Boring or penetrating the earth – Processes – Boring with specific fluid
Patent
1987-12-09
1988-10-04
Novosad, Stephen J.
Boring or penetrating the earth
Processes
Boring with specific fluid
175103, 175107, 175385, E21B 402, E21B 420, E21B 728, E21B 2108
Patent
active
047750170
DESCRIPTION:
BRIEF SUMMARY
This invention relates to drilling holes using downhole tools and particular to drilling large diameter holes.
Current methods employed to drill large diameter holes in the earth's crust for oil and gas or other minerals are varied. The methods employed are normally dependent upon the bore size and formation being cut.
Roller cone bits drilling up to 36" or 1 meter diameter in a single cut are known to have been used in spudding operations (spudding is the initial bore from the earth's surface). Alternatively, as a first option, pilot drilling followed by either a hole opener or under-reamer to enlarge the pilot hole is commonly employed when drilling large diameter bore holes in harder formations or at greater depths. The hole enlarging is carried out either as a secondary operation when rotary drilling, or alternatively, as a simultaneous operation by using a downhole drilling motor or turbine to supply power to the pilot drilling bit and using rotary power to drive the hole opener or under-reamer which is positioned above the downhole drilling motor or turbine. A third option is to use the downhole drilling motor or turbine to supply power to both the pilot drill bit and the hole enlarger.
When drilling with a configuration as illustrated in FIG. 1a, according to the first option, a multi-lobe positive displacement motor (PDM) 1 is preferred to a turbine or conventional 1/2 lobe motor since it offers the combination of low speed and high torque at the drilling bit. A hole enlarger 2 is mounted at the upper end of a drill pipe 3 containing the motor 1 which is coupled through a universal joint transmission 4 to a a lower drive shaft 5 supported in bearings 6 and driving a lower bit box 7 supporting a pilot drill bit 8.
This system has the disadvantage of being unable to maintain constant hydraulic horsepower to both the pilot bit and the hole enlarger (hole-opener or under-reamer) since pressure drop across the PDM varies with load requirements at the pilot drilling bit. This results in uneven wear at the cutting edge and premature dulling of the cutters causing a slow-down in penetration rate and early pulling out of hole to change cutters.
The system of FIG. 1b has the motor 1 mounted in a lower drill pipe 3 driving a lower drive shaft 5 through a universal joint transmission 4, the drive shaft being supported in bearings 6 and is drivingly coupled via a lower bit box 7 to a hole enlarger 2 carrying a pilot drill bit 8 at its lower end.
The system illustrated in FIG. 1b also benefits from the low speed, high torque output characteristics of a multi-lobe positive displacement motor 1 but this system has the disadvantage of having the rotational speed of the pilot drill bit being the same as for the hole enlarger. This results in different cutting speeds at the cutting edges and premature wear of the cutters.
It is an object to provide an improved method of and downhole assembly for downhole drilling using a pilot drill and a hole enlarger.
A method of downhole drilling according to the invention comprises mounting a downhole motor within a drill pipe above a hole enlarger mounted at a lower end of the pipe, with a transmission shaft of the motor extending beyond the lower end of the pipe to a pilot bit spaced downwardly from the hole enlarger; whereby the hole enlarger may be driven from the rotary platform of a drilling and the pilot bit by the motor transmission shaft, and bypassing part of the total fluid flow to the motor and regulating the total fluid flow below the motor between the pilot bit and to the hole enlarger, so that the total flow of fluid to be such as to permit the hydraulic requirements of the pilot bit and the hole enlarger to be met whilst only allowing sufficient fluid to pass through the motor stator/rotor pair to give the required output speed at the pilot bit.
A downhole drilling assembly according to the invention comprises a drill pipe having a hole enlarger at a lower end, a downhole motor mounted within the drill pipe above the enlarger with a transmission shaft extending be
REFERENCES:
patent: 3133603 (1964-05-01), Lagacherie et al.
patent: 3661218 (1972-05-01), Brown
patent: 3802515 (1974-04-01), Flamand et al.
patent: 4401170 (1983-08-01), Cherrington
Washburn, Oil & Gas Journal, vol. 79, No. 10, Mar. 9, 1981, pp. 87-92.
Forrest John
Stewart William
Tulloch Rory
Drilex UK Limited
Novosad Stephen J.
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