鄂尔多斯盆地中部气田奥陶系地层水与水溶气的地球化学特征

The Geochemistry Characteristics of Ordovician Formation Water and Dissolved Gas of Central Gasfield in Erdos Basin

李贤庆¹,侯读杰¹,柳常青¹,张爱云²

Li Xianqing , Hou Dujie, LiuChangqing, et al

1.江汉石油学院地球化学研究中心,2. 中国地质大学能源地质系,北京

Jianhan Petroleum Institute , Hubei 434102 , P. R. China

通过对鄂尔多斯盆地中部气田不同层位地层水的对比分析,奥陶系地层水呈偏酸性—弱碱性(pH 值为3.7～8.7) ,具有总矿化度高、离子组成以Cl ^- 和Ca^{2 +} 为主、水型为CaCl_² 型、有机酸含量(主要是乙酸) 较高等特征,明显不同于石炭—二叠系地层水。研究表明,总矿化度高值区和有机酸总含量高值区与天然气富集区有较好的对应关系。通过对中部气田20 多个奥陶系水溶气样品资料的初步分析,认为该区水溶气可能主要来源于煤成气。

Through the comparison analysis of different age formation water samples selected from central gas field in Erdos Basin , Ordovician formation waters are characterized by its acidity to weak alkalinity (pH = 3.7 - 8.7 ) , high total dissolved solids(TDS) , relative rich Cl - and Ca2 + of total ions composition , CaCl2 type , and higher organic acids (mainly for aceticl acid) . So Ordovician formation waters are obviously different from Permo - Carboniferous formation waters. It has demonstrated that high TDS and relative rich organic acids in formation water are consisted with the abundant distribution area of natural gases. Based on the preliminary analysis of more than twenty dissolved gas samples from central gasfield in Erdos Basin , it is suggested that dissolved gases in this area mainly originate from coal - derived gas.