Tight sandstones in China's Yanchang Formation have different types of changes due to natural processes. Scientists identified five types of changes in the sandstone, like dissolving and filling with minerals. They used a computer program to predict these changes accurately in wells. By studying many wells, they found that the changes in the sandstone are different depending on the direction of the water flow. The sandstone with minerals coating it is found in long shapes near areas where the sandstone dissolved. The changes in the sandstone get bigger as you move from one type to another. The thickness and amount of each type of change in the sandstone are linked to the cycles of the lake's water level.