Stability and Breakdown of Acid-Induced Hydrated Silicate Gels and Metal Silicates Under Geothermal Conditions: A Preliminary Laboratory Study


Seiji NAKAGAWA, William KIBIKAS, Chun CHANG, TimothyKNEAFSEY, Patrick DOBSON, Abraham SAMUEL, Michael OTTO, Stephen BRUCE, Nils KAARGESON-LOE, Stephen BAUER

Key Words:

flow diverter, silicate gel, metal silicate hydrate, gel stability, laboratory experiment


Stanford Geothermal Workshop




Enhanced Geothermal Systems



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We conducted a series of laboratory experiments by mixing sodium silicate with different concentrations of 1) acid (for acid-induced hydrated silicate gel) or 2) metal chloride or acetate (for metal silicates). Stability of the produced gels and precipitates was tested after heating at 200 ˚C for ~72 hours (short-term tests) and up to 28 days (long-term tests). The short-term-test samples were subsequently exposed to high-pH fluid (sodium hydroxide solution) under the same pressure and temperature conditions to investigate the gel breakdown when exposed to alkaline solutions. For homogeneous, continuous gel samples, the gel strength was characterized by performing a mechanical compaction (squeezing) test. The gels produced from high Si/Na ratio sodium silicate solution and moderate concentration acids (HCl and acetic acids) exhibited varying degrees of gel shrinkage (syneresis) and gel collapse. When mixed with high pH NaOH solution, the gels disintegrated and exhibited significant volume reduction. In contrast, metal silicates were stable and did not show visible changes when exposed to NaOHaq. The experiments so far indicates that a combination of high-concentration sodium silicate (10 wt%) and acetic acid (4.6 wt%) produces a high-water-content silica gel that is stable under a high-temperature, closed (no-flow) environment. The objective of this work is to identify materials that can be used to seal unwanted fast-flow pathways in an EGS reservoir, with the potential of dissolving these plugs if needed. Sandia National Laboratories is a multi-mission 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.

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