Study On Low Temperature Oxidation Catalytic Mechanism Of Crude Oil During Air Flooding Process

Due to the gas source and the cost advantage,air injection production technology is getting more and more applications in the world.Many experts and scholars have considerable research on its oil displacement mechanism and field application.However,due to the complexity of the composition of crude oil,the low-temperature oxidation mechanism of crude oil is so far unclear,and the security issue has been the problem restricting the large-scale application of the air flooding.Therefore,the paper is carried out to study the above mentioned problems.Low temperature oxidation mechanism of crude oil is summarized based on studying low temperature oxidation characteristics of crude oil via static oxidation experiments and studying the relationship of low temperature oxidation characteristics and oxidation process of crude oil and its SARA components via TG-DSC and TG-FTIR test.Saturates and aromatics content will decrease and resins and asphaltenes will increase after the low temperature oxidation of crude oil,and the increase of temperature and pressure can promote the low temperature oxidation of crude oil.Under reservoir conditions,the low temperature oxidation activity of SARA components from high to low is as follows:resins>aromatics>saturates.So the higher the heavy component content of resin and asphaltene of crude oil,the stronger the low temperature oxidation activity of crude oil.Low temperature oxidation of crude oil mainly generate carboxylic acid,alcohol,phenol and ether hydrocarbon oxide and a small amount of H₂O and CO₂,and the hydrocarbon oxide is the main production at the initial reaction and the production amount of CO₂ will rise continuously as the reaction proceeds.Saturates,aromatics and resins are the main source of H₂O,CO₂,phenol alcohols and carboxylic acid in the low temperature oxidation of crude oil,but ethers mainly derive from the low temperature oxidation reaction of aromatics and resins.The sources of CO₂ in low temperature oxidation of crude oil are as follows:the decarboxylation of carboxylic acid produced from previous oxygenation reactions,or the associated gas produced during the process of aromatics oxidized to phenol.Most of the CO₂ produced from the oxidation of saturates and resins derived from decarboxylation.But for aromatics,both the two sources are active.Both the oxygenation reaction and decarburization reaction exist in low temperature oxidation reaction of crude oil,and the oxidation characteristics of SARA components is the internal decisive factor of the oxidation characteristics of crude oil.At 50-120?,saturates,aromatics and resins can occur LTO reaction,and the main reaction mode is oxygenation reaction.With the increase of reaction temperature,LTO reaction mode gradually translate into decarburization reaction that contains higher heat production efficiency.In the initial stage of air injection production,the intensity of low-temperature oxidation reaction of saturates is low,and the low-temperature oxidation reaction of aromatics and resins is the main way of oxygen consumption and heat production.But the reaction activity of saturates is continually increased with the elevated temperature which has gradually became a pillar reaction of low temperature oxidation of crude oil.Then the low temperature oxidation characteristics of saturates determines the oxidation reaction characteristics of crude oil.In order to improve the safety of air flooding,the catalytic air flooding is put forward in the term that improves the low temperature oxidation reaction rate of crude oil.The catalyst was optimized and the low temperature catalytic oxidation mechanism has been studied.The metal salts of Mn,Co,Ni,Cu,Fe and Zn can promote the low temperature oxidation of crude oil,but the catalytic effect of organic salt is better than inorganic salt.The catalyst optimized is cobalt naphthenate.The optimal injection mode for the catalyst is alternative injection of catalyst and air.When applied to water-flooding reservoir,the optimal injection time is when the water cut below 30%.The catalyst can significantly change the low temperature oxidation reaction process of SARA components,promote the hydroxyl containing hydrocarbon oxides and CO₂ production in the oxidation reaction of saturates,aromatics and resin,and restrain the production of ethers in the oxidation of aromatics and resins.The catalyst can significantly strengthen the oxygenation reaction and the bond breaking reaction of saturates,aromatics and resins,and the catalytic effect on the bond breaking reaction is continuously enhanced as the reaction progress.This paper has made some progress in the aspect of air injection low temperature oxidation mechanism and catalytic mechanism of crude oil,which has directive significance to the relevant research of air flooding technology and its field application.