Abstract: The present invention provides a downhole method and apparatus using a flexural mechanical resonator, for example, a tuning fork to provide real-time direct measurements and estimates of the viscosity, density and dielectric constant of formation fluid or filtrate in a hydrocarbon producing well. The present invention additionally provides a method and apparatus for monitoring cleanup from a leveling off of viscosity or density over time, measuring or estimating bubble point for formation fluid, measuring or estimating dew point for formation fluid, and determining the onset of asphaltene precipitation. The present invention also provides for intercalibration of plural pressure gauges used to determine a pressure differential downhole.

Abstract: The invention provides a method of detecting, at the surface, the occurrence of torsional vibration in a bottomhole assembly mounted on the drill string of a rotary drilling system. The method includes the steps of: ascertaining natural frequencies of torsional vibration of the bottomhole assembly prior to drilling, and noting at least one reference frequency for an integer wavelength mode of torsional vibration of the bottomhole assembly. During subsequent drilling, the drill string mean square torque at the surface is monitored for a bandwidth around the reference frequency. It is found that peaks in the mean square torque, close to the reference frequency, are indicative of the occurrence of torsional vibration in the bottomhole assembly.