Lattice Boltzmann Simulation of Wormhole Propagation in Carbonate Acidizing

Abstract

In acidizing operations, the acid flows selectively through large pores to create wormholes. Wormhole propagation has been studied by many experts at macroscopic scale. In this paper, the lattice Boltzmann model (LBM), which is a mesoscopic scale method, is adopted to simulate the flow, acid–rock reaction, and rock dissolution in porous media at mesoscopic scale. In this model, a new method based on nonequilibrium extrapolation is proposed to deal with the reactive boundary. On the basis of the model, extensive simulations are conducted on the propagation behavior of wormholes, and the factors influencing wormhole propagation are investigated systematically. The results show that the LBM is a reliable numerical technique to study chemical dissolution in porous media at mesoscopic scale, and that the new method of dealing with the reaction boundary performs well. The breakthrough time decreases with the increase of acid concentration, but acid concentration does not affect the ultimate dissolution pattern. As the reaction rate constant increases, shorter wormholes are created. A higher hydrogen ion diffusion coefficient will result in shorter but wider wormholes. These findings agree well with the previous experimental and theoretical analyses. This study demonstrates the mechanism of wormholing that the unstable growth of pores by the acid rock reaction makes the acid selectively flow through a few large pores which finally form wormholes.