Abstract
Achieving complete wellbore coverage is a challenge for any acidizing treatment performed in a heterogeneous fractured carbonate formation with long intervals. Openhole sections, high temperature, and the presence of depleted layers make the task of acidizing design optimization even more difficult. Existing acidizing diversion studies concentrate either on strongly theoretical or on purely field applications. Coupling these two directions is complicated because of different perceptions of diversion principles and diverting method classification.
The current study introduces a simple and robust diversion method classification and covers both theoretical and practical analysis of the diversion in the fractured carbonates. It is explained in the given study why the maximized rate method cannot be considered as a proper diversion method in fractured carbonates according to the suggested classification. Theoretical aspects of the study also cover the selection criteria suggested for the amount of acid preceding the diverter stage in fractured carbonate formations. A calculation methodology is introduced for the skin caused by the particulate filter cake, with respect to the different fracture plugging scenarios and for the skin development in time.
Practical aspects of the study cover field cases with successful diversion results in a variety of extreme conditions: very long openhole intervals (>1,000 ft), horizontal sections, depleted layers, extremely vuggy and fractured formations, hot formations (>260°F), and restricted completion entry wells. Diversion examples include pressure increase signatures of up to 1,500 psi for skin-forming diverters and 500 psi for viscosified ones. Each field case contains a quantitative interpretation of the diversion according to the skin calculation method introduced in this study.
