Percussion drill string assembly

A combination of a percussion drill string apparatus and tool comprising:

• an upper sub having a substantially vertical axis and forming a conduit along said axis, said upper sub including a packing in said conduit and a packing nut under said packing;
• an outer barrel threadably connected to said upper sub and having a hollow inside forming a shoulder;
• an inner barrel that has a lower tool-holding portion for holding a cutting tool and that lies partially within said outer barrel said inner barrel being slideable along said vertical axis therewithin, said inner barrel having a threaded portion and having a wash pipe extending up from said threaded portion into said conduit and sealed to said packing;
• a hanger nut threadably engaged with said threaded portion of said inner barrel and large enough to rest on said shoulder of said inner barrel;
• the top of said hanger nut lying more than one foot below the level of said packing when said hanger nut rests on said shoulder;
• said outer barrel and upper sub being threadably joined at about the level of said packing nut, so when the outer barrel and upper sub are disconnected, there is ready access to the packing nut but not to said hanger nut;
• a tool of small enough diameter to pass into the top of said outer sub, and which is formed to engage said hanger nut and turn it.

In a percussion drill apparatus which includes a drill string having an outer barrel near its lower end extending along a substantially vertical axis, and a lower inner barrel lying partially within the outer barrel and coupled to the outer barrel by spline means which allows the outer barrel to move along said vertical axis relative to the inner barrel while causing them to rotate together about said axis, the inner barrel having means for holding a drill bit at its lower end, the inner barrel forming an upwardly facing anvil surface and the outer barrel forming a downwardly facing hammer surface which pounds on the anvil surface when the outer barrel drops, the improvement wherein:

• said anvil surface lies substantially no higher than said spline means on said inner barrel, and said inner barrel has a lower outer surface extending downwardly from said anvil surface;
• said outer barrel includes a cage extending downwardly from said hammer surface and surrounding said lower outer surface of said inner barrel;
• and
• a lower seal means lying below said hammer and anvil surfaces and sealing said cage to said lower outer surface of said inner barrel said case being slidable relative to said inner barrel, whereby said seal protects the hammer and anvil surfaces from cuttings.