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.

The present invention relates to a riser system in the form of a pumped riser (1), i.e. a riser (1) having an outlet (6) from the riser (1) at a depth below the surface (S) of a body of water, where the outlet (6) is coupled to a return pump (7) to return fluid from the riser (1) to the surface (S), and various operational methods to facilitate greater versatility when performing hydrocarbon drilling related operations. The arrangement also comprises a sealing element (15, 16) to seal an annulus (5) of the riser (1), and a by-pass (17) around the sealing element (15, 16). Various methods makes it possible to switch between open mode and closed mode, and vice versa, monitoring leakage across the sealing element (15, 16), as well as performing other operations exploiting the advantages of the two different modes.

A dual circulation fluid hammer drilling system (10) has a fluid hammer (12) which is coupled to a drill string (14). The system (10) utilizes 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).

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 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 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 downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

A method for managed pressure drilling comprising: extending a drilling riser (2) with a drill string (20) from a floating installation (52) to a subsea blow-out preventer stack (1); providing a first fluid in the drilling riser annulus (12) and a second fluid in a fluid conduit (6,7) extending from the floating installation (52), where the first fluid has a higher density than the second fluid; circulating the second fluid through a control valve (31) which is fluidly connected to the fluid conduit (6,7) and operating the control valve (31) to apply a surface back-pressure so as to obtain a pre-determined, desired combined hydrostatic and frictional circulation pressure below the subsea blow-out preventer stack (1).

A dual gradient drilling system includes a subsea blowout preventer disposed above a wellhead, the subsea blowout preventer having a central lumen configured to provide access to a wellbore, a lower section of a marine riser fluidly connected to the subsea blowout preventer, a closed-hydraulic positive displacement subsea pump system fluidly connected to the lower section of the marine riser and disposed at a predetermined depth, an annular sealing system disposed above the closed-hydraulic positive displacement subsea pump system, and an independent mud return line fluidly connecting one or more pump heads of the closed-hydraulic positive displacement subsea pump system to a choke manifold disposed on a floating platform of a rig.

A dual gradient drilling system includes a subsea blowout preventer disposed above a wellhead, the subsea blowout preventer having a central lumen configured to provide access to a wellbore, a lower section of a marine riser fluidly connected to the subsea blowout preventer, a closed-hydraulic positive displacement subsea pump system fluidly connected to the lower section of the marine riser and disposed at a predetermined depth, an annular sealing system disposed above the closed-hydraulic positive displacement subsea pump system, and an independent mud return line fluidly connecting one or more pump heads of the closed-hydraulic positive displacement subsea pump system to a choke manifold disposed on a floating platform of a rig.