西昆仑山前柯东构造带侏罗系砂岩成藏古流体特征及其成藏指示意义

Characteristics of paleo-fluid and hydrocarbon accumulation significance of the Jurassic reservoir in the Kedong structural belt in the western Kunlun Mountains

塔里木盆地西南坳陷甫沙8井在侏罗系砂岩中获得工业油流,极大的推动了昆仑山前新层系新领域的油气勘探。本文通过流体包裹体岩相学、均一化温度及储层颗粒荧光定量等方法,对昆仑山前柯东构造带侏罗系储层古流体特征与油气成藏期次进行了研究。结果表明,侏罗系砂岩储层发育两期烃包裹体,第1期为发黄色、黄绿色荧光烃包裹体,以片状或点状分布,为早期原油充注;第2期为蓝白色烃类包裹体,沿裂隙呈线性分布,为晚期高成熟油气充注。颗粒荧光QGF指数主要介于3~7 pc,说明早期发生过原油充注,指示存在古油藏。QGF-E强度指数分布在9.65~73.89,指示现今为凝析油或轻质油特征,这一特征与蓝白色荧光的液态烃包裹体相对应。烃类共生包裹体均一温度峰值主要在95~105℃和115~125℃,结合研究区埋藏史和热演化史模拟结果,表明经历了两期油气充注,第1期在20 Ma以来,以成熟度较低的油气充注为主;第2期在5 Ma以来,主要是高成熟度油气充注。储层颗粒荧光定量分析结果表明,侏罗系早期发育古油藏,现今为凝析油或轻质油特征。

Crude oil was obtained from the Jurassic reservoir in well Fusha-8 located in the Kedong structural belt Study of this reservoir has promoted the exploration for new zones and new reservoir types in the western Kunlun Mountains. Petrography,microthermometry of fluid inclusions, homogenization temperature, quantitative grain fluorescence(QGF) and quantitative grain fluorescence on extract(QGF-E) are used to study the paleo-fluid characteristics and hydrocarbon charging periods of the Jurassic reservoir in the Kedong structural belt. Results show that there were two generations of hydrocarbon inclusions in the reservoirs rocks: the first stage is hydrocarbon inclusions with yellow, yellow-green fluorescence distributed as plate-like or point, color, which indicated the filling of early oil;the second stage is hydrocarbon inclusion with blue-white fluorescence, distributed line-like along fractures, which indicated the filling of late oil. The QGF index is mainly distributed between three and seven % which showed hydrocarbon filling in early periods, and residual oil reservoirs may have existed. QGF-E indexes mainly range from 9.6 to 74, indicating characteristics of condensate oil and light oil, and their characteristics are similar to the characteristics of hydrocarbon inclusions with blue-white fluorescence. Homogenization temperatures of coeval aqueous inclusions show two peaks at 95~105 ℃ and 115~125 ℃. Combined with simulation analysis of burial history and thermal evolution history, two stage hydrocarbon accumulation was identified. The first is the filling of oil since 20 Ma, formed with relatively low maturity hydrocarbon inclusions emitting yellow fluorescence and in the second stage(since 5 Ma) mainly formed with relatively high maturity hydrocarbon inclusions emitting blue-white fluorescence. QGF and QGF-E showed that the Jurassic paleo-oil reservoirs were formed in the early period and now existing condensate or light-oil reservoirs in the Kedong structural belt.