Technical Requirements for Geothermal Resource Confirmation

In 2017-2018, the Bureau of Land Management's Renewable Energy Coordination Office, through its Geothermal Program, funded the National Renewable Energy Laboratory (NREL) to analyze technical and environmental considerations related to geothermal resource confirmation drilling. NREL solicited input from a group of technical and environmental experts in the geothermal industry, along with analyzing National Environmental Policy Act of 1969 (NEPA) documentation for previously approved projects. The collected data and analysis will be used by the Bureau of Land Management to examine the possibility of developing a new classification of wells and/or expediting the NEPA compliance process, which could potentially reduce permitting and regulatory compliance timelines when compared to the current process for obtaining a geothermal drilling permit for resource confirmation drilling activities. This paper provides a summary of the technical requirements for confirming a geothermal resource. The analysis showed that confirming a geothermal resource requires confirming reservoir temperature, chemistry, permeability, and flow rate. Obtaining these data requires drilling at least two-preferably three-successful wells into the resource to conduct the necessary tests, including an interference test. Bottom-hole well diameters of at least 6” to 8” (0.15 to 0.2 m) are needed to limit the wellbore frictional pressure drop to effectively perform well flow and interference tests. Drilling these wells requires a drill rig with a mud pump and derrick capable of holding three drill pipes. This type of rig requires a minimum well-pad size of 2.5 acres (10 ⁴ m ² ) including surface area for a 1 million-gallon (3.8 million-liter) pit. Up to 15 acres (5×10 ⁴ m ² ) of total surface disturbance are needed for developing access roads and well pads to drill a total of three to five wells.