Method and apparatus for determining the azimuth of a borehole b

Details Method and apparatus for determining the azimuth of a borehole b Method and apparatus for determining the azimuth of a borehole b

1990-02-27

1992-04-07

Snow, Walter E.

Electricity: measuring and testing

Of geophysical surface or subsurface in situ

By magnetic means

166255, 175 45, G01V 300, G01V 308, G01V 318, E21B 2516

Patent

active

051031779

ABSTRACT:
Borehole surveying methods and apparatus for surveying the true longitudinal magnetic field within a substantially non-magnetic drill collar. A plurality of longitudinal magnetic field measurements are made to provide a longitudinal-position-dependent series of magnetic field measurements BZ(z) which enable the true magnitude of the terrestial magnetic field BZe in the direction of the longitudinal axis of the borehole to be calculated on the basis that BZ(z)=BZe+E(z), where E(z) is the longitudinal-position-dependent longitudinal magnetic field error induced by the magnetism of the drill string and the bottom-hole assembly. Several different methods of calculation are described, including polar and non-polar magnetic error function models. The methods can be extended to a full survey of the borehole heading by contemporaneous measurements of two further magnetic fields in each of two mutually orthogonal axes each also orthogonal to the longitudinal axis, along with contemporaneous gravity vector component measurements in each of these three axes.

REFERENCES:
patent: 4071815 (1978-11-01), Zemaneh, Jr.
patent: 4649349 (1987-03-01), Chiron et al.
patent: 4794336 (1988-12-01), Marlow et al.

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