Patent ID: 8631874

Claim:
A method for controlling pressure and/or riser fluid density in a marine riser by changing the density of a drilling fluid comprising the steps of: injecting a fluid of a first density through a drill pipe in the marine riser; injecting a fluid of a second density through a concentric riser support body into an annular space between the marine riser and a concentric riser, wherein the concentric riser support body includes a plurality of concentric riser fluid channels and a concentric riser annular channel below said plurality of concentric riser fluid channels, wherein the concentric riser support body is connected to the marine riser with a riser support at a position above the riser support body, mixing the two fluids below the concentric riser; and returning the mixed density fluid toward the top of the riser in an annular space between the drill pipe and concentric riser, wherein the pressure and/or the fluid density in the marine riser is controlled.