注空气开发中地层原油氧化反应特征

Oxidation reaction features of formation crude oil in air injection development

通过分析中国不同类型油藏注空气开发的技术优势,依据室内实验和现场试验的研究成果,阐述了轻质油和稠油不同氧化阶段的氧化反应特征。研究认为,不同氧化阶段地层原油的氧化反应特征存在明显差异:在中低温氧化阶段,氧气直接与原油接触,温度越高氧化反应越强;无论轻质油还是稠油,高温氧化阶段氧化反应的主要对象是焦碳而不是原油。进一步提出了划分轻质油和稠油氧化反应4个阶段的温度区间,轻质油比稠油中温氧化反应的起始温度低,放热量大,轻质油比稠油更容易诱发氧化反应;轻质油高温放热峰值(8.06 mW/mg)略高于中温放热峰值(6.42 mW/mg),而稠油高温放热峰值却是中温放热峰值的5倍,稠油注空气火驱开发应该以实现高温氧化为主要目标。因此,根据油藏温度和油品性质等关键指标可选择空气驱或火驱等注空气开发方式:当油藏温度小于120℃时,由于氧化放热不明显,为了避免注空气开发的爆炸风险,应以减氧空气驱有效补充地层能量的开发方式为主;当油藏温度大于120℃时,在油藏条件下原油就可发生明显的氧化反应,此时可实施不减氧空气驱,充分利用原油氧化反应放热提高采收率;对于油藏温度小于120℃的稠油油藏,可通过电加热器等人工手段实现高温点火,进行高温火驱开发。

The technical advantages of air injection development of different oil reservoirs in China were introduced.Based on the latest research results of laboratory and field tests,the oxidation reaction features of both light and heavy crude oil at different oxidation stages were elaborated.The results show that oxidation reaction features differ noticeably at different oxidation stages.In the midlow-temperature oxidation reaction stage,oxygen is directly contacted with crude oil,and oxidation reaction increases with the temperature rising.Either for light oil or heavy oil,the main object at the high-temperature oxidation stage is coke rather than crude oil.Different temperature ranges of four different oxidation reaction stages were divided for light oil and heavy oil.It is indicated that for the mid-temperature oxidation reaction,light oil has a lower starting temperature and larger heat release,and is more prone to oxidation reaction than heavy oil.Meanwhile,the high-temperature exothermal peak(8.06 mW/mg)of light oil is slightly larger than the mid-temperature exothermal peak(6.42 mW/mg).But for heavy oil,the high-temperature exothermal peak is five times larger than the mid-temperature exothermal peak.The in-situ combustion development for heavy oil mainly aims to achieve high-temperature oxidation.Hence,the selection of air injection development methods such as air flooding and in-situ combustion relies on reservoir temperature,oil property and other key indexes.When the reservoir temperature is lower than 120℃,the oxygen-reduced air flooding method should be mainly adopted to supplement reservoir energy and avoid the explosion risk of air injection development due to insignificant oxidization heat release.When the reservoir temperature is higher than 120℃,obvious oxidation reaction will happen to crude oil under reservoir conditions.In this situation,the air flooding without oxygen-reduced process can be selected to fully exploit the heat release from the oxidization reaction of crude oil for improving enhanced oil recovery.For the heavy oil reservoir with the temperature lower than120℃,high-temperature ignition can be implemented using artificial methods such as electric heater for hightemperature in-situ combustion development.