This work aims to compare the drilling fluid invasion and oil backflow in sandstone and carbonate samples in order to evaluate the influence of kind of rock in the formation damage and its interaction with the drilling tested fluid.

The tests were performed in sandstone and carbonate samples with similar gas absolute permeabilities and under a protocol test in steps that included preparation, characterization, multiphase flow, drilling fluid invasion and oil backflow.

During the work it was observed that carbonate samples were less water wet than sandstone samples. From the obtained results for longer samples was possible to follow the advancing front of the invading fluid with pressure observations along the core. The dynamic flow permitted to conclude that invasion in carbonate samples was faster than in sandstone. It was also observed that in carbonate samples the backflow presented a higher and faster productivity return when compared with sandstone results.

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