Well blowout is an uncontrolled release of flowing fluids (e.g., gas, oil, water, and mud) from a well once pressure control systems such as BOP Stack are completely lost. This uncontrolled flow will end up with a well kick that increases in severity and may result in a “blowout”. The well control can only be recovered by:
- Installing or replacing equipment to permit shut-in.
- Killing the well.
- Drilling a relief well.
It can happen during any of the operational phases:
- Drilling phase.
- Well testing.
- Well completion.
- Production.
- Workover.
Factors Lead To Well Blowout
Many factors cause blowouts. Among those factors, the enormous pressure of the rock formations around an oil reservoir is the most important of all other factors. In general, oil transpires naturally over millions of years, and water is compressed and pressurized during this process. The process happens with the carbon-based substance (e.g., life forms of one type or another) by the sediment layers forming a composite hydrocarbon-bearing zone. Therefore, drillers must take special care when drilling into the rock formation. While drilling, this pressure is offset by using proper drilling mud in the drill string to balance the hydrostatic pressure. If the pressure maintenance is not properly kept, the formation fluid (e.g., water, gas, or oil) can infiltrate the wellbore, quickly escalating into a well blowout if not promptly identified and addressed.
If a kick is detected, the first step is to isolate the formation fluid entry point by closing in the well, thus reducing the chances of a blowout. A heavier fluid will then be introduced to try to raise the hydrostatic pressure and achieve a balance. Meanwhile, the fluid or gas infiltrating the wellbore will slowly be evacuated, controlled, and safely.
Types Of Well Blowouts
There are three main types. They can happen anytime during the drilling process and have devastating consequences. We can classify them as (i) surface blowout, (ii) subsea blowout, and (iii) underground blowout.
Surface Well Blowout
It is the most common type and can expel the drill string out of the well. Sometimes, the force of the formation fluid can be strong enough to damage the drilling rig and surrounding territory. It can also seriously damage the whole area through ignition and explosion. In addition to oil, the output of a well blowout might include natural gas, water, mud, sand, rocks, and other substances. A blowout can happen from sparks of rocks being ejected or simply from heat generated by friction.
Sometimes, blowouts can be very severe and thus become impossible to control directly from the surface, especially if there is huge energy in the formation zones, which do not deplete considerably over time. In such cases, other nearby wells (i.e., relief wells) are drilled to allow the kill mud to reach the desired depth. A surface blowout cannot be controlled alone if it is particularly powerful. Other nearby wells (relief wells) are drilled to introduce heavier balancing fluid at depth.
Underground Type
an underground well blowout is not a common one where fluids from high-pressurized formations flow uncontrolled to lower pressure zones within the wellbore. It may not necessarily result in the release of oil above ground. However, the formation fluid influx at the wellbore can become overpressured, which should be considered during future drilling program plans at the same formation.
Underwater Type.
Because of their location, underwater well blowouts are the most difficult to deal with. The biggest and deepest one in history occurred in 2010 at the Deepwater Horizon well in the Gulf of Mexico. The accident was so serious that it forced the industry to anticipate reevaluating its safety procedures.
Conclusion
In short, well control is considered one of the most crucial aspects in drilling a gas and oil reservoir. In fact, it affects the overall cost of the well completion, and sometimes it leads to fatalities and numerous or great environmental damage. Human errors and equipment failure are the cause of well blowouts, which are uncontrolled by the formation fluids, so well control becomes the most important aspect.
In addition, well monitoring is an important aspect of drilling and production. It gives us a view of what is happening downwards in the well. That is to say, the necessity for the early detection and control of these kicks, losses, and also other abnormal circumstances while drilling is becoming essential as industry drilling has increased in areas that have a challenging environment onshore and offshore as a result of difficulties concerning pressure regimes and equipment stresses. Also, drill string monitoring is an important aspect of well control.