济阳坳陷孤北—渤南地区渤古4潜山天然气地球化学特征及气源探讨

THE GEOCHEMICAL CHARACTERISTICS OF NATURAL GAS AND DISCUSSION ON GAS SOURCE IN BOGU 4 BURIED HILL

济阳坳陷孤北—渤南地区深层天然气来源多,成因复杂,混源现象普遍。针对这一问题,运用天然气组分、稳定碳同位素、轻烃组成和伴生原油生物标志化合物等多种指标,并与邻区天然气进行对比,判识了该区渤古4潜山奥陶系天然气的地球化学特征和成因类型,认为该区天然气主要为高成熟油型气,混有部分煤成气。依据天然气与气源岩地球化学特征并结合成藏地质条件,明确了天然气的来源,认为渤古4潜山天然气主要源自渤南洼陷Es上气源岩,混有孤北C—P煤成气,伴生油具有相似的来源。

The deep natural gas in the Gubei-Bonan area is characterized as multi-source and complex genesis, and source-mixed gas reservoirs are generally formed. In view of this problem, many parameters including chemical component, carbon isotope and light hydrocarbon composition of natural gas and biomarkers of associated crude oil, were used to clarify the geochemical characteristics and genesis of Ordovician natural gas in the Bogu 4 buried hill, in comparison with the geochemistry of natural gas nearby. It is proposed that the natural gas would be mainly composed of high-mature oil-type gas with little mixing of coal-type gas. The gas source is determined by the geochemical characteristics of natural gas and source rocks, combining with analysis on geologic condition of gas pools. The research results show that the gas in the Bogu 4 buried hill is mainly derived from the upper layer of member 4 source rocks in the Shahejie Formation in the Bonan sag, mixed with the gas from the coal measure contribution in Permian-Carboniferous in the Gubei area, and the associated crude oils also have the similar process.