气体钻井声波超前测距方法与数值模拟

气体钻井的安全性受储层地质条件影响明显，在钻井过程中，受气体所产生噪声影响，地层反射信号识别难度大。为提高探测准确度，降低气体钻井过程中钻头前方岩性界面的不确定性，设计了近钻头随钻冲击震源短节，基于地震波自激自收原理，提出了一种适用于气体钻井的声波超前测距方法。通过冲击试验分析聚四氟乙烯对振动尾波的衰减效果，通过数值模拟验证气体钻井声波超前测距方法的可行性，分析探测距离对反射波振幅的影响。冲击试验表明，使用聚四氟乙烯后空心圆柱上振动尾波衰减显著。数值模拟结果表明，PML边界条件可有效消除模型边界反射的干扰，利用反射纵波信号到达时间所计算测距的误差为1 m。随着探测距离增大，反射纵波相对强度逐渐增大，反射波振幅显著降低。研究结果验证了近钻头冲击震源探测钻头前方岩性界面的可行性，为气体钻井随钻声波超前探测技术的发展提供了新思路。 

Acoustic Advance Ranging Method in Gas Drilling and Its Numerical Simulation

The safety of gas drilling is greatly influenced by local geological conditions of reservoirs. It is difficult to identify formation reflection signals in gas drilling due to the influence of noise generated from gas. Therefore, a near-bit impact source sub while drilling was designed, and a method of acoustic advance ranging for gas drilling was proposed on the basis of the self-excitation and self-reception principle of seismic waves. In this way, measurement accuracy could be raised, and the uncertainty of lithological interfaces ahead of the bit could be reduced. Specifically, the attenuation effect of polytetrafluoroethylene (PTFE) on vibration coda waves was analyzed through an impact test; the feasibility of the acoustic advance ranging method in gas drilling was verified through numerical simulations, and the influence of detection distance on the amplitude of reflected waves was analyzed. The impact test revealed that the coda waves of vibration waves on the hollow cylinder were significantly attenuated upon the use of PTFE. Numerical simulations indicated that the boundary conditions of a perfectly matched layer (PML) can effectively eliminate the interference of boundary reflection of the model, and the ranging error calculated from the arrival time of reflected P-waves was 1 m. In addition, the relative intensity of reflected P-waves shows a gradual increase, and the amplitude of reflected waves decreases greatly as the increase in detection distance. The research results verify the feasibility of detecting lithological interfaces ahead of the bit by near-bit impact sources and provide a new idea for the development of acoustic advance detection technology while drilling in gas drilling.