Study On Mechanism Of Acid Leakage In Carbonate Reservoir

During acid fracturing in carbonate reservoirs, large pores or natural fractures are dissolved and expanded by acid to form complex etching apertures, resulting in excessive acid leak-off, which seriously restricts the penetration distance of acid fracturing crack, because of the acid-rock reaction produces CO2and other products making the situation even more complicated. Therefore, further study of acid leak-off mechanism for improving effect of acid fracturing is of great significance.Based on the key state science and technology projects, aiming at the acidizing wormhole forming in acid fracturing in the pore type carbonate reservoir. Established the calculation model for the acid leak-off in acidizing wormhole, and simulated the effect of acid-rock reaction wormhole propagation and free carbon dioxide effect on acid leak-off.Aiming at the fractured carbonate reservoir, carried a corrosion experiment with natural fracture network and tested the ability of major fracture to communicate the branch cracks and acid loss situation. Based on the carbonate formations acidizing physical model of single-fracture, a mathematical model has been developed for acidizing of single-fractured carbonate formation, based on the physical model, mass conservation equation and mass transport balance of acid, and the variety of fracture width, simulated the acid leak-off and dissolution of the acid for single fracture carbonate formation. Based on the finite element theory, using the method of equivalent permeability, on the basis of dual medium model with matrixes and fractures, an equivalent continuum leak-off model with natural fracture networks was established, and using this model analysis the effect of natural fracture network’s morphology on liquid filtration.In consideration of the effect of the fracture extension, the temperature distribution in the fracture, the acid-rock reaction and the compressibility of free CO2, an acid leak-off model in carbonate formation was established, and using this model analysis the impact of etching apertures, free carbon dioxide effect and different construction parameters on acid leak-off. The research shows that the existence of free CO2reduces the amount of acid filtration and the acid filtration has close relations with the construction parameters and reservoir parameters of property, the acid filtration can be reduced effectively and the acid fracturing effect is improved by optimizing the related construction parameters.This paper mainly considering the effect of free CO2and the expansion of etching apertures to establish the acid leak-off model, the research has some new ideas and has an important guiding role for controlling acid leak-off and improving acid fracturing effect.