Digital Core Analysis as an Efficient Tool for Acid Treatment Optimization

Digital rock workflow for acid treatment optimization is developed. It includes construction of a digital rock model based on X-ray microtomography, running a set of multiscale digital experiments and a number of acid flooding experiments on rock samples for the model tuning. Here, we present results of application of the developed workflow for Austin chalk rock treatment by hydrochloric acid on core samples of 8 mm in diameter. Pore-scale simulations were performed using high-resolution 3D microCT models to determine the dependencies of rock permeability, active surface area and effective reaction rate on actual porosity. These properties were used to populate the laboratory-size core models, and Darcy-scale numerical approach was applied to simulate the dissolution at different injection rates. The core-scale simulations demonstrated inhomogeneous character of dissolution process leading to wormhole development in a certain range of injection rates. In parallel to numerical simulations, laboratory experiments on the same rock samples were performed at flow rates close to the optimal regimes followed by microCT imaging of wormhole structures. This information was then used to tune the model parameters. After that, the dependencies of the number of pore volumes injected until the breakthrough (PVBT) on the injection rate were obtained numerically for all the cores considered.