Patent ID: 7418865

Claim:
A method for determining a velocity of ultrasound propagation in a drilling fluid flowing in a mud channel within a borehole of a downhole environment, comprising: disposing a first ultrasound transducer ( 37 ) across the mud channel from a second ultrasound transducer ( 39 ) such that a front face ( 37 f ) of the first transducer ( 37 ) is offset from a front face ( 39 f ) of the second ultrasound transducer ( 39 ) by a predetermined radial offset distance (ΔDf), wherein the transducers are separated from the mud channel by a thin interface for protecting the transducers from the drilling fluid flowing in the mud channel while permitting the ultrasound propagation there through; emitting an ultrasound pulse into the drilling fluid in a borehole using the first ultrasound transducer( 37 ); detecting the ultrasound pulse after the ultrasound pulse has travelled through the drilling fluid a distance (d); determining a travel time (t) for the ultrasound pulse to travel the distance (d) through the drilling fluid in the borehole between the first and second transducers; and determining the velocity of ultrasound propagation in the drilling fluid from the distance (d) and the travel time (t).