Analyzing the Dynamics of Mineral Dissolution During Acid Fracturing byPore-Scale Modeling of Acid-Rock Interaction

摘要

Hydrochloric acid is commonly used in acid fracturing.Given that the interaction between acid androck affects multiphase flow behaviors,it's important to thoroughly understand the relevant phenomena.Darcy-Brinkman-Stokes(DBS)method is most effective to describe the matrix-fracture system among theproposed models.The objective of this study is to analyze the impact of acid-rock interaction on multiphaseflow behavior,by developing a pore-scale numerical model applying DBS method.The new pore-scalemodel is developed based on OpenFOAM,which is an open source platform for the prototyping of diverseflow mechanisms.The developed simulation model describes the fully-coupled mass balance equation andthe chemical reaction of carbonate acidization in an advection-diffusion regime.Volume of Fluid(VOF)method is employed to track liquid and gas phase interface on fixed Eulerian grids.Here,penalizationmethod is applied to describe the wettability condition on immersed boundaries.To compute the numericalsolutions of discretized equations,finite volume method is applied,where the equations of saturation,concentration,and diffusion are solved successively,and momentum equation is solved by using Pressure-Implicit with Splitting of Operators(PISO)method,respectively.The simulation results computed by thisnumerical model have been validated by experimental results.Different injection velocities and the secondDamkohler numbers have been simulated to investigate their effects on the evolving porosity and rocksurface area.The newly developed pore-scale model in this research provides the fundamental knowledgeof physical-and-chemical phenomena of acid-rock interaction and their impact on acid transport.Themodelling results describing mineral aci dization will help us to implement an effective fracturing projectwhile reducing environment impacts.