The Research Of Reducing The Reaction Speed Between Acid With Liquid Nitrogen And Rock In Acid Fracturing

Acid fracturing is a commonly used stimulation measure in carbonate reservoir,the deep buried and high temperature carbonate reservoir has a fast reaction speed between acid and rock and a short length in the process that the effective acid corroded fracture.To promote the flowback,the formations with low formation pressure coefficient often use the method of acid with liquid nitrogen injection.With the low temperature,liquid nitrogen not only can promote flowback but also can reduce the surface temperature of the liquid and the crack,so it can reduce the reaction speed and increase the fracture length.Because there is lacking of relevant research,the temperature and reaction speed reducing of acid with liquid nitrogen injection will be studied in this paper.This paper based on the theory of fluid dynamics,thermodynamics and heat transfer,and it established the mathematical models of wellbore and formation temperature field and crack and weld formation temperature field.It also applied the FLUENT software and aspenONE software to set up a computational model of the temperature field of acid with liquid nitrogen injection.Based on the above models to calculate the wellbore and fracture temperature distribution of different displacements,different amount of liquid nitrogen and different injection time.While it contrasted the temperature difference between only acid injection and acid with liquid nitrogen injection,and then do some relevant experiments.Meanwhile the amount of liquid nitrogen on construction site was optimized.Research shows that the wellbore and fracture temperature will be low when the displacement is higher,the amount of liquid nitrogen is higher and the injection time is longer.For the formation of 4000 m,120℃ and the optimally 3m3/min displacement,the reducing speed of the temperature will be slowing if the amount of liquid nitrogen reach 400L/min.When the injection time get to 60 min,the temperature of the bottom of well is about 50℃;it can produce about 20℃ temperature difference when it applied acid with liquid nitrogen injection or not,and it can produce a different live acid effective time is about 5 min.So the liquid nitrogen injecting has a great effect on cooling and increasing the live acid effective distance.This paper provides a theoretical basis and guidance for the design of acid fracturing in acid with liquid nitrogen injection,and it has some engineering significances to the acid fracturing in carbonate reservoir.