Underbalanced drilling technology.

Underbalanced drilling (UBD) conditions occur when the effective downhole circulation pressure of the fluid system in contact with the rock formation is lower than the existing formation pressure. The reduction in damage to the formation has potential benefits including increased production rate and ultimate recovery. The technology is becoming accepted as a standard method for handling the drilling and completion of wells. The benefits and limiting factors are discussed and the selection of fluid system is considered with reference to gas (air, nitrogen), mist, foam, gasified mud and liquid systems, whose effects on circulation, reservoir damage, sticking, drilling rate. hole cleaning, wellbore stability, water inflows, downhole fires and corrosion are considered.
Underbalanced drilling (UBD) conditions occur when the effective downhole circulation pressure of the fluid system in contact with the rock formation is lower than the existing formation pressure. The reduction in damage to the formation has potential benefits including increased production rate and ultimate recovery. The technology is becoming accepted as a standard method for handling the drilling and completion of wells. The benefits and limiting factors are discussed and the selection of fluid system is considered with reference to gas (air, nitrogen), mist, foam, gasified mud and liquid systems, whose effects on circulation, reservoir damage, sticking, drilling rate. hole cleaning, wellbore stability, water inflows, downhole fires and corrosion are considered.