Borehole azimuth determination using magnetic field sensor

• US 4,472,884 A
• Filed: 01/11/1982
• Issued: 09/25/1984
• Est. Priority Date: 01/11/1982
• Status: Expired due to Term

• Current Assignee: Applied Technologies Associates, Inc.
• Original Assignee: Applied Technologies Associates, Inc.
• Inventors: Engebretson, Harold J.
• Primary Examiner(s): HAROIAN, HARRY
• Application Number:
  US06/338,261
• Time in Patent Office: 988 Days
• Field of Search: 33/301-303, 33/304, 33/310, 33/312, 33/313
• US Class Current: 33/304
• CPC Class Codes: G01V 3/26 operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device with electromagnetic waves G01V3/30
• CPC Class Codes: G01V 7/16 specially adapted for use on moving platforms, e.g. ship, aircraft

Abstract

A well mapping apparatus comprises:

(a) a magnetic field sensing device whose output is proportional to a local magnetic field vector,

(b) an acceleration sensing device whose output is proportional to a local gravity vector,

(c) the devices supported for rotation about a common axis, in a borehole,

(d) the outputs being usable in the determination of azimuth and inclination of the borehole.

Claims

1. In well mapping apparatus, the combination comprising

(a) a single magnetic field sensing device having only one axis of sensitivity whose output is proportional to a local magntic field vector,

(b) a single acceleration sensing device having only one axis of sensitivity whose output is proportional to a local gravity vector,

(c) means supporting said devices for rotation about a single common axis, in a borehole,

(d) said outputs being useable in the determination of azimuth and inclination of the borehole,

(e) means including a drive motor to rotate said devices about said common axis, in a borehole, and said motor being free of operative feedback drive connection to the acceleration sensing device, the magnetic field sensing device having a fixed angular position relative to said axis, at all times during motor rotation of said devices, and said magnetic field sensing device also being free of operative feedback connection to the acceleration sensing device at all times,

(f) circuitry connected to receive the outputs of said magnetic field sensing and acceleration sensing devices, and to process same to provide signals indicative of magnetic azimuth and tilt of the apparatus,

(g) and a resolver rotated by said motor about said axis and connected in controlling relation with said motor, whereby the motor rotates the magnetic field and acceleration sensing devices in a mode selected from the following modes:

i) continuously, and ii) intermittently.

2. The combination of claim 1 that includes apparatus connected to receive the output of said field sensing means for providing an harmonic analysis of said output whereby errors in said azimuth determination, anomalies in the local magnetic field, or nearby magnetic objects may be detected.