Simulation of Nanoparticle-Stabilized CO2-Foam in Sandstone
本论文研究是挪威卑尔根大学物理与技术学院储层物理研究小组正在进行的一个CO2泡沫项目的一部分。该论文旨在通过组分模拟器验证实验结果，以调整历史拟合，研究CO2-盐溶液（基准）和CO2纳米流体共注入过程中的泡沫行为。
使用CMG提供的组分模拟器GEM进行历史拟合和敏感性分析，以研究不同泡沫模型参数对CO2注入过程中泡沫强度的影响，包括参考渗透率降低因子（FMMOB）、最大干燥参数（Sfdry）、干燥斜率（Sfbet）、绝对渗透率和注入速度，以及纳米颗粒的存在与否。
本论文主要关注数值模拟CO2泡沫的过程，包括纳米颗粒和CO2的泡沫质量扫描，以产生用于流度控制的泡沫，并研究基于纳米颗粒的泡沫强度。数值模拟结果与Bentheimer砂岩核心的可用实验数据进行比较。
利用基线泡沫质量扫描实验方法（不使用纳米颗粒），在不同注入速率和气体含量下，注入气体与盐溶液和/或纳米流体以在现场生成泡沫。经验泡沫模型被插入到组分状态方程CMG-GEM模拟器中，该模型包括相对渗透率和泡沫模型参数，例如参考渗透率降低因子（FMMOB）、最大干燥参数（Sfdry）和干燥斜率（Sfbet）。
通过实验，在最佳气体含量（fg = 0.7）下达到最大表观粘度为7.8 cP，而对于基准泡沫质量扫描（无纳米颗粒），相同气体含量的表观粘度几乎降低了3倍。这表明泡沫生成并且纳米颗粒可以稳定CO2泡沫。
该模型可以复现实验数据，当最佳气体含量时，在所有注入速率下，表观粘度增加到最大值（7.7 cP）。实验数据和数值模拟中观察到CO2泡沫呈现近牛顿流体行为，即在泡沫扫描过程中没有观察到剪切变稠行为（流体粘度随注入速率增加而增加）或剪切变稀行为（流体粘度随注入速率增加而减少）。
模型饱和度分布表明，与基准相比，CO2-NP所生成的泡沫更多地将水驱出。总而言之，该研究提供了一种估计纳米颗粒稳定的CO2泡沫模拟的相对渗透率和泡沫模型参数的方法。这些发现对于理解在泡沫扫描中有无纳米颗粒存在时的纳米颗粒稳定的CO2泡沫行为非常有用。
模拟结果显示，在纳米颗粒存在的泡沫质量扫描过程中，泡沫表观粘度比盐溶液下的泡沫质量扫描过程中要高。观察到泡沫模型参数影响水饱和度、压差和表观粘度。最后，模拟结果显示与实验数据吻合良好，并且纳米颗粒稳定的CO2泡沫有望成为一种有前景的CO2流动性控制方法。
挪威卑尔根大学物理与技术系
Summary
The numerical study presented in this thesis is a part of an ongoing CO2-foam project led by the Reservoir Physics group at the Department of Physics and Technology, University of Bergen. The thesis objective was to investigate foam behavior during co-injection of CO2-brine (baseline) and CO2- nanofluid using a compositional simulator validated by history matching the experimental results. The compositional simulator GEM provided by The Computer Modelling Group (CMG) was used to perform history matching and sensitivity analysis to investigate how different foam model parameters, including the reference mobility reduction factor (FMMOB), the maximum dry-out parameter (Sfdry), the dry-out slope (Sfbet), absolute permeability, and injection velocity influence foam strength during CO2 coinjection with and without nanoparticle present. This thesis focuses on the numerical simulation of CO2-foam, that involves the foam quality scan of nanoparticles and CO2 to generate foam for mobility control, and to investigate the foam strength of the nanoparticle-based foam. The numerical simulations were compared with available experimental data from core floods on outcrop Bentheimer sandstone core. The core was fully saturated with brine (no oil) and gas was coinjected with brine and/or nanofluid at different injection rates and gas fractions to generate foam in-situ. An empirical foam model incorporated in the compositional equation-of-state CMG-GEM simulator was utilized. The model included relative permeability and foam model parameters, such as the reference mobility reduction factor (FMMOB), the maximum dry-out parameter (Sfdry) and the dryout slope (Sfbet). In the experimental work, the maximum apparent viscosity of 7.8 cP was achieved at the optimal gas fraction (fg = 0.7), whereas, for baseline foam quality scans (without nanoparticles), the apparent viscosity was almost 3 times lower at the same gas fraction for all injection velocities. This indicated foam generation and that nanoparticles were able to stabilize CO2 foam. The model was capable of reproducing the experimental data with emphasis on the optimal gas fraction, and the apparent viscosity increased to a maximum value (7.7 cP) at the optimal gas fraction for all injection velocities. A near-Newtonian behavior of CO2-foam was observed both in the experimental data and in the numerical simulations; no shear-thickening behavior (fluid viscosity increases with increasing injection rate) or shear-thinning behavior (fluid viscosity decreases with increasing injection rate) was observed during the foam scanning. The model saturation profiles indicated the foam was generated from CO2-NP was displacing more water compared to the baseline. In conclusion, this work provides a methodology for estimating relative permeability and foam model parameters for nanoparticle-stabilized CO2-foam simulation. The findings will be useful for understanding nanoparticle-stabilized CO2-foam behavior during foam scanning with and without nanoparticles present. Simulation results showed that the foam apparent viscosity increased during the foam quality scans with nanoparticles present compared to foam quality scans with brine. It was observed that foam model parameters affect water saturation, differential pressure, and apparent viscosity. Finally, simulations revealed that simulation results were in good agreement with experimental data and that nanoparticle-stabilized CO2-foam has the potential to become a promising method for CO2 mobility control.
