深埋环境方解石中流体包裹体再平衡临界温压条件的确定

The re-equilibration of fluid inclusions in calcite often occur during the deeply buried process, but we haven’t known its critical P-T conditions. This makes a difficulty in extracting useful information from the fluid inclusions in calcite in deep formation (>150℃). Therefore, this project makes some guide samples of synthetic fluid inclusions in calcite at diagenetic P-T conditions, and then the re-equilibration experiments of petrographic observation and homogenization temperature analysis of the primary and re-equilibrated fluid inclusions in calcite, we can determine the critical P-T conditions of re-equilibration of the fluid inclusions in calcite and figure out their dominating control factors. The natural samples from deep carbonate formation in Turim Basin are used to confirm experimental results through characteristic comparison of fluid inclusions, and finally the upper limit P-T conditions of preserving primary information of fluid inclusions in calcite in deeply buried environment. The research results will help us discuss the methods of identification of re-equilibrated fluid inclusions and the availability of the information recorded in re-equilibrated fluid inclusions, and use fluid inclusions to reconstruct the process of fluid evolution in sedimentary basins, and provide reference for the re-equilibration research of fluid inclusions in other geological environments.

方解石中的流体包裹体在深埋过程中易于发生体系再平衡，但对其发生再平衡的临界温压条件认识不清，这对提取深层（>150℃）方解石中流体包裹体的有效信息产生了困扰。因此，本项目以方解石作为寄主矿物，模拟成岩环境下人工合成流体包裹体标样，并在依次升高的温压条件下进行流体包裹体再平衡实验。通过观察流体包裹体再平衡前后岩相学特征和均一温度的变化情况，确定方解石中流体包裹体再平衡的临界温压条件及其主要控制因素，并通过与塔里木盆地深部碳酸盐岩地层样品中流体包裹体的特征对比来进行验证，确定深埋环境下方解石中流体包裹体保存原始信息的上限温压条件。研究结果有助于探讨再平衡流体包裹体的判识方法及保存信息的有效性，便于更好地利用流体包裹体恢复沉积盆地流体演化过程，并为其他地质环境中的流体包裹体再平衡研究提供参考。

本项目通过人工合成流体包裹体及其再平衡实验，阐明了不同捕获条件下的方解石中立体包裹体在“埋深”过程中发生再平衡的温压条件。结合理论计算，认为方解石中的流体包裹体在内外压差超过50MPa的时候，就可以开始发生再平衡了。分析了不同因素与流体包裹体再平衡的相关性，认为在低温、高压和高盐条件下形成的流体包裹体在埋深过程中更加易于发生再平衡。同时探讨了烃类包裹体气液比对PVT模拟的影响是非常大的。此外，讨论了如何有效判识和利用碳酸盐岩中的再平衡流体包裹体。认为结合镜下观察、显微测温及激光拉曼等可以共同判识再平衡流体包裹体。流体包裹体发生再平衡后，仍然可以用来分析再平衡发生时的地质过程，结合未发生再平衡的流体包裹体，可以完整地记录地层所经历的地质事件。

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