In most of its deepwater Campos Basin oilfields, Petrobras' strategy has been to develop the water flooding systems using horizontal gravel packed wells. Both drilling and gravel pack operations are only possible through the presence of a filter cake, 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.

Special tools were developed to perform acidizing jobs, in one trip, just after the gravel packing operation. However, there were few alternatives to correct any eventual acidizing lack of performance, besides using coiled tubing and straddle packers, something that usually takes too much time.

Recently, a pulse-rotating jet tool system was applied in a well that could not be treated after the gravel pack operation. The tre atment, which is simpler and faster than those carried out with straddle packers, was performed in two stages: the first, using just HCl, and the last one, using mud acid.

The subsequent formation test performed after the HCl treatment showed a high skin value and an unacceptable injectivity index, due the need to keep the reservoir pressure above the bubble point. Even so, the test data in association with reservoir simulation, according with the field geology, showed that there was fluid injection throughout the entire horizontal section. Therefore, it was decided to perform a mud acid treatment, again, using the pulse-rotating jet tool system.

This time, a second formation test indicated an excellent injectivity index, confirming the pulse-rotating jet tool system effectiveness and creating perspectives for the application of this technique in future operations.

This paper will describe the technique, job details and the results obtained for this particular operation, which may be applied in other similar offshore environments.

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