Abstract: A straight beam strain gauge sensor and a virtual instrument-based dynamic force wireless measurement device of simulated drill string are developed to study the near-bit bottom drill string dynamics in measurement while drilling. The structure and working principle of the measurement system are expressed. The axial forces, radial forces and torsional moments for rotating simulated drill string are detected multithreadedly in the laboratory. By comparing downhole data transmission methods, an acoustic transmission experimental device is established via longitudinal waves along simulated drill string. Then, the on-off keyed (OOK) modulation of time-delayed pulses is designed. The narrow pulse modulated signal transmission experiments are performed by applying the longitudinal excitation to the length-limited simulated drill string in the axial direction of pipes. The results show that the pulse time-delayed and OOK modulated dynamic force data transmission of bottom drill string is implemented by using low frequency acoustic waves along the simulated drill string channel in the laboratory, which provides the theoretical and experimental basis for the application of low-frequency acoustic transmission system of near-bit sensor measurement data.

Key words: Acoustic transmission, Bottom drill string, Dynamic force, Near-bit, Periodic pipe structure