MAGNETIC DISTURBANCE CAUSED BY BURIED CASING: 
WILLIAM M. BARRET? 
Shreveport, Louisiana 
ABSTRACT 
A vertical string of casing becomes magnetized by induction under the influence 
of the terrestrial magnetic field. For theoretical investigation we may treat such a 
casing as a bar magnet having an exaggerated ratio of length to diameter. Formulae 
are derived, based on the fundamental law of Coulomb, to express the anomalous 
components of the magnetic elements in different horizontal planes and at different 
radial distances from the casing head. Curves representing these equations are shown. 
Graphical illustrations of the composition of these anomalous components and the 
normal components of the earth’s magnetizing field are included, together with typical 
experimental data obtained in the field. 
INTRODUCTION 
In the investigation of magnetic phenomena directly associated 
with oil- and gas-producing fields, as well as in attempting to map geo- 
logic structure along the boundaries of such areas, the magnetic dis- 
tortion traceable to buried casing becomes of vital importance to the 
geophysicist. 
As many of the empirical data that furnish valuable criteria for 
interpretative analysis must necessarily be obtained in regions where 
subsurface features have been disclosed by existing wells, it seems that 
a thorough understanding of the disturbing effect of this metal is essen- 
tial to a proper appreciation of the experimental results. 
In this paper it is intended to present briefly the theoretical aspects 
of the problem and to include such field observations as are considered 
representative of the cases thus far investigated. 
The writer wishes to acknowledge his indebtedness to Randolph 
H. Mayer for his valuable assistance during the preparation of this 
paper, and to express his appreciation to John S. Ivy for the data fur- 
nished regarding the location and completion dates of wells in the Sligo 
field. 
tRead before the Association at the San Antonio meeting, March 21, 1931. Man- 
uscript received, February 1, 1931. 
2Geophysicist, William M. Barret, Inc., Giddens-Lane Building. Introduced by 
D. M. Collingwood. 
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