Thickening Property Of Microbial Polysaccharides And Effect Mechanisms On The Heterogeneous System

In high temperature,high salinity or complex geological condition reservoirs,the effective of the oil displacement agent in chemical flooding reduces or disappear,the applicability is limited,and the oil recovery efficiency dramatically decreases as a result.Although most improved oil displacements have a better performance on temperature/salt tolerance,the defect is the damage to the formation.Therefore,while exploring and developing the new oil fields,it is very important to look for the displacement agents which have a good performance on anti-shear,temperatire/salt tolerance and aging stability in high temperature and high salinity using new technologies and methods to enhanced oil recovery.High yield and stable yield of oil fields are the strategic projects which ensure the sustained and stable development of our oil industry.In the thesis,we studied the thickening property,gelation and temperature/salt tolerance of an environmental friendly microbiological polysaccharide polymer,the stability of heterogeneous system?nanoemulsion and foam?suitable for complex reservoirs,and effect mechanisms of microbiological polysaccharide polymer on heterogeneous systems.In the second part,effects of different inorganic cations(Na⁺,K⁺,Ca²⁺and Al³⁺)on rheological properties of single?Welan gum,Xanthan gum and Gellan gum?and mixture polysaccharide solutions have been systematically investigated in the thesis.The apparent viscosity and viscoelasticity of Welan gum solutions decrease in the environment of inorganic cations.Meanwhile,the addition of Al³⁺and K⁺,respectively,enhances the apparent viscosity and viscoelasticity of Xanthan and Gellan gum solutions by promoting the gelation.The viscosity retention rate of Welan/Xanthan mixtures is higher than that of the single component in Na⁺,K⁺and Ca²⁺solutions,and the viscosity retention rate of Welan/Gellan mixtures is higher than that of the single component in Ca²⁺solutions.The synergy in Welan composite stystems can reduce the viscosity loss of single components in salt solutions to keep the thickening property.In the third part,rheological properties of a new microbial polysacchride,Diutan gum,in aqueous solution have been systematically investigated.It is found that molecular aggregates of Diutan gum can be formed at a very low concentration,and the mechanism of thickening by Diutan gum is proposed.The viscosity retention rate of Diutan gum changes little when increasing the temperature from 298 K to 348 K or in a high salinity solution.Gel structure can be formed in the Diutan gum solution,owing to the finding that the dynamic modulus has an exponential relationship with the concentration.The gel properties of Diutan gum are not sensitive to the temperature,and are virtually independent of the cationic environment(Na⁺and Ca²⁺).The temperature/salt tolerance of the Diutan gum solution is mainly attributed to its perfect double helix molecular conformation,the location of the side chains of its molecules,and its water retention capacity.In the forth part,the study evaluates the potential of diutan gum in enhanced heavy oil recovery in comparison with two conventional EOR polymers?Xanthan gum and HPAM?in high temperature and high salinity.The steady-state viscosity and dynamic modulus of aqueous diutan gum solutions are not sensitive to the temperature,and are virtually independent of the salinity,while those of xanthan gum and HPAM significantly decrease in high temperature and high salinity,respectively.The dense network structure of diutan gum is dependent on the shear rate instead of the shear time or the aging time.Flow tests demonstrated the capacity of diutan gum in mobility control during propagating in porous media,and the permeability reduction of the porous media is caused by adsorption and interception mechanisms.In high temperature and high salinity,diutan/surfactant composite system not only has a high value of viscosity and viscoelasticity,but also can reach a low value of interfacial tension.In flooding tests,the recovery efficiency of diutan gum is raised by 37.4%OOIP and higher than those of xanthan gum and HPAM in the reservoir condition,and the recovery efficiency of diutan/surfactant composite system is higher than that of diutan gum.Results confirm that diutan gum acting as an oil recovery agent has a potential in high temperature and high salinity reservoirs.Meanwhile,the diutan/surfactant composite system will be a new S/P binary system for temperature/salt tolerance.In the fifth part,O/W nanoemulsion has been prepared by the method of emulsion inversion phase.The long-term stability and thermal stability of nanoemulsion have been investigated.The stability and rheological properties of the nanoemulsion have been also studied with the addition of Diutan gum.It is found that the minimum ratio of emulsifier with oil is 1:4 when the water phase content?mass concentration?is 70%,and the highest water phase content is80%when fixing the ratio of emulsifier with oil at 1:4.The thermal stability of nanoemulsion can be controlled by adjusting the ratio of emulsifier with oil and water phase content.The apparent viscosity of nanoemulsion is directly proportional to the emulsifier content and indirectly proportional to the water phase content.The size of the pore could affect the viscosity of nanoemulsion when flowing in the porous media.The addition of dituan gum increases the zero-shear viscosity and apparent viscosity,resists the external disturbance and stabilizes the nanoemulsion.Moreover,the network formed by Diutan gum in water phase effectively supports the O/W droplets,increasing the viscoelasticity of the nanoemulsion.In the sixth part,foam properties of the anionic-nonionic surfactant sodium fatty alcohol polyoxyethylene ether sulfate?AES?and Welan/AES composite systems have been investigated.Both foaming ability and foam stability of Welan/AES composite system are better than for either single component.It is important to control the quantities of the two species when to use,since there exist optimum foaming concentrations for AES(1000 mg?L^-1)and Welan gum(80 mg?L^-1).Competitive adsorption exists between AES and Welan at the air/liquid interface.A network structure is formed in the Welan/AES composite system as the dynamic modulus has exponential relationship with the concentration.High interfacial elasticity is required to prevent the coalescence of the bubbles and the rupturing of interfacial layers.The hydrogen bonds and van der Waals forces between AES and Welan gum may hinder AES molecules from diffusing from the bulk to the interface.The formation of an interface network of Welan gum and the structural stability of double helices,arranged in parallel as zipper model within the network,strengthen the ability of the film to resist disturbance and deformation.