Shale gas reservoirs are characterized by a high proportion of adsorbed gas. In the mid-to-late stages of depletion production

a substantial amount of adsorbed CH

4

remains difficult to mobilize

which severely constrains the improv

ement of recovery efficiency. Gas injection is regarded as a key technical route for enhancing gas recovery; however

during its application in shale gas reservoirs

there is a lack of theoretical foundations and quantitative evaluation methods for optimizing parameters such as the mobilization mechanisms of CH

4

by injection media within multiscale pores

the selection of injection media for different shale types

and the optimization of injection timing and shut-in protocols. Based on total organic carbon (TOC) and clay mineral contents

middle-to-deep shale from southern Sichuan was classified

three typical nanopore models were established

and microscopic molecular simulations of gas huff-n-puff were performed. Further

integrated with the online low-field nuclear magnetic resonance (LF-NMR) monitoring and physical huff-n-puff simulations

the patterns of CH

4

mobilization by CO

2

/N

2

gas mixtures were revealed

and the potentials for gas injection-driven production stimulation and carbon sequestration were evaluated. The results indicate that:CO

2

competitive adsorption is more favorable for CH

4

mobilization within micropores and mesopores

while N

2

is more effective for mobilizing free gas in macropores. For shales characterized by high TOC and low clay content

experimental results show that injection of an 80 % CO

2

+20 % N

2

gas mixture at bottomhole pressures of 6.0-10.0 MPa yields an incremental recovery of 11.2 % -13.7 % and a sequestration rate of 42.7 % -82.2 % . Appropriately extending the shut-in duration is conducive to enhancing CH

4

recovery and CO

2

sequestration efficiency. Furthermore

it is recommended to increase the CO

2

proportion in the injection media for high-TOC

low-water

and low-clay shale reservoirs

whereas increasing the N

2

proportion is advisable for high-clay shale reservoirs. This study provides theoretical and technical support for the applica

tion of enhanced gas recovery and carbon sequestration in shale gas reservoirs.