Well control refers to kick control or pressure control. The various names are essentially the same, all of which are to explain that certain methods are required to control the formation pressure, basically maintain the pressure balance in the well, and ensure the smooth progress of the operation and construction.
According to the scale of well kick and the different control methods, well control operations are divided into three levels, namely primary well control, secondary well control and tertiary well control.
Primary well control is the drilling (workover) process in which the bottom hole pressure is slightly higher than the formation pressure by means of appropriate drilling (workover) fluids and technical measures to control the formation pressure so that no formation fluid enters the well. The well kick is zero, and naturally there is no overflow.
Two-level well control means that overflow occurs when the bottom hole pressure is lower than the formation pressure for some reasons, but wellhead control equipment can be used to control the overflow according to certain operating procedures and establish a new bottom hole pressure. Equilibrium, the process of restoring normal circulation and bringing it back to primary well control.
Three-level well control refers to the process of restoring the control of the well by using appropriate technology and equipment to rescue the well after the blowout is out of control. This is commonly referred to as blowout rescue, which may require various specific technical measures such as fire fighting and rescue wells.