Estimation of bottomhole pressure during a matrix-acidizing treatment provides the information needed to accurately determine the evolution of skin factor during and after the treatment. It could be a very complicated process, especially when compressible fluids, such as foams, are involved. Existing models for estimating bottomhole pressure during a matrix-acidizing treatment ignore the volume reduction of compressible fluids and its effect on the bottomhole pressure. This research developed a model that uses a unique solution to the mechanical energy balance equation, to calculate the bottomhole pressure from known surface measurements during foamed acid stimulation. The model was used to evaluate two stimulation treatments. Field examples are presented which illustrate the application of the model to optimize stimulation treatments. Properly accounting for the flow behavior and tracking the injected volume of the foam diverter used during the treatment resulted in more reliable and accurate bottomhole pressure profile.

Although it has been shown that clean perforation tunnels facilitate the evolution of a single, deeper-penetrating wormhole, there are no reported applications of reactive shaped charges in carbonates prior to acid stimulation. The present study was instigated to evaluate the impact of reactive charges on acid wormholing in representative carbonate cores. A set of oil-saturated Indiana limestone and cream chalk cores have been perforated under simulated downhole conditions using either a conventional or a reactive shaped charge of equal explosive load. After CT scanning to eliminate outlying perforations affected by rock property anomalies, the set of cores were subjected to identical acid injection treatments representative of typical carbonate reservoir stimulations. Time to breakthrough and effluent chemistry were both analyzed and recorded. Finally, post-stimulation CT scans were used to evaluate wormhole morphology. The laboratory experiments showed that reactive charges provide wider perforation tunnels with higher injectivity, which is beneficial for any type of stimulation job. Higher injectivity tunnels help to propagate more dominant and straighter wormholes resulting in less acid to break through the cores. This technology has a significant potential when perforating tight formations or heterogeneous intervals, where obtaining clean tunnels with conventional perforators is most challenging. Further research work needs to be done to evaluate if the difference in acid volume to breakthrough observed in the experiments would have a major impact in the field.