Evaluation and optimization of acoustic sources for advanced detection near drill bits in gas drilling

To optimize the near-bit advanced detection sound source suitable for gas drilling conditions, a near-bit acoustic advanced ranging method is proposed specifically for gas drilling environments. Ultrasonic ranging, shock echo resonance ranging, sweep frequency acoustic resonance ranging, and impact reflection wave ranging experiments were conducted at different detection distances. The feasibility of these four types of acoustic ranging sound sources was analyzed. The near-bit sound source suitable for gas drilling has been optimized based on three aspects: sound source characteristics, detection distance, and resolution. The experimental results indicate that when the frequency of ultrasound is low and the tail wave is short, the reflected wave signal can be identified in the waveform received close to the sound wave emission source, but the detection range is limited. The frequency of the shock echo is significantly influenced by lithology, which prevents the formation of an ideal standing wave between the incident and reflected waves, resulting in large errors in resonance distance measurement. The incident and reflected waves generated by swept-frequency sound source can form relatively ideal standing waves, resulting in small ranging errors. However, this demands high low-frequency performance from the swept-frequency generator. The preferred impact source can be used to detect lithological interfaces, and the tail wave of the impact source is significantly attenuated, which is beneficial for identifying formation reflection wave signals in the time domain. The conclusion is that the preferred shock source has the advantages of strong shock energy, low frequency, and short tail wave, which can meet the sound source requirements for advanced detection under gas drilling conditions. The research results provide a basis for the optimal selection of sound sources for acoustic advanced detection under gas drilling conditions.