Patent ID: 7134514

Claim:
A dual wall drill string assembly which allows dual circulation for directional drilling, said assembly comprising: (A) a metallic outer tube having: (1) an outer tube first end; (2) an outer tube second end opposite the outer tube first end; (B) a flexible, substantially non-metallic inner tube that is substantially enclosed within and generally coaxially aligned with the outer tube, said inner tube having: (1) an inner tube first end; (2) an inner tube second end opposite the inner tube first end which defines a tube length therebetween; (3) an inner tube diameter which is generally constant along the tube length from the inner tube first end to the inner tube second end; (4) wherein the flexible inner tube comprises a plurality of flexible inner tube sections, each of said flexible inner tube sections having a male connection end and a female connection end, each male section end being adapted to be connected to a female connection end on another flexible inner tube section and each female connect and being adapted to be connected to a male connection end on another flexible inner tube section; wherein the inner tube and the outer tube define an annular channel there between, wherein the non-metallic inner tube is formed of a material which allows it to bend to an arcuate path of a borehole for drilling a deviated wellbore without limiting bending of the metallic outer tube; (C) a means for conveying fluid through the annular channel toward the inner tube first end; wherein the annular channel is adapted to convey drilling fluid under pressure toward the inner tube first end, and the inner tube is adapted to convey cuttings toward the inner tube second end.