Alternatives to Reduce the High Cost and Risk of Exploration Drilling for Geothermal Development Case Study-Northern Nevada 2010 to 2012

摘要

The U.S. Department of Energy (DOE) has been on the forefront of the development of geothermal resources in the United States, but interaction between the DOE and the hard rock mining industry has been minimal. In early 2010, SRK Consulting U.S. Inc. (SRK) was contracted to conduct a cooperative investigation of hydrogeologic and geothermal resources at a site in the Black Rock Desert of northern Nevada for the purpose of future mineral development. The hydrogeologic data collected for aquifer characterization and the methods used to collect these data were also used to characterize the geothermal resources within the project area. Initial characterization studies of the geothermal resources were conducted concurrently with mineral resource exploration under an approved mining exploration plan of operations issued through the U.S. Bureau of Land Management (BLM). Characterization and hydraulic testing of structures identified to be influencing or contributing to the hydrothermal regime of the project area were conducted using exploration core drill rigs. Hydraulic testing occurred in HQ (3.75-inch OD) size core holes at depths ranging between 700 and 2,770 feet below ground surface and in temperatures ranging between 110° and 196° Fahrenheit (F). Presently, the acknowledged limit of conventional retrievable packer systems is approximately 175°F. The Standard Wireline Packer System (SWiPS®) manufactured by Inflatable Packers, Inc. was modified with guidance from SRK to provide zonal isolation for hydraulic testing across a series of structures that had corrosive properties, water temperatures near 200°F, and moderate to high differential pressures during testing. Level TROLL® 700 Instrument pressure transducers, manufactured by In-Situ Inc., were utilized as the actual data collection mechanism within the SWiPS. Isolation of specific testing zones using the SWiPS allowed for quality characterization of the hydraulic conductivity, transmissivity, temperature, and chemistry of the water representing a relatively shallow geothermal system. The findings of this case study documented that the collection of hydraulic data across geothermal systems, utilizing low cost core drilling methods and the SWiPS, proved to be an effective means to significantly reduce the cost of traditional geothermal exploration drilling and data collection for preliminary geothermal resource characterization, evaluation, and development. Additionally, this case study identified that combining geothermal exploration permitting with conventional mineral exploration permitting could be advantageous in the collection of geothermal data due to the short permit turnaround period associated with a smaller disturbance area.