Investigation On Emulsion Stability And Demulsification Techniques Of Produced Water From Enhanced Oil Recovery

Enhanced oil recovery(EOR)techniques have been widely applied to the oilfield.In this kind of oil recovery method,oil displacements are injected in to the reservoir to extract oil.During the oil extraction process,the synergistic effect of polymers,surfactants and some other oil displacements make the produced water from EOR become emulsion with high stability.These kinds of produced water contain large amounts of crude oils,salts,colloids,suspended solids and oil displacements such as polymers and surfactants,which make the produced water difficult to handle.Some progresses have been made on the treatments of EOR produced water.However,no systematical treatment processes have been developed to the effective treatment of it.So far most researches focus on the techniques of treating the EOR produced water,few researches focus on the emulsion stability mechanism of the produced water.However,it is important to conduct researches on the emulsion stability of the EOR produced water and to clarify the key components in stabilizing the produced water,which can play key role in guiding the research of destabilization techniques of produced water and the establishments of systematical treatment process along with the resource utilization of it.In general,the influence of natural clay mineral on the emulsion stability of EOR produced water,the interaction between in-situ formed magnesium hydroxide and hydrolyzed polyacrylamide along with the demusification techniques using surface modified membrane and magnetic nanoparticles were investigated in the thesis.The research results of this thesis can provide theoretical guidance in developing demulsification techniques and methods in treating real EOR produced water,oil displacements and the resource utilization of them.The main contents and conclusions of this thesis are as follow:1.The influence of natural clay minerals-Na-montmorillonite on the emulsion stability of produced water from polymer flooding(one EOR technique)were first conducted.Though there are lots of researches regarding competitive adsorption between oppositely charged polymer and surfactant mixtures,few researches focus on the system containing likely charged polymer,surfactants and colloidal particles.In the corresponding chapter,the oil water interfacial tension of WPS(one surfactant used for EOR)and hydrolyzed polyacrylamide(HPAM)in the presence of Na-montmorillonite were measured along with the determination of zeta potential,diffusion of coefficient and the adsorbed amount of WPS and HPAM onto Na-montmorillonite.The simulated produced water containing Na-montmorillonite was also prepared to investigate the influence of natural clay minerals on the emulsion stability of produced water from polymer flooding.The competitive adsorption mechanisms of Na-montmorillonite and WPS/HPAM or their mixtures were discussed according to the experimental results,and finally the influence of Na-montmorillonite on the emulsion stability of produced water were clarified.2.During the research process in previous parts,the key role of HPAM in EOR produced water was revealed.Besides,the removal of polymers in EOR produced water treatments have been a serious issue.In the following parts of this thesis,the adsorption of HPAM onto in-situ formed magnesium hydroxides were researched after selecting different in-situ formed metal hydroxides based on the previous study of EOR oil displacement components treatment using this kind of colloidal particles in our research group.In-situ formed Mg(OH)2 particles were investigated through the direct wet precipitation method in the presence of two partially hydrolyzed polyacrylamides(HPAM)of different molecular weights.The influence of the reaction parameters,such as magnesium chloride concentration,pH,and reaction temperature,on the interactions between in-situ formed Mg(OH)2 particles and HPAM molecules was investigated.The Mg(OH)2 particles obtained in the absence and presence of polymers were characterized in terms of their morphology,particle size,and crystal habit by high-resolution transmission electron microscopy,X-ray diffraction,Fourier transform infrared spectroscopy,dynamic light scattering,and zeta potential measurements.It was found that different pH values of the reaction solution led to different predominant species distribution for MgCl2.Adsorbed polymer led to the formation of four distinct adsorption regions as the concentration of polymer is increased.The adsorption of partially hydrolyzed polyacrylamide on the oppositely charged Mg(OH)2 particles was explained by electrostatic attraction,bridging,and hydrogen bonding.3.When using the in-situ formed magnesium hydroxide to remove the HPAM in the solution,we noticed that the aggregation behavior of in-situ formed colloidal particle in the presence of polyelectrolytes is different from the other inorganic particles.To get a deeper insight into this phenomenon and to help understand the destabilization mechanism of produced water using this kind of,the aggregation and deposition of in-situ formed magnesium hydroxide(IFM)in the presence of hydrolyzed polyacrylamide(HPAM)was investigated next.The relative concentrations of interactants,as well as other experimental conditions,were changed to elucidate the interaction mechanisms from microscopic to macroscopic levels.Light scattering measurements were used to investigate the aggregation kinetics,fractal dimension,and collision efficiency of the aggregates on a microscopic level.Electrophoretic mobility and TEM were utilized to measure the charging properties and morphologies of aggregates,respectively.Adsorption and rheology experiments were performed to determine the deposition mechanism at higher concentrations of interactants on a macroscopic level.The results demonstrate that the initial rapid aggregation of IFM in the presence of HPAM is due to an electrostatic patch mechanism.In addition,the deposition was accelerated by flocculation with different mechanisms.When more IFM is involved,bridging flocculation dominates;when more HPAM is added,depletion flocculation plays a leading role.The results of this work may provide further insight into understanding the aggregation and deposition of in-situ formed natural/engineered particles in the presence of oppositely charged polyelectrolytes,as well as provide new possibilities for produced water treatment,biomineralization,etc.4.The above research contents in this thesis help us understand the influence of natural clay minerals on the emulsion stability of EOR produced water and the interaction between the IFM and HPAM.In next two parts of this thesis,modification of membrane surface using advanced nanomaterials and preparation of magnetic nanoparticle composites were applied to explore the demulsification techniques of oil in water emulsion.In this part,we designed the experiments to explore the role of 2D materials in 3D hierarchical surface layer that contain 1D and 2D materials on the oil/water separation performance of microfiltration membrane.The surface modification of membrane was achieved through a layer by layer process as it is an effective and facile method to acquire microfiltration membranes with desired properties.After the robust and facile membrane modification process,the membrane with desired hierarchical structure and high flux for efficient oil/water separation was achieved.Varieties of methods were used to characterize the surface properties of the modified membrane and the results showed that the surface hierarchical layer was successfully constructed.The wetting behavior and permeation flux was then tested for comparison of these two membranes with different 2D construction layer.The relating result showed that the 2D material have influences mainly in the permeation flux and the recycle properties of the hierarchical surface modification membranes.5.In the last part of this thesis,magnetic graphene oxide(MG)was first prepared and used to interact with LDH through electrostatic interaction to form magnetic/graphene oxide/LDH(MGL)composite.SEM,TEM and FTIR was used to characterize the MGL.The result of oil/water separation experiments showed that MGL had the highest oil/water separation efficiency at LDH/MG=1:1.However,in the oil-water interfacial tension experiment,fastest decrease of oil-water interfacial was observed when LDH/MG=1:3.After the calculation of effective diffusion coefficient,we found that LDH can screen parts of the negative charge so the addition of LDH can increase the diffusion coefficient of MGL.Taking all experimental results into account,we think the oil/water separation mechanism of MGL include the migration of MGL to the oil-water interface and the adsorption of oil onto MGL.After ethanol wash,MGL composites kept high oil/water separation efficiency after 3 cycles.