Formation time and fluid source of calcite veins of Triassic Qinglong Formation in Huangqiao area, Subei Basin
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摘要: 储层中方解石脉体记录了多期流体活动信息,对研究油气成藏过程具有重要的指示作用。本文基于岩石薄片观察、阴极发光和U-Pb同位素定年在厘清苏北盆地黄桥地区三叠系青龙组碳酸盐岩中方解石脉发育期次和形成时间的基础之上,通过稀土元素分析、C、O、Sr同位素综合分析方解石脉体成脉流体来源。黄桥地区青龙组发育四期方解石脉体,四期方解石脉体形成时间分别为115.30±0.42 Ma、97.03±0.43 Ma、85.29±0.25 Ma、45.5±19.0 Ma。第一和第二期方解石成脉流体分别来源于深部热液流体和大气淡水和海水的混合流体。第三期方解石成脉流体来源于同层地层水和深部壳源热液流体的混合流体。第四期成脉流体来源于同层地层水和深部幔源热液流体的混合流体。苏北盆地黄桥地区三叠系青龙组碳酸盐岩储层中四期脉体的形成时间与不同期次构造活动具有对应关系表明构造活动对流体活动的控制作用。储层中三期深部热液流体的注入是因为构造活动导致深大断裂沟通深部流体而注入到储层中的结果,多期的深部热液流体活动可能指示了黄桥地区三叠系青龙组储层具有多期油气成藏的特征。Abstract: Calcite veins in the reservoir record crucial information about fluid activity, which has important indicator for hydrocarbon accumulation process. A multi approaches consisting of thin section observation, cathodoluminescence, U-Pb isotope dating, REE, C, O and Sr isotopes of calcite veins from the Triassic Qinglong carbonate reservoirs in Huangqiao area of Subei Basin is used to analyze the source of calcite vein forming fluid. Four stages of calcite veins were successively formed at 115.30±0.42 Ma, 97.03±0.43 Ma, 85.29±0.25 Ma and 45.5±19.0 Ma, respectively. The first and second stage of calcite veins were derived from deep hydrothermal fluids and the mixed fluids of atmospheric fresh water and seawater respectively. The vein-forming fluid of the third stage of calcite veins was the mixed fluid of the same stratum water and deep shell source hydrothermal fluid. The fourth stage of calcite veins was derived from the same layer water mixed with the deep mantle-derived hydrothermal fluid. The formation time of the four stages of the Triassic Qinglong Formation carbonate reservoir in the Huangqiao area of Subei Basin corresponds to the sub-tectonic activities at different periods, which implies that fluid evolution was controlled by multi stages of tectonic movements. Importantly, three stages of deep hydrothermal fluid in the reservoir is the result of deep fault opening caused by tectonic activities, indicating multi-stages of oil and gas charges in the Qinglong Formation of the Triassic in the Huangqiao area.
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Key words:
- Calcite vein /
- U-Pb isotope age /
- Fluid source /
- Fluid activity /
- Huangqiao gas field
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