Study On Emulsification Mechanism Of Heavy Oil In Formation And Methods Of High-efficient Emulsification Oil Recovery

Emulsification of heavy oil and water is easily occurs when they were mixed due to the the high content of active substances such as resins and asphaltenes in heavy oil.The heavy oil and water have been emulsified in the porous media of the original heavy oil reservoir and the water flooding heavy oil reservoir.Nevertheless,the phase state,flow characteristics and re-emulsification of emulsified heavy oil in porous media affect the development effect of heavy oil reservoirs.At present,extensive and in-depth research has been carried out on the emulsification properties of dehydrated heavy oil with water and the emulsified viscosity reduction of dehydrated heavy oil.However,the emulsification characteristics and emulsified viscosity reduction of dehydrated heavy oil are different from those of "emulsified heavy oil" in the reservoir porous media.The theory of dehydration heavy oil emulsification and emulsification viscosity reduction cannot explain the dynamic law of heavy oil production,and there are problems such as large deviation in the prediction of emulsified viscosity reduction effect and unreasonable design of oilfield emulsified viscosity reduction process.This study mainly focuses on the formation emulsification mechanism and efficient emulsified viscosity reduction in heavy oil reservoirs.First,the emulsification properties of oilfield produced W/O emulsions were studied through rheological experiments and microscopic analysis.Flow experiments were carried out using sand-packed tubes and micro-etching models by simulating heavy oil reservoir conditions.The emulsification characteristics of heavy oil and water in porous media and the influence of permeability,viscosity of heavy oil,oil-water ratio and temperature on the emulsification of heavy oil were studied.Then,the multiple emulsification effect of W/O emulsion in the process of chemical viscosity reduction in the porous medium was studied by combining rheological measurement experiments,microscopic analysis and sand-packed tube flow experiments.The effect of multiple emulsification on the emulsion state and viscosity reduction effect was mainly studied.Thirdly,in view of the poor viscosity reduction effect of conventional emulsification of emulsified heavy oil,an anionic-nonionic surfactant with excellent emulsifying,dispersing and oil-displacing properties was developed.Finally,highefficiency emulsification oil recovery methods of injection mode,compoundsystem and combination of profile control with flooding are presented.Firstly,the emulsion state of produced oil from representative heavy oil reservoirs in China is analyzed,and the water content,resin and asphaltene content of produced oil from 160 heavy oil wells in Yuedong Oilfield are statistically and and calculated.The water content of W/O emulsions produced in heavy oil production wells of Yuedong Oilfield is mainly distributed between 10% and 40%,but the water content of some wells even exceeds 60%.During the development of heavy oil reservoirs,a large amount of W/O emulsions would be generated and distributed on both sides of the water flow channel,which further exacerbates the fingering phenomenon of injected water.The effects of flow distance,permeability,heavy oil viscosity,oil-water ratio and temperature on the emulsification state and average droplet size of W/O emulsion were mainly analyzed.With the increase of oil water content,the droplet size of W/O emulsion increases first and then tends to be stable,while its viscosity corresponding increases linearly and exponentially.Emulsification of heavy oil with water is severe as the temperature increases.In addition,high temperature water/steam would have a certain extraction effect on the light components of heavy oil,which would further aggravate the emulsification.Then,the re-emulsification mechanism of W/O emulsion was revealed by studying the emulsification characteristics,influencing factors and re-emulsification process of W/O emulsion in porous medium.It undergoes the process of "cutting","peeling" and further "cutting" to form a stable W/O/W emulsion when re-emulsification of W/O emulsion happened.The emulsification method,the ratio of emulsified viscosity reducer solution,and the water content of W/O emulsion have a great influence on the viscosity reduction effect and emulsification state of emulsified viscosity reducer.Moreover,with the increase of water content of W/O emulsion,the re-emulsification ability of emulsified viscosity reducer solution on W/O emulsion in porous medium decreases,the droplet size of emulsion increases,and peeling off effect from porous medium is weakened.Thirdly,A high-efficiency emulsified viscosity reducer(AEOSHS)with excellent water solubility,high surface(interface)activity,strong shrinkage oil film ability,low adsorption loss,strong porous medium emulsification ability,formation of small droplet size emulsion and high enhancing heavy oil recovery was developed by using the nonionic surfactant fatty alcohol polyoxyethylene ether(AEO12)as the raw material by means of nucleophilic substitution.Moreover,AEOSHS has a certain dispersing effect on the layered stacked structure of resin and asphaltene of heavy oil and has a good reemulsification effect on W/O emulsion.The dehydration rate of AEOSHS pure agent for W/O emulsion with 70% water content is as high as 93.5%.Finally,high-efficiency chemical flooding methods for heavy oil are proposed through optimization of the injection method of high-efficiency emulsified viscosity reducer(injection timing and injection slug amount),compounding of high-efficiency emulsified viscosity reducer system(colleaborative of anionic and cationic surfactant),construction of high-efficiency chemical oil displacement system(profile modification agent slug + high efficiency emulsifyied viscosity reducer slug),to meet different oilfield construction requirements and reservoir conditions.The above research results put forward about the the heavy oil-water emulsification and W/O emulsion re-emulsification mechanism in the formation porous medium of heavy oil reservoirs,development of high-efficiency emulsification viscosity reducer,and the methods of high-efficiency emulsification oil recovery,provide the provide theoretical basis for the dynamic law and recovery mechanism of heavy oil production,the prediction of chemical viscosity reduction effect and the design of oilfield chemical viscosity reduction process.