An uncontrolled flow of gas, oil, or other well fluids into the atmosphere or into an underground formation.
A blowout, or gusher, can occur when formation pressure exceeds the pressure applied to it by the column of drilling fluid.
An uncontrolled flow of reservoir fluids into the wellbore, and sometimes catastrophically to the surface.
A blowout may consist of salt water, oil, gas or a mixture of these.
Blowouts occur in all types of exploration and production operations, not just during drilling operations.
If reservoir fluids flow into another formation and do not flow to the surface, the result is called an underground blowout.
If the well experiencing a blowout has significant openhole intervals, it is possible that the well will bridge over (or seal itself with rock fragments from collapsing formations) downhole and intervention efforts will be averted.