Primary Well Control
The conventional way of drilling is to maintain an overbalance where the pressure (force per unit area) in the wellbore while drilling is maintained above the formation pressure. The difference between the hydrostatic pressure of drilling fluid in the well and the fluid pressure in the formation is called 'Overbalance'. This hydrostatic pressure prevents reservoir fluid from flowing into the wellbore during drilling operations and is called the 'Primary Well Control' mechanism. A kick, also known as a wellbore influx, can occur when primary well control fails.