Boring or penetrating the earth – With signaling – indicating – testing or measuring
Reexamination Certificate
1999-06-10
2001-05-08
Schoeppel, Roger (Department: 3672)
Boring or penetrating the earth
With signaling, indicating, testing or measuring
C175S057000, C166S066000, C166S113000, C166S250010, C033S303000, C033S310000, C033S313000, C033S35500D, C033SDIG001, C181S104000, C702S006000
Reexamination Certificate
active
06227310
ABSTRACT:
This invention relates to methods and apparatus for use in establishing directional information by reference to the earth's magnetic field.
The earth's magnetic field allows relatively simple and inexpensive methods to be used to establish direction with reference to north. As is well known, however, at any given point on the earth's surface there is a discrepancy (“variation”) between magnetic north and true north, and the variation changes slowly over time. In addition, the variation at any given point is subject to considerable short term alterations including a noticeable diurnal pattern, and can be significantly affected by proximity to masses of magnetic material, whether natural or manmade. These factors limit the usefulness of magnetic techniques in providing accurate positional or directional information.
The present invention is particularly, but not exclusively, concerned with the control of directional drilling of oil wells and the like. In the offshore oil industry, requirements for enhanced recovery and recovery from deep fields have led to an increasing requirement for long range directional drilling of high accuracy, but these techniques are limited by a lack of information as to the position and direction of the working end of the drill string.
It is increasingly common to make use of measurement while drilling (“MWD”) techniques in which instruments located immediately adjacent the drill bit transmit measured information to the surface by means such as mud pulse telemetry. It is possible to make use of magnetic sensors in MWD in an attempt to monitor the orientation of the drill bit with respect to true north, but the accuracy obtainable by magnetic measurement is not sufficient to provide the required degree of positional and directional accuracy.
It is also known that a bore hole can be surveyed to a high degree of accuracy by means of mechanical or solid state gyros. These however cannot be used while drilling, and therefore a survey of this nature requires the drilling operation to be stopped while the bore hole is surveyed with a gyro instrument package inserted on a wireline through the drill string.
One object of the present invention is to provide a method and apparatus which enables the accuracy of magnetic directional sensors to be substantially increased.
The present invention, from one aspect, provides a method of providing a magnetic reference for use in determining direction, the method comprising:
providing a magnetic observatory device which includes magnetometer means for detecting the direction of the earth's magnetic field and telemetry means for transmitting information derived from the magnetometer means to a remote location;
positioning said magnetic observatory device at a fixed location relative to the surface of the earth;
establishing the orientation of the magnetic observatory device with respect to true North;
deriving from said information the instantaneous variation between true North and magnetic North in the vicinity of said location.
From another aspect, the present invention provides a magnetic reference apparatus comprising magnetometer means responsive to the earth's magnetic field to provide output signals representative of the orientation of the apparatus with respect to the earth's magnetic field, and heading reference means providing a directional reference related to true North.
A further aspect of the invention resides in a magnetic reference apparatus comprising magnetometer means responsive to the earth's magnetic field to provide output signals representative of the orientation of the apparatus with respect to the earth's magnetic field, and heading reference means providing a directional reference related to true North.
In a particularly preferred form of the invention, the magnetic observatory device is deployed at a desired location, typically on the sea bed, and provides data for correcting the output of a magnetic MWD system, and the orientation of the magnetic observatory device with respect to true north is determined at the time of deployment by use of the magnetic reference apparatus.
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Ratner & Prestia
Schoeppel Roger
Tech-21 Limited
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