Abstract: A drilling system including a drill string (12) which extends into a borehole (10), and a well closure system which contains fluid in the annular space (16) in the borehole around the drill string, the well closure system having a side bore whereby controlled flow of fluid out of the annular space in the borehole around the drill string is permitted, the side bore being connected to fluid return line (28) which extends from the side bore to a fluid reservoir (34), there being provided in the fluid return line a valve (30a) which is operable to restrict flow of fluid along the fluid return line to variable extent, and a flow meter (32) operable to measure the rate of flow of fluid along the fluid return line, the flow meter being located between the valve and the side bore, wherein a filter (40) is provided between the flow meter and the side bore, the filter including a plurality of apertures which have a smaller cross-sectional area than the smallest fluid flow lines in the flow meter.

Abstract: A blowout preventer assembly comprising a blowout preventer and control apparatus, the blowout preventer comprising a housing a sealing element and a fluid pressure operated actuator mounted in the housing, the actuator 18 dividing the interior of the housing into two chambers, namely an open chamber and a close chamber, substantially preventing flow of fluid between the two chambers, and being movable, by means of the supply of pressurised fluid to the close chamber, to urge the sealing element into sealing engagement with a drill pipe extending through the blow out preventer, the control apparatus including a close line which extends from the exterior of the housing to the close chamber, and a source of pressurised fluid which is connected to the close line, wherein the source of pressurised fluid is located adjacent to the housing.

Abstract: A method of drilling a subterranean well bore using a tubular drill string is described. One embodiment of the method includes the steps of injecting a drilling fluid into the well bore via the drill string and removing the drilling fluid from an annular space in the well bore around the drill string via a return line. The method can also include oscillating the pressure of the fluid in the annular space in the well bore, and monitoring the rate of flow of fluid along the return line.

Abstract: A drill pipe having a tubular body through which is provided a main bore, a side port provided in an exterior surface of the body, a side bore extending through the body from the main bore to the side port, and a valve member which is movable between a closed position in which fluid flow through the side bore is substantially prevented and an open position in which fluid flow through the side bore is permitted, wherein the movement of the valve member between the closed position and the open position comprises translational movement, and the valve member is located at least predominantly within the side bore.

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: An assembly of a drill pipe and a connector (10) for connecting a hose (50) to a side-bore (52) of a the drill pipe (54), the drill pipe (54) having a wall (54a) enclosing a main bore (54b), and the side-bore (52) extending through the wall (54a) from the main bore (54b) to the exterior of the drill pipe (54), the connector (10) comprising a hose connector body (12) which forms a first end of the connector (10) which is adapted to be connected to the hose (50), and a drill pipe connector body (14) which forms a second end of the connector (10) which is connected to the drill pipe (54), the connector (10) having an exterior surface and an interior surface which encloses a bore (20, 22) extending from the first end of the connector (10) to a second end of the connector (10), the drill pipe connector body (12) being provided with at least one bayonet connector formation (44) which extends from the exterior surface of the connector (10) generally radially outwardly relative to the bore (20, 22), the bayonet conne

Abstract: A control apparatus for use in controlling the fluid pressure in a borehole during drilling of the borehole, the apparatus including an inlet suitable for connection to a pump, a main outlet suitable for connection to a drill pipe, and an overflow outlet suitable for connection to a fluid reservoir, the inlet being connected to the main outlet by a main flow conduit, and the overflow outlet being connected to the main flow conduit by means of an overflow conduit, wherein the overflow conduit is provided with a pressure regulator by means of which the pressure of fluid in the main flow conduit may be maintained at or around a predetermined pressure value.

Abstract: A drill pipe (10) having an elongate tubular body (12) with an interior surface enclosing a main bore (14) which extends generally parallel to a longitudinal axis (A) of the tubular body (12) from a first end to a second end of the tubular body (12), a side port (16) provided in an exterior surface of the tubular body (12), a side bore (18) extending through the body (12) from the main bore (14) to the side port (16), and a valve assembly (20, 22) which is operable to substantially prevent flow of fluid along the main bore (14) and to substantially prevent flow of fluid along the side bore (18), wherein the valve assembly (20, 22), side port (16) and side bore (18) are provided in a first connection portion (10a) of the drill pipe (10) at the first end thereof, the first connection portion (10a) comprising a thickened portion of the tubular body (12) in which the separation of the interior surface and the exterior surface is substantially greater than the adjacent portion of the tubular body (12), the length