Integrated Interpretation for Pressure Transient Tests in Discretely Fractured Reservoirs (SPE 154531)

In 2005, Petrobras discovered a fractured Albian carbonate reservoir in Campos Basin. During the evaluation of an appraisal well, a full sequence of well tests (DSTs) and a 4-month extended well test (EWT) were performed to monitor reservoir behavior and to define the most probable geological reservoir model before the final development decision was made. While the results of the well test sequence were sufficiently favorable for development, the well test analysis raised concerns about the quantitative use of these tests for reservoir characterization. The seismic sections of the field indicated faulting, and open fractures were interpreted from image logs in the appraisal wells. However, the response of the DSTs and EWT did not indicate classical dual porosity type behavior that is consistent with an extensive connected fracture network system. The fractures in this reservoir are considered to be predominantly open in one direction only. Few methods exist for the interpretation of the pressure transient response of discretely fractured reservoirs where fractures provide conduits for fluid flow and displacement, but where the fracture network is poorly connected compared to dual porosity models. In this paper, we first outline the gaps in the existing pressure transient well test interpretation methodology for these reservoirs, then we introduce two new techniques developed to address these gaps: 1) A reservoir model-based inversion technique for parameter estimation from pressure transient data, and 2) A boundary element method for determining the pressure transient behavior of the reservoir with arbitrarily distributed finite and/or infinite conductivity vertical fractures. We define a new integrated interpretation methodology for reservoirs with discrete natural fractures making use of these techniques and incorporating openhole log data, seismic and the preliminary geological reservoir model. Finally, we illustrate the use of the methodology using the tested well.