Method and apparatus for gravel packing with a tool that maintains a pressure in a target wellbore section

A method and apparatus for performing a gravel pack operation includes a bypass mechanism (e.g., a bypass valve) that is actuatable between plural positions. The bypass mechanism is part of a tool assembly, with the bypass mechanism providing different flow paths through the tool assembly corresponding to the plural positions of the bypass mechanism. For example, if the bypass mechanism is in a first position, an elevated pressure is communicated from an annular region outside a tool string to a target wellbore section. On the other hand, if the bypass mechanism is in the second position, the elevated pressure is communicated from inside the tool string to the target wellbore section. In either position, an overbalance condition is maintained in the target wellbore section so that swabbing effects are reduced or eliminated due to movement of the tool assembly during a gravel pack operation.