The tight oil resource is extremely abundant in China, but the production and researches of tight oil is just at the beginning stage. There are great challenges in developping the tight reservoirs. Although small pore size and low permeability can greatly increase the development difficulty, spontaneous imbibition mostly resulted from the capillary pressure is a very important and useful way for tight oil production. In the laboratory experiments through the homemade imbibition apparatus and the effects of different parameters on the imbibition recovery factor was investigated. The results show that the imbibition recovery factor is significantly increased with the increasing of temperature. For rocks with similar parameters ,the recovery factor is increased as the formation water salinity decreases within a certain range. The recovery factor by imbibition varied due to the different boundary conditions. In addition, the curves show good normalization character after processing the data with dimensionless, which can be used to estimate the actual production efficiency of the field. Undoubtedly, the research is of great significance for effectively developing the tight oil reservoir.

Cyclic waterflooding is an important method to improve oil recovery of vertically heterogeneous reservoir. The experiment results showed that it was difficult to enhance oil recovery by means of imbibition after a certain degree of waterflooding. Coreflooding experiments confirmed the effectiveness of cyclic waterflooding to increase oil recovery for the vertically heterogeneous reservoir and the increase trend to lower as more cycles were applied. The mechanical mechanism of cyclic waterflooding was investigated by means of capillary bundle model. Imbibition will play a role until the force field on the fluid is balanced. The main mechanism for the cyclic waterflooding method is related to the change of capillary pressure instead of the absolute value of the capillary pressure. Additional pressure between the layers with different permeability which is induced by the change of water injection scheme can cause the corresponding change of capillary pressure in the reservoir. The research provides some insight to improve the understanding and practice of cyclic waterflooding.