In 1985, the Soviet Union suffered its biggest oil blowout, causing a loss of 34 million barrels of oil. The oil gushed 150 meters above the ground and set off a fire. The Soviet Union's emergency mobilization of the best experts and fire brigades could not do nothing about it, and the blowout lasted for 13 months until the arrival of American expert Reed Adel. He digs another pipeline, connects it to the accident drilling, pumps special liquid into the pipelineand terminates the blowout.

In December 2003, a blowout accident occurred in No. 16 well of Luojiazhai in Northeast Sichuan Gas Field, CNPC. The highly toxic hydrogen sulfide took 243 lives, more than 4,000 people were poisoned and 100,000 people were evacuated overnight, and the direct economic loss amounted to 64.3231 million yuan.

Later, the expert appraisal of the State Council Accident Investigation Team identified that the removal of back-pressure valve by relevant personnel in the drilling assembly was the direct cause of blowout out of control.

The above major accidents make us understand that the most significant risk in drilling is well control risk. If wellhead pressure is controlled improperly, unpredictable accidents will occur. Therefore, it is essential to check and maintain well control equipment to prevent downhole and wellhead failures or risks. In particular, the inspection and pressure test of choke manifold and kill manifold are very important.

Once any connection problem of manifolds is found, it is necessary to tighten immediately to ensure the normal connection of manifolds, and to check and maintain the integrity of gas separators, so as to prevent explosion accidents caused by excessive gas and affect the smooth operation of oil drilling. In addition to manifolds and separators, regular inspection and maintenance will be also need for remote consoles. Staff should check the operation of various instruments, collect and analyze drilling construction data in real time. Only by ensuring the normal operation of various control systems, can the safety of the whole process of oil drilling construction be guaranteed.