Modeling and Case Simulation of Pores and Cracks Evolution In Granite Due To Geochemical Reactions Associated With Silica

Deep geothermal reservoirs have high temperature and are abundant, which have great exploitation potential, yet have not been commercially developed so far. One of the key factors is geochemical reactions. The geochemical reactions under deep geothermal reservoir conditions change the characteristics of pores and cracks, and hence induce the productivity change of geothermal reservoirs during exploitation. In this paper, there were four granite samples recovered from Gonghe Basin in Qinghai Province. Lithological observation and X-ray diffraction were performed to identify the minerals and their mass percent. Because the granite samples are rich in silica, the relationship between geochemical reactions associated with silica and the evolution of pores and cracks in rocks was established based on the principles of geochemical dynamics and thermodynamics considering the alteration/dissolution-diffusion-precipitation processes of silica. Finally, the case simulation of pores and cracks evolution was conducted based on the results above, indicating the lowering of pores and cracks surface due to silica release is prior to silica depositing and silica precipitation has a dominated effect.