地层条件下天然气扩散过程中地球化学组分变化的模拟实验研究

EXPERIMENTAL INVESTIGATION ON VARIATION OF GEOCHEMICAL COMPOSITIONS OF NATURAL GAS DURING DIFFUSION UNDER STRATIGRAPHIC CONDITION

马立元 张晓宝 李剑 严启团 李秀芬 宋成鹏

MA Li-yuan ZHANG Xiao-bao LI Jian YAN Qi-tuan LI Xiu-fen SONG Cheng-peng

中国科学院, 兰州地质研究所, 气体地球化学国家重点实验室, 甘肃, 兰州, 730000 2. 中国石油, 勘探开发研究院, 廊坊分院, 河北, 廊坊, 065007

State Key Laboratory of Gas Geochemistry, Lanzhou Institute of Geology, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China 2. Langfang Branch, Research Institute of Petroleum Exploration and Development, CNPC, Langfang, Hebei 065007, China

采用固体样品,实验模拟了地层条件下(8MPa,70℃)气藏天然气在扩散过程中的地球化学变化特征。模拟实验结果研究表明:a)随着天然气扩散作用的进行,气藏气中甲烷的相对百分含量逐渐减少,而乙烷和丙烷的相对含量相应地增大;扩散气与气藏气存在类似的组分变化趋势,但扩散气中甲烷的相对百分含量高于同一时间气藏气中甲烷的相对百分含量,而乙烷及丙烷的相对百分含量低于气藏气中乙烷和丙烷的相应值,这些都是地层色层效应的具体体现;b)同一时间气藏气中正丁烷的相对百分含量高于扩散气中正丁烷的相对百分含量,而异丁烷的相对百分含量低于扩散气中异丁烷的相应值,这也是地层色层效应的结果;c)C1/(C2+C3)和iC4/nC4可作为天然气运移的地球化学指标;d)气藏气和扩散气组分百分含量与气体扩散比例之间分别存在对数线性相关关系和二次函数相关关系,这种函数关系可为应用模拟实验结果计算气藏扩散量,评价气藏天然气资源前景,探讨天然气在扩散过程中的组分变化以及预测同源不同层天然气藏资源量提供启示。

In order to study the geochemical characteristics of natural gas during diffusion,an experimental simulation under stratigraphic condition (70 ℃,8 MPa) has been performed on a solid sample.During the diffusion of natural gas,the relative percentage of methane in reservoir gas gradually decreases,but the relative percentages of ethane and propane increase correspondingly.The diffusive gas shows the same compositional varying tendency as the reservoir gas,but the relative percentage of methane in diffusive gas is higher than that in reservoir gas at the same time,and the relative percentages of ethane and propane in diffusive gas are lower than those in reservoir gas.These phenomena are all caused by stratigraphic chromatographic effect.The relative percentage of normal butane in reservoir gas is higher than that in diffusive gas at the same time,and the relative percentage of isobutane in reservoir gas is lower than that in diffusive gas.This is also the result of stratigraphic chromatographic effect.The C1/(C2+C3) and iC4/nC4 values may be used as the geochemical indexes of natural gas migration.There exist a logarithmic linear correlative relation between the relative percentage of compositions of reservoir gas and the diffusive gas percentage and a quadratic relation between the relative percentage of compositions of diffusive gas and the diffusive gas percentage.These relations may be helpful for calculating the amount of diffusive gas,evaluating the reservoir gas resource prospect,deeply understanding into the variation of compositions of natural gas during diffusion and predicting the total resources of natural gas derived from the same source rock but preserved in reservoirs with different ages.

国家自然科学基金资助项目(49972051;40172053);国家重点基础研究发展规划项目(2001CB209102);中国科学院资源环境领域知识创新工程重大(重要方向)项目(KZCX2-111)

https://doi.org/10.11781/sysydz200404365