Phase behavior of nanoconfined continental shale oil and reservoir fluid phases in the Gulong shale of the Songliao basin

页岩油的相态对于评估页岩油产量、制定开发计划和提高采收率至关重要。以往对页岩油相态的研究主要集中在基于钻井获取的流体组成的整体流体相态，而基于原位流体组成的纳米限域页岩油相态很少被讨论。本研究建立了一种新的工作流程，使用保压岩心和热解气相色谱（Py-GC）从不同热成熟度的页岩中获取原位页岩油组成。结果表明，随着热成熟度的增加，古龙页岩油中的甲烷含量从10.11%增加到23.39%，而C7+烃类从64.73%下降到41.13%。在低热成熟度（Ro小于1.4%）时，页岩油为黑油相；在高热成熟度（Ro大于1.4%）时，页岩油为凝析油相。研究表明，使用保压岩心获取的原位页岩油组成进行纳米限域相态分析可以更好地预测页岩油产量。

CMG软件应用情况

在本研究中，CMG软件被用于进行油藏数值模拟，以评估纳米限域效应对页岩油产量的影响。通过将从井口、井底和保压岩心获取的页岩油组成与纳米限域相态模型相结合，CMG软件生成了多个页岩油井的生产曲线。结果表明，使用纳米限域相态模型的生产曲线与实际生产数据拟合得最好，而基于井口流体的整体相态模型预测的累积油产量最低。这表明在页岩油生产中，纳米限域效应不可忽视，传统的整体流体相态分析不适合用于识别页岩油储层流体相态和预测产量。

结论

  1. 从保压岩心获取的整体烃类组成能更好地代表页岩储层原位流体组成。随着热成熟度的增加，古龙页岩油中的甲烷含量从10.11%增加到23.39%，而C7+含量从64.73%下降到41.13%。
  2. 整体流体相态分析表明，古龙页岩油主要为黑油相。只有在Ro大于1.6%的区域，储层油相才会转变为凝析油相。
  3. 纳米限域流体相态和储层流体相态分析表明，热成熟度小于1.4%的古龙页岩油主要为黑油相，主要分布在北部齐家坳陷、黑鱼泡坳陷、大庆古隆起南坡、齐家-古龙坳陷坡区和三肇坳陷。而在热成熟度大于1.4%的区域，油的物理性质更好，页岩油主要为凝析油相，主要分布在齐家-古龙坳陷，是古龙页岩油开发的核心区域。
  4. 古龙页岩油长期生产数据表明，纳米限域相态模型能更好地预测产量，表明传统的整体流体相态分析不适合用于识别页岩油储层流体相态和产量预测。

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Abstract

The shale oil phase state is essential for assessing shale oil production, establishing development plans, and enhancing oil recovery. Previous studies on shale oil phase state mainly focused on bulk fluid phase based on fluid composition retrieved from drill holes, while nano-confined shale oil phase state based on subsurface in-situ fluid compositions is rarely discussed. In this work, we established a new workflow that used pressure-preserved shale cores and pyrolysis gas chromatogram (Py-GC) to retrieve in-situ shale oil compositions from various shales with different thermal maturities. The workflow includes retrieving pressure-preserved shale cores, cutting, transporting, and then preparing samples under the protection of liquid nitrogen; the new process makes the evaporation loss of lightweight hydrocarbons the least. By comparison, fluid samples from wellheads and wellbores were also retrieved from Gulong shale oil reservoirs in the Songliao Basin. Both bulk and nano-confined shale oil phases were then analyzed, and the results showed that methane content in the Gulong shale oil increased from 10.11 to 23.39% with increasing thermal maturity; by contrast, C7+ hydrocarbons decreased from 64.73 to 41.13%. As for bulk fluid phases, Gulong shale oils are black oil phases, while in terms of nano-confined fluid phases, their phases are controlled by thermal maturity. They are black oil phases at lower thermal maturity with vitrinite reflectance (Ro) less than 1.4% and are condensate phases at higher thermal maturity with Ro greater than 1.4%. Shale oil production data showed that nano-confined phase analysis using in-situ shale oil compositions from pressure-preserved cores can best predict shale oil production in this study.

 

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