Dual gradient drilling system and method
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.
1. A distributed riser-less dual gradient drilling system comprising:
a subsea blowout preventer disposed above a wellhead, the subsea blowout preventer comprising a central lumen configured to provide access to a wellbore;
an annular sealing system fluidly connected to the subsea blowout preventer;
a closed-hydraulic positive displacement subsea pump system fluidly connected to a fluid diversion port of the annular sealing 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 rig without use of an additional pump system,
wherein a pump speed of the closed-hydraulic positive displacement subsea pump system is adjusted to achieve a target amount of fluid mass in a fluidly connected system upstream of the closed-hydraulic positive displacement subsea pump to achieve a target inlet pressure of the closed-hydraulic positive displacement subsea pump.
2. The distributed riser-less dual gradient drilling system of claim 1 , further comprising:
a bypass riser injection system fluidly connected to the independent mud return line configured to bypass the annular sealing system and the closed-hydraulic positive displacement subsea pump system for injection of fluids into the wellbore in total loss drilling conditions.
3. The distributed riser-less dual gradient drilling system of claim 1 , further comprising:
an anti-u-tubing flow stop valve disposed on the drill string.
4. The distributed riser-less dual gradient drilling system of claim 1 , further comprising:
an annular packer or sealing device disposed before the closed-hydraulic positive displacement subsea pump system.
5. The distributed riser-less dual gradient drilling system of claim 1 , wherein the closed-hydraulic positive displacement subsea pump system comprises a first pump head, an independent linear drive motor, and a second pump head.
6. The distributed riser-less dual gradient drilling system of claim 5 , wherein each of the first pump head and the second pump head comprise an inlet port, a bottom check valve assembly, a fluid cavity disposed between pressure balanced liners, a top check valve assembly, and an outlet port.
7. The distributed riser-less dual gradient drilling system of claim 5 , wherein the independent linear drive motor comprises a reciprocating piston having a first piston face and a second piston face that is electronically actuated to compress or uncompress a hydraulic drive fluid in a closed-hydraulic system.
8. The distributed riser-less dual gradient drilling system of claim 1 , wherein the closed-hydraulic positive displacement subsea pump system comprises a hydraulic drive fluid that is wholly contained by the pump system and is not vented into a sea.
9. The distributed riser-less dual gradient drilling system of claim 6 , wherein the pressure balanced liners isolate drilling fluids from hydraulic drive fluid.
10. The distributed riser-less dual gradient drilling system of claim 1 , wherein the closed-hydraulic positive displacement subsea pump system does not include dynamic seals exposed to drilling fluids.
11. The distributed riser-less dual gradient drilling system of claim 1 , wherein the annular sealing system comprises an active control device, a rotating control device, or an annular seal configured to seal an annulus surrounding a drill string disposed therethrough.
12. The distributed riser-less dual gradient drilling system of claim 1 , wherein the annular sealing system comprises one or more sealing elements.
13. The distributed riser-less dual gradient drilling system of claim 1 , wherein dual gradient drilling operations are conducted with continuous circulation.
14. The distributed riser-less dual gradient drilling system of claim 1 , wherein gas in the wellbore is controlled by the annular sealing system and diversion of riser fluids through the independent mud return line to a choke manifold and a mud-gas-separator disposed on the floating platform of the rig.