Simulation Study of Closed Fracture Acidizing in Carbonate Formations
The conductivity of acid-fractured fractures will gradually reduce after a period of times.Closed fracture acidizing is often used to improve the conductivity of acid-fractured fractures,and closed acidizing simulation is of great significance to the design of closed acidizing.Therefore,closed fracture acidizing modeling and numerical simulations were performed for this problem.Firstly,a mathematical model of closed acidizing was established based on Darcy's theorem,material balance principle and acid rock reaction ki-netics.Then the initial spatial distribution of spatially correlated fracture width and matrix permeability distribution on fracture surface were generated by sequential Gaussian simulation algorithm in geological statistics.Numerical solution of the model was using the finite volume method and developing the simulation calculation program.Finally,an extensive numerical simulation study was conducted based on the model to analyze the feature of acid distribution,the feature of dissolution,the factors and features influencing the acid action distance,and to form a plate of the acid action distance under various conditions.The study results show that the initial fracture width and fracture surface roughness play a dominant role in the fracture surface dissolution morphology,and the fracture surface disso-lution morphology has uniform pushing,finger-in dissolution and groove dissolution.The smaller the fracture width and the greater the roughness,the stronger the competition for dissolution on the fracture surface,the easier it is to form grooves,and the farther the dis-tance of the acid action.The rate of acid injection and volume are positively correlated with acid action distance,and acid transfer coef-ficient is negatively correlated with acid action distance.The distance of acid action in closed acidizing is 20～60 m under typical rate of injection,acid volume,and commonly used acid type.This model can predict the acid action distance and acid corrosion fracture surface dissolution morphology under different conditions,optimize the closed acidizing parameters,and provide theoretical basis and guidance for the construction design of closed fracture acidizing in the field.
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