Boring or penetrating the earth – Boring a submerged formation
Reexamination Certificate
2000-03-23
2003-09-30
Shackelford, Heather (Department: 3673)
Boring or penetrating the earth
Boring a submerged formation
C166S358000, C175S135000, C175S293000, C405S249000
Reexamination Certificate
active
06626248
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to deep water offshore drilling operations which utilize floating rigs, and more particularly, to a method for installing a drilling assembly, including a drive pipe, into a sea-bottom formation.
BACKGROUND OF THE INVENTION
In deep water drilling operations, shallow water flow (SWFT) hazards have become increasingly troublesome. SWF derives its name from the phenomena of a flow, emanating from a subsurface and overpressurized zone, back to the seafloor. An overpressurized subsurface zone is formned naturally when an impermeable seal is formed over sandy settlements by rapid deposition of silty material. As the silty material is deposited over the sealed, sandy aquifer, the trapped water in the sandy settlement is unable to escape. Over time, the pressure increases in the sandy aquifer until the pressure developed is equal to or greater than the hydrostatic pressure at the depth of water at the location of the sandy aquifer. A shallow water flow occurs when the impermeable seal of silty material is penetrated to release the overpressure within the sandy aquifer. In some cases, the pressures are high enough to cause powerful flows of water and sand into the well bore. Waterflows destabilize the wellbore through erosion to collapse and in some cases damage the well bore and others adjacent thereto. Shallow waterflow hazards have been encountered in many areas of the world and continue to be a problem in deepwater drilling operations.
One solution for avoiding shallow waterflow hazards is to use a drive pipe. The drive pipe is driven into the formation past the high pressure sandy aquifer. The purpose of the drive pipe is to prevent the formation from collapsing into the borehole during this initial drilling. Since the drive pipe is driven into the formation, the soil is compressed and compacted in the immediate vicinity of the drive pipe. Compacted soil seals the drive pipe in the formation to prevent shallow water flow around the drive pipe. The drive pipe becomes the casing for the well bore through which subsequent drilling operations may be conducted.
In a typical offshore drilling installation, a length of drive pipe is hung from the floating rig by a string of drill collars and drill pipe lowered to the sea bottom. In such a deepwater installation, the water depth may be up to 10,000 feet or greater. In the drilling assembly, the string of drill collars are connected to the top of the drive pipe by way of a running tool having a J-latch, or other releasing mechanism. The drilling assembly may also be connected to the drive pipe by way of a conventional J-latch assembly engaged with lugs or other means attached to the inside or outside of the drive pipe. The drill string continues below the running tool and extends down the entire length of the interior of the drive pipe. The lower end of the drill string assembly terminates with a jet sub or downhole motor connected to a stabilized drill bit.
In a conventional assembly, the drill bit is located at the mouth or lower opening of the drive pipe, and is driven by the motor to function as a jetting assembly to drill a hole approximately the size of the inner diameter of the drive pipe. The drill string is initially connected to the drive pipe through a first position of the running tool to enable both elements to move downwardly together. Therefore, as the drill bit penetrates the sea bottom formation, the drill string lowers, and the drive pipe falls snugly into the bore hole made from the rotating and jetting action of the bit. This drilling continues until substantially the entire section of drive pipe penetrates the formation or until such time as the gravitational forces acting on the drive pipe will no longer overcome the effect of skin friction. Once this is accomplished, the drill string is disconnected from the drive pipe at the running tool connection to enable the drill string to move independently with respect to the drive pipe, and continue its drilling operation. In this mode, the drill bit continues to drill beyond the drive pipe, into the formation, while the drive pipe remains stationary.
During the initial drilling, when the drive pipe is penetrating into the formation due to gravitational force, regular seawater is utilized as the drilling fluid. Thus the sea water, traveling down through the interior of the drill string, functions to clean the bore hole bottom, and carry the cuttings up the annulus formed by the exterior of the drill string and the interior of the drive pipe. This fluid then exits the annulus at the top of the drive pipe to be released into the sea.
For subsequent drilling, the drill string is pulled out of the hole and the drill collars are stood back on the derrick of the floating platform. A conductor pipe is lowered from the rig to extend and attach to the top of the drive pipe to communicate with the annulus inside the drive pipe. Regular drilling mud is then utilized in the drilling operation by having it pumped down the drill string and up through the annuluses of the drive pipe and the conductor pipe. This conductor pipe also serves as a means to bring cuttings from the drill bit to the surface.
Drive pipes are usually 30 to 36 inches in diameter, having a wall one inch thick, although in some instances, the drive pipe can be 42 inches, or larger, in diameter, with a two inch wall thickness. Drive pipes are typically 350 to 450 feet in length for shallow water drilling operations if driven from the surface. In conventional drilling operations, it has been found that a drive pipe can not penetrate beyond a certain amount, usually around the 450 feet length, because at that length, the resistance caused by skin friction becomes greater than the force of gravity and the force applied from the surface by conventional hammer means. The drive pipe will reach a point of refusal and any further force applied to the uppermost section of the drive pipe will cause yielding of the pipe material and any further driving efforts must be discontinued.
In deep water drilling operations, drive pipes having lengths of 1000 feet or more are sometimes required to mitigate shallow water flow hazards. Therefore, auxiliary means for driving drive pipes are necessary to augment the gravitational forces acting on the drive pipes to increase the depth of penetration of the drive pipes.
One option has been to use a hammer applied to the top of the drill string to help drive the drive pipe at the end of the drill string downward. However, because of the great drill string lengths involved, the energy transferred to the drive pipe through the drill string is not sufficient.
A further option has been to apply conventional hammers directly to the top of the drive pipe at the connection between the drive pipe and the drill sting. Hydraulic pile and pipe drivers of various configurations are known. An example of a hydraulic pipe driver attached to the top of the pipe is disclosed in U.S. Pat. No. 4,964,473, incorporated herein by reference. The device has a submerged power converter wherein hydraulic pressure energy is generated in the power converter to drive the driver and wherein the power converter is driven by pressurized surrounding water after the energy transfer is exhausted into the surrounding water. Further examples of pipe drivers used to drive pipes and piles into a sea bed for securing platforms and other structures are disclosed in U.S. Pat. No. 4,601,349; 5,662,175; 5,090,485; 4,817,734; 4,818,149; 4,856,938; 5,088,567; 4,872,514; and 5,228,806, all incorporated herein by reference.
In any drive system using a conventional hydraulic hammer applied to the top of the drive pipe, there are significant drawbacks: (1) an umbilical conduit must be run from the floating vessel to the hammer; (2) conventional hydraulic hammers apply relatively low impacts; and (3) the drive pipe is not driven vertically. First, typical drive pipe hammers have umbilical cables which supply electrical or hydraulic forces to the hammers. At water depths whe
Lee Arley G.
Roberts Billy J.
Roberts Jenova J.
Kreck John
Roberts Jenova J.
Shackelford Heather
Smith International Inc.
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