A triangular electrode triboelectric nanogenerator for monitoring the speed and direction of downhole motors

Downhole motors are essential in providing rotational power to the drill bit and achieving the desired trajectory of the wellbore, making them the most reliable component of the bottom-hole assembly. Monitoring their speed and direction is critical to improving drilling efficiency. In this paper, we propose the use of a triangular electrode triboelectric nanogenerator (T-TENG) for monitoring downhole motor speed and direction. The T-TENG employs triangular copper foils as the electrode layer and can determine the direction of rotation based on the transient characteristics of the output signal. Experimental results show that the T-TENG exhibits a measurement error of less than 3 % for speeds within the monitoring range of 0-1200 rpm, and demonstrates good linearity. To enable real-time detection of the downhole motor's instantaneous speed, we introduce an instantaneous speed algorithm based on MATLAB. The average speed curve is obtained by fitting the instantaneous speed using variational mode decomposition (VMD) analysis. Furthermore, the T-TENG exhibits impressive power generation performance and can simultaneously power a low-power temperature and humidity sensor and 436 seriesconnected light-emitting diodes (LEDs). Compared to conventional downhole sensors, the T-TENG obviates the requirement for an external power source and enables simultaneous measurement of speed and direction. Hence, it offers a fresh perspective for the advancement of next-generation downhole sensors.