大港滩海区沙一段下部方解石脉的地球化学与包裹体特征——以港深 67井为例

Geochemical characteristics and fluid inclusion in calcite viens of lower part of member 1 of Shahejie Formation,offshore area,Dagang oilfield:a case study of well Gangshen 67

大港滩海区港深67井第三系沙河街组一段下部处于超压带的顶部,其泥晶灰岩和钙质细砂岩中以方解石脉发育为特征。方解石脉以块状结构为主,少量为纤维状结构,部分方解石脉中分布有原地微角砾。方解石脉中石油包裹体的均一温度为120～140℃,其中,液烃包裹体显蓝色荧光;盐水包裹体的均一温度为80～170℃。方解石脉的δ13C为2.30‰～5.92‰(PDB),δ18O为-14.16‰～-7.89‰(PDB)。方解石脉宿主裂缝的形成与超压破裂有关,方解石脉的成脉流体和成脉物质来自下伏泥岩层中封存的同生水和围岩。

The lower part of member 1 of Shahejie Formation(Tertiary), as represented by well Gangshen 67 in Dagang oilfield, contains an overpressured belt on the top, which is characterized by the development of calcite veins in micritic limestone and calcareous fine sandstone. Blocky calcite is the dominant vein texture , fibrous calcite is subordinated. Some of the calcite veins contain in situ micro-fragments of host rock.Homogenization temperatures of hydrocarbon inclusions within calcite vein are between 120℃ and 140℃, of them, liquid hydrocarbon inclusions possess blue and blue-fluorescing. The homogenization temperatures of aqueous inclusions are 80～170℃.The range of δ^(13)C is 2.30‰～(5.92‰(PDB),)δ^(18)O is -14.16‰～ -7.89‰(PDB)in calcite veins. The host fractures of calcite veins are related to overpressured fracturing and the material and fluid of vein-forming came from underlying connate enclosed within mudstone layers and host rocks.