Referring to the previous section, primary well control is hydrostatic pressure bore that prevents reservoir influx while performing drilling operations (drilling, tripping, running casing/completion, etc). When primary well control is failed, it causes kick (wellbore influx) coming into wellbore. Therefore, this situation needs special equipment which is called “Blow Out Preventer” or BOP to control kick.
Well, we can call that “Blow Out Preventer” or BOP is Secondary Well Control. Please also remember that BOP must be used with specific procedures to control kick such as driller method, wait and weight, lubricate and bleed and bull heading. Without well control practices for using BOP’s, it will just be only heavy equipment on the rig.
There are several types of “Blow Out Preventer” (BOP) which have different applications. I will talk about BOP categories later.
Well Control Book 
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