Abstract: To reveal the mesoscopic seepage behavior of tight sandstone after thermal treatment,laboratory electric heating experiments on tight sandstone were combined with a heterogeneous grain-flow model and finite element method(GBM-FEM)to investigate the generation of thermally induced microcracks,changes in seepage pathways,and permeability variations in tight sandstone after heat treatments at 300-900 ℃,clarifying the evolution of thermally induced microcracks and seepage behavior at the mesoscopic level.Results show that after lower-temperature treatment,uneven thermal expansion between minerals causes the development of microcracks,providing a small number of high-permeability points;the pressure drop tends toward linear,and flow paths are mainly through pore throats.As temperature increases,intragranular cracking turns significant,high-permeability points are widely distributed,and pressure presents sudden-drop phenomena,and microcrack pore-throat seepage becomes pro minent.Thermally induced microcracks exhibit stage-wise nonlinear growth with increasing temperature,developing first as intergranular microcracks followed by intragranular microcracks;their heterogeneous propagation leads to transformations in mesoscopic seepage pathways.700 ℃ is the threshold at which intragranular microcracking and permeability sharply increase.These findings provide a theoretical basis for optimizing parameters in tight sandstone reservoir wellbore thermal stimulation techniques.

Key words: tight sandstone, thermally induced microcracks, mesoscopic seepage, grain-flow model, finite element method