East Sichuan is rich in shallow natural gas; however, such gas substantially influences tunnel construction in the region. Accordingly, we analyzed the geological characteristics of shallow natural gas in eastern Sichuan and evaluated the risk the gas poses to tunnels along the Chongqing–Wanzhou (YW) high-speed railway employing a fuzzy synthetic evaluation approach. We conducted isothermal adsorption, gas chromatography, total organic carbon (TOC), carbon isotope, porosity and permeability, and field gas pressure test experiments and thin section examination of rock. Our results showed that the potentially harmful components in shallow natural gas in East Sichuan are mainly CH₄, with small amounts of H₂, CO, CO₂, and H₂S. The shallow natural gas mainly derives from shale and limestone in the Xujiahe and Ziliujing formations, but migrates to adjacent reservoirs through intraformational shear fractures in the strata. Sandstones of the Xujiahe and Shaximiao formations are porous reservoirs, with the best reservoir physical properties, belonging to the main enrichment strata of shallow natural gas in the region. Compared with the west of the study area, shallow natural gas is more developed in the east. According to synthetic evaluation of shallow natural gas influence presented in the paper, tunnels along the YW high-speed railway number eight in high-gas zones, four in medium gas zones, and two in no or low-gas zones.

川东地区富含浅层天然气；然而，这种气体极大地影响了该地区的隧道建设。据此，我们分析了川东浅层天然气的地质特征，并采用模糊综合评价方法评估了天然气对渝万高铁沿线隧道的风险。我们进行了等温吸附、气相色谱、总有机碳（TOC）、碳同位素、孔隙率和渗透率，以及现场气体压力测试实验和岩石薄片检查。结果表明，川东浅层天然气中潜在有害成分主要为CH ₄，少量H ₂、CO、CO ₂和H _{2 。}S. 浅层天然气主要来源于须家河组和自流井组的页岩和石灰岩，但通过地层内的层内剪切裂缝运移至邻近储层。须家河组和沙溪庙组砂岩为孔隙型储层，储层物性最好，属于该地区浅层天然气的主要富集层系。与研究区西部相比，东部浅层天然气较为发育。根据本文提出的浅层天然气影响综合评价，YW高铁沿线隧道高含气区8个，中含气区4个，无气区或低含气区2个。