Abstract: A method for maintaining wellbore pressure includes reducing flow rate of a drilling fluid pump fluidly connected to a drill pipe in the wellbore. Flow out of the well is enabled into a first auxiliary line associated with a drilling riser. A seal around the drill pipe is closed. Fluid is pumped down a second auxiliary line at a rate selected to maintain a specific pressure in the wellbore. Drilling fluid flow through the drill pipe is stopped.

Abstract: A method for determining formation integrity during drilling of a wellbore includes determining an annulus fluid pressure in a wellbore during drilling thereof. The annulus pressure is adjusted by a predetermined amount. Flow rate of drilling fluid into the wellbore is compared to drilling fluid flow rate out of the wellbore. At least one of a formation pore pressure and a formation fracture pressure is determined from the annulus pressure when the compared flow rates differ by a selected amount. The method alternatively to determining pore and/or fracture pressure includes determining a response of the wellbore to the adjusted fluid pressure and determining the optimum annulus fluid pressure from the wellbore response.

Abstract: A method for determining existence of a borehole fluid control event by controlling formation pressure during the drilling of a borehole includes selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole. The drilling fluid leaves the annular space proximate the surface. Existence of a well control event is determined when at least one of the following events occurs: the rate of the selective pumping remains substantially constant and the annular space pressure increases, and the rate of the selective pumping remains substantially constant and the annular space pressure decreases.

Abstract: A method of drilling a bore hole in a fractured formation. A drill pipe is deployed into the borehole, whereby an annular space is formed between the drill pipe and the borehole wall. A drilling fluid is pumped, by means of primary pumps, into the borehole via an internal conduit of the drill pipe and a drill pipe fluid outlet present in the vicinity of a distal end of the drill pipe. The annular space is pressure sealed using a pressure seal such as a rotating head on a BOP. A well control fluid is pumped into the annular space via a well control conduit that fluidly connects the annular space, in a location between the pressure seal and the drill pipe fluid outlet, to a backpressure system. The well control fluid is pressure-balanced against the pressure seal and the backpressure system.

Abstract: A method for controlling formation pressure during drilling includes pumping a drilling fluid through a drill string in a borehole, out a drill bit at the end of the drill string into an annular space. The drilling fluid is discharged from the annular space proximate the Earth's surface. At least one of a flow rate of the drilling fluid into the borehole and a fluid flow rate out of the annular space is measured. Pressure of the fluid in the annular space proximate the Earth's surface and pressure of the fluid proximate the bottom of the borehole are measured. Pressure of the fluid proximate the bottom of the borehole is estimated using the measured flow rate, annular space pressure and density of the drilling fluid. A warning signal is generated if difference between the estimated pressure and measured pressure exceeds a selected threshold.

Abstract: Drilling system and method for drilling a bore hole into an earth formation, the bore hole having an inside wall. A drill string reaches into the bore hole and leaves a drilling fluid return passage between the drill string and the bore hole inside wall. A drilling fluid discharge conduit is in fluid communication with the drilling fluid return passage, and pump means are provided for pumping a drilling fluid through the drill string into the bore hole and to the drilling fluid discharge conduit via the drilling fluid return passage. The drilling fluid back pressure is controlled utilizing back pressure control means for controlling back pressure means. The system further provides fluid injection means comprising an injection fluid supply passage fluidly connecting an injection fluid supply with the drilling fluid return passage and further comprising an injection fluid pressure sensor arranged to provide a pressure signal in accordance with an injection fluid pressure in the injection fluid supply passage.

Abstract: A drilling system for drilling a bore hole into an earth formation, the bore hole having an inside wall. A drill string reaches into the bore hole from a surface, leaving a drilling fluid return passage between the drill string and the bore hole inside wall. A bottom hole assembly is supported by the drill string, and a drilling fluid discharge conduit is provided in fluid communication with the drilling fluid return passage. A drilling fluid is pumped through the drill string into the bore hole and to the drilling fluid discharge conduit via the drilling fluid return passage. Means are provided for obtaining information on the existing down hole pressure of the drilling fluid in the vicinity of the bottom hole assembly and back pressure means for controlling the drilling fluid back pressure.