Lost circulation, or the loss of drilling fluids while drilling, and its remedial treatment represent a significant technical and financial challenge to efficient geothermal energy production. While management of lost circulation has been conducted for more than a century, preventing fluid losses in geothermal systems presents unique technical challenges due to the rock types, flow pathways, and high pressure/temperature conditions. The different materials used to treat lost circulation are expected to vary in behavior at elevated at such extreme conditions. To understand this, a high pressure/temperature flow loop system was constructed to simulate flow conditions in a geothermal reservoir. A vessel containing a gravel pack simulating a highly fractured reservoir rock was placed in the system, and water was flowed through the pack while heated to ~190-225 ˚C. At these temperatures, nine tests were conducted by injecting different types of commonly used lost circulation materials mixed with xanthan gum and water into the gravel pack for a period of three days. For comparison, mixtures consisting of multiple materials were also tested to examine the impact of wider grain size distribution on clogging efficiency. Flow rate and fluid pressure were monitored throughout the tests to study how the different materials modified flow over time. After the tests, each gravel pack was dried and filled with low viscosity epoxy, then the epoxied sample was cut into sections. These sections were examined microscopically to evaluate the amount and distribution of the lost circulation materials that remained within the gravel pack clogging the pores. The experiments show how different types of lost circulation treatment materials modify flow while drilling in a high pressure/temperature geothermal system. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. This presentation describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. SAND2023-08985A

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