What Is a Blowout Fracture?

Well blowout is a phenomenon in which the pressure of formation fluids (oil, natural gas, water, etc.) in the drilling process is greater than the pressure in the well, and a large number of surges into the wellbore, and the phenomenon of uncontrolled discharge from the wellhead. However, blowout accidents are caused by injuries and property damage caused by huge pressure and shock waves during the eruption. A blowout accident is a very harmful drilling accident. Once it occurs, it often has serious consequences, and strict precautions must be taken. When a well rush occurs, the main well must be closed quickly and accurately to control the wellhead and prevent blowout accidents.

Blowout accident

The blowout was caused by drilling

In oil and gas exploration,

(1) the drill bit breaks the gas in the rock pores;

(2) Gas released from the cuttings due to the gradual decrease in pressure during the upward return process;

(3) Gas that diffuses or immerses directly into the wellbore during drilling;

(1) Bit diameter: The larger the bit diameter, the more rock that is broken during the drilling process.

Blowout accident normal compaction

When encountering normal compacted formations, the formation pressure is equal to the drilling fluid pressure. The gas in the mud comes from the gas in the pores of the broken rock cuttings of the drill bit, and the gas released from the cuttings during the return of the cuttings and the formation into the mud. Diffused gas; the detected single gas varies depending on the energy of the open oil and gas layer. This single gas does not change much each time; sometimes because the formation energy is low, the display is not good. Not observed.

Blowout accident undercompacted formation

In the normal drilling process, when drilling into an under-compacted formation, the formation pressure is greater than the drilling fluid pressure. The gas in the mud comes from the gas in the pores of the broken rock cuttings of the drill bit. The rock cuttings are released as the pressure decreases during the return process. Gases and formations diffuse and immerse into the mud. The single gas detected at this time is mainly the gas immersed in the formation into the mud. As the single gas continues to be pumped, more fluid is immersed in the formation into the wellbore, and the single gas Large, this is the front picture of the occurrence of well surge and blowout. At this time, we should pay more attention and take measures to prevent accidents.

In June 2002, after drilling through the reservoir, Bao 2417, Baolang Oilfield, Yanqi Basin, Xinjiang, drilled quickly. When drilling to 2516.38 meters, a single root was connected. After the pump was turned on, a single gas was apparent on the recorder. Before opening the oil and gas layer, it is not obvious to connect a single gas; when drilling to 2525.73 meters, it is more obvious than 2516.38 meters, and then it becomes larger and larger; during the whole process, the total mud volume and displacement do not change significantly. When drilling to 2562.18 meters, At one time, a well surge occurred.

Limitations of blowout accidents

When using a single gas to judge a well surge or blowout accident, you must not detect formation pressure changes at any time when you connect a single gas. Compared to using a volume sensor to detect formation pressure, there is a certain hysteresis; moreover, when underpressure When the formation energy is too large, it is more time-consuming to receive a single gas; this method is suitable for under-compacted formations where the amount of energy is not very large, and it is more effective when it is not detected by the volume sensor. Surge and blowout accidents.