Shale gas reservoirs

which develope micro-nano pore throats and fractures

have high clay mineral content

and strong heterogeneity of porosity. Therefore

large-scale hydraulic fracturing is usually needed to realize the effective exploitation. In the process of hydraulic fracturing

the spontaneous imbibition of the water phase will trigger a series of physical and chemical effects on the shale gas reservoir

changing the pore structures

physical and chemical properties of shale gas reservoirs

thereby affecting the production of shale gas. In order to further clarify the influence mechanism of water phase imbibition in shale gas reservoirs

multiple repetitive imbibition experiments were carried out. Based on the changes in rock sample quality caused by mineral dissolution

the visual characteristics of samples from scanning electron microscope

the observation of nuclear magnetic resonance pore structures

and the change of physical properties

the impact of imbibition on the microscopic pore structure

permeability and porosity of shale are revealed. The results show that: ① Water imbibition causes fractures in shale

thus changing the pore structure; ② The proportion of macropores increases in shale samples with significantly improved porosity

which indicates that water imbibition will increase the pore space in shale; ③ The imbibition capacity is positively correlated with the porosity and permeability of shale

and the physical properties of shale are significantly improved after imbibition. In addition

the time index is found to be able to quantitatively characterize the influence of imbibition on the pore-throat connectivity of shale.