An Experimental Study of Matrix Dissolution and Wormhole Formation Using Gypsum Core Flood Tests: 1. Permeability Evolution and Wormhole Geometry Analysis

Core flood tests were conducted to study the effect of flow rate on the dissolution of the gypsum rock matrix and the formation of wormholes. An effluent chemistry monitoring system was designed and integrated into a triaxial system to provide continuous effluent concentration measurements, in addition to the pressure and flow measurements during the core flood tests. X-ray computed tomography (CT) was used to study the geometry of the wormholes after the tests. The core flood tests showed agreement with experiments reported in the literature regarding permeability evolution and wormhole breakthrough. By continuously monitoring the effluent concentration, the effluent chemistry monitoring system advanced the experimental study by showing how the dissolution kinetics evolved with the formation of wormholes. Three-dimensional topological and morphological algorithms were developed to analyze the CT data and provide quantitative descriptions for the wormhole geometry. The CT analysis showed that higher flow rates resulted in more complex wormhole geometries regarding the number of wormholes and branches.