Monitoring method for formation pore pressure while drilling based on rate of penetration

Accurate monitoring of formation pore pressure is a crucial foundation to adjust drilling parameters promptly and ensure safe drilling operations. Currently, domestic formation pore pressure monitoring while drilling is difficult and less accurate. In response, the near-wellbore formation pore pressure redistribution caused by drilling fluid flow during the drilling process was taken into consideration. The correlations among bottom-hole pressure difference, depth of drill bit penetration into the bottom rock and penetration rate were analyzed, and a model (penetration rate method) for monitoring formation pore pressure while drilling was derived and established. Finally, the monitoring results from the penetration rate method were analyzed and compared with the computation results obtained using d_c index method and rock strength method. The research results show that there exists a positive correlation between bottom-hole pressure difference and drilling fluid permeation intensity as well as penetration rate, while a negative correlation with the penetration depth of single tooth of the drill bit into the bottom rock. The single-point monitoring accuracy of the penetration rate method is consistently above 95%, with an average error as low as 1.63%, demonstrating its greater applicability. The research results can provide a theoretical support for the timely adjustment of drilling parameters, especially in narrow-density window intervals, ensuring the safety and efficiency of drilling operations.