Reamer

A reaming tool for enlarging an underground borehole, comprising:

• a tool body having a longitudinal axis therethrough;
• and
• at least three cutter assemblies coupled to the tool body and distributed azimuthally around the longitudinal axis of the tool body, the at least three cutter assemblies being radially expandable relative to the tool body and the longitudinal axis, wherein:
• a first cutter assembly of the at least three cutter assemblies includes a first supporting structure having a length along the longitudinal axis between uphole and downhole ends of the first supporting structure, the first cutter assembly bearing a first sequence of cutters which are distributed along the length of the first supporting structure, cutters of the first sequence of cutters having hard surfaces facing in a direction of rotation of the tool about the longitudinal axis;
• a second cutter assembly of the at least three cutter assemblies includes a second supporting structure having a length along the longitudinal axis between uphole and downhole ends of the second supporting structure, the second cutter assembly bearing a second sequence of cutters which are distributed along the length of the second supporting structure, cutters of the second sequence of cutters having hard surfaces facing in the direction of rotation of the tool;
• a third cutter assembly of the at least three cutter assemblies includes a third supporting structure having a length along the longitudinal axis between uphole and downhole ends of the third supporting structure, the third cutter assembly bearing a third sequence of cutters which are distributed along the length of the third supporting structure, cutters of the third sequence of cutters having hard surfaces facing in the direction of rotation of the tool;
• the cutters of the first sequence of cutters are spaced along the length of the first supporting structure and relative to each other with a spacing equal to spacing between the cutters of the second sequence relative to each other along the second supporting structure, and spacing between the cutters of the third sequence relative to each other along the third supporting structure, except that a distance from the first sequence of cutters to the downhole end of the first supporting structure, a distance from the second sequence of cutters to the downhole end of the second supporting structure, and a distance from the third sequence of cutters to the downhole end of the third supporting structure are each different;
• and
• an outer face of each of the first, second, and third support structures includes surfaces at the same radial distance from the longitudinal axis as extremities of cutters in the respective first, second, and third sequences of cutters, where cutters in each of the first, second, and third sequences of cutters are at different radial distances from the longitudinal axis.