An independent evaluation of current industry standard and state-of-the-art drilling fluid inflow and outflow meters was conducted during the drilling of a geothermal exploratory well. Four different types of fluid inflow meters and three different types of fluid outflow meters were tested and evaluated during actual drilling operations. The tested drilling fluid inflow meters included conventional pump stroke counters, rotary pump speed counters, magnetic flow meters, and a Doppler ultrasonic flow meter. On the return flow line, a standard paddle meter, an acoustic level meter, and a prototype rolling float meter were evaluated to measure drilling fluid outflow rates. The prototype outflow meter utilizes a rolling float which rides on the surface of the flow thereby measuring the fluid height in the pipe. Both the prototype meter and the conventional paddle meter were also extensively tested under a variety of drilling conditions in a full-scale laboratory test facility. The meters were evaluated and compared on the basis of reliability and accuracy, and the results are presented in the paper
