Patent ID: 7587936

Claim:
A downhole measurement tool, comprising: a substantially cylindrical tool body having a cylindrical axis; first and second standoff sensors deployed on the tool body, the standoff sensors being radially offset from one another with respect to the longitudinal axis, each of the standoff sensors configured to (i) transmit an ultrasonic pressure pulse into a borehole and (ii) receive a reflected waveform; and a controller including instructions for determining a drilling fluid acoustic velocity according to the following equation: c f = 2 ⁢ L 2 - 2 ⁢ L 1 T 2 - T 1 ≈ 2 ⁢ L 0 Δ ⁢ ⁢ T wherein c f represents the drilling fluid acoustic velocity, L 1 and L 2 represent standoff distances at the first and second standoff sensors, L 0 represents a radial offset distance between the first and second standoff sensors, T 1 and T 2 represent arrival times of wellbore reflection components received at the first and second standoff sensors, and ΔT represents a difference between the arrival times.