Boring or penetrating the earth – With signaling – indicating – testing or measuring – Tool position direction or inclination measuring or...
Patent
1986-10-01
1989-02-28
Novosad, Stephen J.
Boring or penetrating the earth
With signaling, indicating, testing or measuring
Tool position direction or inclination measuring or...
175 61, 175 76, 175325, E21B 708
Patent
active
048077089
DESCRIPTION:
BRIEF SUMMARY
This invention rleates to means for and a method of controlling the direction of a drill bit at the downhole end of a drill string.
When drilling with a drill bit at the downhole end of a drill string it is important to control the direction of the bore hole to reach a desired objective. Forces which act on the drill bit are gravity, torque developed by the bit, the end load applied to the bit, and the bending moment from the drill assembly. These forces together with the type of strata being drilled and the inclination of the strata to the bore hole create a complex interactive system of forces which make it impossible to drill a hole on a constant course without having means for generating forces to change the direction of the drill bit. Withdrawal of the drill string to provide such means is time consuming.
It is known to provide sleeve type stabilisers along a drill string, and in particular at the downhole end of the string to support the drill string and the drill bit generally centrally of the bore hole.
It is an object to provide downhole means for generating forces controllable from the surface for changing the direction of travel of a drill bit of a drill string.
According to one aspect of the invention a method of controlling the direction of a drill bit at the downhole end of a drill string drilling from a surface comprises providing two steerable stabilisers at the downhole end of the drill string at locations spaced longitudinally in the drilling direction and adjusting the orientation of the stabilisers from the surface to create reactive forces from the bore hole to deflect the course of the bit in a desired direction.
Suitably the drill string rotation is stopped when adjusting the stabilisers, and the adjustment is made in response to downhole measurements as to direction of the drill bit. Means for effecting the measurements are suitably mounted above a downhole motor or turbine powering the drill bit.
According to another aspect the invention includes means for controlling the direction of a drill bit at the downhole end of a drill string which comprise a lower drill string drill sub-assembly extending axially in the drilling direction and provided with a pair of bore hole stabilisers spaced apart longitudinally in the drilling direction and steerably mounted in relation to the sub-assembly by means adapted to be remotely controlled whereby adjustment of the stabiliser can alter the inclination of the sub-assembly in relation to the bore hole axis to alter the drilling direction.
Suitably the sub-assembly is a downhole motor or turbine and the steerable stabilisers are mounted on the motor casing, one at the bottom adjacent the drill bit and the other near the top of the motor or at the bottom of the superjacent drill string assembly.
A third stabiliser fixedly mounted on the motor casing and concentric with the drilling axis may be provided approximately midway between the adjustable stabilisers.
The steerable stabilisers are suitably sleeve type stabilisers eccentrically arranged in relation to each other. Suitably the steerable stabilisers are offset from the axis of the downhole motor and drill bit assembly in opposite directions, and in particular by 180.degree..-+.60.degree..
In normal drilling the downhole motor is rotated by the drill string such that the steerable sleeve type stabilisers are rotated and engage the bore hole to support the motor against lateral or tilting movement under reaction of the drilling forces, and the adjustable stabilisers are free in the bore hole and the assembly will drill at a near constant course and direction according to the strata being drilled.
The bore hole path is determined by continuous survey, typical survey instruments giving hole direction, inclination and tool face. The tool face measurement determines the orientation of a reference line on the circumference of the drill string, usually known as a scribe line, which is aligned with a known reference line on the steerable stabilisers.
When the survey instrument indicates to an operator
REFERENCES:
patent: 3224513 (1965-12-01), Weeden, Jr.
patent: 3544957 (1970-12-01), Smetanin et al.
patent: 3561549 (1971-02-01), Garrison et al.
patent: 4185704 (1980-01-01), Nixon, Jr.
patent: 4317493 (1982-03-01), Thompson
patent: 4319649 (1982-03-01), Jeter
Catherall Roger
Forrest John
Pounds Randall J.
Stewart William
Drilex UK Limited and Eastman Christensen Company
Novosad Stephen J.
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