A Rotational High Pressure Viscosimeter

Sage appears to have been the first (1933) to design a rolling ball viscosimeter for the express purpose of measuring the viscosity of oils with natural gas in solution, i.e., under reservoir conditions. In 1940 Hocott and Buckley further refined the rolling ball instrument in both design and method of operation, and their instrument, known as the Humble type, was the forerunner of present day viscosimeters used in petroleum production and research laboratories. They also initiated the technique of charging the viscosimeter with a sample directly from a bottom hole sampler. In 1948 the committee on engineering research of the Petroleum Division of the AIME in Part 3 (1) of the Physical-Chemical Topics of Table 1 suggested the "development of improved and simpler methods of measuring viscosity of reservoir fluids." This note will describe a rotational, high pressure viscosimeter which has been developed in response to this suggestion but whose relative merits are yet to be determined fully. The Instrument Fig. 1 is a photograph and Fig. 2 is a cross sectional drawing of the instrument. It consists of a non-magnetic, stainless steel rotor about 4 in. in length and 1 in. in diameter centered axially within a non-magnetic, stainless steel, pressure vessel of cylindrical bore. The rotor is mounted on miniature, precision ball bearings and has a radial clearance of about 1/64 in. Alnico magnets are inserted perpendicular to the axis of rotation on either end of the rotor, those at the top to serve as indicator magnets, those at the bottom, as the driven magnets which turn the rotor. A constant (but variable) speed motor outside the pressure vessel turns the rotor by means of a driving magnet attached to the motor shaft. The motor speed is checked using an aircraft type, precision, spring-wound interval timer and an electric impulse counter to record revolutions by means of an electric contactor on the motor shaft.