高—过成熟页岩CH4/N2/CO2混合气体竞争吸附特征与地质意义

为研究高—过成熟页岩对N₂、CH₄及CO₂混合气体的竞争吸附特征及其地质意义，通过混合气体吸附—解吸装置，结合穿透曲线法，对四川盆地周缘NY?1井龙马溪组1 420.90 m、1 422.75 m、1 423.75 m和牛蹄塘组2 261.53 m、2 265.80 m、2 268.37 m 6个深度的岩样，开展了20 ℃、注气压力0.25 MPa条件下N₂、CH₄和CO₂等比例混合气体的竞争吸附实验，得到了各岩样对混合气体的竞争吸附规律；并通过低温N₂和CO₂吸附法，分析了6个岩样的孔隙结构，探究了其对竞争吸附的影响。结果表明：龙马溪组页岩中N₂出口端浓度有超过初始浓度的现象，而牛蹄塘组页岩中N₂、CH₄和CO₂出口端浓度均未超过初始浓度；实验结果与Yoon?Nelson模型拟合结果较好，R²值可达0.9以上，各岩样吸附速率常数均有N₂>CH₄>CO₂的规律，故N₂相较CH₄和CO₂可先被样品吸附，随后吸附速率慢的CH₄和CO₂被吸附，岩样对2种气体吸附选择性更强，所以将N₂置换出，导致龙马溪组岩样N₂出口端浓度超过初始浓度；龙马溪组岩样中微孔发育程度较高，孔径小、比表面积大、吸附能力强，能更好地吸附CH₄和CO₂这2种吸附选择性强的气体，使得已吸附的N₂被置换出，从而造成游离气中N₂浓度增加。实验结论为我国页岩气勘探开发提供了理论依据，同时对部分地区页岩气组分中N₂的成因具有一定指导意义。

Competitive adsorption characteristics and geological significance of CH4/N2/CO2 mixture in high and over mature shale

In order to study the competitive adsorption characteristics and geological significance of high-over mature shale for N₂， CH₄ and CO₂ mixed gas， through the mixed gas adsorption desorption device and combined with the penetration curve method， the N₂， CH₄ and CO₂ samples at the depths of 1 420.90 m， 1 422.75 m and 1 423.75 m of Longmaxi Formation of Well NY-1 and 2 261.53 m， 2 265.80 m and 2 268.37 m of Niutitang Formation in the periphery of Sichuan Basin were carried out under the conditions of 20 ℃ and gas injection pressure of 0.25 MPa. Through the competitive adsorption experiment of CH₄ and CO₂， the competitive adsorption law of each rock sample to the mixed gas is obtained. The pore structure of six rock samples was analyzed by low-temperature N₂ and CO₂ adsorption method， and its influence on competitive adsorption was explored. The results show that the concentration of N₂ at the outlet of Longmaxi Formation exceeds the initial concentration， while the concentrations of N₂， CH₄ and CO₂ at the outlet of Niutitang Formation do not exceed the initial concentration. The experimental results fit well with the Yoon-Nelson model. R² can reach more than 0.9. The adsorption rate constants of each rock sample have the law of N₂>CH₄>CO₂. Therefore， N₂ can be adsorbed by the sample first compared with CH₄ and CO₂， and then CH₄ and CO₂ with slow adsorption rate are adsorbed. The rock sample has stronger adsorption selectivity for them. Therefore， N₂ is replaced， resulting in the concentration of N₂ at the outlet of Longmaxi Formation rock sample exceeding the initial concentration. The rock samples of Longmaxi Formation have high degree of micropore development， small pore size， large specific surface area and strong adsorption capacity， which can better adsorb CH₄ and CO₂， two gases with strong adsorption selectivity， so that the adsorbed N₂ is replaced， resulting in the increase of N₂ concentration in free gas. The experimental conclusion provides a theoretical basis for shale gas exploration and development in China， and has certain guiding significance for the genesis of N₂ in shale gas components in some areas.