| Self-diverting acidizing technology is a new method for heterogeneous reservoir stimulation.Transformation of viscoelastic surfactant micelle improves the viscosity of the system and temporarily plugs high permeability layer.Due to the complex process of seepage-reaction-tackifying-diverting of acid in porous medium,how to accurately simulate and predict the dynamic changes of self-diverting acid is one of the major difficulties in current research.In this study,an industrialized VDA-KLM liquid was selected as the main agent of self-diverting acid.On this basis,the optimum composition was screened as15%HCl+20%VDA based solution+2%inhibitor+0.05%YND1223.Diverting performance,temperature resistance and gel breaking performance were studied by measuring apparent viscosity.Laboratory experiment found that the viscosity of spent acid could reach357.49mPa·s.Factors of the reaction between self-diverting acid and carbonate were studied by static and dynamic methods.Study showed that acid/rock reaction rate was accelerated by increasing temperature and concentration of acid.A series of regressive equations of reaction kinetics was fitted according to acid/rock reaction parameters by rotating disk experiments,which would provide guidance on optimization design of carbonate reservoir acidizing.Self-diverting acid has a property of“flowing-reacting-thickening-diverting”,which can be reflected in core flow experiment directly.After self-diverting acidizing,the core permeability improved from 21.67×10-3?m2 to 33.61×10-3?m2,by about 55%.Based on the acid flow pressure drop curves of single cores,a method to determine the best time for diverting through calculating acid viscosity in impedance zone and wormhole zone and establishing the relationship between reaction time and acid viscosity was put forward.In this way,dynamic simulation and prediction of the diverting process were achieved.For the parallel cores with different ranges of permeability,self-diverting acid performed better than conventional acid.However,if the permeability range of two cores was too large,self-diverting acid had little help.On the basis of the parallel cores flow experiment,diverting standard of self-diverting acid was derived,and the criteria for uniform acidizing of the self-diverting acid were given. |
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