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Does Brine Influence the Short-Term Strength of Sandstone? Implications for Geothermal in the Upper Rhine Graben
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 81st EAGE Conference and Exhibition 2019, Jun 2019, Volume 2019, p.1 - 5
Abstract
Laboratory studies designed to measure the strength of rocks from a geothermal reservoir, to assist geothermal reservoir prospection, stimulation, and optimisation strategies, often perform experiments on dry or water-saturated samples. Since these rocks in-situ are saturated with hydrothermal brine, we performed laboratory strength experiments to explore the influence of brine on the short-term strength of sandstones (from the Buntsandstein, a lithostratigraphic unit common to many geothermal sites in the Upper Rhine Graben) from the EPS-1 exploration well at the Soultz-sous-Forêts geothermal site (France). Our experiments show that, although the water- and brine-saturated sandstones were weaker than their dry counterparts, there was essentially no difference between the strength of the sandstones saturated in water and brine. We consider the reduction in strength in the presence of water or brine as the result of a decrease in specific surface free energy. A decrease in the short-term strength of reservoir sandstones in the presence of hydrothermal brines likely require brines with higher salinities and/or lower values of pH than those typically found within the Upper Rhine Graben (salinity of ~10% and a pH of 5.5).