Research And Evaluation Of Heat Resistant Self-diverting Acid Applicable To Tuff Reservoir

With the increasing development of the oil and gas reservoir,inhomogeneity of the reservoir stratum has been increasely strengthened.Stimulation with conventional acid can no longer stimulate the low permeable area.Improving the covered area has been a great challenge in current reservoir stimulation.Diverting acid technique is a new approach to deep stimulation for inhomogenous reservoir.In order to improve the acid stimulation effect of horizontal wells of tight gas reservoir in Yaoyingtai Old area of Sunnan Gas Field,studies of diverting acid fluids system were carried out aiming at the the mineral characteristics of volcanic tuff reservoir of 135?i n Yingcheng Group of this area.A type of zwitterionic Gemini viscoelastic surfactant?VES?was designed ofter carfull analysis of structure-function relationship.Three surfactants with similar structures and significant viscosity change performance with the variation of acid concentration were synthesized in the lab.And one of them with the best performanc was selected to be the thickener of diverting acid in this study by viscosity variation performance evaluation.Combined with the acid system construction,a diverting acid system suitable for the research area reservoir request was achieved after auxiliary reagents screening and evaluation.The research results were shown as follow:?i?Viscosity of the spent acid maintained at around 40mPa·s after shearing 1h under the conditions of 135?and 170 s^-1,which showed a good heat resistance and shearing resistance property.?ii?This system also showed a good performance of slowing down the acid rock reaction in target reservoir rock dissolution experiments,relative retarding rate can be up to 54.99%in10 min and 34.25%in 30min.?iii?In parallel core displacement experiments,the acidification performance of this diverting acid system for low permeable core were over 1.5,even to 3.01,which showed a significant diverting performance compared to the conventional acidification of 1.15.?iv?This system has a good corrosion inhibition performance and the performance reached to level one.Anti-inflation rate of target reservoir cuttings reached to 71.43%.?v?This system was broken thoroughly with low surface and interface tension after construction,which is good for residual acid flowing back.The successful development of this diverting acid system helps to improve the acid stimulation effect for the target reservoir,reaching homogeneous acidification in deep reservoir.