Wells – Valves – closures or changeable restrictors – Fluid operated
Reexamination Certificate
2001-02-08
2002-06-11
Tsay, Frank (Department: 3672)
Wells
Valves, closures or changeable restrictors
Fluid operated
C166S321000
Reexamination Certificate
active
06401823
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to drilling systems and operations. More particularly, the present invention is a method and system for handling the circulation of drilling mud in deepwater offshore drilling operations.
Drilling fluids, also known as muds, are used to cool the drill bit, flush the cuttings away from the bit's formation interface and then out of the system, and to stabilize the borehole with a “filter cake” until newly drilled sections are cased. The drilling fluid also performs a crucial well control function and is monitored and adjusted to maintain a pressure with a hydrostatic head in uncased sections of the borehole that prevents the uncontrolled flow of pressured well fluids into the borehole from the formation.
Conventional offshore drilling circulates drilling fluids down the drill string and returns the drilling fluids with entrained cuttings through an annulus between the drill string and the casing below the mudline. A riser surrounds the drill string starting from the wellhead at the ocean floor to drilling facilities at the surface and the return circuit for drilling mud continues from the mudline to the surface through the riser/drill string annulus.
In this conventional system, the relative weight of the drilling fluid over that of seawater and the length of the riser in deepwater applications combine to exert an excess hydrostatic pressure in the riser/drill string annulus.
Systems have been conceived to bring the drilling fluid and entrained cuttings out of the annulus at the base of the riser and to deploy a subsea pump to facilitate the return flow through a separate line. One such system is disclosed in U.S. Pat. No. 4,813,495 issued Mar. 21, 1989 to Leach. That system requires complex provisions to ensure the closely synchronous operation of the supply and return pumps critical to the approach disclosed. However, the durability and dependability of such a mud circulation system is suspect in the offshore environment and particularly so in light of the nature of the fluid with entrained cuttings that is handled in valves and pumps on the return segment of the circuit.
A greatly improved system is illustrated in assignee's related invention, a Subsea to Drill fluid Pumping and Treatment System for Deepwater Drilling, published Apr. 1, 1999 as WO 99/15758, the disclosure of which is hereby incorporated by reference. That application includes a disclosure of a method and apparatus for reducing the excess hydrostatic pressure exerted by the mud column return in the riser/drill string annulus and which isolates the excess pressure from formation during operations, maintaining an ambient pressure when pump operations cease.
However, the practice of that illustrative embodiment which is disclosed in that publication ordinarily employs a significant pressure drop across the drill string shut-off valve, causing a significant energy loss due to friction and challenging the operational life expectancy of the valve. Further, those illustrative embodiments do not provide for easily adjusting the drill string shut-off valve characteristics to accommodate changing downhole conditions during the course of drilling a well.
A SUMMARY OF THE INVENTION
One aspect of the present invention is a drill string shut-off valve system for controlling the mud circulation system for deepwater marine drilling operations, the drill string shut-off valve having a valve body having a cylinder, a main flow path, and a drilling mud flow channel, an upper and a lower connector on the valve body for installing the drill string shut-off valve into a drill string, and a valve positioned to selectively interrupt in the main flow path through the valve body or to complete the main flow path through the drilling mud flow channel. A piston in the cylinder is operably connected to the valve to drive it from an open to closed position. The piston has a first pressure face, a port presenting pressure from the upstream side of the valve to the first pressure face, and a second pressure face on the back of the piston. Exhaust ports present pressure from the annulus to the second pressure face and a spring biases the drill string shut-off valve to a closed position, but balanced with the area of the first pressure face to ensure valve opening at normal pump operation pressures.
Another aspect of the invention is a spring adjustment assembly whereby the tension of the spring can be readily adjusted to allow for different drilling conditions.
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“Riserless Drilling/Deepwater Technology Symposium”, by Allen D. Gault, World Oil, pp. 1-11.
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Gonzalez Romulo
Smits Frans Sippo Wiegand
Shell Oil Company
Tsay Frank
LandOfFree
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