1. Field of the Invention
This invention relates to a percussive tool, and in particular but not exclusively to a percussive tool for use in drilling operations utilizing drilling fluid or xe2x80x9cmudxe2x80x9d.
2. Description of the Prior Art
It has long been appreciated that providing a percussive action to a drill bit can increase the drilling rate, particularly when drilling through hard rock. Air driven percussion drills have been used successfully for a number of years in the mining industry. Also, hydraulic fluid driven percussion tools are well established in the construction industry. However, attempts to provide a percussion drill utilizing drilling fluid or xe2x80x9cmudxe2x80x9d as the working fluid have met with difficulties; the evasive nature and high solids content of drilling fluid tends to damage the valve mechanisms necessary to provide the percussive effect.
It is among the objectives of embodiments of the present invention to provide a percussion drill which will operate successfully and reliably utilizing drilling fluid or mud as the working fluid.
According to the present invention there is provided a percussion drill comprising:
a fluid transmitting body;
a drill bit support;
a mass movable relative to the body for impacting on the drill bit support;
means associated with the mass for creating a fluid pressure force on said mass; and
a rotating valve for controlling flow of fluid through the body to produce a varying fluid pressure force on the mass and induce acceleration of the mass.
The use of a rotating valve facilitates use of the drill in applications where the working fluid contains solids, such as drilling fluid.
According to another aspect of the present invention there is provided a percussive drilling method comprising the steps:
providing a drill having a fluid transmitting body, a drill bit support, a mass movable relative to the body for impacting on the drill bit support and a rotating valve for controlling flow of fluid through the body; and
passing drilling fluid through the body to the drill bit support via the rotating valve to vary the flow of the fluid through the body and produce a varying fluid pressure force on the mass to induce acceleration of the mass.
Preferably, the valve rotates around a longitudinal axis, and most conveniently around the central longitudinal axis of the body. In other embodiments the valve may rotate around a transverse or lateral axis.
The valve may be provided separately of the means for creating fluid pressure force on the mass, or may be integral therewith.
Preferably also, the valve comprises two portions, each defining a fluid port, such that relative rotation of the parts varies the alignment of the ports and varies the flow area defined thereby. Most preferably, one portion is rotatable relative to the body. The valve ports may be in the form of slots on a common axis. In an alternative embodiment, one of the valve portions provides fluid communication with alternative fluid paths through the body, one of said fluid paths providing fluid communication with the means for creating fluid pressure force on the mass, and another of said paths by-passing said means.
Preferably also, the valve permits fluid flow through the body in all valve configurations, to assure a continuing supply of drilling fluid to the drill bit.
Preferably also, the mass is spring mounted in the body, to provide a return force; the fluid pressure force will tend to induce acceleration of the mass in one direction, and the return action of the spring will accelerate the mass in the opposite direction, when the spring force is greater than the fluid pressure force. In other embodiments, the return force may simply be gravity, or may be an opposing fluid pressure force.
The mass may define a flow passage therethrough, and the flow passage may define a restriction such that fluid flowing through the mass is subject to a pressure drop, creating a pressure force across the restriction.
The drill bit support will typically be adapted for mounting a drill bit to the body and the mass will impact directly on the support. However, in some embodiments the mass may not impact directly on the support; there may be an intermediate member or other force transmission means therebetween.
Preferably also, the drill bit support is spring mounted in the body, and is preferably splinted to the body.
Preferably also, the body is adapted for mounting to a drill string.
Preferably also, the drill includes means for driving the valve, such as a valve motor, and most preferably a drilling fluid driven positive displacement motor.
According to a further aspect of the present invention there is provided a percussion tool comprising:
a fluid transmitting body;
a bit support;
a mass movable relative to the body for impacting on the bit support;
means associated with the mass for creating a fluid pressure force on said mass; and
a valve for providing a continuing but varying flow of fluid through the body to produce a varying fluid pressure force on the mass and induce acceleration of the mass.
The use of a valve which is not required to stop flow through the body, that is the valve is not required to seal, facilitates use of the drill in applications where the working fluid contains abrasives or solids, such as drilling fluid; as the valve is not required to be fluid tight, clearances, materials and other aspects of the valve specification may be selected with the primary aim of withstanding operation using abrasive working fluid.
According to a still further aspect of the present invention there is provided a method of providing a percussive action in a downhole tool, the method comprising the steps:
providing a tool having a fluid transmitting body, a bit support, a mass movable relative to the body for impacting on the bit support and a valve for controlling flow of fluid through the body; and
passing drilling fluid through the body and the valve to provide a varying but continuing flow of fluid through the body and producing a varying fluid pressure force on the mass to induce acceleration of the mass.
The bit support may be integral with a bit, or may provide mounting or support for a separable bit. The bit may be a drill bit, a chisel or a hammer.