Numerical Simulation and X-ray Imaging Validation of Wormhole Propagation during Acid Core-Flood Experiments in a Carbonate Gas Reservoir

Acidizing is a sophisticated stimulation treatment that significantly improves production rate particularly in the carbonate reservoirs. However, performance evaluation of the treatment requires extensive laboratory experiments. This includes investigation of various parameters such as temperature, pressure, mineralogy of the rock and the effect of chemical diverters in the zones with high contrast permeability (Safari et al. (2014). A tuned mathematical model, capable of describing the acidizing in core-scale, can play a vital alternative role due to high expenses of the required experiments. In this paper, we used a simulation model, tuned by experimental data, to be used as an alternative tool for modeling acidization. Since wormhole propagation is strongly geometry dependent, the model was solved in a 3D domain rather than its original dimension, i.e. 2D in Panga (2005) model, to simulate the propagation more accurate.

Mass transfer, continuity, and energy equations were combined to develop a model, which simulates the acid flow in porous media accurately. The model, a cross-link between two different scales: pore-scale and Darcy-scale considers the effect of convection, diffusion, and particularly chemical reactions.

In this study, a complete package including acid core-flood experiment, X-ray imaging and numerical simulation of the wormhole propagation was performed to study acid flow in the porous media. The acid core-flood experiment was performed on a core sample from a gas reservoir in south of Iran. In addition to X-ray imaging technique employed to visualize the result of acid core-flooding, a simulation model was developed in finite element analysis software. The model has the dimensions of the core sample. The required chemical reaction equations were implemented in the simulation model to simulate the wormhole propagation process. A very good agreement was achieved when the simulation results were compared with experimental results and X-ray imaging outputs.

The model, as an invaluable tool could be used to study the different aspects of acidizing treatment such as acid efficiency curve, simulation of parallel flooding, etc. This then helps to determine key parameters and optimized conditions for achieving a successful acidizing treatment.