Patent ID: 8037950

Claim:
A wellbore under reamer apparatus comprising: a) a drill string; b) a bit in fluid communication with the drill string wherein an annulus is defined between the well bore and an exterior surface of the drill string and the bit above a terminal end of the bit that is substantially uninterrupted along an extent of the drill string and the bit; c) at least one nozzle in fluid communication with the drill string; d) a mixture of a pressurized circulating fluid and a plurality of impactors flowing through the drill string and being discharged directly into the annulus from a nozzle exit that is oriented so that when the drill string and nozzle are disposed in a wellbore a portion of the plurality of impactors are discharged from the nozzle exit directly into the annulus to intersect and contact a formation with sufficient velocity to structurally alter the formation and increase the wellbore diameter.