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Paramagnetism shielding in drilling fluid

Li, Zhuo
Master thesis
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URI
http://hdl.handle.net/11250/182561
Date
2013
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  • Master's theses (TN-IMN, 2007-2017) [233]
Abstract
In drilling operations, drilling fluid containing magnetic materials

is used when drilling a well. The materials can significantly shield

the Earth’s magnetic field as measured by magnetic sensors inside

the drilling strings. The magnetic property of the drilling fluid is

one of the substantial error sources for the determination of magnetic

azimuth for wellbores. Both the weight material, cuttings, clay and

other formation material plus metal filings from the tubular wear may

distort the magnetometer readings. This effect is obviously linked to

the amount and kind of magnetic material in the drilling fluid, and

the development of corrective means has therefore highlighted the

drilling fluid.

The influence on directional Measurement While Drilling (MWD)

from drilling fluids has been studied using finite element modeling

techniques. The simulations have been performed for several cases

with realistic representations of MWD tool geometries and varying

location of Bottom Hole Assembly (BHA) versus the wellbore. The

wellbore, tools and magnetic fields were modeled by finite element

methods. The wellbore is modelled as a perfect circular cylinder. With

unsymmetrical geometry the placement of the magnetic MWD sensors

may become more sensitive to magnetic shielding effects, and

small position changes may result in significant errors in the measured

magnetic field components, both attenuation and amplification

[1]. One important result is that for situations with perfect axial symmetry,

the magnetometer readings are attenuated proportionally to

the square of the magnetic susceptibility. Since the magnetic susceptibility

is a small number, this means that the effect on magnetometer

readings is generally negligible. However, if the symmetry is broken,

the distortion on the magnetometer readings can be increased significantly.

This means that segregation of cuttings, metal filings or weight

material can strongly influence the strength of the measured magnetic

fields [1].

It has been shown sometimes to cause significant errors in the accuracy

of drilling hole positioning using magnetic surveying. Here we

present a general physical approach for correcting the measured magnetic

fields from paramagnetism by the paramagnetic material for such

in drilling fluid. Based on information of the paramagnetic properties

of the drilling fluid and the well geometry, applied to a sufficiently

long straight section of a well [2] this paper will show how the magnetic

field in a cylindrical wellbore can be calculated analytically by

using conformal mapping .
Description
Master's thesis in Applied science
Publisher
University of Stavanger, Norway
Series
Masteroppgave/UIS-TN-IMN/2013;

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