Complicated well control problems could be divided into two categories: the conventional well control method in which the bottom hole pressure can always be kept equal to the formation pressure during the killing operations and \ill\ the unconventional method in which the pressure can not be in equilibrium with the formation pressure. Three kinds of unconventional well control methods: low choke pressure method, killing an empty well and killing a blowout well are discussed in this paper. The formation, borehole and wellhead are considered as a communicating system, in which the three are influenced and restrained by each other. Based on reservoir gas filtration mechanism in steady and unsteady states, the basic principles of unconventional well control have been studied, and the related mathematical models and calculating methods have been established. The calculation results, have been compared and checked with laboratory experiments and field data(1).

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