沾化凹陷孤西断裂带古生界煤成气的实质

ESSENCE OF PALAEOZOIC COAL-BED GAS IN GUXI FAULT ZONE OF ZHANHUA SAG

针对以前的研究认为济阳拗陷孤西断裂带深层天然气主要发育煤成气,以烃源岩特征分析为基础,综合运用天然气组分、稳定碳同位素、稀有气体同位素、轻烃组成和伴生油生物标志物等多种指标,并结合成藏地质条件分析,系统剖析了孤西断裂带古生界天然气的成因和来源。认为该区并非都为煤成气,发育有3种类型的混源气:孤北潜山主要为C—P来源的煤成气,混入了部分油型气;渤古4和渤深6潜山均以渤南洼陷Es4上生成的高成熟油型气为主,前者还存在煤系的贡献,后者则混有部分源自Es3下的伴生气。

Previous research has concluded that the natural gas is mainly composed of coal-bed gas in Guxi fault zone,one of the richest areas of deep natural gas in Jiyang depression.Based on the analysis of source rock characteristics,many indicators,such as chemical component,carbon isotope,rare gas isotope and light hydrocarbon composition of natural gas and biomarkers of associated crude oil,combining with the study on geologic condition of gas pools,are used to clarify the genesis and source of Paleozoic natural gas in Guxi fault zone.It is proposed that there are three types of source-mixed gas in Guxi fault zone rather than coal-bed gas.Natural gas in Gubei buried hill is mainly composed of coal-bed gas sourced by C-P source rocks,mixed with part of oil-type gas.Gas from Bogu 4 and Boshen 6 buried hill are both mainly consisted of high-mature oil-type gas generated by upper Es4 source rocks in Bonan Sag.The former is mixed with coal-bed gas,and the latter is mixed with oil-associated gas from lower Es3 source rocks.