Abstract: An apparatus for drilling a subterranean wellbore using a drill string. The apparatus includes a riser, a sealing device arranged in the riser so as to form a first riser chamber and a second riser chamber, and a riser booster pump. The riser at least partly contains the drill string and defines a substantially annular space around the drill string. The second chamber is in a fluid communication with the riser booster pump so that a kill fluid stored in the second riser chamber may be maintained at a first pressure which is greater than a second pressure of a drilling fluid in the first riser chamber.

Abstract: An apparatus for drilling a subterranean wellbore using a drill string. The apparatus includes a riser, a sealing device arranged in the riser so as to form a first riser chamber and a second riser chamber, and a riser booster pump. The riser at least partly contains the drill string and defines a substantially annular space around the drill string. The second chamber is in a fluid communication with the riser booster pump so that a kill fluid stored in the second riser chamber may be maintained at a first pressure which is greater than a second pressure of a drilling fluid in the first riser chamber.

Abstract: A method of drilling a subterranean wellbore using a drill string including the steps of estimating or determining a reduced static density of a drilling fluid based on the equivalent circulating density of the drilling fluid in a section of the wellbore, providing a drilling fluid having substantially that reduced static density, introducing the drilling fluid having said reduced static density into the wellbore, and removing the drilling fluid from the wellbore via a return line.

Abstract: A method of drilling a subterranean wellbore using a drill string including the steps of estimating or determining a reduced static density of a drilling fluid based on the equivalent circulating density of the drilling fluid in a section of the wellbore, providing a drilling fluid having substantially that reduced static density, introducing the drilling fluid having said reduced static density into the wellbore, and removing the drilling fluid from the wellbore via a return line.

Abstract: A method of drilling a subterranean borehole comprising: a) pumping a drilling fluid down a drillstring (12), the drillstring (12) having a bit (14) at an end thereof, b) rotating the drillstring (12) about its longitudinal axis so that the bit forms a borehole (10) in the ground, the method further comprising the steps of: c) determining a desired drilling fluid flow rate range d) determining the desired upper and lower limits of the fluid pressure at the bottom of the wellbore (the BHP); e) determining the viscosity of drilling fluid which will maintain the BHP within the range set by the upper and lower BHP limits over the entire or the majority of the required drilling flow rate range; f) adjusting the composition of a drilling fluid to bring the drilling fluid to the viscosity calculated in step e above.

Abstract: A method of drilling a subterranean borehole comprising: a) pumping a drilling fluid down a drillstring (12), the drillstring (12) having a bit (14) at an end thereof, b) rotating the drillstring (12) about its longitudinal axis so that the bit forms a borehole (10) in the ground, the method further comprising the steps of: c) determining a desired drilling fluid flow rate range d) determining the desired upper and lower limits of the fluid pressure at the bottom of the wellbore (the BHP); e) determining the viscosity of drilling fluid which will maintain the BHP within the range set by the upper and lower BHP limits over the entire or the majority of the required drilling flow rate range; f) adjusting the composition of a drilling fluid to bring the drilling fluid to the viscosity calculated in step e above.