EP1088152A1 - Method of determining azimuth of a borehole - Google Patents
Method of determining azimuth of a boreholeInfo
- Publication number
- EP1088152A1 EP1088152A1 EP99927912A EP99927912A EP1088152A1 EP 1088152 A1 EP1088152 A1 EP 1088152A1 EP 99927912 A EP99927912 A EP 99927912A EP 99927912 A EP99927912 A EP 99927912A EP 1088152 A1 EP1088152 A1 EP 1088152A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- borehole
- drill string
- magnetic field
- cos
- location
- Prior art date
- Legal status (The legal status 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 status listed.)
- Granted
Links
- 238000000034 method Methods 0.000 title claims abstract description 24
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 6
- 238000005259 measurement Methods 0.000 claims description 9
- 239000013598 vector Substances 0.000 description 11
- 230000000694 effects Effects 0.000 description 3
- 230000005484 gravity Effects 0.000 description 3
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
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 an azimuth angle of a borehole formed in an earth formation using magnetometer tool arranged in a drill string extending longitudinally in the borehole.
- magnetometer tool arranged in a drill string extending longitudinally in the borehole.
- the borehole inclination can be determined using accelerometer measurements in the borehole and the Earth gravity field as a reference.
- the borehole azimuth is determined using a package of magnetometers included in the Bottom Hole Assembly (BHA) of the drill string.
- BHA Bottom Hole Assembly
- the magnetometers are operated to measure the components of the local magnetic field from which the borehole azimuth is determined using the Earth magnetic field as a reference. In many instances however the measured local magnetic field includes, apart from the Earth magnetic field components, components attributable to drill string magnetisation. In order to obtain sufficiently accurate azimuth data it is required that such drill string magnetisation effects are taken into account.
- EP-A-0 193 230 discloses a method of determining azimuth of a borehole formed in an earth formation using a magnetometer package included in a drill string extending into the borehole, wherein the effect of drill string magnetisation is taken into account by first eliminating the effect of cross-axial drill string magnetisation prior to eliminating the influence of axial drill string magnetisation.
- the cross-axial drill string magnetisation is eliminated by taking so-called rotational shots, i.e. by measuring the local magnetic field at different rotational locations of the magnetometer tool and determining the cross-axial drill string magnetisation from the magnetic field data thus obtained.
- the axial drill string magnetisation is computed from the measured magnetic field and from the Earth magnetic field.
- the borehole azimuth is determined from the corrected field and from the Earth magnetic field which is generally known for most places on Earth.
- the computed azimuth however is very sensitive to inaccuracies in the Earth magnetic field data, especially in case of highly inclined boreholes extending substantially in east or west direction.
- a method of determining an azimuth angle of a borehole formed in an earth formation using a magnetometer tool arranged in a drill string extending in the borehole, the magnetometer tool having a selected orientation relative to the drill string comprising a) selecting at least two locations along the borehole at which the borehole has selected different borehole inclinations; b) for each selected location, arranging the drill string in the borehole such that the magnetometer tool is positioned at the selected location and operating the magnetometer tool so as to measure a component of a local magnetic field along an axis having a selected orientation relative to the magnetometer tool, the local magnetic field including the earth magnetic field and a drill string magnetisation field; c) determining from the measurements and from the selected borehole inclinations, a contribution from the drill string magnetisation field to the measured components; d) correcting the measurements for said contribution from the drill string magnetisation field; and e) determining from the corrected measurements, the borehole azimuth.
- the contribution from the earth magnetic field to each measured component along the axis of selected orientation is different for the different borehole locations because the drill string, and therefore also said axis, is oriented differently relative to the earth magnetic field at the different locations .
- the contribution from the drill string magnetisation field to the measured component is the same for the different borehole locations because the orientation of said axis relative to the drill string magnetisation field does not change. Since the orientation of said axis is directly related to the orientation of the drill string and therefore to the borehole inclination, the contribution from the drill string magnetisation field to the measured component can be determined from the difference between the measured components at the different locations and from the different borehole inclinations at the different locations. An example of such determination is presented in the detailed description below.
- said component of the local magnetic field is the axial component of the local magnetic field, which is the component in axial direction of the drill string. It is to be understood that the contribution from the drill string magnetisation field to the cross-axial component (if any at all) of magnetic field generally is an order of magnitude smaller than the axial contribution. Therefore, for most applications it is sufficiently accurate to disregard such cross-axial contribution. Alternatively, the measured magnetic field can be corrected for a cross-axial contribution from the drill string magnetisation field prior to step c) .
- the method can suitably be applied for a borehole of which the longitudinal axis at the selected locations is substantially located in a vertical plane.
- the borehole inclinations at at least two of said locations differ from each other by an angle of at least 40°.
- the borehole inclination angle at the second location is suitably between 80°-100°.
- the wellbore inclination at the first location exceeds 45° it is preferred to determine the contribution to the axial components attributable to drill string magnetisation from the horizontal component of the Earth magnetic field. If furthermore the drill string magnetisation at the first location is different than at the second location, the borehole inclination angle at the second location is suitably between 0° and +10°.
- Fig. 1 shows a horizontal plane of the (N,E,V) coordinate system
- Fig. 2 shows a vertical plane through line H of the coordinate system of Fig. 1;
- Fig. 3 shows a borehole-fixed coordinate system (HS,
- HSR HSR, z
- a tool-fixed coordinate system (x,y,z)
- Fig. 1 is shown the horizontal N-E plane of the North (N) , East (E) , Vertical (V) coordinate system, wherein line H is a projection in the N-E plane of the longitudinal axis of a borehole 10 (Fig. 3) and angle A indicates the borehole azimuth. It is to be understood that angle A may vary along the length of the borehole.
- BN represents the horizontal vector component of the earth magnetic field.
- Fig. 2 is shown a vertical plane through line H.
- Line T represents the longitudinal axis of the borehole and angle I the borehole inclination which varies along the length of the borehole.
- B v represents the vertical vector component of the earth magnetic field and B n .cos A is the projection of the horizontal component of the earth magnetic field on line H.
- Fig. 3 a cross-sectional view of the borehole 10, a co-ordinate system (HS, HSR, z) fixed to the borehole 10 and a co-ordinate system (x, y, z) fixed to a magnetometer tool (not shown) for measuring the components of a local magnetic field B in the (x, y, z) co-ordinate system.
- the magnetometer tool is fixedly arranged in a drill string (not shown) extending through the borehole, therefore the (x, y, z) co-ordinate system can be thought of as being fixed to the drill string.
- the HS-, HSR-, x-, and y-axes extend in the transverse plane of the borehole at point P whereby the x-, y-axes are rotated relative to the HS-, HSR-axes about an angle ⁇ which is referred to as the tool-face angle.
- the z-axis extends in longitudinal direction of the borehole 10.
- the drill string is furthermore provided with an accelero- meter tool (not shown) for measuring the components of the earth gravity field G in the (x, y, z) co-ordinate system.
- the magnetometer tool measures the components B x , By, B z of the local magnetic field vector B and the accelerometer tool measures the components G x , Gy, G z of the gravity field vector G while the drill string is kept stationary.
- the tool-face angle ⁇ and the inclination angle I are determined from the equations :
- G ⁇ 5 G x cos ⁇ - GySin ⁇ (1)
- G j -jg is the component of G in HS-direction
- G v is the (known) component of G in V-direction.
- the components of B in the (HS, HSR, z) co-ordinate system are determined thus yielding the local magnetic field vector (B ⁇ g. B H g R , B z ) .
- Axial drill string magnetisation depends primarily on the magnetic properties of the BHA, not on borehole inclination. Therefore it is considered that at least as long as the BHA is not changed:
- Equations (7), (8), (9) contain the unknowns B v , C z 2 and C z 2-
- the inclinations I ⁇ _ and I2 are known from measurements using one or more accelerometer meters included in the drill string. It is found that o
- the local magnetic field at each point can now be corrected for axial drill string magnetisation.
- Eq. (17) is a quadratic expression in C z with generally two solutions for C z .
- the solution which gives a horizontal magnetic field component closest to the expected horizontal magnetic field component is to be selected from the two.
- the local magnetic field at each point can then be corrected for axial drill string magnetisation .
- At least one survey point is at a borehole inclination between 80°-100°, preferably about 90°, because then one of the components C z cos 1 or C z 2 cos I2 in eqs . (7), (8) substantially vanishes.
- At least one survey point is at a borehole inclination between 0° and +10°, preferably about 0°, because then either C zj sin I j or C z 2 sin I 2 in eq. (17) substantially vanishes.
- more than two survey points can be used to correct for axial drill string magnetisation.
Landscapes
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Geophysics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geophysics And Detection Of Objects (AREA)
- Measuring Magnetic Variables (AREA)
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99927912A EP1088152B1 (en) | 1998-06-18 | 1999-06-14 | Method of determining azimuth of a borehole |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP98304821 | 1998-06-18 | ||
EP98304821 | 1998-06-18 | ||
EP99927912A EP1088152B1 (en) | 1998-06-18 | 1999-06-14 | Method of determining azimuth of a borehole |
PCT/EP1999/003940 WO1999066173A1 (en) | 1998-06-18 | 1999-06-14 | Method of determining azimuth of a borehole |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1088152A1 true EP1088152A1 (en) | 2001-04-04 |
EP1088152B1 EP1088152B1 (en) | 2005-01-12 |
Family
ID=8234883
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP99927912A Expired - Lifetime EP1088152B1 (en) | 1998-06-18 | 1999-06-14 | Method of determining azimuth of a borehole |
Country Status (9)
Country | Link |
---|---|
EP (1) | EP1088152B1 (en) |
CN (1) | CN1305565A (en) |
AU (1) | AU748917B2 (en) |
BR (1) | BR9911307A (en) |
CA (1) | CA2334920C (en) |
DE (1) | DE69923179T2 (en) |
ES (1) | ES2237113T3 (en) |
NO (1) | NO320686B1 (en) |
WO (1) | WO1999066173A1 (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB0102900D0 (en) | 2001-02-06 | 2001-03-21 | Smart Stabiliser Systems Ltd | Surveying of boreholes |
US6854192B2 (en) | 2001-02-06 | 2005-02-15 | Smart Stabilizer Systems Limited | Surveying of boreholes |
GB0221753D0 (en) | 2002-09-19 | 2002-10-30 | Smart Stabilizer Systems Ltd | Borehole surveying |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB8504949D0 (en) * | 1985-02-26 | 1985-03-27 | Shell Int Research | Determining azimuth of borehole |
US4709486A (en) * | 1986-05-06 | 1987-12-01 | Tensor, Inc. | Method of determining the orientation of a surveying instrument in a borehole |
EG20489A (en) * | 1993-01-13 | 1999-06-30 | Shell Int Research | Method for determining borehole direction |
US5321893A (en) * | 1993-02-26 | 1994-06-21 | Scientific Drilling International | Calibration correction method for magnetic survey tools |
WO1996002733A1 (en) * | 1994-07-14 | 1996-02-01 | Baker Hughes Incorporated | Method of correcting for error components in wellbore survey data |
-
1999
- 1999-06-14 CA CA002334920A patent/CA2334920C/en not_active Expired - Fee Related
- 1999-06-14 CN CN 99807513 patent/CN1305565A/en active Pending
- 1999-06-14 BR BR9911307-4A patent/BR9911307A/en not_active IP Right Cessation
- 1999-06-14 DE DE69923179T patent/DE69923179T2/en not_active Expired - Fee Related
- 1999-06-14 WO PCT/EP1999/003940 patent/WO1999066173A1/en active IP Right Grant
- 1999-06-14 EP EP99927912A patent/EP1088152B1/en not_active Expired - Lifetime
- 1999-06-14 AU AU45093/99A patent/AU748917B2/en not_active Ceased
- 1999-06-14 ES ES99927912T patent/ES2237113T3/en not_active Expired - Lifetime
-
2000
- 2000-12-18 NO NO20006450A patent/NO320686B1/en unknown
Non-Patent Citations (1)
Title |
---|
See references of WO9966173A1 * |
Also Published As
Publication number | Publication date |
---|---|
NO320686B1 (en) | 2006-01-16 |
CA2334920C (en) | 2008-04-29 |
EP1088152B1 (en) | 2005-01-12 |
NO20006450L (en) | 2001-02-16 |
WO1999066173A1 (en) | 1999-12-23 |
ES2237113T3 (en) | 2005-07-16 |
CN1305565A (en) | 2001-07-25 |
CA2334920A1 (en) | 1999-12-23 |
DE69923179T2 (en) | 2006-01-05 |
DE69923179D1 (en) | 2005-02-17 |
NO20006450D0 (en) | 2000-12-18 |
AU748917B2 (en) | 2002-06-13 |
AU4509399A (en) | 2000-01-05 |
BR9911307A (en) | 2001-03-13 |
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