A proposal for reservoir geostatistical modeling and uncertainty analysis of the Curimã Field, Mundaú Sub-Basin, Ceará Basin, Brazil

Abstract

Geological modeling represents one of the most important phases in reservoir characterization, in terms of workload, uncertainties and impact on final results. Modeling of oil reservoirs consists of the construction of the structural, stratigraphic, and petrophysical models; the calculation of the volume of oil in place; and the analysis of uncertainties. This study integrates reservoir data obtained from a variety of disciplines (geophysics, petrophysics, sedimentology, geology, and engineering), with the purpose to build a reliable geological reservoir model. To better represent the reservoir heterogeneities and integrate geological concepts and observations, geostatistical principles were applied to geological modeling. Therefore, the main objective of this study is to characterize the geometry and petrophysical properties of the Curimã Field, a deltaic reservoir in the Paracuru Formation of the Mundaú sub-Basin (Ceará Basin), using advanced geostatistics in order to evaluate the uncertainties of the reservoir volume. The integration of reliable data using geostatistical techniques to simulate reservoir properties provided a reliable geological model that matches, in terms of original volume in place, with that published by the Brazilian National Agency of Oil, Natural Gas and Biofuels (ANP). In addition, the sensitivity and uncertainty analysis of the variables used to build the geological model allowed to rank them according to their impact on the volume calculation - thus, from greatest to the lowest impact: i) the porosity cutoff for the NTG calculation; ii) the mean porosity value for sandstones; iii) the depth of water-oil contact. The final results were based on the analysis of 500 simulation runs and generated pessimistic and optimistic probabilistic scenarios (P10, P50, and P90) of the volume in place. These results will aid a detailed dynamic assessment of the exploitation potential of the Curimã Field.