Portable high-temperature, high-pressure viscometer development

A field instrument for measuring the rheological characteristics of drilling mud at temperatures up to 260 C and pressures of 12,500 psi was developed. This instrument allows a direct determination of fluid viscosity under simulated downhole conditions. The instrument is comprised of a rotational viscometer packaged in a high temperature, high pressure vessel and weighs approximately 60 pounds. The design and construction of the instrument are described and the results of measurements of six different drilling fluid formulations are presented. These test results show that water based samples exhibit a marked increase in viscosity with increasing pressures. In oil based muds the thinning effect caused by increasing temperature is partially compensated for by the thickening effect of increasing pressure.