Geothermal Drilling: A Baseline Study of Nonproductive Time Related to Lost Circulation

A single production geothermal well costs up to seven million dollars and a typical geothermal field contains 10 to 20 wells for a development cost of potentially $140 million according to a Geothermal Resources Group study. Capital cost coupled with exploration and resource uncertainty lead to high upfront project risk. This study analyzed the time and cost of detailed geothermal drilling operations. We found the largest cause of nonproductive time in geothermal wells is advancing through lost circulation zones, where drilling fluid is lost from the well. Mitigation measures implemented during lost circulation events can increase drilling time by a significant fraction of the drilling days. There is opportunity to reduce the drilling costs by addressing logistical inefficiencies and ineffective mitigation measures to minimize nonproductive time. This study reviewed daily drilling data for 38 geothermal wells drilled since 2009 in the U.S. The analysis presented here summarizes the lost circulation events identified in the available drilling data by assessing time per event, costs incurred, materials used, success of mitigation strategies, and resolution time. This study found that wells averaged over 100 hours of unprogrammed nonproductive time due to lost circulation, adding an estimated $185,000 to each well in rig costs. A plan for future research aimed at reducing lost circulation nonproductive time and cost is presented. operations. We found the largest cause of nonproductive time in geothermal wells is advancing through lost circulation zones, where drilling fluid is lost from the well. Mitigation measures implemented during lost circulation events can increase drilling time by a significant fraction of the drilling days. There is opportunity to reduce the drilling costs by addressing logistical inefficiencies and ineffective mitigation measures to minimize nonproductive time. This study reviewed daily drilling data for 38 geothermal wells drilled since 2009 in the U.S. The analysis presented here summarizes the lost circulation events identified in the available drilling data by assessing time per event, costs incurred, materials used, success of mitigation strategies, and resolution time. This study found that wells averaged over 100 hours of unprogrammed nonproductive time due to lost circulation, adding an estimated $185,000 to each well in rig costs. A plan for future research aimed at reducing lost circulation nonproductive time and cost is presented.