Blowouts
A blowout is an uncontrolled flow of gas, oil, or other well fluids occurring when formation pressure exceeds the pressure applied to it by the column of drilling fluid.
Blowouts may occur when the formation fluid pressure exceeds the hydrostatic pressure of the circulating fluid in the well annulus such as the totally unexpected encountering of unpredictable pressures and/or when mechanical controlling methods (e.g., blowout preventers (BOP's) or other pressure-control techniques) fail through misuse, misapplication, or malfunction. During a drilling operation, the mud serves as the first control method.
Most wells are drilled in oil fields with predictable formation pressures. BOP's selected to be compatible with these pressures are installed as soon as the surface casing is in place. BOP's function by sealing off the well bore. A series of hydraulic (and some manual) rams activated from ground level (not on the derrick) seal and contain the formation pressures.
A kick is the entry of water, gas, oil, or other formation fluid into the well bore. It occurs because the pressure exerted by the column of drilling fluid is not great enough to overcome the pressure exerted by the fluids in the formation drilled. If prompt action is not taken to control the kick or kill the well, a blowout will occur.
If the kick is not noticed in time or the techniques used to control the formation pressures are not adequate, then a blowout occurs. Since blowouts and subsequent fires involve the loss of equipment and time (as well as employee exposure to extremely hazardous conditions), the industry usually takes great care to prevent their occurrences.
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3-6. When may blowouts occur on a wellsite?
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