A dual circulation fluid hammer drilling system (10) has a fluid hammer (12) which is coupled to a drill string (14). The system (10) utilises a first fluid (16) and a second fluid (18). The first fluid (16) is delivered through the drill string (14) to drive or otherwise power the fluid hammer (12). The second fluid (18) is also delivered through the drill string (14) but in isolation of the first fluid (16) so they do not mix within the drill string (14). The second fluid (18) passes through a hammer bit (38) of the hammer drill (12) and is directed to flow out from a bit face (20). Thus when the system (10) is in use the second fluid (18) will flow across the bit face (20). The first fluid (16) also exits the drilling system (10) at the hammer drill (12). However the first fluid (16) exits upstream or up-hole of the bit face (20).

The present invention relates to a riser system in the form of a pumped riser, i.e. a riser having an outlet from the riser at a depth below the surface of a body of water, where the outlet is coupled to a return pump to return fluid from the riser to the surface, and various operational methods to facilitate greater versatility when performing hydrocarbon drilling related operations. The arrangement also comprises a sealing element to seal an annulus of the riser, and a by-pass around the sealing element. Various methods makes it possible to switch between open mode and closed mode, and vice versa, monitoring leakage across the sealing element, as well as performing other operations exploiting the advantages of the two different modes.

A riser system in the form of a pumped riser, i.e. a riser having an outlet from the riser at a depth below the surface of a body of water, where the outlet is coupled to a return pump to return fluid from the riser to the surface, and various operational methods to facilitate greater versatility when performing hydrocarbon drilling related operations. A sealing element to seal an annulus of the riser, and a by-pass around the sealing element. Various methods make it possible to switch between open mode and closed mode, and vice versa, monitoring leakage across the sealing element, as well as performing other operations exploiting the advantages of the two different modes.

A flow stop valve positionable in a downhole tubular, and a method, in which the flow stop valve is in a closed position when a pressure difference between fluid outside the downhole tubular and inside the downhole tubular at the flow stop valve is below a threshold value, thereby preventing flow through the downhole tubular. The flow stop valve is in an open position when the pressure difference between fluid outside the downhole tubular and inside the downhole tubular at the flow stop valve is above a threshold value, hereby permitting flow through the downhole tubular.

A method of running casing in a dual gradient system includes lowering a casing into a low density fluid region and allowing the low density fluid to enter the casing; releasing a plug into the casing; supplying a high density fluid behind the plug; and lowering the casing into a high density fluid region until target depth is reached.

A method, comprising acquiring annular pressure data from a wellbore where the annular pressure data is acquired over a time interval and at least a portion of the annular pressure data is acquired during a pumps-off period. At least first and second values are identified from the annular pressure data and the variation between the first and second values are compared to a first threshold. Drilling equipment is operated based on the comparison with the first threshold.

The present invention relates to deep-water drilling in petroleum engineering and, in particular, to a subsea wellhead pressure indicating and automatic adjusting device for deep-water dual-gradient drilling, comprising a subsea drilling fluid manifold system and a subsea wellhead pressure indicating and automatic adjusting system, wherein the subsea drilling fluid manifold system provides a flow channel for the drilling fluid returning through the wellbore so that the drilling fluid can smoothly return to a drilling platform, and provides a basis for the subsea wellhead pressure indicating and automatic adjusting system; and wherein the subsea wellhead pressure indicating and automatic adjusting system can display and adjust the subsea wellhead pressure in real time, in order to keep the subsea wellhead pressure to be constantly equal to the hydrostatic pressure of the seawater at the seabed. The present invention makes it possible to keep the subsea wellhead pressure to be constantly equal to the hydrostatic pressure of the seawater at the seabed in an automatic and real-time way, ensuring successful implementation of the dual-gradient drilling.

A method and system for creating a multi-gradient pressure regime within a wellbore annulus. A plurality of valve subs provided along a drill string with each sub including a port for selectively venting supply fluid from the drill string to the annulus. A valve is coupled to the port to control the supply fluid flow into the annulus. The valve has a stator fixed in relation to the valve sub housing. A rotor is in sealing contact with the stator, the rotor being rotatable with respect to the stator. The stator and rotor each have apertures formed therethrough, so that the rotor may be oriented between a fully shut position in which the stator and rotor apertures are not in alignment and a fully open position in which the stator and rotor apertures are in maximum alignment. The valve allows precise metering between the fully open and shut positions.

A pump with a position indicator is disclosed. The pump includes a pump housing, wherein the pump housing includes a flexible bladder disposed therein; a first fluid zone, wherein the first fluid zone is operable to allow flow of a first fluid into and out of the first fluid zone; and a second fluid zone, wherein the second fluid zone is operable to allow flow of a second fluid into and out of the second fluid zone. The pump further includes a flexible position indicator disposed in the first fluid zone and in communication with the flexible bladder, wherein the flexible position indicator is operable to detect a linear position of the flexible bladder, and wherein the flexible bladder fluidly isolates the first fluid zone from the second fluid zone.

A method for drilling a wellbore comprises using drilling mud having a mud weight less than the formation pore pressure while drilling the horizontal section, to release some formation gas to mix with the drilling mud. As the mixture flows up the wellbore annulus, the resulting pressure in the vertical section is within the mud weight window (MWW) of the weak zones, thereby maintaining wellbore stability without the need for intermediate casings. The wellbore is killed by introducing a volume of heavy mud via a circulation sub in the drill string and periodically introducing additional heavy mud to fill the void left behind by the drill string as it is pulled uphole. The ratio of light mud and heavy mud in the killed well is such that the resulting pressure in the vertical section is within the MWW of the weak zones.