准噶尔盆地东北部恰库尔特草原北下石炭统南明水组烃源岩有机地球化学特征及其地质意义

Geochemical Characteristics of Lower Carboniferous Nanmingshui Formation Source Rock and Their Geologic Implications,Qiakuerte Prairie,Northeastern Junggar Basin

准噶尔盆地石炭系烃源岩主要分布在准东地区,已在该区五彩湾凹陷与滴水泉断裂带发现了来源于石炭系的工业性天然气藏,勘探前景十分可观。通过对准噶尔盆地东北部的恰库尔特草原北东侧下石炭统南明水组野外泥岩样品的常规有机地球化学分析测试,系统地剖析了该地区南明水组泥岩有机质生烃潜力、沉积环境、母质输入以及热演化程度等地球化学特征,结果表明:南明水组部分泥岩层段有机质丰度好,RO>1.5%,已达到高成熟阶段,干酪根类型主要为Ⅲ型;有机质沉积主要以微咸水的还原环境为主,有机质输入以陆源高等植物的输入为主,可能还有藻类的贡献,芳烃化合物中屈艹、菲、惹烯、萤蒽、苯并[e]芘、苯并萤蒽以及硫芴化合物的丰度明显偏高。指出石炭纪时准噶尔盆地南缘主要为海相沉积环境,向北过渡至腹部和西北部广泛分布有火山岩或火山碎屑岩,东部及东北部则出现了前三角洲相沉积以及滨浅湖相或沼泽相沉积体系,但是沉积范围较小;从准噶尔盆地东部地区发现的来源于石炭系的天然气可以看出,石炭系存在较好的烃源岩,其主要以生气为主。

The distribution of Carboniferous source rock in eastern Junggar basin is extensive. Presently, commercial natural gas reservoirs are mainly derived from Carboniferous mudstones in Wucaiwan depression and Dishuiquan fault belts. According to the conventional geochemical analysis of Lower Carboniferous Nanmingshui Formation field mudstone samples in north Qiakuerte prairie of northeastern Junggar basin, the geochemical characteristics were examined including hydrocarbon generation potential, depositional environment, organic matter input and maturation. The organic matter content of partial samples is high, and its vitrinite reflectance is beyond 1.5%, which reflect the high maturity of the organic matter, and the type of the organic matter is the third kind of kerogen. Based on n-alkanes, isoprenoids and gammaceranes, the organic matter of mudstone is formed in anoxic and slightly saline or fresh water. Combined with the characteristics of tepanes＇and steranes＇ biomarkers, it is suggested that the organic matter is originated from the higher plant, and also algaes input possibly. And therefore the relative abundances of Aromatic hydrocarbons such as chrysene, phenanthrene, retene, fluoranthene, benzo[e]pyene, benzofluoranthene and dibenzothiophene are higher. The isotope values of kerogen and group compositions from core extracts of Nanmingshui Formation mudstones also demonstrate above-mentioned views. In the Carboniferous Period, the sedimentary facies of Junggar basin changed from south to north, which was deposited in marine environment in south, but in north it was prodelta and shoreside or shallow lacustrine facies, locally swamp deposit. Carboniferous source rocks generate natural gas and have a great significance of petroleum geology.