Simulation of Dissolution Front Propagation During Acid Injection Into Porous Media: A CFD Approach

Acid is often injected into porous media to dissolve rock material and enhance flow capability of the rock. Most simulation studies on the propagation of the dissolution front are based on constant injection rate (CIR). Therefore, the objective of this work is to develop numerical model to study acid dissolution front under constant injection pressure (CIP) and also incorporate the effect of fluid temperature on acid–rock interaction. Commercial computational Fluid Dynamics (CFD) software (ANSYS Fluent) is used to solve three-dimensional acid-rock interaction model in cylindrical coordinates. In this work, correlated porosity and permeability distributions are generated. Effect of heat transfer between the injected fluid and the formation on fluid properties and surface reaction rate are accounted for in the model. The study confirmed that all types of acid dissolution patterns exist during constant injection pressure. CIP technique requires lower acid volume to achieve breakthrough in the conical and branched dissolution regimes, than that is required for CIR technique. In dominant wormhole pattern, both techniques require nearly the same acid volume to breakthrough. Thermal interaction between the injected fluid and the formation leads to change of surface reaction rate and physical properties of the fluid, such as viscosity, density, and diffusivity. Injection of cold fluid into heated formation leads to a higher wormhole density as found from experimental studies due to retardation of surface reaction rate. The model developed in this work accurately captures different dissolution patterns. The model shows that the acid volume required for wormhole breakthrough depends on the inlet conditions (CIR or CIP) and the thermal interaction between the injected fluid and formation. This modeling study attempts to answer the critical questions pertaining to the effect of temperature and injection conditions on acid-rock interaction.