不同煤系烃源岩热解气地球化学差异及其在苏里格气田的应用

Geochemical features of hydrocarbon gas generated from different coaly source rocks by pyrolysis experiments:Case study of the Sulige Gas Field in the Ordos Basin,China

为了研究不同煤系烃源岩(煤、暗色泥岩和炭质泥岩)生气差异,对三者进行了高压釜热模拟实验,并对热模拟气进行了组分分析、碳氢同位素分析和轻烃地球化学分析。实验结果表明:煤的产气率高于暗色泥岩和炭质泥岩,并在热模拟初期阶段产生大量CO_2气体,煤在低温阶段的CO_2产气量可达20%;暗色泥岩热模拟气甲烷含量在整个热模拟阶段都处于领先地位,炭质泥岩的C_2—C_4烷烃气的含量高于煤和暗色泥岩,煤生成的非烃气体含量最多;在整个热模拟阶段,煤热解气的碳、氢同位素略重于暗色泥岩和炭质泥岩热模拟气(δ^(13)C_(2煤)>δ^(13)C_(2暗泥)>δ^(13)C_(2炭泥)),热模拟温度高于500℃后,热模拟气出现碳同位素序列倒转现象;在轻烃产物中,煤热模拟气具有较高含量苯、甲苯以及2,3-二甲基戊烷,而炭质泥岩热模拟气具有较高含量的2,4-二甲基戊烷。将热模拟实验结果应用到苏里格气田,可以得到如下启示:(1)苏里格气区煤系烃源岩生烃早期形成的CO_2可能与储层致密化有一定关系;(2)轻烃特征可作为不同煤系烃源岩生气鉴别指标,苏里格气田天然气的主要贡献者是煤。

In order to study the gas generation process of different coaly source rocks,we did thermal simulation experiments on coal,coaly mudstone and carbon mudstone.And a series of geochemical analysis including chemical composition,carbon and hydrogen isotope composition as well as light hydrocarbon analysis on thermal simulation gas are also carried out in this study.It revealed coal has the highest gas production rate,in addition,it yields a large amount of CO2 gas in the early stage of simulation experiment.Carbon and hydrogen isotope of coalthermal simulation gas is slightly heavier than that of coaly mudstone and carbonaceous mudstone gas.Before 500℃,carbon and hydrogen isotope of these three kinds of gases became lighter and then higher with the increase of temperature,but after 500℃,they became lighter all the time.Carbon isotope series reversal is observed in this process.The coal thermal simulation gas has the highest content of benzene,toluene and 2,3-methyl pentane.This study indicated 2high lights on Sulige Gas Field:(1)CO2,formed in the early stage of hydrocarbon generation,may have a direct relationship with reservoir densification in the Sulige Gas Field.(2)According to the analysis of light hydrocarbon,coal should be the dominant contributor for the accumulation of the Sulige natural gas,but the contribution of coaly mudstone and carbonaceous mudstone cannot be ignored.