Rotational impact drill assembly

A method for drilling a subterranean formation with a PDC drill bit depending from a drill string, the method comprising the steps of:

• providing an assembly adjacent the drill bit;
• rotating the assembly to rotate the drill bit at a rotational speed at least equal to a rotational speed of the assembly;
• rotating a hammer to store potential energy in the assembly;
• and
• periodically impacting the rotating hammer with an anvil on the drill bit so as to impart the stored potential energy to the drill bit for periodically driving the drill bit at a rotational speed greater than that of the housing and increasing drilling torque.

A rotational impact assembly for a drill bit comprising:

• a housing adapted to be rotated by a first rotary drive;
• a drill bit extending from the rotating housing for co-rotation at a rotational speed at least equal to a rotational speed of the housing;
• and
• a second rotary drive located in the housing for periodically and rotatably impacting the drill bit to increase drilling torque.

A rotational impact assembly for a drill bit comprising:

• a housing adapted to be rotated by a first rotary drive, the housing having a bore;
• a motor located in the bore for rotating a stator shaft;
• a bit shaft extending from the bore of the housing and being adapted at a downhole end for rotatably driving the drill bit;
• means for normally driving the drill bit with the housing at a rotational speed at least equal to a rotational speed of the housing;
• and
• means for periodically coupling the stator shaft and bit shaft for co-rotation whereby rotational energy is transferred from the stator shaft to the bit shaft for increasing dulling torque.

A rotational impact assembly for a drill bit comprising:

• a housing adapted to be rotated by a rotary drive;
• a bit extending from the housing and being rotatably driven thereby;
• and
• a motor located in the housing, driven by drilling fluids and comprises a stator shaft having a first downhole position and in which a frictional interface is engaged between the stator shaft and the housing to prevent operation of the motor, and a second uphole position in which the frictional interface is disengaged for permitting operation of the motor, for periodically and rotatably impacting the drill bit.