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Recently, a new fiber-laden, self-diverting, and viscoelastic acid has been successfully used for matrix acidizing of highly heterogeneous carbonate formations The fibers have been designed to be inert under surface and pumping conditions, and their geometry allows them to form strong and stable fiber networks that can effectively bridge across natural fractures, wormholes, and perforation tunnels. Eventually, the fibers degrade into a water-soluble organic liquid that is produced back to the surface during flowback.In the case of perforated wells, experiments suggest that diversion with fibers operates in three phases. First, as the early volumes of fiber-laden acid reach the perforations, the acid penetrates the reservoir as if no fibers were present. Second, as the fibers bridge, they accumulate inside the perforations and form a fiber cake. Third, the fibers plug the perforation, and the injectivity decreases locally, promoting diversion into other perforations. The pressure drop through a plugged perforation was analyzed by performing 340 separate fine-scale 3D simulations. The original work was based on theoretical and laboratory-based experiments, considering typical perforation schemes and for various permeability ratios between the generated fiber cake and the formation's original permeability. The results were compiled, and a correlation was made to model the resulting skin. The model was implemented into an acid placement simulator and was extensively tested and validated in the field.In this paper, we present the model that describes the effect of fiber accumulation within perforations and explain how some of the model parameters such as formation-permeability contrast, fiber-cake permeability, and total permeability thickness (kh) may affect diversion efficiency. Case studies from field testing of the model illustrate methods of pressure history matching, job design, and treatment history evaluation.

fax 01-972-952-9435. AbstractSelf-diverting acids are commonly used in matrix acidizing treatments of carbonate formations, not only to increase permeability by generating wormholes, as with conventional acids such as HCl, but also to self-divert into zones of lower injectivity, in the goal of optimizing zonal coverage. In this paper, a new model for wormhole propagation is proposed, which describes both stimulation and diversion processes. A preliminary model is presented, which predicts wormhole propagation under radial-flow conditions for conventional acids. Then, a new set of parameters characterizing the reactive flow of self-diverting acids is developed, and the above model is extended to include self-diverting mechanisms. In particular, it is shown how the new parameters related to wormhole growth and those to diversion can be assessed from linear core-flood experiments and integrated into a new radial-flow model for field-scale prediction. Using this model, a new criterion is developed for diverter efficiency as a function of permeability contrast. Finally, the model is validated against radial flow experiments. It is found that self-diverting acids are characterized by two new parameters which, when combined with the model for wormhole propagation, can be used to predict the performance of self-diverting acids, both in terms of wormhole penetration and in terms of zonal coverage. Some criteria are also developed to assess the diversion ability of acids.

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