With the goal of increasing understanding of drilling fluid temperature beh
aviour during geothermal well drilling operations, and for providing a data
base for a better development of numerical wellbore simulators, an experime
ntal work based on a rheological evaluation of drilling fluids was carried
out. High-temperature drilling fluid systems (HTDFS) which are most commonl
y used in the Mexican geothermal well drilling industry were selected and e
valuated. Eleven water-based drilling fluids were formulated and chemically
characterised in order to carry out the rheological evaluation. Dynamic ex
perimental tests considering the non-Newtonian behaviour of such HTDFS were
performed using a coaxial cylinder-type viscometer (Fann 50C). Drilling fl
uid viscosities in a programmed temperature range of 25-180 degreesC (at a
constant reservoir pressure and a shear rate of 3448.2 kPa and 170 s(-1) re
spectively) were measured. These dynamic viscosity measurements were then f
itted to derive correlating equations for determining the drilling fluid vi
scosity as a function of temperature. Details of the experimental rheologic
al tests including a complete description of the equipment and all the HTDF
S used as well as the derived viscosity-temperature equations are presented
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