Extension of an Empirical Wormhole Model for Carbonate Matrix Acidizing Through Two-Scale Continuum 3D Simulations

Abstract

Abstract The optimum design of matrix acidizing operations in carbonate reservoirs is a discussion in progress. Although there are several models available to the industry for predicting wormhole propagation, most of them are not practical enough to be used in real treatment designs, or were developed to represent core flood data and cannot be simply scaled up to represent wormhole formation in complex well geometries. This problem is addressed by Furui's wormhole propagation model, which is a modification of Buijse and Glasbergen empirical correlation including a scale up procedure to represent field carbonate acidizing operations using laboratory core flood data. It is a practical engineering tool that can be used for treatment designs in horizontal wells, including barefoot and perforation-cluster completions in fairly isotropic and homogeneous reservoirs. In this work an analysis of Furui's model is performed, including the effect of anisotropy in the carbonate reservoir. The analysis includes both radial or elliptical wormhole propagation that forms from an openhole completion and the spherical or ellipsoidal wormhole propagation that emerges from each perforation in a perforation-cluster completion that makes use of a limited-entry technique for achieving good acid placement. The development is made using extensive 3D numerical simulations with a two-scale continuum model and finite volumes method to represent the dissolution of the porous medium. The numerical model is tuned to represent real results through matching experimental core flood data and dissolution patterns. Some conclusions are obtained regarding both isotropic and anisotropic formations. In isotropic formations with radial propagation of wormholes, simulations indicate that a number from four to six wormholes propagate radially in each plane. When the propagation is spherical, simulations result in a number from 16 to 24 wormholes propagating spherically from the point of acid injection. In anisotropic formations, the radial stimulated zone might become an elliptic stimulated zone, depending on the acid injection rate and the permeability heterogeneity magnitude. The major axis of the elliptic stimulated zone coincides with the direction of higher permeability and longer permeability correlation length, and it is longer for larger acid injection rates. Analogously, the spherical wormholes propagation pattern might become an ellipsoidal stimulated zone in anisotropic formations.