Use and Validation of Electrical Measurements in MWD Drillings-Paper

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The paper evaluates electrical measurements for Measurement While Drilling (MWD) using a prototype geotechnical rig that replaces a combustion engine and hydraulic systems with electric motors. Monitoring motor current and voltage provides a direct basis for estimating drilling forces and torque, potentially improving accuracy over indirect hydraulic-pressure measurements. Electrification also reduces noise and fuel use.<br /><br />Five investigations, three presented in detail, were conducted in Osthoffen, France. Continuous flight augers drilled to depths of 6–9 m, alongside pressuremeter testing. The study compared drilling parameters and calculated indices—including Specific Drilling Energy (SDE) and the Somerton index—with soil descriptions and pressuremeter results. A moving-median filter was used to remove abnormal values, particularly those associated with pauses to extend the drill string.<br /><br />The profiles generally comprised shallow silty and gravelly sand fill, loess, and underlying clay. In the loess, torque and SDE increased as drilling resistance and pressuremeter measurements rose; both became more stable in the clay. The Somerton index remained comparatively constant and did not reflect these changes. Results suggest that torque, and the SDE incorporating it, best captured the response of fine-grained soils during auger drilling. By contrast, drilling parameters did not correspond well with pressuremeter readings in the coarse-grained fill.<br /><br />The authors conclude that electrical measurements yield interpretable drilling logs comparable to those from conventional rigs, with promising correlations in cohesive soils. Further work is needed to determine how much measured torque is consumed by friction between the auger and borehole wall, and to assess performance in granular soils.

Keywords

measurement while drilling

electrical measurements

prototype geotechnical rig

specific drilling energy

torque

motor current

pressuremeter testing

continuous flight auger

loess

soil resistance