兴城地区天然气组分分布规律及其指导意义

兴城地区天然气组分和碳同位素具有"杂、干、重、反"4个基本特征,表明该区存在无机成因天然气.无机成因天然气的形成与岩浆侵位、火山活动密切相关,在早白垩世登娄库期已聚集成藏;而烃源岩在泉头末期才达到生气高峰,青山口期开始大量充注,显然有机成因气生成与充注滞后.有机成因气以甲烷气体为主,在进入圈闭后,它们将逐渐把早期以N2和CO2为主的气体置换,并将其推出圈闭,而沿不整合面、裂隙向凹陷边缘上倾方向的圈闭充注,进而富集成藏.如此便形成了以烷烃为主的天然气分布在构造位置较低的断陷中部,而那些含N2和CO2较多的天然气则富集在外围高部位的圈闭内.天然气组分的分布规律对气田的勘探开发具有重要的指导意义.

Rules of Natural Gas Composition Distribution in Xingcheng Area and Its Significance

Natural gas composition and carbon isotopes have the characteristics of complexity, dryness, heavy and reversion, it shows that there exists an inorganic genetic gas in the area. The inorganic genetic gas is related closely with the activities of magma and volcanism and accumulated at early Cretaceous Denglouku Stage and the organic gases are not accumulated until the Qingskankou Stage. The organic gas dominated by CH4 replaces the gas dominated by CO2 and N2 because of the difference of their density, thus the latter migrates along the unconformity surfaces and fractures into the reservoirs located in the depression margin. Thus the natural gas dominated by hydrocarbon is distributed in the centre of the depression and those consisting of more CO2 and N2 are distributed in the margin of the depression. The distribution pattern of the natural gas is significance of guiding the exploration and development of the gas fields.