东方1-1气田天然气组成的不均一性与幕式充注

Heterogeneity of natural gases and the episodic charging process: a case study for Dongfang 11 gas field, Yinggehai basin.

莺歌海盆地东方１１气田天然气的主要组成（烃气、ＣＯ２和Ｎ２）在侧向上和垂向上的变化很大。烃类气（生物气除外）主要来自成熟—高成熟的中新统烃源岩；无机成因ＣＯ２可能主要是气源岩进入高成熟晚期以后，其中的钙质成分热分解或与粘土矿物反应的产物；Ｎ２则为有机成因且较无机ＣＯ２生成早。天然气组成的不均一性和同位素变化表明，该气田储集层之间存在泥岩隔层，各断块之间互不连通，甚至同一断块的个别单元储集层在横向上亦局部存在非渗透带。据此，结合流体包裹体信息及烃源岩的生气演化史，认为该区地质历史时期中至少发生过４期天然气充注：第一期充注为生物气，第二期、第三期充注以ＣＨ４、Ｎ２热成因气为主，第四期充注以无机ＣＯ２为主并伴生高熟烃气。这一幕式充注过程与由于盆地深部超压释放引起的底辟活动密切相关。

There is a complex distribution of the main components (CH4, CO2 and N2) of gases in the Dongfang 11 gas field, the Yinggehai basin. The study indicates that hydrocarbon gas (except for biogas) was generated from mature to highmature Miocene sourcerocks; CO2 was principally formed from inorganic sources involving the thermodecomposition of carbonate minerals and the reaction of carbonate minerals with silicate minerals, after the Miocene calcitemudstones entered the late period of high maturation ;N2 was derived from the maturation of organic matters. Both lateral and vertical compositional heterogeneities and isotopic variations of gases of the whole field suggest that those reservoir zones have been compartmentalized by the faults, shalebreaks and even nonpermeable zones causng in the Yinggehai basin. The data combined with fluid inclusions as well as thermal evolution of the sourcerocks can be used to trace and identify that the field has been charged by at least 4 episodes of gases over geologic time. The episodic gas charging process closely relates to the actions of a diapir caused by deep overpressure releasied by lateral lithofacies variations, and lead to a better understanding of the charging history.