Patent ID: 7748478
Filing Date: 2010-07-06
Classification: E21B

Abstract:
1. A percussion drilling assembly for drilling through earthen formations and forming a borehole, the assembly coupled to the lower end of a drillstring and comprising: a fluid conduit including a tubular body having a first end, a second end, a through passage extending between the first end and the second end, an inlet port in fluid communication with the through passage, and at least one outlet port in fluid communication with the through passage of the fluid conduit; and an adjustable choke at least partially disposed in the through passage and adapted to decrease the volumetric flow rate of a compressed fluid through the first bypass port; a first annulus positioned radially between the adjustable choke and the at least one outlet port of the fluid conduit, wherein the first annulus is in fluid communication with the through passage of the flow conduit and the at least one outlet port of the flow conduit; wherein the adjustable choke comprises: