涟源凹陷上二叠统大隆组泥页岩裂缝方解石脉体流体包裹体特征及其启示

Characteristics of Fluid Inclusions in Fracture Calcite Veins and Implications of Upper Permain Dalong Formation Shale at the Lianyuan Depression

针对湘中涟源凹陷上二叠统大隆组黑色泥页岩中油气特征及微观保存条件,选择涟源凹陷XY1井大隆组泥页岩中高角度裂缝方解石脉体,开展了脉体岩相学和阴极发光观察、脉体盐水包裹体和烃类包裹体特征及温压研究,结合泥页岩有机质成熟度及油气生成阶段分析和埋藏-热演化-构造抬升史模拟,确定了裂缝脉体形成时期和深度,讨论了泥页岩油气微观保存条件。研究表明:大隆组泥页岩有机质成熟度R_o为1.2%~1.3%,原始有机质中发育有机孔,泥页岩孔隙内液态油中很少发育有机孔;裂缝方解石脉体由早晚两期形成,边界清晰;早期脉体中发育大量蓝白色荧光的液相烃包裹体和气-液两相烃包裹体,发微弱荧光的气相烃包裹体和不发荧光的甲烷包裹体,盐水包裹体均一温度主要介于93~138℃间,对应古埋深为2 000~3 000 m;晚期脉体中包裹体发育程度差,仅零星见烃类包裹体,盐水包裹体均一温度主要介于50~62℃间,对应古埋深为900~1 100 m;依据早期裂缝方解石脉体中甲烷包裹体激光拉曼参数和甲烷体系状态方程估算甲烷包裹体捕获压力为28.92~41.47 MPa,相应古压力系数为1.10~1.57。根据早晚两期裂缝方解石脉体中气-液两相盐水包裹体和烃类包裹体的发育程度以及捕获温压信息推断,在燕山-喜山期大幅度构造抬升和地层剥蚀过程中,泥页岩中多期裂缝形成和开启以及成脉古流体活动,对大隆组泥页岩中滞留油气的微观保存条件产生了一定程度的不利影响。

Aiming at oil and gas characteristics and micro-preservation condition in the black shale of the Upper Permian Dalong Formation in Lianyuan Depression,the high-angle fracture calcite veins in the Dalong Formation shale of Well XY1 in Lianyuan Depression were selected to study veins petrography and CL observation,characteristics of brine and hydrocarbon inclusions in veins,temperature and pressure.Combined with the analyses of organic matter maturity of shale,hydrocarbon generation stage and the simulation of burial-thermal evolution-tectonic uplift history,the formation period and depth of fracture veins are determined,and the micro-preservation condition of shale oil and gas are discussed.The results show that the maturity R_o of organic matter in shale of Dalong Formation is about 1.2%-1.3%,while original organic matter has developed organic pores seldom developed in liquid oil in shale pore.Fractured calcite veins are formed in the early and late stages with clear boundaries.A large number of liquid and gas-liquid two-phase hydrocarbon inclusions with blue-white fluorescent,gas hydrocarbon inclusions with weak fluorescent and non-fluorescent methane inclusions are developed in the early veins.The homogenization temperature of brine inclusions is mainly between 93-138℃,corresponding to the paleo-burial depth about 2 000-3 000 m.The development of inclusions in late veins is poor and hydrocarbon inclusions can be seen sporadically.The homogenization temperature of brine inclusions is mainly between 50-62℃,corresponding to the paleo-burial depth about 900-1 100 m.The capture pressure of methane inclusions is estimated to be 28.92-41.47 MPa and the corresponding paleo-pressure coefficient is 1.10-1.57 based on the laser Raman parameters of methane inclusions in early fracture calcite veins and the equation of state of methane system.Based on the development degree of gas-liquid two-phase brine inclusions and hydrocarbon inclusions in the early and late fracture calcite veins and the information of captured temperature and pressure,the formation and opening of multi-stage fractures in shale and vein-forming paleo-fluid activity are found to have some adverse effects on the micro-preservation conditions of oil and gas in the Dalong Formation shale during structural uplift and stratum denudation process in Yanshanian-Himalayan epoch.