Acidizing is a widely used technique for intensification of wells. At certain conditions, acid injection results in a formation of highly conductive channels, e.g. wormholes. The associated rock matrix dissolution is highly nonlinear and may influence the fluid flow as well as rock properties. Wormhole patterns and breakthrough time are mainly controlled by acid strength and injection rate. We developed a fully implicit method (FIM) to numerically solve the reactive flow and transport problem coupled with equilibrium and kinetic reactions associated with the acid injection. The developed framework is aimed to predict a pattern of dissolution as well as wormhole breakthrough time. For an accurate description of species interactions, we directly connect PHREEQC equilibrium computation with FIM framework for kinetic dissolution using an element balance approach¹³. This coupling was achieved with an application of an Operator-Based Linearization scheme¹⁴ utilized within DARTS.

The developed solution is validated against experimental study¹⁴, which also includes the full physics numerical model. Results are given in Fig.14. Two numerical results obtained starting from the same porosity distribution but processed by very different technique demonstrate similar wormhole formation.

Full 3D model for dissolution in the core is shown in Fig.15. Main criteria for validation are wormhole breakthrough time and amount of rock matrix dissolved. A qualitative comparison shows a reasonable match in terms of break-through time and competing wormholes spatial distribution. The wormhole formation and propagation are accurately captured in high-resolution 3D geometry.