Geometrical instruments – Indicator of direction of force traversing natural media – Borehole direction or inclination
Patent
1998-03-16
2000-02-08
Fulton, Christopher W.
Geometrical instruments
Indicator of direction of force traversing natural media
Borehole direction or inclination
33302, 175 45, E21B 47022, E21B 706
Patent
active
060215771
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the surveying of boreholes at drilling sites.
It is well known to survey boreholes which are not cased with a steel lining by making measurements at a series of downhole locations utilising a survey instrument incorporating two or three mutually orthogonal fluxgates and two or three mutually orthogonal accelerometers disposed in a non-magnetic drill collar so as to determine a series of parameters, such as the inclination angle and the azimuth angle, indicative of the orientation at a series of locations along the borehole.
British Patent Specification No. 1578053 describes a survey method in which a corrected azimuth angle measurement, corrected to compensate for the effects of perturbing magnetic fields associated with magnetised sections of the drill string both above and below the survey instrument, is obtained as a function of the horizontal and vertical components of the earth's magnetic field, as ascertained from look-up tables for example, the downhole magnetic field as measured by the instrument, and measured values of the inclination angle and the azimuth angle relative to the apparent magnetic North direction at the location of the instrument. British Patent Specifications Nos. 2158587 and 2185580 describe other, related survey methods.
All these survey methods rely on measurement of the orientation of the borehole relative to the geomagnetic field so that the borehole orientation can then be referred to the geographical coordinate system from knowledge of the orientation of the geomagnetic field relative to true North and the horizontal plane. Calibration of the survey instrument also relies on knowledge of the intensity of the geomagnetic field. Geomagnetic field data indicative of the direction and intensity of the geomagnetic field is usually obtained from look-up tables which provide such parameters for the local area based on a mathematical model of the global geomagnetic field. However such survey methods ignore the effects of short-term variations in the geomagnetic field caused by electrical currents in the ionosphere. The effect of such short-term variations is to provide significant errors in the measurement data which severely limit the accuracy of the survey results.
Furthermore it is known to obtain local geomagnetic field data by direct measurement in the vicinity of the drilling site. In theory, if sufficient measurements of the local geomagnetic field are taken, errors due to short-term variations in the geomagnetic field can be eliminated. However, in practice, it is not feasible to measure the geomagnetic field and its variation at the drilling site because of the magnetic interference produced by the drilling hardware.
It is an object of the invention to provide a borehole surveying method which overcomes the problems of such prior methods.
According to the present invention there is provided a method of surveying a borehole at a drilling site, which method comprises: earth's magnetic field at a local measurement site which is sufficiently close to the drilling site that the measurement data is indicative of the earth's magnetic field at the drilling site but which is sufficiently remote from the drilling site that the measurement data is unaffected by magnetic interference from the drilling site and other man-made installations; geomagnetic field data with data indicative of variation of the geomagnetic field with respect to time obtained by monitoring variation of the earth's magnetic field with respect to time at a remote monitoring site (which will usually be at a substantially greater distance from the drilling site than the local measurement site); surveying instrument the magnetic field in the vicinity of the borehole at a series of locations along the borehole; and field data and said time-varying geomagnetic field data.
Such a method, which may be referred to as Interpolated In-Field Referencing (IIFR), relies on spot measurement of the values of the geomagnetic field, such as the intensity and direction of the geomagnetic field for example,
REFERENCES:
patent: 4361192 (1982-11-01), Trowsdale
patent: 4682421 (1987-07-01), Van Dongen et al.
patent: 4761889 (1988-08-01), Cobern et al.
patent: 4956921 (1990-09-01), Coles
patent: 5103920 (1992-04-01), Patton
patent: 5155916 (1992-10-01), Engebretson
patent: 5435069 (1995-07-01), Nicholson
patent: 5452518 (1995-09-01), Dipersio
patent: 5469736 (1995-11-01), Moake
patent: 5787997 (1998-08-01), Hartmann
Kerridge David John
Shiells Gordon Malcolm
Baroid Technology Inc.
Doan Quyen
Fulton Christopher W.
LandOfFree
Borehole surveying does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Borehole surveying, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Borehole surveying will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1672383