Experimental Study On Oil Oxidation Mechanism And Displacement Efficiency During Air Injection Process In Light Oil Reservoir

In recent years,the demand of social development for petroleum is getting higher and higher.With the deepening of oilfield development,conventional oil resources continue to fail.At present,most of the oilfields in China have entered the middle and high water cut stage,crude oil production decreases significantly.Meanwhile,the exploration of new oil and gas resources is becoming more and more difficult.In order to maintain the oil production of the aging oilfield,to find an economical and effective enhanced oil recovery technique(EOR)has become the focus of researchers.Traditional chemical flooding,gas flooding,microbial flooding and other oil recovery technologies have the disadvantages of high cost,environmental pollution,limited supply and application scope.Therefore,high pressure air injection(HPAI)as a promising secondary or tertiary recovery technology has received more and more attention in recent years.However,the chemical reactions and physical flooding involved in the process of reservoir air flooding are extremely complex,the relevant domestic theoretical research is still scarce at present and the successful field experience is also very little.Thus,there are some urgent to carry out research on the mechanism of oil oxidation and air displacement experiment.In this paper,the low-temperature oxidation characteristics and oxidation process of a light crude oil in Xinjiang oilfield are studied by static isothermal oxidation tube experiment.The changes of liquid hydrocarbons molecular structure in the oxidation process are analyzed from the microscopic point of view by the combination of chromatographic analysis,infrared spectrum analysis and physical property measurement.Finally,the main oxidation reaction modes of the crude oil are described as follows:oxygen addition reaction,condensation reaction and carbon bond stripping reaction.At the same time,the sensitivity of crude oil low-temperature oxidation is studied.The effects of water saturation,oxygen concentration,specific oil composition and reservoir rock on crude oil oxidation are analyzed from the aspects of composition and physical property change of exhaust gas and oxidized oil.Subsequently,the thermal behaviors of oil samples,such as the reaction temperature range,the peak temperature,the mass loss and the thennal effect,are obtained quantitatively by thermogravimetry/differential thermogravimetry and differential thermal analysis(TG/DTG-DTA),to analysis the influence of crude oil composition,oxygen concentration and reservoir rock.Based on the classical kinetic theory of oil oxidation,the kinetic parameters of activation energy and Arrhenius constant are obtained to discuss the feasibility of implementation of high-pressure hypoxic air injection process in light reservoir.Based on the analysis of the oxidation characteristics and oxidation activity of crude oil,the air flooding experiment is carried out.The effects of low-temperature xidation on the recovery of crude oil under different air injection pressures,different air injection rates and different oxygen concentrations are investigated by using long tube model.The conditions of real reservoirs are simulated by using long core flooding device.The mechanism of air flooding in light reservoir is improved by comparing the oil displacement efficiency under different permeable porous media and different flooding medium.In this paper,the oxidation reaction and corresponding sensitivity of crude oil during HPAI process are investigated by static isothermal oxidation tube and non-isothermal thermogravimetric tests.Some understandings about low-temperature oxidation mechanism,oxidation reaction mode and crude oil oxidation activity have been made.At the same time,the indoor evaluation of air flooding is carried out to understand the air flooding mechanism,and to further develop enhanced oil recovery technology.In addition,in the practical view,it can provide reference value and instructive significance on the theoretical study and field application for the air injection technology in light reservoirs.