川东北龙岗东地区二叠系—三叠系热液活动证据及意义

The Evidence of Hydrothermal Activity and Its Significance of Permian-Triassic Strata,Eastern Longgang Area,Northeastern Sichuan Basin

基于川东北龙岗东地区长兴组—飞仙关组岩石学特征研究,结合储层段白云岩和非储层段海相沉积灰岩及其充填矿物的稀土元素、流体包裹体、激光拉曼等分析,认为该地区二叠系—三叠系地层中存在鞍状白云石—黄铁矿、萤石—石英等热液矿物组合,对应的流体包裹体均一化温度均高于正常地层温度。所有长兴组—飞仙关组储层段白云岩样品均具有与海相沉积灰岩相同的Ce显著正异常特征,而大部分则具有与鞍状白云石相似的REE配分曲线特征,呈显著Eu正异常。热液矿物萤石和石英内普遍具有含沥青包裹体,为龙潭组生油高峰所捕获到的含油包裹体高温裂解后的产物。根据矿物占位关系和油气充注时期,可将该区热液活动划分为两期,第一期对应晚二叠世—早三叠世,作用方式为热液流体对白云岩储层形成的促进作用和后期改造作用;第二期对应晚三叠世,作用方式为鞍状白云石、石英、萤石对储渗空间的充填作用。晚二叠世—早三叠世初期活跃的张性深大断裂可以为热液流体的活动提供运移通道。

Based on the analysis of petrology of Changxing Formation-Feixianguan Formation in eastern Longgang Area,NE Sichuan Basin,combing with analytical method such as rare earth elements（ REE）,fluid-inclusions and laser Laman,it is illustrated that there exist mineral assemblages including saddle dolomite-pyrite,fluorite-quartz and corresponding homogenization temperatures is above normal formation temperature. All the rock samples from reservoirs of Changxing Fm-Feixianguan Fm shares the same positive Ce anomaly with marine sedimentary limestone and most of them are characterized by the similar REE patterns and significant positive Eu anomaly of saddle dolomite. There exist bitumen-bearing inclusions,which are products of oil-bearing inclusions trapped by the period of oil generation peak of Longtan Formation after high-temperature cracking in hydrothermal minerals of fluorite and quartz. The hydrothermal activity can be divided into 2 periods on the basis of relationship between mineral occupation and hydrocarbon charging timing： The first stage corresponding to the late Permian-early Triassic and the action mode of is to promote the formation process and late-reformation of dolomite reservoir; the second stage corresponding to Late Triassic and the action mode is filling of saddle dolomite,quartz and fluorite in reservoir spaces.