A novel method for wireless telemetry during air drilling based on air pressure pulses

Utilization of air drilling and horizontal well drilling is theorized to be one of the most effective methods for drilling in tight sandstone reservoirs. However, only a few horizontal wells were successfully drilled with air over the decades. One major setback is the lack of an effective downhole wireless telemetry technique. This study offered an innovative solution to wireless telemetry in air drilling, which is called as air pressure pulse telemetry, wherein the downhole decoded information is transmitted via air pressure pulses signals. For the method to work, an air pulse generator was designed to create sufficiently strong positive pulses at the bottom of the well for telemetry. The generator can totally cut off air flow when closed. Theoretically, pressure pulses of any intensity can be generated on demand. Unipolar return to zero (Unipolar RZ) modulation was applied herein for signal modulation. Baseband filter and differential processing technique were used to cancel the noise and enlarge the weak signals, and a method of threshold line is used to decode the signals. To evaluate the performance of the method, a laboratory experimental set was built, and all the sub-methods, such as air pulses generator, signal modulation, noise cancellation, data decoding methods, were tested. The results show that the pulse generator can create sufficiently strong pressure pulses on demand, while signals can be successfully captured and decoded after transmission 2000 m. The experimental results have confirmed the functionality of the novel method of air pressure pulse telemetry. Increasing operating pressure can both create stronger pressure pulses and reduce the attenuation of pulse signals. Reducing the time slot can improve the transmission rate, but it can also cause severe signal attenuation, ultimately leading to telemetry failure. Based on our results, it is recommended that the time slot be no less than 4 s. The proposed method provides a new pathway to achieving reliable wireless telemetry in air drilling. The method was compared with the existing wireless telemetry, and some potential challenges and future research directions were also discussed.