Carbonate acidizing: A mechanistic model for wormhole growth in linear and radial flow

Abstract

Highly conductive fluid flow paths, known as wormholes, are formed when acids are injected in carbonate reservoirs during a stimulation treatment. In matrix acidizing treatments, these wormholes are desired whereas in acid fracturing treatments, they are undesirable because they reduce efficiency of the process. Two main types of models are available in the literature for wormhole growth. Semi-empirical models are computationally fast; however, they do not scale well to core dimensions or to radial flow. Numerical simulation models represent the physics of the individual processes well; however, they are computationally intensive and impractical to use on a field scale.To address the shortcomings of these models, a computationally fast mechanistic model is developed for wormhole growth. The model scales well with flow rate and core dimensions. It hence allows scale-up from linear laboratory core flow experiments to field scenarios of radial flow. Accurate scaling with core dimension and with injection rate in linear flow is a necessary precondition for a model to be considered for scale-up to radial flow where both cross-sectional area to flow and the fluid Darcy velocity change as the wormholes grow. Previous computationally fast models did not satisfy this precondition and therefore are not suitable for scaleup to radial flow.The model is validated against more than 50 published and internal sets of linear core-flood experiments on limestone and dolomite cores treated with HCl and emulsified acids. The validation dataset covers a wide range of acid concentrations, temperatures, rock types and core dimensions. The modeling equations extend to radial flow based on the change in the domain area with wormhole progression. The radial model was tested against 10 published radial flow experiments and a reasonable match was obtained. The model predictions were also tested against field results and again a good match was obtained.