准噶尔盆地陆梁隆起东部滴北凸起天然气成因来源再认识

Re-examination of genetic types and origins of natural gases from Dibei Uplift,eastern Luliang Uplift,Junggar Basin

陆梁隆起东部地区是准噶尔盆地天然气勘探的主战场。目前,在滴南凸起及周缘已经发现了一批大、中型气田(藏)。位于滴南凸起以北的滴北凸起被多个生烃凹陷环绕,发育多套烃源岩层系,天然气成藏条件十分优越。研究基于滴北凸起9个天然气样品分子和稳定碳同位素组成,并与滴南凸起天然气地球化学特征开展对比研究,结合主要烃源岩层系的埋藏史和生烃史,全面系统地梳理了滴北凸起天然气成因来源及遭受的次生改造作用。滴北凸起天然气的成因来源复杂,主要存在3类天然气:第一类是上石炭统巴山组煤系烃源岩生成的高熟煤成气;第二类是下石炭统姜巴斯套组/松喀尔苏组海相烃源岩在高成熟阶段生成的油型气;第三类是原油遭受生物降解后形成的次生生物甲烷。滴北凸起原生热成因气现今处于高成熟阶段,其非烃气体含量、稳定碳同位素组成和热成熟度等特征都与滴南凸起天然气存在显著差别,天然气的成熟度与乌伦古坳陷烃源岩匹配程度更好,推断其来自乌伦古坳陷。

The eastern part of Luliang Uplift has currently become the main target for gas exploration in the Jung gar Basin.By now,several giant-medium gas fields(reservoirs)are discovered in the Di nan Uplift.Located north to the Di nan Uplift,the Dibei Uplift is surrounded by several hydrocarbon generating sags and developed several sets of source rocks,which promises a favorable gas accumulation condition.Based on molecular and stable carbon iso topic compositions of 9 gas samples from Dibei Uplift,in cooperation with the burial and hydrocarbon generation history of source rocks,genetic types and origins of natural gases and related secondary alterations were fully dis cussed in this study.A comparative study was also carried out with the geochemical characteristics of natural gases from Di nan Uplift.Gases from Dibei Uplift have complicated origins which could primarily be divided into three types:(1)Highly-mature coal-derived gas generated from the Upper Carboniferous Bashan coal measures;(2)High-ly-mature oil-type gas generated from the marine source rocks in the Lower Carboniferous Jiangbasitao Formation or Songkaersu Formation);(3)Secondary microbial methane generated via the biodegradation of oils.Significant differences have been observed between gases from Dibei and Dinan Uplifts in the concentration of non-hydrocarbon gases,carbon isotopes and thermal maturities.Gases from the Dibei Uplift are at highly mature stage,which corre lates well with the maturities of Carboniferous source rocks in the Wulungu Depression.Thus,these gases are most probably derived from the Wulungu Depression.