摘要
通过对四川盆地及其周缘地区中二叠统野外露头及典型井的岩心微观薄片的观察，发现中二叠统主要发育细晶白云岩、中粗晶白云岩与灰质云岩。物性分析表明，中-粗晶白云岩储层物性最好，可以作为有效储层；结合地质背景，对-中粗晶白云岩开展的多种地球化学分析，认为中-粗晶白云岩为深部热液成因，云化流体来自于深部热液。其成因证据包括以下5个方面：单井岩心和微观照片显示中-粗晶白云岩具有鞍状白云石特征，并伴有低温热液矿物；中-粗晶白云石中发育气、液烃流体包裹体，包裹体均一化温度较高，白云石化流体温度明显高于围岩温度，且中二叠统中-粗晶白云石两相流体包裹体基于冰点温度测试的盐度是正常海水的3～5倍，成岩流体为高盐度流体；中-粗晶白云岩稳定氧同位素值极偏负，均在-9‰以下，多数样品的测试值高达-13‰；中-粗晶白云岩的Sr同位素具有幔源特征，反映深部热液特征；白云岩横向和纵向分布变化快，目前已发现的白云岩主要沿深大断裂与火山岩发育地区分布。中-粗晶白云岩的晶间溶孔多为沥青充填，结合典型井的埋藏史、包裹体均一温度及烃源岩的成烃史分析，认为中-粗晶白云岩形成时间较早，至少在中-晚三叠世油气大量充注之前。在以上分析基础上，利用发育白云岩的典型井及地震剖面，结合成因认识建立了中-粗晶白云岩的热液成因模式。
Abstract
Observation of the Middle Permian outcrops and thin sections of cores from typical wells in Sichuan Basin and its periphery reveals that the Middle Permian consists mainly of micro-dolomite,medium-macro-crystalline dolomite and calcitic dolomite.And the petrophysical properties analysis shows that reservoir quality of the medium-macro-crystalline dolomite is the best,so it can act as effective reservoir.,Various geochemical analyses in combination with the geological background indicate the medium-macro-crystalline was formed by the deep thermal fluids.There are five major evidences concerning their genesis.The medium-macro-crystalline shows the characteristics of saddle-dolomites and is associated with some low temperature hydrothermal minerals;Gas-liquid hydrocarbon fluid inclusions with homogenization temperature higher than the surrounding rocks occur in the medium-macro-crystalline,,and the salinity of two phase fluid inclusions tested based on the freezing point temperature is three to five times of normal sea water,indicating high salinity digenetic fluids;The stable isotope values are extremely biased,and they all are less than -9‰ and mostly are up to -13‰;Their Sr isotopes have the characteristics of mantle-derived medium-macro-crystalline dolomite,indicating the existence of deep thermal fluids;The lateral and vertical distributions of dolomite vary dramatically,and dolomites are found to distribute along the deep-large faults and in areas with volcanic rocks.Most of the intergranular dissolved pores of medium-macro-crystalline dolomite are filled by asphalt.Comprehensive analysis based on the bury history of typical wells,homogenization temperature of fluid inclusions and hydrocarbon generation history of source rock reveals that the medium-macro-crystalline dolomites were formed early,at least prior to the Middle-Late Triassic,when large amount of hydrocarbons were charged.Based on the above mentioned analysis,a hydrothermal genetic model was established for the medium-macro-crystalline dolomite was established by using the typical wells and seismic profiles.
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