Magnetic materials in the drilling fluid used for drilling a petroleum well can significantly shield the Earth’s magnetic field as measured by magnetic sensors inside the drilling pipe. This has been shown to sometimes cause significant errors in the accuracy of borehole positioning using magnetic surveying. In this paper we present a physical approach for correcting the measured magnetic fields for such shielding. An explicit solution of the shielding problem is derived for the simplest case of a magnetic sensor on the axis of the borehole.

1.
Wilson
,
H.
, and
Brooks
,
A. G.
, 2001, “
Wellbore Position Errors Caused by Drilling Fluid Contamination
,” Paper No. SPE 71400 presented at the SPE Annual Technical Conference and Exhibition, New Orleans, LA, Sept. 30–Oct. 3.
2.
Ekseth
,
R.
, 1998, “
Uncertainties in Connection with the Determination of Wellbore Positions
,” Dr.-ing. Thesis NTNU, Trondheim, Norway.
3.
Williamson
,
H. S.
, 1999, “
Accuracy Prediction for Directional MWD
,” Paper No. SPE 56702 presented at the SPE Annual Technical Conference and Exhibition, Oct. 3–6 Houston, TX.
4.
Torkildsen
,
T.
, and
Lotsberg
,
O.
, 2001, “
Acceptance Values for MWD Magnetic Wellbore Surveying
,” paper presented at the 13th ISCWSA meeting, Haarlem, The Netherlands, 2 March.
5.
Torkildsen
,
T.
,
Edvardsen
,
I.
,
McCulloch
,
S.
,
Fjogstad
,
A
,
Saasen
,
A.
,
Amundsen
,
P. A.
, and
Omland
,
T. H.
, 2004, “
Drilling Fluid Affects MWD Magnetic Azimuth and Wellbore Position
,” Paper No. SPE/IADC 87169 presented at the IADC/SPE Drilling Conference held in Dallas, TX, March 2–4.
6.
Saasen
,
A.
,
Hoset
,
H.
,
Rostad
,
E.
,
Fjogstad
,
A.
,
Aunan
,
O.
,
Westgård
,
E.
, and
Norkyn
,
P. I.
, 2001. “
Application of Ilmenite as Weight Material in Water-Based and Oil-Based Drilling Fluids
,” Paper No. SPE 71401 presented at the SPE Annual Technical Conference and Exhibition, New Orleans, LA, Sept. 30–Oct. 3.
7.
Stratton
,
J. A.
, 1941,
Electromagnetic Theory
,
McGraw-Hill
, New York, Chap. IV.
8.
Jackson
,
J. D.
, 1998,
Classical Electrodynamics
,
3rd. ed.
,
Wiley
, New York, Chap. 5.
9.
Jaeger
,
J. C.
1940, “
Magnetic Screening by Hollow Circular Cylinders
,”
Philos. Mag.
0031-8086,
29
(
S7
), pp.
18
31
.
10.
Amundsen
,
P. A.
,
Torkildsen
,
T.
,
Saasen
,
A.
, and
Omland
,
T. H.
, 2005, Working Papers from the University of Stavanger, Stavanger, Norway, No. 8.
You do not currently have access to this content.