Abstract: Damages of cased wells in Daqing Oilfield mainly occur in the shale formations, and water soaking in shale is one of the main causes for such damages. The regime and velocity of water soaking in water are studied by experimental methods, taking core samples from Well 342-Jian-21 in Daqing Oilfield. Results show that water soaking in shale extends not only in the direction of stratification, but also in the perpendicular direction to stratification, and water flow occurs mainly in the micro-fractures; water soaking depth is determined by water injection pressure, and water soaking velocity increases rapidly with the pressure going up.