准噶尔盆地东部白家海凸起天然气轻烃地球化学特征

Geochemical characteristics of light hydrocarbons associated with natural gas in the Baijiahai Bulge,eastern Junggar Basin

准噶尔盆地东部白家海凸起天然气成藏条件优越,但目前勘探程度较低。由于研究区气样少,加之天然气成分简单,可用的判别参数有限,天然气的成因来源判别难度较大,制约了该区的天然气勘探。基于轻烃色谱分析,利用与白家海凸起天然气伴生的C_(5-7)轻烃化合物,系统探讨了天然气的成熟度、成因来源和可能的次生改造。结果表明:研究区天然气整体进入成熟阶段,等效镜质体反射率为1.12%~1.48%,平均为1.33%。在研究区识别了2类天然气:第一类为煤成气,来自下石炭统松喀尔苏组腐殖型烃源岩,构成了该区天然气的主体;第二类为油型气,来自下二叠统平地泉组咸水湖相烃源岩。研究区天然气基本未遭受生物降解、水洗和蒸发分馏等常见次生改造作用的影响,说明白家海凸起具备较好的天然气保存条件,是准噶尔盆地今后值得持续关注的天然气勘探重要接替领域。

The natural gas formation conditions in the Baijiahai Bulge in the eastern Junggar Basin are superior, but the current exploration level is low. Due to the small number of gas samples in the study area, coupled with the simple gas composition and limited available discriminatory parameters, it is not easy to discern the genetic types and origins of the gas, which restricts gas exploration in this area. Based on light hydrocarbon chromatography analysis, this study systematically explores the gas maturity, genetic origin, and possible secondary alterations using C_(5-7)light hydrocarbon compounds associated with gas from the Baijiahai Bulge. The natural gas in the study area is generally mature, with equivalent vitrinite reflectance ranging from 1.12% to 1.48%, with an average of 1.33%. Two types of gas were identified in the study area. The first type is coal-formed gas from the humic source rocks of the Lower Carboniferous Songkharsoo Formation, which constitutes the main body of natural gas in the study area;the second type is oil-type gas from the saline lacustrine source rocks of the Lower Permian Pingdiquan Formation. The natural gas in the study area is largely unaffected by common secondary alterations such as biodegradation, water washing, and evaporative fractionation, indicating that the Baijiahai Bulge has better natural gas preservation conditions and is a critical succession area for future natural gas exploration in the Junggar Basin that deserves continued attention.