Development Of Variable Viscoelastic Acid And Kinetics Of Acid-Rock Reaction In Heterogeneous Carbonate Reservoir

Matrix acidizing and acid fracturing are the most important stimulation treatments used in low-permeability carbonate reservoirs.This is because the reservoir has the characteristics of strong heterogeneity and difference of damage.By taking the measures to acidize the whole hole section,the reservoir damage can not be relieved well, but will increase the difference of the vertical permeability of the reservoir, and make it difficult to distribute acidizing fluids to low-permeable zone. Therefore, the performance of the acidizing fluids is one important factors of affecting the yield of stimulation treatments, even to the success or failure of acidification.There are many kinds of acidizing fluids used in heterogeneous carbonate,and the crosslinking acid, emulsified acid are most popular. Clean acidizing fluids is a new type recently,and the one prepared by viscoelastic surfactant is particular important.The variable acidizing fluids prepared by the viscoelastic surfactant have the characteristics of self-diverting viscosity,fluids loss and no damage.They can achieve the purpose of vertical stimulation treatment in one times and uniform reconstruction, and compared with the conventional cross-linked acidizing fluids,the variable viscoelastic acidizing fluids have the significant advantage of high rate of residual acid flowback after acidification, without crosslinker and breaker,no sensitivity to content of sulfide, simple operation, easy preparation in-site,and low dependence to device, Variable viscoelatic acidizing fluids have been successful used all over the world,and the effect is remarkable.From the relationship of structure and properties of the surfactant,the passage analyzes the characteristics of surfactant micelle formation, in particular the relationship between the amphoteric surfactant molecular structure and properties, and designs the viscoelastic molecular structure of amphoteric surfactants, named erucic acid amide propyl betaine. Synthetic method of Erucic acid amide propyl betaine are studied to explore the synthetic methods and procedures, and the optimal conditions of the condensation reaction and quaternary amination reaction are optimized by orthogonal experiments to form the successful product of erucic acid amide propyl betaine.The product of erucic acid amide propyl betaine is used as self-diverting agent in clean vaviable viscoelastic acidizing fluids,include the determination of the optimized amount, selecting acid additives (corrosion inhibitors, iron ion stabilizer, cleanup agent, anti-emulsifying agent) and optimazation the amount, the acid system are successfully developed in the end. By the analysis characteristics of acid system with variable viscosity,viscosity-temperature resistance,shear resistance, compatibility, broken glue,test results showed that the variable viscoelastic acidizing fluid system can effectively apply to carbonate reservoir layer acidification construction in certain reservoir temperature.In view of the acidizing properties of flow in the pipeline, wellbore, fracture,by experiments of steady-state shear flow,the thixotropy,a slight conclusion,the microscopic studies on the performance of the acid determined to improve understanding of the simulation of the real flow situation of acid in the formation of cracks, annulus or pump the acid on the viscosity of the acid, fresh acid and residual acid viscoelastic including acid rheological constitutive equation recovery performance, the viscoelastic properties of shear,further confirmed the feasibility of the acid system used for the acidification of carbonate reservoirs. Based on the reaction mechanism of acid-rock,a rotating disk testing device is used to simulate formation temperature, pressure, acid flow state and the conditions of the common ion effect, to determine parameters of the reaction rate constant of the acid-rock, the reaction order, activation energy, hydrogen ion effective mass transfer,in order to study the micro-heterogeneous reaction kinetics of acid-rock, especially the study of kinetics parameters of acid-rock surface reaction,the outcomes offer the parameters and basis for optimization of acidification/acid fracturing design and optimized acidizing fluids system in-site.