Hammer drill

1. A downhole apparatus connected to a workstring within a wellbore, said workstring being connected to a bit member having a motor means comprising:

a power mandrel operatively connected to the motor means;

an anvil sub including an upper section, a lower section and an internal bore, the upper section having an enlarged outer diameter relative to the outer diameter of the lower section, the upper section of the anvil sub including an outer side wall having an external surface and an internal surface, the internal surface extending from a top anvil surface to a radial shoulder, the internal surface containing a plurality of partial concave-shaped cavities positioned adjacent to the radial shoulder, wherein the lower section of the anvil sub is operatively connected to the bit member, wherein the power mandrel extends through the internal bore of the anvil sub and is operatively connected to the bit member;

a plurality of rolling elements, each of the rolling elements partially disposed within one of the partial cavities of the anvil sub;

a radial bearing housing unit operatively connected to the workstring, the radial bearing housing unit being disposed about the power mandrel;

a spring saddle operatively attached to the radial bearing housing unit;

a spring spacer disposed about the spring saddle;

a spring having a first end and a second end, the first end abutting the spring saddle;

a hammer member slidably attached to the spring saddle and abutting the second end of the spring, the hammer member including a top section and a bottom section, the top section having an outer diameter larger than an outer diameter of the bottom section, the top section terminating at an outer hammer surface and the bottom section extending from the hammer surface and terminating at a radial cam surface, the radial cam surface disposed within the upper section of the anvil sub and positioned adjacent to the internal surface of the outer side wall, the radial cam surface of the hammer member cooperating with the rolling elements disposed in the anvil sub for axially displacing the hammer member from the anvil sub and generating an axial impact upon rotation of the anvil sub.

2. The apparatus of claim 1 , wherein the hammer member and the anvil sub are below the radial bearing housing unit.

3. The apparatus of claim 2 , wherein the workstring is a tubular drill string or a coiled tubing string.

4. The apparatus of claim 1 , wherein the hammer surface contacts the top anvil surface to generate the axial impact upon rotation of the anvil sub.

5. The apparatus of claim 1 , further comprising a thrust race and a plurality of thrust bearings disposed within the anvil sub, wherein the plurality of thrust bearings are disposed between the radial shoulder and the thrust race, wherein the thrust race is in contact with the rolling elements, and wherein the thrust race rotates relative to the anvil sub as the rolling elements engage the radial cam surface of the hammer member.

6. The apparatus of claim 5 , further comprising an internal housing disposed within the anvil sub, said internal housing including a partial cavity dimensioned to partially house one of the rolling elements so that the rolling element is retained between the inner wall of the anvil sub and the internal housing, and wherein the radial cam surface of the hammer member is disposed between the inner wall and the internal housing of the anvil sub.

7. A method for drilling a wellbore with a workstring, comprising:

a) providing a downhole apparatus connected to the workstring within the wellbore, the downhole apparatus being connected to a bit member and comprising: a power mandrel operatively connected to a motor means; an anvil member with a radial cam surface operatively formed on the bit member, said anvil sub including an upper section, a lower section and an internal bore, the upper section having an enlarged outer diameter relative to the outer diameter of the lower section, the upper section of the anvil sub including an outer side wall having an external surface and an internal surface, the internal surface extending from a top anvil surface to a radial shoulder, the internal surface containing a plurality of partial concave-shaped cavities positioned adjacent to the radial shoulder, wherein the lower section of the anvil sub is operatively connected to the bit member, wherein the power mandrel extends through the internal bore of the anvil sub and is operatively connected to the bit member; a plurality of rolling elements, each of the rolling elements partially disposed within one of the partial cavities of the anvil sub; a radial bearing housing unit operatively connected to the workstring, the radial bearing housing unit being disposed about the power mandrel; a spring saddle operatively attached to the radial bearing housing unit; a spring spacer disposed about the spring saddle, a spring having a first end and a second end, the first end of the spring abutting the spring saddle; a hammer member slidably attached to the spring saddle and abutting the second end of the spring, the hammer member including a top section and a bottom section, the top section having an outer diameter larger than an outer diameter of the bottom section, the top section terminating at an outer hammer surface and the bottom section extending from the hammer surface and terminating at a radial cam surface, the radial cam surface disposed within the upper section of the anvil sub and positioned adjacent to the internal surface of the outer side wall, the radial cam surface of the hammer member cooperating with the rolling elements disposed in the anvil sub for axially displacing the hammer member from the anvil sub and generating an axial impact upon rotation of the anvil sub;

b) lowering the workstring into the wellbore;

c) contacting the bit member with a reservoir interface;

d) engaging a distal end of the power mandrel with a surface of the bit member;

e) slidably moving the anvil sub;

f) engaging the radial cam surface of the hammer member with the rolling elements disposed in the anvil sub to axially displace the hammer member from the anvil sub and to generate an axial impact upon rotation of the anvil sub, thereby imparting an impact force on the bit member.

8. The method of claim 7 , wherein the method further provides that static weight on the bit member is transmitted to the bit member different than the impact force created by the hammer member and anvil sub whereby the maximum force on the bit member is the sum of the static weight on bit member and the impact force created by the hammer member and the anvil sub.

9. The method of claim 7 , wherein the method further provides that independent of the amount of weight on the bit an oscillating impact force will be generated if the radial cam surface of the hammer member and the rolling elements disposed in the anvil sub are engaging each other.

10. The method of claim 7 , wherein the method further provides that the impact force is transmitted through the hammer surface and the top anvil surface.

11. The method of claim 7 , wherein the motor means is simultaneously rotationally driving the bit member and axially driving the hammer member.

12. The method of claim 7 , wherein there is no axial movement of the radial bearing housing unit relative to the power mandrel that is rotationally driving the bit member and axially driving the hammer member.