Microscopic Mechanism of Clay Minerals on Reservoir Damage during Steam Injection in Unconsolidated Sandstone

In this work, the swelling, transformation, and dissolution of clay minerals after steam injection in heavy oil reservoir were investigated, and the damage mechanism of steam injection was discussed to research the microscopic mechanism of clay minerals on reservoir damage during steam injection in unconsolidated sandstone. The results show that the swelling of clay minerals increases with the increase of the pH of the brine and decreases with the increase of the salinity of the brine. As we all know, the swollen clay minerals are liable to fall from the inner wall of the pass, which may cause the blockage of reservoirs. What is more, the environment of high temperature and high pH would promote the transformation of the clay minerals. Montmorillonite can be transformed into illite and analcime, and kaolinite can be transformed-due to the water sensitivity of the clay mineral-to montmorillonite and analcime, whereas illite is relatively stable. For the movement of particles in the reservoir during the injection of steam, the water sensitivity of clay mineral montmorillonite and the new clay minerals analcime can easily plug the small reservoir pore, which is one of the main ways to cause damage to the reservoir during steam injection. The dissolution of clay minerals increases with the increase of temperature and increases with the increase of the pH of the brine. The dissolution of clay minerals would produce a large number of particles and make the rock matrix more loose, which may cause some reservoir damage, such as reservoir collapse, and so on.