11- Why Preventative Well Control is Essential in Well Planning

The term "Well Control Situation" is always associated with disastrous and severe consequences. In reality this proves to be inaccurate. A Well Control situation is an undesired flow of formation fluid (oil, gas, and in some occasion water) into the wellbore. This flow might result in a significant drop of hydrostatic pressure which causes more fluid to enter the wellbore. A widely used term in the industry is a "kick". Mismanaged kicks can lead to a more sever condition called blow-out.

How To Respond When There Is Doubt of a Kick?

Without having a second thought, if in Doubt, shut-in the well using the blow-out preventer and observe pressures. If a kick is confirmed, well killing operation should take place without any further delays.

What Is The Difference Between a Well Control and a Blow-Out?

A Well Control Situation is an unintentional and undesired flow of formation fluid (Oil, Gas, or Water) into the wellbore. A blow-out an unintentional and uncontrolled release of hydrocarbon fluids (oil or gas) to the atmosphere. A blow-out requires highly experienced personnel and sophisticated equipment and techniques to regain control of the well.

Well Control and Blow-Out are two distinct terms. this article touches ONLY on Well Control Situations.

What Causes a Well Control Situation?

We have categorized the main causes of well control situations under four categories:

Human Error

• Failure to maintain fluid level in the hole while pulling out of the hole (POOH). This occurs because the pumped drilling fluid doesn't compensate for the metal displacement

• Swabbing a kick. Usually happens when POOH at high speed with heavy and/or viscous mud in the hole. Also, a packed BHA and/or slim hole might contribute to severity of the situation

• Surging. Formation might breakdown due to the surge pressure which results from RIH at excessive speed. The lost fluid will result in a drop in hydrostatic pressure

• Unprepared to drill into high pressure and permeable zones. Example could be failure to raise mud weight prior penetrating such zones

• Failure to properly recognizing TVD, and/or mud programs not taking TVD into account resulting in miscalculating required mud weight

• Failure to operate, inspect or maintain vacuum degasser

Procedure

• Poor well design and or improper casing setting selection

• Selected Mud weight is not enough to maintain formation pressure

• Excessive penetration rates in porous and permeable formations, resulting in an increasing amounts of gas cut mud

• Lack of proper Preventative Well Control Training

• Failure to replace ECD margin when tripping

• Trip margin too low in the drilling program

Equipment

• Failure or inefficient vacuum degasser operation

Geological Anomaly

• In some occasions, a geological structure might result in an unusual accumulation of high pressure fluids. This anomaly couldn't have been identified with the existing set of data.

Final Words

Well Control Situations are usually caused by factors that are under the direct control of people. Establishing and following a complete Well Engineering Management System is a necessity. it ensures a:

• Comprehensive Basis of Design document

• Detailed Drilling Program and Drilling Instructions

• Proper Preventative Well Control measures

• Proper personnel training and competency enhancement

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