How a Large Loop Field Was Redesigned to Overcome a Complete Loss of Mud-Rotary Circulation at Depth in the Boreholes

     Mud-rotary drilling has to maintain the continuous circulation of the drilling mud in order to remove the cuttings and to keep the borehole walls from collapsing.  Air-rotary drilling is not quite as dependent on continuous circulation of the air, water, and cuttings, and so some air rotary bore holes are completed to depth with limited circulation to the ground surface.  This case-history example shows how, when all mud-rotary circulation was lost at depth while drilling geothermal boreholes in a commercial loop field, the borehole depths and the loop field design were changed to provide the same heat-transfer capacity while maintaining mud circulation.            

     The new borehole depth and loop field design provided the driller with the opportunity to drill and loop a 150-foot borehole and be set up on the next borehole in only 45 minutes.  The loop field design was revised from a parallel-header, reverse-return layout to include series connections of adjacent loop to maintain the same design flow path length and head loss for each loop on a header.  In a parallel-header loop field design it is essential to maintain equal lengths of each loop so their head-losses are equal and each loop receives equal flow.  This case-history example will show all of the step-by-step loop field design changes necessary to complete the mud-rotary borehole drilling and to maintain the heat-transfer capacity required for this commercial loop field.