Characterizing the Namorado Sandstone in southern Brazil through the analysis of a multi-borehole database and utilizing a contemporary workflow

Abstract

The petrophysical characterization of reservoirs requires the identification of sedimentary facies based on the integration of geophysical well logs and rock analyses in the laboratory, which is one of the significant challenges for the petroleum industry. In this work, laboratory analysis results were linked to quality controls of data pre-processing in a new workflow by integrating several techniques. The wells studied were zoned and laterally correlated based on electrofacies characteristic core analysis and petrographic descriptions. This integration resulted in a modeled geologic section for the Namorado Sandstone in the Campos Basin of southeastern Brazil, created based on various data from each well. The borehole NA2 was selected as the key wellbore after creating this section. The logs from this borehole were then analyzed to separate the permo-porous (reservoirs) and non-porous (non-reservoirs) horizons. The zones containing water and hydrocarbons in the permo-porous sections of interest were split along the wells. Subsequently, the identified sectors were interpreted using petrophysical techniques to confirm the preliminary categorization. After combining all quantitative products to quantify the porous layers capable of producing mobile oil, the cut-off factors were introduced. The next step was determining the parameters of the Archie equation, the amount of clay present, and the water saturation from core descriptions, which led to the discovery of deep laminated sandstones. The results strongly correlate with lithology, geological facies, borehole logs, and petrophysical laboratory data. Based on these findings, it is evident that the clay concentration is the primary factor influencing the oil saturation in this reservoir.