In offshore horizontally completed wells, an acid job is usually pumped to remove the filter cake, previously createdto allow sand control equipment and gravel be placed across the entire extended section. When such wells are acidized to remove the filter cake with a hydrochloric: hydrofluoric acid mixture, the resulting skin values are still in the positive range. An improved HF acid system has been introduced in the Campos Basin-offshore Brazil with outstanding results. The HF acid system uses an organophosphonic acid complex to control the generation of HF and to dramatically reduce potentially damaging secondary and tertiary precipitates. This paper describes the results of field treatments showing truly stimulated wells with negative skins – a first in this Campos Basin field for deepwater horizontal wells. Case histories with conventional regular hydrochloric: hydrofluoric acid mixture and with the improved acid system used will be presented. Laboratory core flow tests were performed in advance of the field program with seven different acid blends. Only one acid blend resulted in complete mud damage removal and true stimulation. Innovative equipment design, a state-of-the-art vessel with real-time monitoring capabilities, improved placement techniques and environmentally-friendly materials, are helping to transform acidizing into a valuable method in the quest for optimum performance from every injector, oil and gas well asset.
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