Carbonate reservoirs are one of the most important sources of fossil fuels, which have rich reserves but underdevelopment. Acid stimulation is one of the most effective stimulation techniques widely used to stimulate wells in carbonate reservoirs, in which acid solution is pumped into the carbonate rocks under the formation fracture pressure to dissolve the rock matrix and connect isolated fracture and vug, increasing formation permeability while bypassing damaged domains around the wellbore. This book is motivated to provide a theoretical basis and technical support for carbonate acid stimulation design. In this book, the two-scale continuum is developed to consider the mass, momentum, and energy changes during the acid stimulation process and the mineral composition heterogeneity. It helps readers obtain an understanding of modeling reactive flow in porous media with coupling multi-physical fields, including hydrologic–chemical-thermal processes and multi-scale characteristics. A series of numerical cases are presented to discuss different processes influencing acid stimulation, including convection, diffusion, and reaction, and different models, including classical and new two-scale continuum models. A comprehensive parametric study is conducted to study the effect of parameters with respect to acid and rock physical parameters on the acid stimulation process. Besides, the two-scale continuum model is used to study the acid stimulation process in two typical core-scale isolated fracture and vug porosity systems. Besides, a detailed description of finite volume methods and sequential decoupling algorithms is provided to show specific examples of numerical discretization and solving decoupled solutions on staggered grids. It also delves into scale-up methods, such as the theoretical foundations and important theorems of the volume averaging approach. The book stands as a fundamental guide in implementing acid stimulation techniques in carbonate reservoirs. It can be an excellent reference for reservoir engineers, academics, and students interested in studying and performing acid stimulation in carbonate reservoirs. The book can also serve as an excellent foundation for numerical simulation. It is appropriate as a textbook for senior undergraduate and graduate courses in petroleum engineering.