Fixed-cutter drill bit assembly and method

A rotary drill bit assembly having a longitudinal axis of rotation, said drill bit assembly being adapted to drill into an earth formation to form a drill hole having a hole side wall and a hole end wall, said assembly comprising:

• a. a drill bit housing having an upper end adapted to be connected to a drill string means and a lower end at which the housing has an operating surface, said housing being configured and arranged for rotation about said longitudinal axis;
• b. a plurality of cutter units, mounted at said operating surface at different circumferential axes along a circumferential cutting path having a circumferential axes at a pre-determined radial distances from the longitudinal axis, in a manner that as said drill bit assembly rotates about said longitudinal axis, said cutter units travel along said circumferential cutting path in a forward direction around said longitudinal axis;
• each cutter unit comprising:
• i. a forwardly located lead positioning cutter having a lower relatively hard positioning portion having at a lower end thereof a downwardly facing relatively blunt contact surface, which contact surface is located axially at a lower positioning location at the lower end of said positioning cutter to engage material at the drill hole end wall at said circumferential path;
• ii. a trailing cutter having a relatively sharp cutting edge portion which is positioned at said circumferential axis rearwardly of said lead positioning cutter at an axial location operationally lower than the contact surface of the positioning cutter, in a manner to be positioned and configured to cut into said drill hole end wall as said drill assembly advances into the drill hole;
• iii. a secondary trailing cutter which has a cutting edge and is positioned on said circumferential axis rearwardly of said trailing cutter, which is a primary cutter,
• whereby, in operation, said lead positioning cutters engage the drill hole end wall to locate the drill bit assembly axially relative to the end wall of the drill hole, and thus locate the cutting depth of the trailing cutter axially relative to the circumferential path.

A rotary drill bit assembly having a longitudinal axis of rotation, said drill bit assembly being adapted to drill into an earth formation to form a drill hole having a hole side wall and a hole end wall, said assembly comprising:

• a. a drill bit housing having an upper end adapted to be connected to a drill string means and a lower end at which the housing has an operating surface, said housing being configured and arranged for rotation about said longitudinal axis;
• b. at least one cutter unit mounted at said operating surface along a circumferential cutting path having a circumferential axis at a pre-determined radial distance from the longitudinal axis, in a manner that as said drill bit assembly rotates about said longitudinal axis, said cutter unit travels along said circumferential cutting path in a forward direction around said longitudinal axis;
• said cutter unit comprising:
• i. a forwardly located lead positioning cutter having at a lower end thereof a lower relatively hard positioning portion having a downwardly facing relatively blunt contact surface, which contact surface is located axially at a lower positioning location at a lower end of said positioning cutter to engage material at the drill hole end wall at said circumferential path;
• ii. a trailing cutter having a relatively sharp cutting edge portion which is positioned at said circumferential axis rearwardly of said lead positioning cutter at an axial location operationally lower than the contact surface of the positioning cutter, in a manner to be positioned and configured to cut into said drill hole end wall as said drill assembly advances into the drill hole;
• c. said assembly being arranged in a manner that said cutter unit travels axially in a generally helical path having a helical axis, as the drill bit assembly, in operation, rotates and travels downwardly as said drill bit assembly removes material from the end wall of the drill hole;
• d. said assembly having an operational depth dimension reference line, measured at angularly spaced locations around a circumferential axis of said helical path relative to axial distance from said helical path;
• e. said assembly having an axial depth dimension reference line measured relative to locations on the drill bit assembly along a plane that is fixedly located at an axial location on the drill bit assembly perpendicular to the longitudinal axis;
• f. said trailing cutter having a lowermost cutting edge portion which is lower, relative to the operational depth dimension line, than a lowermost portion of the contact surface of the positioning cutter;
• g. a liquid jet cutter positioned on said circumferential axis between said positioning cutter and said trailing cutter, said liquid jet cutter being arranged to direct a high velocity liquid jet downwardly against said end wall at a location forwardly of said trailing cutter,
• whereby, in operation, said lead positioning cutter engages the drill hole end wall to locate the drill bit assembly axially relative to the end wall of the drill hole, and thus locate the cutting depth of the trailing cutter axially relative to the circumferential path.

A rotary drill bit assembly having a longitudinal axis of rotation, said drill bit assembly being adapted to drill into an earth formation to form a drill hole having a hole side wall and a hole end wall, said assembly comprising:

• a. a drill bit housing having an upper end adapted to be connected to a drill string means and a lower end at which the housing has an operating surface, said housing being configured and arranged for rotation about said longitudinal axis;
• b. at least one cutter unit mounted at said operating surface along a circumferential cutting path having a circumferential axis at a pre-determined radial distance from the longitudinal axis, in a manner that as said drill bit assembly rotates about said longitudinal axis, said cutter unit travels along said circumferential cutting path in a forward direction around said longitudinal axis;
• said cutter unit comprising:
• i. a forwardly located lead positioning cutter having at a lower end thereof a lower relatively hard positioning portion having a downwardly facing relatively blunt contact surface, which contact surface is located axially at a lower positioning location at the lower end of said positioning cutter to engage material at the drill hole end wall at said circumferential path;
• ii. a trailing cutter having a relatively sharp cutting edge portion which is positioned at said circumferential axis rearwardly of said lead positioning cutter at an axial location operationally lower than the contact surface of the positioning cutter, in a manner to be positioned and configured to cut into said drill hole end wall as said drill assembly advances into the drill hole;
• iii. a liquid jet cutter positioned on said circumferential axis between said positioning cutter and said trailing cutter, said liquid jet cutter being arranged to direct a high velocity liquid jet downwardly against said end wall at a location forwardly of said trailing cutter,
• whereby, in operation, said lead positioning cutter engages the drill hole end wall to locate the drill bit assembly axially relative to the end wall of the drill hole, and thus locate the cutting depth of the trailing cutter axially relative to the circumferential path.

A rotary drill bit assembly having a longitudinal axis of rotation, said drill bit assembly being adapted to drill into an earth formation to form a drill hole having a hole side wall and a hole end wall, said assembly comprising:

• a. a drill bit housing having an upper end adapted to be connected to a drill string means and a lower end at which the housing has an operating surface, said housing being configured and arranged for rotation about said longitudinal axis;
• b. at least one cutter unit mounted at said operating surface along a circumferential cutting path having a circumferential axis at a pre-determined radial distance from the longitudinal axis, in a manner that as said drill bit assembly rotates about said longitudinal axis, said cutter unit travels along said circumferential cutting path in a forward direction around said longitudinal axis;
• said cutter unit comprising:
• i. a forwardly located lead primary cutter having a cutting edge with a lowermost cutting edge portion located axially at a lower location at the circumferential path;
• ii. a trailing secondary cutter having a cutting edge with a lowermost cutting edge portion, said secondary cutter being positioned at said circumferential axis rearwardly of said lead primary cutter;
• iii. a liquid jet cutter positioned on said circumferential axis behind said trailing cutter, said liquid jet cutter being arranged to direct a high velocity liquid jet downwardly against said end wall at a location rearwardly of said trailing cutter;
• c. said cutter unit being arranged to travel axially in a generally helical path having a helical axis, as the drill bit assembly, in operation, rotates and travels downwardly as said drill bit assembly removes material from the end wall of the drill hole;
• d. said lead cutter having a lead cutter operational depth dimension reference line, which is coincident with a helical path traveled by said lead cutter, and with location from said lead cutter operational depth dimension lines being measured at angularly spaced locations around said operational depth dimension reference line;
• e. said lead cutter having an axial depth dimension reference line measured relative to locations from a plane that is located at a fixed axial location on the drill bit assembly perpendicular to the longitudinal axis, and passing through the lowermost edge portion of the lead cutter;
• f. the trailing cutter being positioned relative to the lead cutter so that the distance of the lowermost edge portion of the trailing cutter is above a depth location of below said operational depth dimension reference line of the lead cutter by a distance of one half the axial distance that the cutter unit travels in one revolution,
• whereby said lead cutter cuts to a greater material depth along said circumferential path than said trailing cutter.

A method of drilling into an earth formation to form a drill hole having a hole side wall and a hole end wall, said method comprising:

• a. providing a rotary drill bit assembly having a longitudinal axis of rotation, with said drill bit assembly comprising:
• i. a drill bit housing having an upper end adapted to be connected to a drill string means and a lower end at which the housing has an operating surface, said housing being configured and arranged for rotation about said longitudinal axis;
• ii. at least one cutter unit mounted at said operating surface along a circumferential cutting path having a circumferential axis at a pre-determined radial distance from the longitudinal axis, in a manner that as said drill bit assembly rotates about said longitudinal axis, said cutter unit travels along said circumferential cutting path in a forward direction around said longitudinal axis, said cutter unit comprising:
• 1. a forwardly located lead positioning cutter having at a lower end thereof a lower relatively hard positioning portion having a downwardly facing relatively blunt contact surface, which contact surface is located axially at a lower positioning location at the lower end of said positioning cutter to engage material at the drill hole end wall at said circumferential path;
• 2. a trailing cutter having a relatively sharp cutting edge portion which is positioned at said circumferential axis rearwardly of said lead positioning cutter at an axial location operationally lower than the contact surface of the positioning cutter, in a manner to be positioned and configured to cut into said drill hole end wall as said drill assembly advances into the drill hole;
• 3. a secondary trailing cutter which has a cutting edge, positioned on said circumferential axis rearwardly of said trailing cutter, and positioning a lowermost cutting edge portion of said secondary trailing cutter at a depth location no higher than the lowermost cutting edge portion of the trailing cutter, relative to an operational depth dimension line of the trailing cutter,
• b. rotating said drill bit assembly with an axial downward force exerted by said drill bit assembly against said end wall, in a manner that said lead positioning cutter engages the drill hole end wall to locate the drill bit assembly axially relative to the end wall of the drill hole, and thus locate the cutting depth of the trailing cutter axially relative to the circumferential path.

A rotary drill bit assembly having a longitudinal axis of rotation, said drill bit assembly being adapted to drill into an earth formation to form a drill hole having a hole side wall and a hole end wall, said assembly comprising:

• a. a drill bit housing having an upper end adapted to be connected to a drill string means and a lower end at which the housing has an operating surface, said housing being configured and arranged for rotation about said longitudinal axis;
• b. at least one cutter unit mounted at said operating surface along a circumferential cutting path having a circumferential axis at a pre-determined radial distance from the longitudinal axis, in a manner that as said drill bit assembly rotates about said longitudinal axis, said cutter unit travels along said circumferential cutting path in a forward direction around said longitudinal axis;
• said cutter unit comprising:
• i. a forwardly located lead positioning cutter having a lower relatively hard positioning portion having a downwardly facing relatively blunt contact surface, which contact surface is located axially at a lower positioning location to engage material at the drill hole end wall at said circumferential path;
• ii. a trailing cutter having a relatively sharp cutting edge portion which is positioned at said circumferential axis rearwardly of said lead positioning cutter at an axial location operationally lower than the contact surface of the positioning cutter, in a manner to be positioned and configured to cut into said drill hole end wall as said drill assembly advances into the drill hole;
• iii. a secondary trailing cutter which has a cutting edge and is positioned on said circumferential axis rearwardly of said trailing cutter, which is a primary cutter,
• c. said cutter unit being arranged to travel axially in a generally helical path having a helical axis, as the drill bit assembly, in operation, rotates and travels downwardly as said drill bit assembly removes material from the end wall of the drill hole;
• d. said assembly having an operational depth dimension reference line, measured at angularly spaced locations around a circumferential axis of said helical path relative to axial distance from said helical path;
• e. said assembly having an axial depth dimension reference line measured relative to locations on the drill bit assembly along a plane that is fixedly located at an axial location on the drill bit assembly perpendicular to the longitudinal axis;
• f. said trailing cutter having a lowermost cutting edge portion which is lower, relative to the operational depth dimension line, than a lowermost portion of the contact surface of the positioning cutter,
• whereby, in operation, said lead positioning cutter engages the drill hole end wall to locate the drill bit assembly axially relative to the end wall of the drill hole, and thus locate the cutting depth of the trailing cutter axially relative to the circumferential path.

A method of drilling into an earth formation to form a drill hole having a hole side wall and a hole end wall, said method comprising:

• a. providing a rotary drill bit assembly having a longitudinal axis of rotation, with said drill bit assembly comprising;
• i. a drill bit housing having an upper end adapted to be connected to a drill string means and a lower end at which the housing has an operating surface, said housing being configured and arranged for rotation about said longitudinal axis;
• ii. at least one cutter unit mounted at said operating surface along a circumferential cutting path having a circumferential axis at a pre-determined radial distance from the longitudinal axis, in a manner that as said drill bit assembly rotates about said longitudinal axis, said cutter unit travels along said circumferential cutting path in a forward direction around said longitudinal axis, said cutter unit comprising:
• 1. a forwardly located lead positioning cutter having a lower relatively hard positioning portion having a downwardly facing relatively blunt contact surface, which contact surface is located axially at a lower positioning location to engage material at the drill hole end wall at said circumferential path;
• 2. a trailing cutter having a relatively sharp cutting edge portion which is positioned at said circumferential axis rearwardly of said lead positioning cutter at an axial location operationally lower than the contact surface of the positioning cutter, in a manner to be positioned and configured to cut into said drill hole end wall as said drill assembly advances into the drill hole;
• 3. a liquid jet cutter positioned on said circumferential axis between said lead positioning cutter and said trailing cutter;
• b. rotating said drill bit assembly with an axial downward force exerted by said drill bit assembly against said end wall, in a manner that said lead positioning cutter engages the drill hole end wall to locate the drill bit assembly axially relative to the end wall of the drill hole, and thus locate the cutting depth of the trailing cutter axially relative to the circumferential path, and
• c. directing a high velocity liquid jet from said liquid jet cutter downwardly against said end wall at a location forwardly of said trailing cutter.