij B.V. Procede de determination de l'azimut d'un trou de forage
CN112963093A (zh) * 2021-01-26 2021-06-15 长江大学 一种旋转导向钻井工具的姿态动态测量和解算方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4709486A (en) * 1986-05-06 1987-12-01 Tensor, Inc. Method of determining the orientation of a surveying instrument in a borehole
US5103177A (en) * 1989-03-17 1992-04-07 Russell Anthony W Method and apparatus for determining the azimuth of a borehole by deriving the magnitude of the terrestial magnetic field bze
US5321893A (en) * 1993-02-26 1994-06-21 Scientific Drilling International Calibration correction method for magnetic survey tools

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4709486A (en) * 1986-05-06 1987-12-01 Tensor, Inc. Method of determining the orientation of a surveying instrument in a borehole
US5103177A (en) * 1989-03-17 1992-04-07 Russell Anthony W Method and apparatus for determining the azimuth of a borehole by deriving the magnitude of the terrestial magnetic field bze
US5321893A (en) * 1993-02-26 1994-06-21 Scientific Drilling International Calibration correction method for magnetic survey tools

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998021448A1 (fr) * 1996-11-08 1998-05-22 Baker Hughes Incorporated Procede de correction des erreurs d'un magnetometre dans un puits de forage
GB2334109A (en) * 1996-11-08 1999-08-11 Baker Hughes Inc Method of correcting wellbore magnetometer errors
GB2334109B (en) * 1996-11-08 2000-07-05 Baker Hughes Inc Method of correcting wellbore magnetometer errors
WO1999066173A1 (fr) * 1998-06-18 1999-12-23 Shell Internationale Research Maatschappij B.V. Procede de determination de l'azimut d'un trou de forage
CN112963093A (zh) * 2021-01-26 2021-06-15 长江大学 一种旋转导向钻井工具的姿态动态测量和解算方法

Also Published As

Publication number Publication date
AU7190294A (en) 1996-02-16

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