鄂尔多斯盆地中部上古生界天然气运移特征分析

根据对鄂尔多斯盆地中部石炭二叠系压力孕育史模拟，晚三叠世和早白垩世其烃源岩内异常流体压力均明显大于静水压力，形成２个过剩压力高峰（不同地区前、后峰的大小关系不同），之后对应的泄压段可作为两个重要排烃期，中西部的主排烃期在早白垩世—晚白垩世，东部的主排烃期在晚三叠世—中侏罗世。根据对研究区５条剖面的水动力模拟结果，认为气势分布的演化可分为３个阶段（晚三叠世至中侏罗世，早白垩世，晚白垩世至今），各阶段气势分布特征有所不同，不同阶段之间天然气运移方向变化较大。通过对层组间过剩压力分布、气势对比及奥陶系地层水和天然气化学性质的综合分析，认为沿垂直方向运移的天然气向上可到达下石盒子组，向下通过古侵蚀沟等可进入奥陶系，成为奥陶系大气田的一部分气源。图５参７（梁大新摘）

Migration of gas in Upper Palaeozoic Group, Middle Ordos basin.

Two excess pressure (overpressure) climaxes in source rock (C 2 3 P 1) were developed in Late Triassic and Early Cretaceous epochs respectively, and could be divided into two types in different areas by way of their relative sizes, so the major expulsive period is T 3 J 2 in eastern area and K 1 K 2 in others. Migration direction in reservoir rock was controlled by distribution of fluid (gas) potential, and would be adjusted evidently in three stages of gas potential evolution ( T J, K 1, K 2 up to now). By means of comprehensive analysis of distribution of excess pressure and gas potential in Upper Palaeozoic Group, and chemical property of subsurface water and gas in Ordovician system, it is suggested that gas could get to Lower Shihezi Formation (P 1) upwards, and into Ordovician system downwards by way of erosional valley.