Patent ID: 6047778
Filing Date: 2000-04-11
Classification: E21B

Abstract:
A percussion drill assembly for drilling a borehole in a formation, said drill assembly comprising:an elongated housing assembly having a first end adapted to removably connect said drill assembly to a drill string, and a second end adapted to receive a drill bit;a first compartment formed within said housing assembly and having a longitudinal axis;a shaft rotatably mounted in said housing assembly and extending into said first compartment, said shaft having an outer wall;a motor positioned in said housing assembly and adapted to rotate said shaft;an annular compressor piston having an inner annular wall, said annular compressor piston being positioned outwardly from and at least substantially concentrically with said shaft and being positioned within said first compartment for reciprocating motion within said first compartment along the longitudinal axis of said first compartment, said annular compressor piston dividing said first compartment into a first chamber and a second chamber which are fluidly isolated from each other;one of said outer wall and said inner annular wall having at least one circumferential endless groove formed therein and in the form of an endless loop which is inclined at an acute angle to the longitudinal axis of said shaft, and the other of said outer wall and said inner annular wall having at least one roller element carried thereby which extends into a respective endless groove so that rotation of said shaft in a first direction causes said compression piston to repeatedly cycle through its reciprocating movements within said first compartment along the longitudinal axis of said first compartment;a second compartment formed within said housing assembly and having a longitudinal axis;a hammer piston positioned within said second compartment for reciprocating motion within said second compartment along the longitudinal axis of said second compartment, said hammer piston dividing said second compartment into a third chamber and a fourth chamber which are substantially fluidly isolated from each other;a first passageway providing fluid communication between said first chamber and said third chamber;a second passageway providing fluid communication between said second chamber and said fourth chamber;seals for sealing said first and second compartments and said first and second passageways from fluid communication with any fluid received from the drill string, whereby said first and second compartments and said first and second passageways constitute a closed fluid system;each of said first, second, third, and fourth chambers, and said first and second passageways being filled with a fluid at a superatmospheric pressure;wherein movement of said compressor piston toward said first chamber increases the pressure of the fluid in said first chamber, in said first passageway, and in said third chamber, thereby causing the movement of said hammer piston toward said fourth chamber;wherein, movement of said compressor piston toward said second chamber increases the pressure of the fluid in said second chamber, in said second passageway, and in said fourth chamber, thereby causing the movement of said hammer piston toward said third chamber; andwhereby a predetermined extent of movement of said hammer piston toward one of said third and fourth chambers imparts an impact force to said drill bit.