Study On Characterization And Stabilization Mechanism Of Produced Liquid And Produced Water From Weak Base Petroleum Sulfonate Surfactant ASP Flooding

In this paper,weak base petroleum sulfonate surfactant ASP flooding produced water and produce liquid from N2 W area were studied.During the recovery peak of oil displacement agent from the N2 W area,properties such as pH value,salinity,composition,phase structure and separation characteristics of ASP flooding produced liquid and produced water were tracked and monitored.Through experimental simulation and theoretical analysis,the effects of alkali,surfactant and polymer in oil displacement agent on oil-water separation characteristics,interfacial characteristics and rheology were studied.By simulating the evolution process of water phase microemulsion in the injection of ASP flooding,the source and formation mechanism of nano and sub micron scale oil droplets in the ASP flooding water were studied.By studying the oil-water interfacial property and rheological property of the produced liquid,the main factors affecting oil-water separation characteristics of the produced liquid of the weak alkaline system ASP flooding were determined,and the characteristics,causes and reasons of the produced water were explored.Thus solutions to improve the effect of oil-water separation were concluded.It was found that the produced water of ASP flooding contained sub-micron oil droplets with a diameter of 8?m~1?m of about 40 mg/L.These oil droplets form multiple emulsions such as O/W and W/O/W.The size of the oil droplets coincides with some of the hydrolyzed polyacrylamide molecular clumps highly,so they have not been identified as the disperse phase of the emulsion.These droplets were small in size,and poor in accumulation and floating capacity.It was difficult to pass through settlement and filtration,which is the main reason for the difficulty of oil removal from the ASP flooding produced water in this experimental area.In the process of emulsification and destabilization of the O/W type petroleum sulfonate surfactant weak base system ASP flooding,two main aspects of the influence by alkali were(1)to reduce the interfacial tension,forcing the O/W type ASP flooding emulsification degree increases,and forming the oil beads into smaller particle size;(2)the high content of alkali compressed the interfacial diffuse double layer,suppress the electrostatic repulsion between the remote oil droplets,promoting oil droplets between aggregation and coalescence.The results of the two kinds of antagonism was that the oil content of water phase decreases with the increase of alkali content in the liquid phase separation process of O/W type petroleum sulfonate surfactant weak base system ASP flooding.In the process of emulsification and destabilization of the O/W type petroleum sulfonate surfactant weak base system ASP flooding,there are three main aspects of petroleum sulfonate surfactant's influence:(1)to reduce the interfacial tension,forcing the O/W type of petroleum sulfonate surfactant ASP flooding emulsification degree increases,forming the oil droplets into smaller particle size;(2)increasing long-range electrostatic repulsion and excess negative charge density between the oil droplets,thus hinder the accumulation and coalescence between oil droplets;(3)through the Marangoni effect hindering discharge of coalescence plate water film in the process of phase seperation.The superposition of the above three actions resulted in the increase of oil content in the aqueous phase during the production of liquid phase separation of O/W petroleum sulfonate surfactant ASP flooding.In the process of emulsification and destabilization of the O/W type petroleum sulfonate surfactant weak base system ASP flooding,two main aspects of the influence by polymer were(1)increase the viscosity of water phase,making the O/W type of petroleum sulfonate surfactant ASP flooding emulsification degree increases,forming the oil droplets into smaller particle size and oil droplet rising rate decline;(2)promoting oil droplets aggregation and coalescence through depletion flocculation,thus the floating rate of oil droplets increase.The two superimposed antagonistic effect resulted in that with the increase of the content of the polymer,oil content decreases first and then increases for the O/W type petroleum sulfonate surfactant ASP flooding.By simulating the evolution of microemulsion in injection fluid during migration in reservoir and surface gathering and transportation,it was found that a considerable number of nano-and sub-micron-scale oil droplets were injected into the produced water of ASP flooding with petroleum sulfonate surfactant weak base system whose surfactant concentration is lower than the critical micelle concentration.The swelling micelles in the solution collapse when the surfactant concentration drops below the critical micelle concentration.When the swelling micelles collapse,the solubilized crude oil is released to form small size and highly dispersed oil droplets.How to effectively remove these nano-and sub-micron-scale oil droplets is the key to determine whether the produced water of ASP flooding with petroleum sulfonate surfactant weak alkali system can reach the standard.Oil-water separator SP1013,which is composed of non-ionic surfactant with water-soluble block polyether and polyacrylic acid derivative structure and active agent with good dehydration effect,can effectively promote the coalescence of oil droplets,especially between small oil droplets and large oil droplets.At the same time,in the field test,the injection point was moved forward to the wellhead,and the oil gathering and transportation time and mixing effect of the produced liquid between the oil well and the oil transfer station were used in the pipeline to make it easier to remove oil,which greatly increases the chance of oil droplet collision,strengthened the capture and annexation of small oil droplets by large oil droplets,and effectively reduced the content of nano and submicron oil droplets in the produced fluid and produced water by ASP flooding.