Abstract: 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.

Abstract: 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.

Abstract: This disclosure includes riser flange assemblies and related methods. Some assemblies include first and second flanges each defining a plurality of counterbored bolt holes and having a plurality of concave bearing surfaces each disposed around one of the counterbored bolt holes, a plurality of bolts each having a head and a male threaded portion, a plurality of washers each having a convex bearing surface configured to correspond to the concave bearing surface of a bolt hole when one of the bolts extends through the washer and the bolt hole and a plurality of nuts each having a convex bearing surface and a female threaded portion configured to receive the male threaded portion of one of the bolts, the convex bearing surface configured to correspond to the concave bearing surface of a bolt hole when one of the bolts extends through the bolt hole and is received in the nut.

Abstract: This disclosure includes auxiliary-line riser segment assemblies (e.g., with isolation units) that are suitable for managed pressure drilling (MPD) and that can be lowered (e.g., when connected to other riser segment assemblies) through a rotary of a drilling rig. Some embodiments are configured to have portions of the auxiliary lines connected (e.g., without welding) below the rotary.

Abstract: A riser assembly is disclosed comprising: a main tube; two flanges coupled to the main tube, each flange comprising: a central lumen configured to be in fluid communication with the main tube; at least one choke/kill hole configured to receive a choke/kill line; at least one booster hole configured to receive a booster line; and a plurality of bolt holes, each bolt hole comprising a tapered portion and a dowel slot, where each bolt hole is configured to receive a nut, a bolt, and a dowel. In certain embodiments, riser strings comprising at least two riser assemblies coupled to each other are disclosed.

Abstract: Some embodiments of the present clamps include a first clamp portion having a first end defining a recess and a second end configured to be coupled to a first structure, a second clamp portion having a first end configured to be coupled to a second structure and a second end configured to be received in the recess of the first clamp portion, and a shear pin configured to secure the second clamp portion relative to the first clamp portion. Some embodiments include a retaining member disposed in the recess. In some embodiments, the recess and/or retaining member is configured to resist shearing of the shear pin if a force is applied to the second clamp portion in a first direction, but not if the force is applied in a second direction. In some embodiments, the first direction is substantially parallel with, but opposite to, the second direction.

Abstract: This disclosure includes auxiliary-line riser segment assemblies (e.g., with isolation units) that are suitable for managed pressure drilling (MPD) and that can be lowered (e.g., when connected to other riser segment assemblies) through a rotary of a drilling rig. Some embodiments are configured to have portions of the auxiliary lines connected (e.g., without welding) below the rotary.

Abstract: This disclosure includes flow spool riser segment assemblies that are suitable for managed pressure drilling (MPD) and that can be lowered (e.g., when connected to other riser segment assemblies) through a rotary of a drilling rig. Some embodiments are configured to have portions of the flow spool connected (e.g., without welding) below the rotary.

Abstract: This disclosure includes auxiliary-line riser segment assemblies (e.g., with isolation units) that are suitable for managed pressure drilling (MPD) and that can be lowered (e.g., when connected to other riser segment assemblies) through a rotary of a drilling rig. Some embodiments are configured to have portions of the auxiliary lines connected (e.g., without welding) below the rotary.