Self actuating underreamer
OwnerRonald George Minshullinventor
Life of this patent
Estimating the term…
Abstract
An underreamer for well drilling comprises pivotally extendible roller cutters that extend slightly beyond the diameter of the pilot drill bit but are retained in their retracted position by the casing. Upon encountering an obstruction, the underreamer is pushed out of the casing, allowing the outer edges of the cutters to contact the obstruction. Continued downward pressure of the drill stem causes the roller arms to pivot outward to a fully extended position in which the cutters enlarge the hole to a diameter larger than the casing by rotation of the drilling stem. The advance of the casing relative to the underreamer forces the cutters to retract into the casing.
Claims13
An underreamer comprising:
- an upper body portion having an upper body diameter;
- a lower body portion having a lower body diameter smaller than said upper body diameter;
- at least one non-spring-actuated cutter mounted in a cavity for pivotal movement between a retracted position and an extended position;
- wherein:
- in said retracted position, said cutter being defined substantially within said upper body diameter but having an overlap portion thereof extending outside said lower body diameter;
- in said extended position, said cutter extending outside said upper body diameter;
- and
- wherein pivotal movement of said cutter from said retracted position to said extended position is actuated by urging said overlap portion of said cutter downward against an obstruction.
A method of overcoming an obstruction in simultaneous drilling and casing of boreholes using a drill stem, a drill bit and at least one section of casing having a reading end diameter, comprising:
- providing an underreamer having at least one non-spring-actuated cutter mounted for pivotal movement between a retracted position and an extended position;
- inserting said underreamer into said casing, said casing adapted to contain said cutter in said retracted position by contact with said cutter;
- displacing said underreamer in relation to said casing toward said obstruction to at least a point that said cutter exits said casing and is no longer contained by contact with said casing in said refracted position, but is not automatically actuated to pivot to said extended position;
- before, after or simultaneous with said previous step, causing said drill bit to drill a pilot hole in said obstruction;
- urging said cutter against said obstruction at the edge of said pilot hole whereby said urging causes said cutter to pivot to said extended position outside said leading end diameter;
- and,
- using said cutter to ream said pilot hole.
Dependencies are inferred from the claim text.