Tubing collar position sensing apparatus, and associated methods, for use with a snubbing unit

This patent describes an apparatus for sensing the entry into a predetermined longitudinal section of a pipe extending downwardly into a well bore, of an anomaly of an elongated structure being axially moved through the interior of the pipe. It comprises: anomaly detecting means along the longitudinal section of the pipe, the anomaly detecting means for detecting variations in the longitudinal position of the anomaly relative to the longitudinal section of the pipe, and responsively generating output signal means indicative of the entry of the anomaly ins aid longitudinal section of the pipe; and isolating means for isolating the pipe interior above the section of pipe from the well bore pressure while permitting the axial passage of the elongated structure through the section of pipe