An experimental rig for near-bit force measurement and drillstring acoustic transmission of BHA

An experimental rig for near-bit force measurement and drillstring acoustic transmission of bottom-hole assembly (BHA) is designed and implemented to investigate downhole dynamic behaviors of BHA. By using a developed dynamic force sensor device with a four-straight beam strain gauge, the rig can measure axial, lateral forces and torques exerted on simulated drillstring while rotating. For the upward transmission of downhole dynamic force data, drillstring acoustic telemetry method is further analyzed by transient numerical simulation. Considering acoustic signal attenuation and transmissibility, a narrow pulse on–off keyed modulated time-delay signal transmission method is developed. The near-bit force measurement experiments of BHA are performed under different weight on bit loads, deviation angles and drill pipe combinations. The obtained force data are transmitted via acoustic waves propagating along the simulated drillstring. The results show that acoustic transmission rate is approximated 77 bit/s along 6.4-m simulated drillstring under 1-W power excitation in the laboratory.