Multi-factors model of pores geometries interplayingly affecting spontaneous imbibition in reservoir rock

China is short of natural gas resources, and these low-permeable reservoirs (such as tight gas, shale gas and coalbed methane) being difficultly developed account for a large proportion. How to efficiently developed this part of strategic resources is of great significance. Presently, hydraulic fracturing technology is regarded as an effective method for developing low-permeability reservoirs. However, it is confronted with the seepage and suction of fracturing fluid into reservoirs which traps the channels of gas escaping to reduce their recovery rate. In order to fully reveal the mechanism of the influence of the geometrical parameters of reservoir rock pore structure on its macroscopic spontaneous imbibition, assuming that the wetting phase is Newtonian fluid and migrated as laminar flow and simplifying the pore structure as a capillary bundles, a universal spontaneous imbibition (SI) model considering the porosity, pore size, phase saturation and pore geometry is established along with the acquirement of comprehensive geometry parameter and pore-throat factor by utilizing the Hagen-Poiseuille (H-P) equation. The model is verified against the experimental data and is compared with the various existing models along with evaluation of their advantages and disadvantages. Based on the model, the quantitative relationship between comprehensive geometric parameter and porosity is obtained by fitting the experimental data, and the SI mechanism of porous rock is revealed in the coupling effect of various micro geometric factors. The results are as follows. The comprehensive geometric parameter is directly proportional to the quadratic power of pore-throat factor, cubic power of shape factor and topological factor, and inversely proportional to the quadratic power of tortuosity factor. The smaller the comprehensive geometric parameter, the weaker the water SI. The influence sensitivity of channel tortuosity, pore shape, pore-throat characteristics and topological characteristics to imbibition velocity increases successively. The comprehensive geometric parameter tends to decay exponentially with the increase of porosity and thus the rocks with large porosity may have weak water SI. The topological factor increase with the increase of porosity, whereas the tortuosity, shape and pore-throat factors increase with the decrease of porosity.