Isubs: A New Generation of Autonomous Instrumented Downhole Tool

摘要

The paper describes a short autonomous instrumenteddownhole tool (Isub) which incorporates multiple sensors(accelerometers, strain gauges, and magnetometer), a completedata acquisition line, a microprocessor, memory chips andbatteries. The tool, available in three sizes (7”, 9” and 10” 1/4)can be located anywhere within the BHA even behind a mudmotor or rotary steerable system as its total exposed length isof 350 mm. The tool records at a scanning rate of 50 Hz (up to250 Hz) several tens of hours (100 to 300 hours) forces,moment as well as centripetal, tangential and axialaccelerations used to reconstruct the instantaneous bitkinematics (RPM, off axis rotation, side acceleration).Due to its high scanning rate and precision (each sub is fullycalibrated) on all channels, the Isub has many benefits, itoffers a complete vibration diagnosis: nature (torsional, lateral,axial) , amplitude (stick-slip, backward and forward whirl,bouncing), susceptibility to surface control parameters (WOB,RPM), tracking of bit efficiency and wear, and assessment ofdownhole equipment “real” performance: hydraulic motor orturbine (power delivered, staling events), rotary steerablesystem (side force, vibrations).This paper illustrates by two examples some of the insight tothe drilling response of the system such tool can provide. Thedata reveal the occurrence of phenomena (vibrations, motorperformance) neither detected nor suspected on surface. It alsocaptures all inappropriate drilling practices.The analysis shows strong evidences of the tremendouspotential of such tool not only to gain a better understandingof the drilling process but also to provide a non-bias measureof the drilling performance. Eventually, such tool should helpin improving drilling performance and build best drillingpractices rules.