Active control method and control device for wellbore pressure in the open-cycle drilling of marine natural gas hydrates

摘要

An active control method and control device for wellbore pressure in the open-cycle drilling of marine natural gas hydrates comprises following steps: (1) optimized design of drilling parameter; (2) carry out open-cycle drilling according to the designed drilling parameters; (3) utilize the APWD to monitor the bottom-hole temperature and the bottom-hole pressure in real time for real-time correction of the wellbore annulus temperature and pressure calculation models; determine whether a hydrate decomposition has occurred in the annulus and then infer whether a shallow gas intrusion has occurred in the bottom hole; (4) Intelligent active control: control and adjust the mixed density of drilling fluid, the injection displacement of drilling fluid as well as the injection temperature of drilling fluid and the pump pressure in wellhead automatically during the well killing based on the real-time treatment results of the computer terminal for the signal fluctuations detected by the APWD.