06985814 is referenced by 27 patents and cites 44 patents.

A method for surveying a borehole is provided. The method includes providing a tool having a magnetic field measurement device disposed thereon and positioning the tool in a borehole. Magnetic interference vectors are determined at at least two positions in the borehole by comparing the measured magnetic fields at those positions with a known magnetic field of the earth. The magnetic interference vectors indicate a direction to a target subterranean structure. Various embodiments of the invention compare the directions to the target subterranean structure with a historical survey thereof, so as to determine a distance between the borehole and the subterranean structure and an azimuth of the borehole. The surveying methodology of this invention may advantageously improve borehole surveying data obtained, for example, in relief well and/or well twinning drilling applications.

Title
Well twinning techniques in borehole surveying
Application Number
10/705562
Publication Number
6985814 (B2)
Application Date
November 11, 2003
Publication Date
January 10, 2006
Inventor
Graham McElhinney
Inverurie
GB
Assignee
PathFinder Energy Services
TX, US
IPC
G01V 3/26
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