First, the blowout Causes
Looking at the various oil and gas field blowout instance, analyze the direct cause of the runaway well control can be broadly attributed to the following aspects.
(1) is not strong sense of well control, illegal operation.
① not install wellhead blowout preventer. Which is mainly one-sided understanding: First, one-sided pursuit workover cost savings, try to invest less workover equipment, occupy less depreciation; second, that is the old oil fields (or low formation pressure), does not occur blowout, no need to install the blowout preventer; Third, lack of well control equipment, only a special process to ensure that the focus of wells and wells; Fourth, think workover process is simple, no need to install the blowout preventer.
② installation and pressure testing of well control equipment does not meet the requirements.
③ empty well a long time, no one to observe the wellhead. Empty wells is generally too long since finished the column due to repair equipment, or other technical measures. As a long time can not be empty well workover fluid circulation, causing gas have enough time to slip upward migration. When the ship was too late to move to the next wellhead tubing, which does not work when the ram BOP, BOP ring, although they are not installed or installed but plastic core failure, often resulting in a blowout.
④ flushing is not complete.
⑤ can not be found, or found not timely overflow shut properly after the overflow.
(2) generate excessive force when pumping from the column. Since the column too fast such that pumping force generated is too large, especially when starting with a large diameter tool (packer, etc.) column, must be put on the speed control.
(3) from the string when no irrigation or no repair and filled with fluid.
(4) Construction design workover fluid density in the one-sided emphasis reservoir protection and use of small, resulting in wellbore pressure liquid column can not balance the formation pressure.
(5) casing design unreasonable and soundness poor. Some parts of the casing corrosion or other causes severe compressive strength declined significantly, as part of the shallow gas casing corrosion cracks caused by corrosion of shallow gas wells produce intrusion, invasion because of gas from the wellhead near the site, a small column pressure shallow oil and gas channeling fast, time is short you can reach the wellhead, it is easy to surprise. So, for a long time, well or production wells serious corrosion and has shallow gas wells, to special treatment.
(6) the design of geological formation pressure failed to provide accurate information, resulting in the use of low-density workover fluid, resulting in wellbore pressure liquid column can not balance the formation pressure, resulting in the formation fluid invasion wells.
(7) after the occurrence of lost circulation, failed to timely treatment or improper treatment measures. Since the occurrence of lost circulation, the liquid column pressure is reduced when the pressure is lower than the formation pressure liquid column wells invasion occurs, kick and blowout.
(8) injection well injection or decompression stop. After years of development due to oilfield water injection, formation pressure is not the original reservoir pressure, particularly when high pressure closed block, the pressure is often much higher than the original reservoir pressure. If you only consider the crude oil production plant yield, unwilling to quit adjacent injection wells, or to stop injection, but not relief, often result in complex and other workover blowout accident.

Second, the blowout hazards
Due to objective or subjective reasons, blowout happened quite frequently. The facts tell us a lot, underground blowout serious nature of the job, the loss of a huge catastrophic accidents, harm it causes can be summarized as the following aspects:
(1) damage to the device. Easily result in the formation or the entire device into the fire burned.
(2) casualties. Due to uncontrolled blowout fire or toxic gases emitted casualties.
(3) a waste of oil and gas resources. Uncontrolled blowout profuse only oil and gas, but also for the reservoir is difficult to calculate the energy loss can be said that the oil and gas reservoirs catastrophic damage.
(4) contamination of the environment. Spray oil and gas on the surrounding environment causing serious pollution, especially ejecta contain hydrogen sulfide (hydrogen sulfide containing products are Swivel joint, hammer union, high-pressure plug valves, high pressure Pup joint and Integral fittings, etc.) when upsets neighbors uneasy, panic.
(5) oil and gas wells scrapped. Blowout to the time can not be processed, and finally had to scrap the wellbore.
(6) cause significant economic losses to deal with blowout invested a lot of manpower, material and financial resources to the fire, killing, etc., but also other damages caused due to a blowout.