鄂尔多斯盆地北部塔巴庙地区下古生界奥陶系天然气的气源追踪研究

鄂尔多斯盆地北部塔巴庙地区奥陶系天然气的赋存分布以风化壳最具工业价值，另一类尚待进一步勘探研究的天然所则分布于奥陶系内部或盐下，对这两种分布形式的天然气，在通过天然气组分，同位素以及相伴生的凝析 化学特征研究对比的基础上，与其可能来源的烃源岩层即上覆石炭系煤系烃源岩和奥陶系碳酸盐岩烃源岩的生源地化特征相对比，结果表明塔巴庙区块北部以鄂5－鄂8井为代表的奥陶系风化壳工业性天然气具有双重母质的混合型天然气特征，即来源于上古生煤成气和下古生界油型气，该区南部以伊24井为代表风化壳非工业性天然气则来源于奥陶系典型腐泥型面因的有机质；对于奥陶系内部或盐下天然气显示而言，均属单一海相碳酸盐岩来源的油型天然气，因此，奥陶系风化壳相对发育与生烃气强度中心相叠合的区域是当前在勘探上古生界时兼顾下古生界天然气的最佳地区。

STUDY ON THE SOURCE OF NATURAL GAS IN ORDOVICIAN IN TABAMIAO AREA OF NORTH ORDOS BASIN

In Tabamiao area of northern Ordos Basin, natural gas is widespread in Ordovician.However, the commercial gas is mainly produced from the weathered crust lying at the top of Ordovician. In order to track the origin of gas in Ordovician,associated condensate and indigenous gas in Ordovician carbonate source rock in upper and lower Paleozoic were correlated from such geochemical characteristics as component, compounds and isotope.Detailed study showed that (a) the commercial gas in Ordovician weathered crust in northern Tabamiao was originated mainly from coal-bearing source rock in upper Paleozoic, (b) the non-commercial gas in Ordovician in southern Tabamiao is formed on the spot, and (c) the gas below salt bed in Ordovician is also formed on the spot. The author suggested that both Ordovician weathered crust and upper Paleozoic are the superior objects for gas exploration in northern Tabamiao and upper Paleozoic is the only one of object for gas exploration in southern Tabamiao.