超低渗油藏活性纳米流体降压增注及渗吸排驱机理研究

Many difficulties are encountered during the development of ultra-low permeability oil reservoir, such as micro-nano meter pore throat, low permeability, low recovery, difficulty in energy supply, low flooding efficiency of the oil in matrix, and etc. The conventional EOR methods for medium and high permeability oil reservoir could not meet the urgent demandment of EOR in ultra-low permeability oil reservoir. In response to this problem, nanometer materials get many attentions due to their unique characters. The nanometer materials are characterized of small particles, high surface energy, thus poses several disadvantages, such as hard to disperse in water, self-aggregation and settling, and etc. Molecular Simulation technology facilitates the design of the molecular structure of a novo active nano material. The structure-activity relationship will be clarified between functional groups and active nano material. Water based active nano material will be prepared with properties of cheap and easy access, good interfacial activity, self-stabilized dispersion. With the functional characteristic study of thermodynamics, rheology, interfacial, and application of active nano material, the functional mechanism of active nano fluid at pore throat surface and oil/water interfacial tension is clarified. The self-designed micro-channels and nano-micro fluidic chip visualization models will be manufactured to simulate the matrix, matrix and fracture dual medium accurately. Distribution characters of the flow-field will be quantitively analyzed. The oil transportation from matrix to fracture between fractures within the finite field will be clarified. The mechanism of pressure reduction and injection augment, high-efficient flooding and drainage of active nano-fluid will be revealed. New EOR method with active nano-fluid for ultra-low permeability oil reservoir will be developed. This study will provide the theoretical basis of high efficient development of ultra-low permeability oil reservoir in China.

超低渗油藏面临储层微-纳米级孔喉、渗透率低、天然能量采收率低、能量补充困难、基质油驱替效率低等难题。针对这一难题，纳米材料因其优异性能备受关注，但又存在粒径小、表面能大，在水中不易分散，自聚沉降等问题，本研究利用分子模拟技术设计活性纳米材料分子结构，阐明官能基团与活性纳米材料性能间的构效关系，制备廉价易得、界面活性好、自稳定分散的水基活性纳米材料；研究活性纳米流体的热力学、流变、界面及应用等功能特性，阐明活性纳米材料在孔喉表面、油水界面的作用机制和渗吸效率；采用自行设计高度仿真的可视化微通道和纳-微尺度流控芯片模拟基质、基质-裂缝双重介质，定量分析微通道内流场分布特征，阐明活性纳米材料在孔喉表面粗糙度变化和纳米颗粒排布特征和裂缝间有限域内基质油向裂缝驱替规律，揭示活性纳米流体降压增注及渗吸排驱的机理，形成超低渗油藏活性纳米流体提高采收率新方法，为我国超低渗油藏高效开发提供理论基础。

超低渗油藏面临储层微—纳米级孔喉、渗透率低、天然能量采收率低、能量补充困难、基质油驱替效率低等难题。针对这一难题，本项目首先利用分子模拟手段研究了化学官能团对纳米颗粒修饰后分散稳定性的影响规律，通过分析平衡构型、相互作用、颗粒聚并的势能变化等因素，揭示了改性纳米颗粒聚集和分散的微观机制。基于分子模拟结果，通过化学表面修饰技术对纳米SiO2颗粒进行表面改性，研制出系列价格低廉、活性好、稳定分散的水基纳米SiO2材料。并以此为基础构建了活性纳米流体，阐明了不同影响因素（浓度、温度、矿化度等）对活性纳米流体的稳定性、吸附特性、渗吸的影响规律。表面改性纳米颗粒在油水界面的吸附稳定性较好，稳定时间长达60天，扩张模量可达154.5 mN/m，界面膜表现出明显的弹性，能够形成稳定的油水界面膜，有助于后期采收率的提高。并通过岩心流动试验系统评价了活性纳米流体的降压增注和渗吸排驱性能，降压率30%以上，渗吸采收率42%。最后采用直微通道和孔喉微通道模型，结合分子模拟手段，建立了微流动下边界层厚度的测定方法，阐明了微流动下纳米流体调控边界层规律和微通道内流动特征，深入分析了纳米颗粒、水和石英壁面的相互作用机制，揭示了活性纳米流体降压增注的微观作用机理。采用可视化多管束微通道模型，通过高速显微摄像系统，建立了基质-裂缝模型渗吸过程微尺度观测方法，明确了流体流速、纳米流体浓度对界面运移速率、三相接触角的作用特征，阐明了不同条件微尺度基质通道中剩余油分布规律，并结合核磁共振手段揭示了活性纳米流体的渗吸排油机理。最后借助高仿真微观三维孔喉模型和高速摄像系统，探究了受限空间内纳米颗粒对油滴破裂、聚并及抗奥斯瓦尔德熟化的的影响机制，揭示了高效驱油作用机理。通过本课题的研究，形成了超低渗油藏活性纳米流体提高采收率新方法，为我国超低渗油藏高效开发提供技术支持，对提高我国石油天然气开采行业的国际竞争力、促进行业科技水平进步具有非常积极的作用。