The Effects of Long-Term Waterflooding on the Physical and Mechanical Properties of Tight Sandstones

Waterflooding is an important means to increase production of tight sandstone reservoirs, however, waterflooding for a long period of time (decades) will have a significant impact on the physical and mechanical properties of the sandstone. In order to explore the effects of long-term waterflooding on the physical and mechanical properties of tight sandstones, we carried out the study based on real formation cores with waterflooding for 15 years. For comparison, the experiments of real formation cores without waterflooding were also conducted. Through triaxial compression tests, the difference in elastic properties between the rocks with and without waterflooding was obtained. And the influence of waterflooding on mineral composition of rocks was also obtained. Finally, the change in microstructure after being waterflooded was gained from scanning electronic microscope (SEM) images and nuclear magnetic resonance (NMR). During long-term waterflooding, scour action and water-rock reaction eroded the internal structure of the rock. Especially the loss of clay minerals in the form of cement and fillers causes a decrease in cohesion among the rock particles and an increase in porosity.