In most of its deepwater Campos Basin oilfields, Petrobras' strategy has been to develop the waterflooding systems by using open hole horizontal gravel packing. Both, perforation and gravel packing operations, are only possible by the presence of the filtercake, formed on the formation face during the drilling process. Nevertheless, that film becomes an impediment to injection and must be removed to obtain good injectivity.

Despite the development of special tools that permit to acidize just after the gravel packing operation, there was still a need for reducing the operation time and to increase the damage removal efficiency.

With this purpose, changes were made in the diverting systems to allow each acidizing stage to treat larger intervals, thus reducing the treatment's total number of stages. This improvement was possible by modeling the fluid flow through the tool's perforated extension, which saved 30% of the pumping time.

Parallel to this development, acidizing historical data were revised and filtercake invasion studies were performed. The conclusion was that more aggressive acidizing formulations could be used, what reduced the pumping volume and reduced the job time even further, to about 50% of the previous times.

Post job formation tests performed have shown that not only a job time reduction was achieved, but also, a better formation damage removal.

The good effects observed have resulted in a general review in the design of the horizontal injectors acidizing jobs, improving the operation's safety, efficiency and effectiveness.

This paper will describe the technique, job details and the results obtained for these particular operations.

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