Patent ID: 7705295

Claim:
A method for determining a downhole parameter in a drilling environment wherein a drill string is positioned in a borehole such that a drilling fluid supplied along the drillstring returns along an annulus around the drillstring while serving to carry drilling cuttings out of the borehole, the method comprising: using an activation device to activate the drilling fluid flowing past the activation device; measuring the activity level of the activated drilling fluid with a measuring device at a known distance d from the activation device; communicating to a processor an initial measurement of the activity level at a time t 0 when the time-of-flight for the fluid between the activation device and the measurement device is known; thereafter communicating further measurement of the activity level to said processor and using said processor to compare the further activity levels to the initial activity level at said time t 0 when the time-of-flight for the fluid between the activation device and the measurement point is known; and using said processor to device from the comparison a measurement of the time-of-flight at the time of the further activity measurement.