Synthesis And Performance Evaluation Of Hydrophobically Modified Xanthan Gum Oil Displacement Agent

Polymer flooding is the method that use polymer as an oil displacement agent(adding water-soluble polymer into injected water)to increase the viscosity of water phase,decrease the ratio of water-oil mobility and stabilize displacement front to increase oil recovery.At present,the most commonly used oil displacement agents are HPAM and some kind of vegetable gums.While charge shielding effect reduces the electrostatic repulsion in HPAM solution,which means the viscosity of HPAM is significantly affected by the salt concentration.What's more,the problem that the residul acrylamide monomers in HPAM have a damage on environment limits the use of it in polymer flooding.In this case,Xanthan Gum,an environmental polymer with good performance,has been widely concerned by petroleum workers.However,Xanthan Gum is easily degraded at high temperature,which makes it difficult to be used in some high-temperature oil reservoirs.So,Xanthan Gum was modified in this paper to get a kind of oil displacement agent with good temperature and salt resistance.Hydrophobic long carbon chains(C16)of 1-bromohexadecane were grafted onto the main chains of Xanthan Gum by etherification to prepare modified Xanthan Gum(XG-C16).The optimum synthesis condition was found through the single factor experiments:the addition of Xanthan Gum was 25%,the addition of 1-bromohexadecane was 12.5%of Xanthan Gum mass,the reaction temperature was 60? and the reaction time was 9h.The structure of XG-C16 was characterized by FT-IR.The results indicate that XG-C16 is successfully synthesized.Rheology and pyrene fluorescence spectroscopy experiments discovered that the critical association concentration(CAC)of XG-C16 solution is 0.16%.Hydrophobic microregions produced by molecular interactions in XG and XG-C16 solutions were tested by ANS fluorescence probe,and the associating microstructures in XG and XG-C16 solutions were observed by SEM,the results show that compared with XG,XG-C 16 solution produced more hydrophobic microregions and had better spatial network structure,which proved the association thickening mechanism of XG-C16.Through rheological experiments,XG-C16 solution was found have good temperature and salt resistance,it retained 330mPa s at 140?,2.7 times the apparent viscosity of XG(125mPa·s),Adding NaCl up to the salt concentration of 40000mg/L,XG-C 16 still maintained well spatial network structure and a high apparent viscosity(728mPa·s),and the salt resistance curve showed a salt thickening effect.The variation trend of interaction between XG-C 16 and surfactant(SDS and OP-10)strictly meets the three-stage growth model.With the addition of SDS and OP-10,the viscosity of compound system reached its peak and then decreased.The temperature and salt resistance of the XG-C 16 were further improved in the compound system with the optimal addition of surfactant,this is the result of the interaction between surfactant and hydrophobic chain of XG-C16,which formed the blend micelles and enhanced association.The results of laboratory displacement experiments show that t XG-C16 has better fluidity control ability and lower core permeability than XG,which can improve the oil recovery to 10.67%in 80?,19334mg/L of salinity conditions,value of the increased oil recovery 4.98%higher than XG.