Underreamer Apparatus and Method

Abstract

A wellbore underreamer has a tubular body, a central body cavity, and pivotally mounted blades in slots on the periphery of the tubular body. A translatable piston in the central body cavity is urged away from cam surfaces on the blades by a biasing spring. The piston has an orifice restricted fluid passage and translates in response to fluid pressure determined by the selected piston orifice and biasing spring. Fluid circulates through the piston fluid passage and fluid passages in the underreamer while piston movement is restrained by the spring. At a predetermined fluid pressure, the piston moves to engage the blade cam surfaces to pivotally extend the blades outward from the blade slots. The blades are held in the slots by a spring biased ball until they are extended by the piston.

Description

PRIORITY[0001]This application claims priority to U.S. provisional application Ser. No. 61 / 837,004 filed by Applicant on Jun. 19, 2013 for Underreamer Apparatus and Method, the entire content of which is incorporated by reference.FIELD OF THE INVENTION[0002]This invention pertains to downhole equipment for oil and gas wells. More particularly, it pertains to an underreamer apparatus for use on a drillstring, coiled tubing, or mud motor and, more particularly, this invention relates to an apparatus for enlarging a borehole. This apparatus is used to enlarge or clean out a wellbore below a wellbore restriction such as the end of a casing or tubing string.BACKGROUND OF THE INVENTION[0003]During drilling or workover of a wellbore, it is often deemed necessary to lower an underreamer tool and tool string through a narrow diameter section of tubing or casing then deploy the cutting blades of the underreamer tool to increase the cutting or cleaning diameter of the wellbore. It is also nece...

AI Technical Summary

Benefits of technology

The underreamer apparatus has a piston that moves to open the blades. This piston is pushed by a spring and moves up and down in the housing to control the blades. By adjusting the spring force and the piston's movement, the blades can be opened to different degrees for underreaming. This design allows for easy and flexible control over the blades' movement.

Problems solved by technology

During the use an underreamer is subjected to tremendous vibration.

This vibration may lead to the weakening or loosening of the pivot pins securing the underreamer blades and substantially increase the likelihood these pivot pins will fail leaving the underreamer blades loose in the wellbore.

If the underreamer blades are loose, drilling can no longer continue and the underreamer blades must be fished from the wellbore costing time and money.

During the use the blades of an underreamer are covered or coated with mud, clay or other debris making these blades less efficient.

This collection of debris in the blade pockets or recesses can create problems as debris lodged in the blade pocket may prevent the cutting blades from closing or collapsing fully.

If the cutting blades are not fully closed within the blade pockets, the extending blades may prevent the underreamer from being pulled back through any previously encountered wellbore restriction, the extending blades may cause the underreamer to become stuck in the wellbore.

A serious problem is created when an underreamer is stuck at a wellbore restriction and often the drillstring must be cut and the underreamer must be left in the wellbore.

When an underreamer is left in the wellbore further drilling cannot proceed unless the underreamer can be removed or the well is sidetracked.

Both required costly and time consuming procedures.

Most underreamer tools have no means to retain the cutting blades within the tool when the blades are in a closed or un-open position.

This reliance on gravity works well when drilling vertical wells, but not as well when drilling horizontal wells, as is becoming common.

During horizontal drilling the cutting blades of such underreamer tools have a tendency to be unexpectedly deployed and opened which presents unnecessary complications in the drilling process.

There is also no means in the prior art of cleaning debris from blade pockets or recesses.

This can create problems when debris becomes lodged in the blade pocket, preventing the blades from closing or retracting fully.

When the blades are not fully retracted, the extending blades may prevent the underreamer apparatus being pulled back through wellbore restrictions cleared when the blades were fully retracted and cause the underreamer to become stuck in the wellbore at the uncleared restriction.

A struck underreamer tool can create a very serious problem often remedied only by cutting the drillstring just above the underreamer so that the underreamer is left or dropped in the wellbore.

If this occurs the dropped underreamer will likely prevent further drilling and requiring the well to be sidetracked, which is a costly and time consuming procedure.

Images