Effect of Temperature and Acidification on Reinjection of Geothermal Water into Sandstone Geothermal Reservoirs: Laboratory Study

Abstract

Geothermal reinjection is a new method of geothermal development which can maintain regional geothermal reservoir pressure, and it is conducive to the sustainable development and utilization of geothermal heat. However, geothermal reinjection blockage has always been a problem that restricts geothermal development and utilization, causing geothermal reservoirs, especially the attenuation of sandstone geothermal reservoirs. Considering an example of a typical sandstone geothermal reservoir in Binzhou, in this study, in situ geothermal fluids and borehole cores were collected to conduct automatic rotary reactor experiments under different temperature and acidification conditions in laboratory studies. The chemical compositions of geothermal fluids and core samples before and after the experiment were compared. The results show that both temperature and acid have significant effects on the water–rock interaction. The effect of temperature is mainly shown on mineral solubility, while the effect of acidification is shown in the increased dissolution of calcite and feldspar minerals. Compared with high temperature (65 °C) reinjection conditions, the calcite precipitation at a low temperature (45 °C) is largely reduced, but with larger total mineral volume changes, mainly due to the formation of montmorillonite. Therefore, from the laboratory studies, it is recommended to preform reinjection using a low-temperature fluid, without adding acids.