Numerical Simulation on Channel Optimization of Drill String in Acoustic Transmission While Drilling
The research on the transmission characteristics of drill string is the key to complete the acoustic wave propagation. In view of the non-uniformity of various drilling tools and drill string sizes, a channel model is proposed in this paper, which is convenient to analyze according to the different drill string characteristics of each well. Then, the transmittance and reflection coefficient of joint structure to acoustic signal in downhole drill string channel is analyzed, and the vibration transmission relationship of the drill pipes’ channel is obtained. For the first time, the quantitative study on the relationship between the joint size and the frequency cycle period of the acoustic transmission is carried out, which shows that the joint length of the drill string in the combination of the periodic drill string and the frequency cycle period of the drill string channel have a fixed inverse proportion relationship. The results show that the frequency period of the channel can be reduced and the bandwidth of the passband can be increased to more than twice when a certain length of short drill collar is connected in series in the middle of the drill string. The channel model can be used in wells with different drill string sizes. By analyzing the actual channel characteristics of the well, and optimizing the channel in real time, the best acoustic transmission scheme for each well is provided.