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The delineation of microscopic pore structure heterogeneity and the evaluation of gas adsorption capability in tight shales are critical for assessing shale gas resources and production potential. This study provides a comprehensive investigation of pore structure, heterogeneity, and their impact on gas adsorption capacity in the Bossier Shale from Eastern Texas, USA, utilizing an integrated approach that includes low-temperature gas physisorption, multifractal heterogeneity analysis, and high-pressure methane adsorption. Results indicate that the Bossier Shale is a mesopore-dominant system, with mesopore (2–50 nm in dia.) accounting for approximately 86% of the total pore volume. The samples exhibit significant heterogeneity in the meso-macropore range (>50 nm), alongside moderate heterogeneity in micropores (<2 nm). Pore composition and spatial distribution are identified as key factors controlling heterogeneity and connectivity. The codevelopment of meso- and macro-pores, combined with limited development of micropores, leads to high heterogeneity but relatively low connectivity in the larger pore ranges. In terms of gas adsorption, organic matter contributes by providing adsorption sites and enhancing pore connectivity, whereas clay minerals primarily function by supplying additional adsorption surface area for adsorption. In the mesopore-dominant Bossier Shale, clay minerals play a dominant role in controlling gas adsorption capacity. Consequently, stratigraphic intervals rich in high clay minerals show significant potential as high-quality gas-bearing zones, providing valuable insights for reservoir evaluation and gas enrichment prediction.