MEASUREMENT OF STAND-OFF DISTANCE AND DRILLING FLUID SOUND SPEED WHILE DRILLING

摘要

An MWD measuring apparatus and technique using a single transducer mounted on an MWD drill collar near a tubular member, such as an upset or stabilizer blade. The minimum stand-off is the radial difference between the MWD drill collar and the tubular member when the drillstring is side-walled against the borehole wall. Control apparatus connected to the transducer determines elapsed time for each pulse transmitted towards and reflected from the borehole wall. A plurality of round-trip transit time (RTT) values are measured and the results statistically analyzed to identify and verify the RTT min value corresponding to the minimum stand-off distance. The RTT values may be analyzed directly or using histogram techniques. Once determined, the sound speed of the drilling fluid is calculated as twice the radial difference between the MWD collar and stabilizer blade or upset divided by the RTT min value. Also, the sound speed is used to calculate the stand-off distance corresponding to other RTT values, if desired.