Perpustakaan Digital ITB

This paper investigated the failure cause of phantom downlinks of a flow rate detection mechanism in a rotary steerable system and developed a prevention algorithm. Downlinking is the process of controlling a drilling tool from the surface by sending commands to downhole. Directional drillers send downlinks to the rotary steerable system to adjust steering parameters to achieve the desired well plan. The downlink demodulation of downhole tools is achieved through the measurement of flow rate and correlation of waveform with predefined command models; downlink acceptance is based on the correlation rate. One case study revealed that phantom downlinks were due to the variation of turbine rotation speed, which was the result of alternator load changes. A prevention algorithm of conducting a signal energy check was proposed and implemented. The algorithm can successfully prevent phantom downlinks that are usually of low-level energy and only accept authentic downlinks. The work improved the downlinking reliability of the rotary steerable system. This methodology can be further applied to other downlink demodulation mechanisms using collar speed or pressure measurement.