What is Blow-Out?

In the previous blog we discussed about what is kick and its occurrence. Drillers play a major role in detecting and handling the kick. 

As discussed, if the early warning signs of kick is unnoticed by the driller, more and more kick enters the wellbore. As the kick is always lighter than the drilling mud, its presence in wellbore further reduces the bottom hole pressure (BHP) of the wellbore. The further reduction in BHP encourages further flow of kick in the wellbore but now with more strength than before! It rushes into the wellbore with maximum available strength, offloading the mud from the well. The offloading of mud by the kick can be observed on flow line. The volume of mud coming out of well through flow line increases. This increases the percentage of flow out through flow line. The flow-out percent can be read by the driller on his console.

Along with flow out percent, we also have an option to set alarm for flow-out. Once can set an upper and lower limit alarm for flow-out. If the flow equals or crosses the limit, the alarm is activated and the driller and other nearby crew member comes to know that the flow-out percent has changed and some required action is to be taken.

The next question which arises is: "Is increase in return flow (flow-out) the only sign of kick?

The answer is NO. There are several other signs which can warn or confirm the presence of kick. To make things easy, we can divide the signs and symptoms in two categories: (a) Early Warning Signs of Kick (b) Positive Signs of kick. We shall discuss on these topics in depth in coming blogs.

So lets get back to the situation where the wellbore got a kick and the driller has yet not detected any sign of kick on surface. Now, three situations may arise:

i. Driller fails to detect any sign or symptom of kick, kick reaches upto surface

ii. Driller detects the kick sign and symptom, successfully closes the Blow Out Preventer (BOP) 

iii. Driller detects the kick sign and symptom but the BOP system malfunctions and the well cannot be closed.

SITUATION (i)

The first situation shows a condition where driller fails to detect any sign of kick and is working in a relaxed mood as if 'All is going well'. At the same time, slowly, the kick enters the wellbore in increasing fashion. A situation may arise where the pressure exerted by the mud column is incapable to control and push the formation fluid down into wellbore. And suddenly, BOOM!! The kick reaches the surface with maximum potential, the wellbore is completely filled with kick. It rushes out of wellbore, passing through blow out preventer opening, out through the rotary opening. If the formation pressure is high, it will act like an uncontrolled dragon. A high potential kick can destroy entire rig unit in minutes.

The situation is something similar to the image below:

What happens next?

The answer to this question is "How experienced is your Driller?". If the Driller is well experienced, he can try to close the well even in this situation. He simply has to somehow reach the BOP control panel and try to close BOP. If BOP functions properly, the well can be successfully closed. But if the Driller is inexperienced, he will panic for sure!

If the Driller is unable to shut the well, the kick becomes uncontrolled and we say that there is a blow-out. The uncontrolled flow of formation fluid from the wellbore is called Blow-out. In short, Blow-out is uncontrolled kick.

Remember, a kick will for sure give you goose bumps in the first encounter!

SITUATION (ii)

In the second situation the Driller detects the kick sign and symptom in later stage and somehow manages to successfully closes the Blow Out Preventer (BOP). Once the BOP is successfully closed, the situation is under our control. The well can be killed using well killing methods.

SITUATION (iii)

In the third situation, the Driller detects the kick sign and symptom and immediately tries to close the BOP but the BOP system malfunctions. In simple language, the BOP fails to close the well. Again, things become similar to situation (i). The kick becomes uncontrolled and we have a blow-out! Similar was the case of Mocondo Blow-out. The BOP stack failed to close the wellbore and the result was as stated in figure below.

Figure: The Deepwater Horizon oil spill (also referred to as the BP oil spill, the BP oil disaster, the Gulf of Mexico oil spill, and the Macondo blowout) began on 20 April 2010 in the Gulf of Mexico on the BP-owned Transocean-operated Macondo Prospect. It claimed eleven lives and is considered the largest accidental marine oil spill in the history of the petroleum industry. The US Government estimated the total discharge at 4.9 million barrels (210 million US gal; 780,000 m3).

REMEMBER,

1. Once the wellbore has taken a kick, it continuously gives to signal at surface. Keep monitoring the drilling and mud parameters on regular interval.
2. The more early you detect the kick, the more easy is to kill the well.
3. If the kick has reached the surface, DO NOT PANIC!
4. Do not risk your life to close the well or control the kick.
5. When the situation seems out of control, evacuate the place.