Experimental and Simulation Studies on Optimum Hydraulics Conditions in Long Extended-Reach Geothermal Well Drilling

Abstract

An ongoing geothermal R&D project in Japan aims to develop an environment-friendly, low-cost, extended-reach drilling technology that enables access to geothermal resources from outside the national parks where they occur. Drilling long, tangential sections using low-density drilling fluid in extended-reach geothermal wells with subnormal pressure and lost circulation zones is challenging. Implementation of both effective cuttings transport and maintenance of an appropriate equivalent circulating density (ECD) in geothermal wells is contradictory and much more difficult than in oil and gas wells. We conducted a number of experiments to optimize the drilling hydraulics in highly inclined geothermal wells using a large-scale flow-loop apparatus. Optimum hydraulics conditions were obtained in terms of both hole cleaning and ECD management. To evaluate the experimentally obtained optimum conditions at field scale, we conducted numerical simulations on the drilling hydraulics for a long, extended reach model well. Recommendations for preventing drilling problems such as poor hole cleaning, high torque and drag, stuck pipes, borehole instability and lost circulation are presented.