轻质油藏空气驱原油氧化自燃理论及预测模型研究

In order to give a safe and effective guide for high-pressure air injection (HPAI) project design, it is necessary to accurately predict the spontaneous ignition of the oxidized crude oil in light oil reservoirs. However, the spontaneous ignition behaviour has been ignored in the mathematical model of the current commercial numerical simulation software, which often leads to the unreliable results of project design, safety and dynamic prediction. In this project, the mechanism of thermal induced spontaneous ignition of crude oil during oxidation process is revealed for the first time based on thermal analysis both from the internal factors (crude oil component) and external factors, mainly including temperature, pressure, fluid saturation, gas injection rate, specific surface area of rock particle, clay. The TG/PDSC/ARC are employed to study the effects of crude oil component and physical properties on the oxidation kinetics, and to decide the exothermic region to preliminary understand the spontaneous ignition behaviour. The developed thermal effect monitoring device is used to investigate the influences of all factors concerned on temperature rising during the oxidation process of crude oil. The data obtained in the experiments are used to establish the numerical model of thermal spontaneous ignition which is applied to predict radical formation temperature, oxygen concentration distributions and formation properties with time and space. The properties and control method of thermal spontaneous ignition are discussed by factor analysis. The mathematical model gives a more comprehensive consideration and is more approach to practical situation. The research results will provide significant guidelines for further riching the mechanism of HPAI in light oil reservoirs as well as revealing the rule of crude oil autoignition.

准确预测轻质油藏空气驱中原油氧化升温至自燃现象可安全、高效地指导开发方案设计。现有的商业油气藏数值模拟软件的数学模型未考虑轻质原油受多因素影响下的氧化升温至自燃的规律，导致方案设计、安全性和开发动态预测存在不可靠性。本项目首先利用热分析实验手段从内因（原油组成）和外因（温度、压力、流体饱和度、注气速率、岩石颗粒比表面积、粘土）两方面着手，揭示原油氧化放热机制；利用TG/PDSC/ARC研究原油组成对原油氧化动力学影响，判定放热区间，对升温规律作出初步认识；利用研制的热效应实验监测装置研究各因素对多孔介质中原油氧化升温规律的影响，基于实验和理论建立原油氧化自燃综合预测模型，预测沿井筒径向地层温度、氧浓度分布及升温对储层物性的影响规律，探讨原油氧化自燃机理及调控机制。建立的模型考虑的因素较为全面，更符合实际，研究成果对于丰富空气驱机理，探索原油氧化自燃规律具有重要意义。

原油在低温氧化过程中能否实现自燃一直困恼着学术界。本项目采用实验研究、理论分析和数值模拟相结合的方法，系统地研究了原油氧化自燃机理与预测方法，相继开展了原油氧化动力学实验、多孔介质中原油氧化实验以及空气驱机理数值模拟，取得了诸多创新性认识和成果。（1）粘土矿物在原油氧化过程中可起到催化作用，高岭石催化氧化能力最差，伊利石和蒙脱石催化氧化能力较强。采用定性的氧化动力学分析手段TG/DTG/DTA方法依然具有较高的准确性，同样也能够反映油藏条件下原油氧化特征。建议采用多级升温速率和多种动力学模型对比研究获取动力学参数，通过分析动力学参数之间的差异，可确定其合理取值范围，用于数值模拟以提高模型可靠性。（2）原油中质组份C7-C15过多将不利于耗氧，胶质、沥青质、芳香烃和重质组份（C17+）的存在利于低温氧化，为参加反应的主体组份，原油低温氧化过程具有“组份优势”特点，即含量高的碳烃组份具有优先参与氧化反应能力。采取油溶性Cu(C11H7O2)2催化剂辅助空气驱或空气吞吐将是稠油高效开发的一种新途径。（3）研发了高压注空气氧化热效应检测跟踪实验装置，监测到了轻质原油低温氧化升温范围为2-8℃，实验室无法观测到剧烈升温或自燃，数值模拟明确了影响轻质原油低温氧化热效应的主控因素，依次为模型尺寸、氧气浓度和边界热损失。（4）研发了考虑气-液-固三相非平衡传质传热与扩散的空气驱模拟器，将相间的质量交换考虑成动态过程，可更准确模拟空气驱过程温度变化以及组份浓度分布，捕获温度前缘特征，弥补了当前主流油藏模拟软件CMG-STARS在空气驱数值模拟方面的局限。数值模拟验证了轻质油藏空气驱中的孔喉堵塞效应，揭示了“气窜自控”机理，阐述了空气驱提高采收率的影响因素。探索了页岩油藏注空气原油氧化机理，明确了注空气吞吐提高页岩油采收率潜力。研究成果丰富了空气驱油机理，对该技术的发展具有重要推动作用。