Scaling Mechanism and Permeability Evolution of Sandstone Reservoir

Abstract

Knowledge of scaling mechanisms and the permeable behavior of rocks is highly important for geothermal energy development. In this study, the sandstone was soaked in a solution with the same chemical composition as geothermal water in Linyi City, Shandong Province. Permeability tests, scanning electron microscope tests, and nuclear magnetic resonance tests were performed on sandstone samples after different soak times (0, 30, 60, and 90 days) and temperatures (25 and 85 °C) to characterize the changes in microstructure and permeability properties. In addition, the changes in ion concentration in chemical solutions were compared. The results show that the wet mass and porosity of sandstone increase with the increase of soak time (0-70 d), and then entered the stable periods (70-90 d). As the soaking time, the medium and large pores inside the sandstone are transformed into small pores. The permeability of sandstone shows an overall decreasing trend, with the maximum decline when the soaking time is 30 d. At 25 °C, the scaling behavior is mainly involved by Ca2+, but at 85 °C Mg2+ is also involved in the scaling behavior. The scaling mechanism becomes the joint participation of Ca2+ and Mg2+. The results of the PHREEQC simulations are almost the same as the laboratory test results, indicating that sodium feldspar, potassium feldspar, and chlorite are generated slowly during the fouling process.