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Methods and systems are provided for drilling a well bore 60 through a subterranean formation using a drilling rig 25 and a drill string 50, whereby the bottom hole pressure while circulating drilling fluid ("ECD") may be substantially maintained when circulation is interrupted or altered, such as w

Methods and systems are provided for drilling a well bore 60 through a subterranean formation using a drilling rig 25 and a drill string 50, whereby the bottom hole pressure while circulating drilling fluid ("ECD") may be substantially maintained when circulation is interrupted or altered, such as when adding a joint of drill pipe to or removing a joint of drill pipe from the drill string. The method includes controllably applying and maintaining a desired variable annulus fluid pressure in the well bore, and thereafter controllably releasing the pressure from the well bore 60. In addition, methods and systems are provided for rotating the drill string while trapping, maintaining and/or releasing the well bore pressure. A substantially constant ECD pressure may be maintained on a formation, thereby facilitating the use of a lower density drilling fluid than may otherwise be required to maintain well control. In one embodiment, a drill pipe connection may be made up and/or broke out while the drill string continues to rotate.

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1. A method of drilling a well bore through a subterranean formation using a drilling rig and a drill string having a through bore and including interconnected joints of drill pipe, the method comprising:providing a rotating BOP to maintain a desired variable annulus fluid pressure within a well bor

1. A method of drilling a well bore through a subterranean formation using a drilling rig and a drill string having a through bore and including interconnected joints of drill pipe, the method comprising:providing a rotating BOP to maintain a desired variable annulus fluid pressure within a well bore annulus between the drill string and the well bore; providing a drilling fluid choke in fluid communication with the well bore annulus; pumping a drilling fluid into an upper end of the drill string, then through the drill string, then through the well bore annulus, and then substantially back to the drilling rig, the drilling fluid being pumped at at least one of a selected drilling fluid circulation rate and a selected drilling fluid pump pressure; activating the BOP to maintain the desired variable annulus fluid pressure within the well bore annulus greater than a baseline drilling fluid annulus pressure while pumping the drilling fluid into the upper end of the drill string; selectively closing the choke to maintain the desired variable annulus fluid pressure within the well bore annulus; substantially simultaneously controlling both (a) an altered drilling fluid circulation rate less than the selected drilling fluid circulation rate, and (b) the desired variable annulus fluid pressure within the well bore annulus, such that the drilling fluid choke is substantially closed and the altered drilling fluid circulation rate is reduced to substantially zero; and thereafter substantially simultaneously (a) increasing the altered drilling fluid circulation rate to the selected drilling fluid circulation rate, and (b) selectively activating the drilling fluid choke to release the desired variable annulus fluid pressure in the well bore annulus, such that the drilling fluid choke is substantially opened and pressure in the well bore annulus is substantially the baseline drilling fluid annulus pressure while pumping the drilling fluid into the upper end of the drill string.