DUAL WALL DRILL STRING ASSEMBLY

摘要

A coil tubing or jointed dual wall drill string assembly for subsurface drilling. The drill string assembly includes a metallic outer tube having an outer tube first en d and an outer tube second end opposite the outer tube first end. The assembly also include s a flexible, substantially non- metallic inner tube that is substantially enclosed within and generally coaxially aligned with the outer tube. The flexible, substantially non- metallic inner tube has an inner tube first end, an inner tube second end opposite the inner tub e first end, and an inner tube inner diameter. The inner tube and the outer tube define an annular channel therebetween. The drill string assembly also includes a means for conveying fluid through the annular channel toward the inner tube first end. 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.