Experimental and Molecular Insights on Mitigation of Hydrocarbon Sieving in Niobrara Shale by CO2 Huff ‘n’ Puff
Experimental and Molecular Insights on Mitigation of Hydrocarbon Sieving in Niobrara Shale by CO2 Huff ‘n’ Puff
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DOI：
10.2118/196136-pa
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发表时间：
2020-08
期刊：
影响因子：
3.6
通讯作者：
Ziming Zhu;Chao Fang;R. Qiao;Xiaolong Yin;E. Ozkan
中科院分区：
文献类型：
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作者：
Ziming Zhu;Chao Fang;R. Qiao;Xiaolong Yin;E. Ozkan
在纳米多孔岩石中，纳米孔和孔喉中潜在的尺寸/流动性排阻和流体-岩石相互作用可以将岩石变成半透膜，阻止或阻碍某些分子的通过，同时允许其他分子自由通过。在这项工作中，我们进行了几个实验，以研究CO2是否可以减轻对流经Niobrara样品的烃分子的筛分效应。分子动力学（MD）模拟的吸附平衡与无CO2进行，以帮助了解在实验中观察到的趋势。实验过程包括将已知组成的液态二元烃混合物（C10和C17）泵入Niobrara样品中，收集来自样品的流出物，并分析流出物的组成。一个专门的实验装置，使用一个在线过滤器作为一个微型核心保持器，建立了这项调查。将Niobrara样品取芯并机加工成0.5英寸。直径和0.7英寸。长度迷你将烃混合物注入微芯中，定期收集流出物并使用气相色谱法（GC）进行分析。在观察微矿石的筛分效果后，在600 psi下进行CO2吞吐，该压力远低于可筛分压力。从生产侧注入CO2以浸泡样品一段时间，然后恢复混合物的流动，并使用GC分析流出物。实验结果表明，在几个实验中，CO2吞吐明显减轻了较重组分（C17）的筛分。所观察到的采出液中C17分数的增加可以是暂时的，也可以是持久的。在大多数实验中，还观察到流速的暂时增加。分子动力学模拟结果表明，对于与C10和C17的二元混合物平衡的方解石表面，更多的C17分子吸附在碳酸盐表面上比C10分子。一旦将CO2分子加入到系统中，CO2就会从方解石中置换C10和C17。因此，实验观察到的C17分数的增加可归因于吸附的C17的释放。这项研究表明，表面效应在影响致密地层中流体的流动和组成方面起着重要作用。在非常规油藏中，除了公认的热力学相互作用机制之外，观察到的CO2吞吐提高采收率可能部分归因于地面效应。
In nanoporous rocks, potential size/mobility exclusion and fluid–rock interactions in nanosized pores and pore throats can turn the rock into a semipermeable membrane, blocking or hindering the passage of certain molecules while allowing other molecules to pass freely. In this work, we conducted several experiments to investigate whether CO2 can mitigate the sieving effect on the hydrocarbon molecules flowing through Niobrara samples. Molecular dynamics (MD) simulations of adsorption equilibrium with and without CO2 were performed to help understand the trends observed in the experiments. The experimental procedure includes pumping liquid binary hydrocarbon mixtures (C10 and C17) of known compositions into Niobrara samples, collecting the effluents from the samples, and analyzing the compositions of the effluents. A specialized experimental setup that uses an in-line filter as a minicore holder was built for this investigation. Niobrara samples were cored and machined into 0.5-in. diameter and 0.7-in. length minicores. Hydrocarbon mixtures were injected into the minicores, and effluents were collected periodically and analyzed using gas chromatography (GC). After observing the sieving effect of the minicores, CO2 huff ‘n’ puff was performed at 600 psi, a pressure much lower than the miscibility pressure. CO2 was injected from the production side to soak the sample for a period, then the flow of the mixture was resumed, and effluents were analyzed using GC. Experimental results show that CO2 huff ‘n’ puff in several experiments noticeably mitigated the sieving of heavier components (C17). The observed increase in the fraction of C17 in the produced fluid can be either temporary or lasting. In most experiments, temporary increases in flow rates were also observed. MD simulation results suggest that for a calcite surface in equilibrium with a binary mixture of C10 and C17, more C17 molecules adsorb on the carbonate surface than the C10 molecules. Once CO2 molecules are added to the system, CO2 displaces C10 and C17 from calcite. Thus, the experimentally observed increase in the fraction of C17 can be attributed to the release of adsorbed C17. This study suggests that surface effects play a significant role in affecting flows and compositions of fluids in tight formations. In unconventional oil reservoirs, observed enhanced recovery from CO2 huff ‘n’ puff could be partly attributed to surface effects in addition to the recognized thermodynamic interaction mechanisms.