DUAL CONCENTRIC DRILLPIPE

摘要

A dual concentric drillstring assembly for use with rotary drilling apparatus and a downhole percussion motor in which the inner and outer pipes of each stand of drillpipe are rigidly secured together by full-length welded webs for minimized reduction in the annulus and maximized heat transfer between the inner and outer members of each stand of dual-wall pipe. Each stand of dual-wall pipe is equipped with web-welded dual box-and-pin tool joints so that coupling rotation of one stand of the drillpipe will simultaneously form two fluid-tight thread-coupled joints; the outer joint is fully thread-coupled while the inner joint is thread-coupled and includes a resilient seal at the interface between adjacent pipe joints so that full make-up of the inner pipe joint is not essential for sealing. For replacement of a worn pipe joint, cutting of the single outer pipe weld permits uncoupling of the dual pipe joint from the inner and outer pipe members of a stand.