气体钻井近钻头超前探测声源评价与优选

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

  • 摘要: 为了优选适用于气体钻井条件下的近钻头超前探测声源,提出了气体钻井条件下近钻头声波超前测距方法,进行了不同探测距离下的超声波测距、冲击回波共振测距、扫频声波共振测距、冲击反射波测距试验,分析了4类声波测距声源的可行性,并从声源特征、探测距离、分辨率3个方面优选了适用于气体钻井的近钻头声源。试验验结果表明:当超声波的频率较低且尾波较短时,可从靠近声波发射源接收到的波形中识别出反射波信号,但探测距离近;冲击回波频率受岩性影响较大,导致入射波与反射波之间未形成理想的驻波,其共振测距的误差较大;扫频声波产生的入射波和反射波可形成较为理想的驻波,测距误差较小,但对扫频发生器的低频性能要求高;通过试验优选出的冲击震源可用于探测岩性界面,该冲击震源的尾波被显著衰减,有利于识别时域内的地层反射波信号。研究表明,优选出的冲击震源具有冲击能量强、频率低、尾波短的优势,可满足气体钻井条件下超前探测的声源要求。

     

    Abstract: 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.

     

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