An Experimental Study of Matrix Dissolution and Wormhole Formation Using Gypsum Core Flood Tests: 2. Dissolution Kinetics and Modeling

In the parallel paper by Li et al. (2019; ), an effluent chemistry monitoring system was designed and used in core flood experiments to continuously measure the effluent concentration and study the evolution of the rock-fluid system. In this study, the results from the parallel paper were used for interpretation and modeling of the dissolution and wormhole formation. Based on the behavior of the effluent concentration, two transient states and two quasi-steady states were defined to describe the dissolution in the rock-fluid system. Dimensional analysis was used to identify the controlling mechanisms of the dissolution and transport in the matrix and the wormholes. The dimensional analysis showed that the dissolution in the matrix was reaction controlled, while the dissolution in the wormholes was diffusion controlled. It also showed that the rock-fluid system evolved from reaction-controlled dissolution to diffusion-controlled dissolution during the core flood tests. A continuum model and the extended Graetz solution were used to model the dissolution in the matrix and in the wormholes, respectively. In the continuum model, this study estimates the effective surface area as a function of the flow rate (injection flux), to account for the effect of flow conditions on dissolution. Finally, a semiempirical model combining the continuum model and the extended Graetz solution was developed to simulate the formation of wormholes and the evolution of the dissolution kinetics during core flood tests.