Evaluation and Optimization of Acoustic Sources for Advanced Detection nearDrill Bits in Gas Drilling

To optimize the acoustic sources for advanced detection near drill bits in gas drilling environments, a near-bit acoustic ranging method was proposed. This method is specifically tailored for gas drilling conditions. Experiments were conducted on ultrasonic ranging, impact echo resonance ranging, sweep-frequency acoustic resonance ranging, and impact reflection wave ranging at various detection distances. The feasibility of these four types of acoustic sources for ranging was evaluated. The near-bit acoustic source suitable for gas drilling was optimized based on three factors: acoustic source characteristics, detection distance, and resolution. Experimental results indicate that when the ultrasound frequency is low and the tail wave is short, the reflected wave signal can be identified in the waveform received close to the acoustic wave emission source, but the detection range is limited. The frequency of the impact echo is highly influenced by lithology, which prevents the formation of an ideal standing wave between the incident and reflected waves, leading to significant errors in resonance ranging. The incident and reflected waves generated by sweep-frequency acoustic sources form relatively ideal standing waves, resulting in smaller ranging errors. However, this requires high low-frequency performance of the sweep-frequency generator. The preferred impact source can effectively detect lithological interfaces, and its tail wave experiences significant attenuation, which is beneficial for identifying reflected wave signals from the formation in the time domain. The results show that the preferred impact source offers advantages such as strong impact energy, low frequency, and short tail wave, which meet the acoustic source requirements for advanced detection under gas drilling conditions.