一种新型两性表面活性剂自转向酸体系

常规自转向酸体系在乏酸(2< pH< 4)时变黏,影响转向效率,使转向酸化具有一定的局限性。根据黏弹性表面活性剂的变黏机理,研制了一种新型两性表面活性剂(VES)自转向酸,该转向酸在酸岩反应过程中黏度逐渐升高,乏酸时黏度又降低。考察了表面活性剂、盐酸、钙离子对转向酸黏度的影响;模拟了酸岩反应过程,根据酸岩反应速率拟合了酸岩反应动力学方程;对新型VES体系耐温、流变和破胶性能进行了研究。结果表明:酸岩反应至盐酸浓度为5%时VES黏度最大(144 mPa·s),酸液转向;温度高于90℃时VES黏度下降,因此该转向酸适用于中低温储层;该转向酸体系具有较好的耐剪切性能,剪切黏度恢复率大于90%;VES酸岩反应速率约为普通盐酸酸岩反应速率的1/2,有利于缓释转向;乏酸黏度较低(小于30 mPa·s),遇烃类或地层水容易破胶水化,破胶液具有较低的黏度和表/界面张力,对地层不产生污染。该新型两性表面活性剂自转向酸现场应用后,增油效果明显,具有较好的应用前景。 

A New Amphoteric Surfactant Self-diverting Acid System

In acidizing work, conventional self-diverting acid becomes viscosified at pH between 2 and 4, thus limits the function of converting acids. A new amphoteric surfactant self-diverting acid (VES) was developed based on the viscosifying mechanism viscoelastic surfactant. The viscosity of this acid is increasing during the reaction of acid and rocks, and decreasing when the pH of the reaction system is becoming low. The effects of surfactant, hydrochloric acid, calcium ions on the viscosity of the diverting acid were explored and acid-rock reactions simulated. The equation of kinetics of acid-rock reactions was fitted in accordance with the reaction rate of the acid and rocks. Heat resistance, rheology and gel-breaking ability of VES were studied. In acid-rock reaction, VES had the highest viscosity (144 mPa·s) at hydrochloric acid concentration of 5%, and the acid was diverted. The viscosity of VES was decreasing at temperature above 90℃, indicating that this self-diverting acid is suitable for use in medium- to low-temperature reservoirs. VES has good shear-thinning capacity; more than 90% of the viscosity of VES can be recovered. The reaction rate of VES is 1/2 of the reaction rate of hydrochloric acid, which is beneficial to slow-release diverting. The spent acid, whose viscosity is low (30 mPa·s), is easy to gel-broken and get hydrated when in contact with hydrocarbons and formation water, and the solution after gel-breaking has lower viscosity and surface tension, meaning that it will impose no damage to reservoir formations. VES in field application has obviously enhanced oil production, and shows good prospect in well stimulation.