Gas-in-place (GIP) content and gas-adsorbed ratio are crucial parameters for resource potential assessment, sweet spot prediction, and production strategy optimization. Various methods have been proposed from different perspectives to evaluate these parameters; however, none have been widely accepted. The carbon isotope fractionation (CIF) model provides a powerful tool for clarifying the mechanism of isotopic fractionation during natural gas transport and evaluating key parameters of unconventional gas resources. In this study, five shale samples from the Longmaxi Formation in the Jiaoshiba area, Sichuan Basin, China, were subjected to canister degassing experiments to investigate degassing behaviors and their variations in the isotopic compositions of methane (δ¹³C₁), ethane (δ¹³C₂), and carbon dioxide (δ¹³C_CO2). The results showed that the degassing volume (rate) and isotopic fractionation amplitude (slope) of methane positively correlate with the TOC content after controlling the lost time. The released ethane was more enriched in ¹²C than methane and did not fractionate during degassing, resulting in an increased isotope reversal. The δ¹³C_CO2 exhibited complex fractionation features corresponding to later stages (stages III and IV) in the general pattern. Furthermore, we evaluated the GIP content, gas-adsorbed ratio, and in-situ Langmuir parameters (V_L and P_L) using the CIF model. The calculated GIP content ranges from 3.48 cm³/g to 7.29 cm³/g with an average of 5.32 cm³/g, and the gas-adsorbed ratio is between 13.87% ~ 43.75% (average 30.79%). The optimized V_L and P_L show an excellent correlation with TOC content, demonstrating the great advantage of the CIF model in evaluating Langmuir parameters. Compared with the CIF model, the traditional USBM method underestimated shale gas resources in the Jiaoshiba area by 2% ~ 22%, with an average of 11.5%.

就地气体 (GIP) 含量和气体吸附比是资源潜力评估、甜点预测和生产策略优化的关键参数。已经从不同的角度提出了各种方法来评估这些参数；然而，没有一个被广泛接受。碳同位素分馏（CIF）模型为阐明天然气输送过程中同位素分馏机理和评价非常规天然气资源关键参数提供了有力工具。本研究对四川盆地焦石坝地区龙马溪组 5 个页岩样品进行筒式脱气实验，研究脱气行为及其对甲烷同位素组成的变化 ( δ ¹³ C ₁)、乙烷 ( δ ¹³ C ₂ ) 和二氧化碳 ( δ ¹³ C _CO2 )。结果表明，在控制损失时间后，甲烷的脱气体积（速率）和同位素分馏幅度（斜率）与TOC含量呈正相关。释放的乙烷比甲烷更富含¹² C，并且在脱气过程中没有分馏，导致同位素反转增加。的δ ¹³ C ^ _CO2表现出复杂的分馏对应于后级的特征（阶段III和IV）中的一般模式。此外，我们评估了 GIP 含量、气体吸附率和原位朗缪尔参数（V_L和P _L ) 使用 CIF 模型。计算出的GIP含量范围为3.48 cm ³ /g～7.29 cm ³ /g，平均为5.32 cm ³ /g，气体吸附率在13.87%～43.75%（平均30.79%）之间。优化后的V _L和P _L与 TOC 含量显示出极好的相关性，证明了 CIF 模型在评估朗缪尔参数方面的巨大优势。与CIF模型相比，传统的USBM方法低估了焦石坝地区页岩气资源量2%～22%，平均为11.5%。