Rheological property measurement of drilling fluids used in geothermal wells

With the goal of increasing understanding of drilling fluid temperature behaviour during geothermal well drilling operations, and for providing a database for a better development of numerical wellbore simulators, an experimental work based on a rheological evaluation of drilling fluids was carried out. High-temperature drilling fluid systems (HTDFS) which are most commonly used in the Mexican geothermal well drilling industry were selected and evaluated. Eleven water-based drilling fluids were formulated and chemically characterised in order to carry out the rheological evaluation. Dynamic experimental tests considering the non-Newtonian behaviour of such HTDFS were performed using a coaxial cylinder-type viscometer (Fann 50C). Drilling fluid viscosities in a programmed temperature range of 25–180°C (at a constant reservoir pressure and a shear rate of 3448.2 kPa and 170 s−1, respectively) were measured. These dynamic viscosity measurements were then fitted to derive correlating equations for determining the drilling fluid viscosity as a function of temperature. Details of the experimental rheological tests including a complete description of the equipment and all the HTDFS used as well as the derived viscosity–temperature equations are presented.