鄂尔多斯盆地东南部气田上古生界致密砂岩气藏气源对比

Sources of tight sandstone gas and its migration in the Upper Paleozoic,Yan’an Gasfield

本文通过碳同位素数据比对、常规天然气组分分析,结合区域地质背景,对鄂尔多斯盆地东南部气田的气源进行了研究。结果表明:鄂尔多斯盆地东南部气田的主力烃源岩为煤层,含气层位出现碳同位素倒转现象,山西组山2段和本溪组主要为煤型气中混入少量油型气,而山西组山1段和石盒子组盒8段则是成藏期经历了多期充注所导致;CH_4、CO 2和iC_4/nC_4三个指标在近源和远源层位之间分馏效应明显,层位之内分异不明显,这与致密砂岩近源的“幕式”充注和远源的“准幕式”充注有关。通过对气源的研究,认为优质煤层和近源厚层砂体叠合的区域是本地区未来勘探开发的首选区域。

In this paper,the gas source of Yan’an Gasfield in southeastern Ordos Basin is studied through the comparison of carbon isotope data,the analysis of components of natural gas,and the consideration of regional geological background.The results show that the main source rocks in Yan’an Gasfield are coal seams.The carbon isotope inversion occurs in the gas-bearing strata,mainly caused by the mixing of a small amount of oil-type gas in the second number of Shanxi Formation and Benxi Formation or caused by multiple gas fillings in the first number of Shanxi Formation and the eighth number of Shihezi Formation.The fractionation effects of CH_4、CO_2 and iC_4/nC_4 between near-source rocks and far-source rocks are obvious while the differentiation within a layer is not obvious,which is related to the distances of episodic fillings in tight sandstone.Through the study of gas source,it is considered that the overlapping area of high quality coal seam and thick sandstone is the preferred area for future exploration in the region.