WO1997025683A1 - Method for conducting moving or rolling check shot for correcting borehole azimuth surveys - Google Patents
Method for conducting moving or rolling check shot for correcting borehole azimuth surveys Download PDFInfo
- Publication number
- WO1997025683A1 WO1997025683A1 PCT/US1997/000401 US9700401W WO9725683A1 WO 1997025683 A1 WO1997025683 A1 WO 1997025683A1 US 9700401 W US9700401 W US 9700401W WO 9725683 A1 WO9725683 A1 WO 9725683A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- cross
- axial
- interference
- locations
- azimuth
- Prior art date
Links
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP 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 generally to methods used to determine the path of a well bore that extends into the Earth. More particularly, the present invention pertains to a method that uses a reduced number of measurements to correct azimuth determinations made from terrestrial magnetic readings distorted by the magnetic interference produced by the survey tool and drill string assembly. Determinations of the inclination and azimuth of a well bore are customarily made by measuring gravitational and terrestrial magnetic fields existing in the well bore. The terrestrial components of the magnetic field are distorted by the magnetic fields associated with the drill string assembly and the survey tool. This distortion, together with measurement errors and random noise errors produce errors in the determined value of the azimuth. The prior art has suggested a number of methods and apparatus for reducing the effects of the magnetic error in the determination of azimuth.
- the magnetic field In dealing with the magnetic measurements, it is customary to define the magnetic field in terms of its components in the coordinate system of the survey tool.
- the central axis of the tool is commonly designated as the z-axis.
- Mutually perpendicular x and y axes intersect the z-axis and lie in a plane perpendicular to the z-axis.
- the x and y components of the interfering magnetic field are referred to as the cross-axial or x-y interference.
- the z component of the interference is referred to as the axial or z axis interference.
- the method of the '069 patent requires that the azimuth be determined at each axial location without applying a correction for magnetic interference.
- the azimuth is determined algebraically with the result that the method can be applied, at most, to three measurements at a time without overdetermining the equations.
- reliable estimates of magnetic interference require more than three measurements.
- the '069 method when only two measurement points are employed, it is necessary to add a consistency condition in order to have a sufficient number of equations to solve for the unknowns. While either of the '069 techniques may work well in the absence of measurement noise, the presence of such measurement noise will significantly degrade the results.
- the method taught by the '893 patent is concerned with axial interference rather than cross-axial interference.
- the method requires the explicit use of a model of drill string magnetization and also requires the use of measurement vectors and measurement matrices.
- the '486 patent method also deals only with axial magnetic interference and treats the cross-axial interference as non-existent.
- the multiple measurements used in the method must be made at noncollinear points and are used to determine the algebraic sign of the calculated tool-axis magnetic field.
- the '421 patent method describes a technique for correcting for the cross-axial and axial magnetic disturbance using measurements taken at different axial locations in the well bore and at random tool face angles.
- the method requires that the x, y and z axis components of the magnetic field be measured at each measuring point.
- the interference is determined using a statistical method in which a correlation is made between the measured field and a series of magnetic measurements obtained randomly.
- the '421 method employs the z-axis measurements in determining the cross-axis correction, the resultant calculations of azimuth are subject to producing erroneous results. This follows from the fact that, if interference exists in the x and y axes, it almost certainly exists in the z axis. The z axis readings are thus subject to being corrupt and their use in the calculations of the azimuth will also produce corrupted azimuth determinations. Since the z axis interference changes only very slowly as the survey tool progresses down the borehole, the z axis reading can not be of any use in determining the interference. Moreover, while the method described in the '421 patent employs a statistical solution, the method lacks an iterative solution step that may be used to improve the azimuth calculations when the inclination and azimuth vary substantially between measurements.
- measurements of the gravitational and cross axis magnetic fields acting on the survey tool are made at two differing tool face angles in as few as two axial locations in the well bore.
- the variation in the cross-axis magnetic field measured at the different tool face angles is used to statistically estimate the cross-axis interference.
- the estimated interference is used to improve the azimuth calculation at each axial location. Where the inclination or azimuth change between measurements, the statistical estimates and azimuth calculation are iterated to further improve the azimuth calculation.
- the method steps are applied to more than the minimum measurements to obtain improved accuracy.
- the method is used to directly calculate corrected azimuth without iteration.
- the characteristics of the cross-axial magnetic field are evaluated to improve survey results. In situations where the interfering field varies slowly from one measuring location to another, it may be treated as a constant to permit simplification of the calculations.
- the existence of an external field may be detected from the presence of residual error that varies in magnitude and direction along the borehole trajectory.
- a primary object of the present invention is to provide a method for correcting cross-axial magnetic interference produced by a drill string assembly and survey tool using cross-axial measurements at a minimum of two differing well bore locations and two differing tool face angles without regard to the axial component of the magnetic field.
- Another object of the present invention is to iterate statistical adjustments of the cross-axial magnetic measurements to compensate for changes in the inclination and azimuth of the survey tool at each of the two different measuring locations to improve initial azimuth estimates.
- Yet another object of the present invention is to provide a method for directly calculating the cross-axial interference in a well survey tool where the inclination and azimuth of the tool remain substantially constant from one measuring point to the next.
- Another important object of the present invention is to employ the determined values of cross-axial interference in situations where the interference changes in the tool axis at different measuring locations to calculate the trend in the change of the cross-axial field.
- Still another object of the present invention is to determine the presence of rapidly changing cross-axial interference that will identify faulty surveys.
- a basic principle employed in the present invention is that by referring all measurements made by the survey tool to the tool coordinate system, it is possible to use the variations introduced by the different tool face angles to calculate cross-axial interference.
- the magnetic interference is due to the magnetic field properties introduced by the drill string assembly and the survey tool. Accordingly the magnitude and direction of the introduced interference remains fairly constant relative to the tool's coordinate system even as the tool is rotated to different tool face angles or is moved to different axial positions within the well bore.
- the single collar solution such as taught in U.S. Patent No. Re. 33,708, or an equivalent method, is used to obtain the azimuth.
- the measurements obtained at the various survey stations in the process are mapped to a first survey station that becomes a "reference" station.
- This mapping step involves a knowledge of the tool inclination, tool face angle and azimuth at each station.
- B m is the cross-axial x-axis interference
- B ⁇ is the cross-axial y-axis interference
- B ⁇ . is the j" 1 measurement of the x-component of the field in the tool's coordinate system
- B jj . is the j" * measurement of the y-component of the field in the tool's coordinate system
- B ⁇ is the estimated x-component of the earth's magnetic field in the tool coordinate system at station j
- B ⁇ is the y-component of the earth's magnetic field in the tool coordinate system of station j.
- the B ej are to be estimated from ⁇ j , ⁇ ⁇ and the measured fields, or equivalently from the estimated azimuth ⁇ j * , we cannot estimate by plugging back into the general azimuth equations since this would be circular.
- the iteration may be performed as follows:
- Equations (9) and (10) can be solved simultaneously, then the process defined through equations (1) - (10) can be iterated. Note that an iterative solution for z-axis interference could also be included as a separate step.
- equations (11) and (12) may be good working approximations.
- a best fit, in the least squares sense, can be performed for a minimum of 3 successive survey stations with similar inclinations and azimuths using
- the method of the present invention compensates for cross-axial magnetic interference and bias errors using measurements at multiple points along a well bore that need not be at the same inclination.
- a method of the present invention further permits the determination of trends in cross-axial magnetic interference and bias errors using measurements along a well bore and compensating for these errors.
- Another method of the invention includes the step of detecting the presence of random cross-axial magnetic interference and/or bias errors. Where the cross-axial field is determined to vary rapidly between measuring stations such that it is only possible to determine that there is interference, without being able to quantify the direction or magnitude of the interference, this information is employed to identify faulty surveys taken at the measuring stations.
- a method of the invention includes the steps of making all corrections for cross-axial interference and identifying the presence of a residual error that is variable in magnitude and direction along the bore hole trajectory to establish the presence of an external field. While preferred embodiments of the methods of the present invention have been described in detail herein, it will be understood that the described steps of the methods may be altered or supplemented without departing from the spirit and scope of the invention which is defined in the following claims.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU16959/97A AU1695997A (en) | 1996-01-11 | 1997-01-10 | Method for conducting moving or rolling check shot for correcting borehole azimuth surveys |
CA002242850A CA2242850C (en) | 1996-01-11 | 1997-01-10 | Method for conducting moving or rolling check shot for correcting borehole azimuth surveys |
GB9814912A GB2324608B (en) | 1996-01-11 | 1997-01-10 | Method for correcting borehole azimuth surveys for cross-axial magnetic interference |
NO983170A NO983170L (en) | 1996-01-11 | 1998-07-09 | Method for performing moving and rolling control recordings to correct azimuth monitoring of boreholes |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US983396P | 1996-01-11 | 1996-01-11 | |
US60/009,833 | 1996-01-11 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1997025683A1 true WO1997025683A1 (en) | 1997-07-17 |
Family
ID=21739976
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1997/000401 WO1997025683A1 (en) | 1996-01-11 | 1997-01-10 | Method for conducting moving or rolling check shot for correcting borehole azimuth surveys |
Country Status (4)
Country | Link |
---|---|
AU (1) | AU1695997A (en) |
GB (1) | GB2324608B (en) |
NO (1) | NO983170L (en) |
WO (1) | WO1997025683A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN106522924A (en) * | 2016-11-15 | 2017-03-22 | 北京恒泰万博石油技术股份有限公司 | Acquisition method for azimuth angles in measurement while drilling |
Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4761889A (en) * | 1984-05-09 | 1988-08-09 | Teleco Oilfield Services Inc. | Method for the detection and correction of magnetic interference in the surveying of boreholes |
US4819336A (en) * | 1986-01-22 | 1989-04-11 | Nl Sperry-Sun, Inc. | Method of determining the orientation of a surveying instrument in a borehole |
US4956921A (en) * | 1989-02-21 | 1990-09-18 | Anadrill, Inc. | Method to improve directional survey accuracy |
US5064006A (en) * | 1988-10-28 | 1991-11-12 | Magrange, Inc | Downhole combination tool |
US5155916A (en) * | 1991-03-21 | 1992-10-20 | Scientific Drilling International | Error reduction in compensation of drill string interference for magnetic survey tools |
US5321893A (en) * | 1993-02-26 | 1994-06-21 | Scientific Drilling International | Calibration correction method for magnetic survey tools |
US5452518A (en) * | 1993-11-19 | 1995-09-26 | Baker Hughes Incorporated | Method of correcting for axial error components in magnetometer readings during wellbore survey operations |
-
1997
- 1997-01-10 WO PCT/US1997/000401 patent/WO1997025683A1/en active Application Filing
- 1997-01-10 GB GB9814912A patent/GB2324608B/en not_active Expired - Lifetime
- 1997-01-10 AU AU16959/97A patent/AU1695997A/en not_active Abandoned
-
1998
- 1998-07-09 NO NO983170A patent/NO983170L/en not_active Application Discontinuation
Patent Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4761889A (en) * | 1984-05-09 | 1988-08-09 | Teleco Oilfield Services Inc. | Method for the detection and correction of magnetic interference in the surveying of boreholes |
US4819336A (en) * | 1986-01-22 | 1989-04-11 | Nl Sperry-Sun, Inc. | Method of determining the orientation of a surveying instrument in a borehole |
US5064006A (en) * | 1988-10-28 | 1991-11-12 | Magrange, Inc | Downhole combination tool |
US4956921A (en) * | 1989-02-21 | 1990-09-18 | Anadrill, Inc. | Method to improve directional survey accuracy |
US5155916A (en) * | 1991-03-21 | 1992-10-20 | Scientific Drilling International | Error reduction in compensation of drill string interference for magnetic survey tools |
US5321893A (en) * | 1993-02-26 | 1994-06-21 | Scientific Drilling International | Calibration correction method for magnetic survey tools |
US5452518A (en) * | 1993-11-19 | 1995-09-26 | Baker Hughes Incorporated | Method of correcting for axial error components in magnetometer readings during wellbore survey operations |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN106522924A (en) * | 2016-11-15 | 2017-03-22 | 北京恒泰万博石油技术股份有限公司 | Acquisition method for azimuth angles in measurement while drilling |
Also Published As
Publication number | Publication date |
---|---|
GB2324608B (en) | 2000-02-02 |
GB2324608A (en) | 1998-10-28 |
AU1695997A (en) | 1997-08-01 |
GB2324608A8 (en) | 1999-02-15 |
NO983170L (en) | 1998-09-11 |
GB9814912D0 (en) | 1998-09-09 |
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