Traditionally, reservoir engineers interpret the pressure transient response in formations with natural fracture networks using dual porosity models. However, some reservoirs that appear fractured fail to exhibit classic dual porosity behavior. These may be “discretely” fractured reservoirs, in which fractures contribute to fluid flow but are poorly connected. Properly interpreting well test results in such cases is critical to understanding reservoir compartmentalization, optimizing development strategies, and predicting future production. Schlumberger developed two new interpretation techniques for pressure transient tests in fractured reservoirs, and first applied them in the field to assist Petrobras in characterizing a discretely fractured carbonate reservoir in the Campos Basin. This case study describes a new seven-step GeoTesting pressure transient testing, design, and interpretation workflow that can be used, in fact, to characterize any type of fractured reservoir.