Preparation And EOR Feasibility Study Of Oil-displacement Amido Betaine Surfactants

Combined chemical flooding is one of the most effective EOR techniques for oil production enhancement in high water cut oilfields,contributing greatly to the steady oil production.Side-effects,however,such as formation damage,production well scaling,lifting difficulty,and hard demulsification of produced liquid caused by alkali in the combined formulations increased the technical challenge and operation cost.Surfactant/Polymer binary flooding is a kind of technique developed on the basis of ASP combination flooding.In SP flooding,visco-elastic properties of polymer can be effectively maintained and cost can be decreased without alkali.Nevertheless,Oil-dislpacement surfactants for alkali-free flooding need to have high interfacial activity.Most of these surfactants are in laboratory preparation and evaluation stage.The related R&D work lags far behind field tests demand.Large enough hydrophobic radical is needed for alkali-free surfactant in order to reach ultralow interfacial tension(IFT).But large carbon chain causes poor solubility,leading to precipitation in solution.Contradiction between 'long carbon chain' and'solubility' should be thoroughly considered in structure design.Related references manifested hydrophobic radicals with double bond or branching structure could increase critical micelle concentration(CMC)of surfactants so as to improve solubility.In this study,long chain unsaturated fatty acids,oleic acid,peanut acid,erucic acid,mixed acids,and branching synthetic acid of 9-xylyl-octadecyl acid were utilized as raw materials.Five fatty acid amidopropyl carboxyl betaines,OBC,PBC,EBC,MBC and XBC were prepared through the amidation and quatemization reactions.For amidation reaction of betaine OBC,oleic acid was screened and craft was optimized.The structures of five betaine compounds were characterized and proved by FTIR and MS analyses.Surface/interface properties of five betaines were evaluated.CMC and nmin were measured for betaine OBC,PBC and EBC.Related surface parameters were also calculated.CMC decreased with the increase of hydrophobic chain.nmin of 3 tested betaines were all 16.Interfacial activities of prepared betaines at alkali-free condition were evaluated with crude oil of Daqing,Changqing,and Sudan.The results manifested ultralow IFTs were reached with Sudan crude oil for simulated water solutions of 0.05?0.30%OBC and EBC,and 0.03?0.20%XBC.IFTs reached ultralow level for produced water solutions of 0.05?0.20%EBC with crude oil of 1st,3rd oil-production factories of Daqing.In concentration range of 0.001?0.20%,IFTs between EBC/DABS(8:2,wt/wt)combined formulation and crude oil of Changqing oilfield reached ultralow IFTs.Viscosifying capabilities of OBC and EBC in high salinity brine solutions were tested.Obvious viscosifying effect was oberserved.Viscosity of 2.0%OBC solution reached 180 mPa.s.Worm-like micelle could be formed in OBC and EBC solutions,grealy increasing viscosity with the network formation through micelle tangling.For high temperature low salinity(HTLS)sandstone reservoir(85?,1269 mg/L)and high temperature high salinity(HTHS)carbonate reservoir(104?,84715 mg/L),betaine XBC and EBC were evaluated respectively.Interfacial activity,phase behavior,and adsorption property were tested.Core flooding tests were performed utilizing connected natural cores to evaluate the oil-displacement efficiency of SP binary formulations.For Sudan medium-low permeability cores and high permeability cores,incremental oil recoveries of SP flooding were 15.93%and 14.53%respectively,after water flooding with recoveries of 60.71%and 52.75%.In the core flooding tests for HTHS carbonate reservoir,the average incremental oil recovery of SP formulations was 20.61%after water flooding with recoveries of around 52%.Fatty acid amidopropyl carboxyl betaines have several advantages,such as extensive availability of raw materials,relatively simple production crafts,and high oil-displacement efficiency,etc.These betaines have potential in the field application of alkali-free binary flooding technique.