Lowest Required Surface Temperature for Thermal Spallation in Granite and Sandstone Specimens: Experiments and Simulations

Abstract

Thermal spallation may be economically advantageous for the drilling of deep wells and is of strong interest for the development of oil, gas and geothermal energy. The lowest required surface temperature (LRST) represents the minimal surface temperature that can induce the spallation of rock. A deeper understanding of the LRST can be used to determine when thermal spallation can be successfully initiated. However, to the best of our knowledge, comparisons of LRST in sandstone and granite have not been performed. Based on experiments and simulations, this study investigated the LRST of one type of granite and one type of sandstone in thermal spallation. First, we conducted thermal spallation experiments using rock specimens and measured the LRST by an infrared thermometer. Then, the heat flux was evaluated and compared between the sandstone and granite specimens. Meanwhile, a three-dimensional numerical model was built to simulate the heat transfer and stress distribution in the granite and sandstone specimens. The temperature and von Mises stress between the granite and sandstone specimens were compared, and then the breakage-probability factors were investigated to compare the experimental results and simulation results. This study clarifies the differences in LRST between one type of granite and one type of sandstone.