Design of a near-bit downhole measurement system wlile drilling for wireline coring

Abstract:

When applied to core drilling， the traditional measurement methods while drilling are limited by the blockage of the mud pulse transmission channel by the core barrel. The measurement instrument are installed behind the core drilling assembly， resulting in a large distance between the instrument and the bit， which leads to significant lag in trajectory and operating condition data， and thereforea affects the precise control of drilling process and trajectory. A near-bit measurement system while drilling for wireline coring is proposed to address this issue. The system utilizes a near-bit transmitting unit to collect operating conditions and trajectory data in real time. The collected data is transmitted via very low frequency electromagnetic waves to be stored in a receiving unit connected to the core drilling assembly’s inner tube. After core extraction， the instrument is lifted along with the core barrel for data retrieval. This paper introduces the system’s overall scheme and circuit design， moreover， experiments for short-range transmission function are carried out. The results demonstrate that the system can achieve near-bit information transmission across the core drilling assembly downhole， with a wireless transmission distance of up to 8m. These research findings can serve as a reference for researchers in the field of near-bit measurement system while drilling.