Multiscale flow unit characterization in a mature field using capillary pressure curves, well logs, and petrophysical data: a case study for Potiguar Basin, Brazil

This study integrates geological/geophysical, petrographic/diagenetic, and petrophysical data to individualize rocks with different flow capacities in the Alto do Rodrigues (ARG) Field, a producing oil field in the Potiguar Basin, NE, Brazil. The work used information from over 800 vertical wells, 19 with rock data, and petrophysical analysis. Seven wells provided most of the data for the present study because of the greater thickness of cores recovered. Implementing the multiscale approach was essential in understanding the geological aspects that influence the reservoir production capacity. At the micro-scale, thin section analysis allowed us to identify clay minerals. These minerals can obstruct pore throats, affecting rock permeability and productivity at the meso scale. The study of cores in different portions of the field characterized the depositional systems in the area and quantified factors that influence oil entry into the reservoir. In the ARG Field’s producing reservoirs, diagenesis is relatively incipient but intensifies in samples with porosity under 10%. Finally, through the correlation of rock vs. profile at the macro scale, the distribution of the flow units defined for the other wells were estimated, thus allowing the construction of maps and petrofacies sections with geological and dynamic significance. At this last scale, the geometry of the sedimentary deposits and their heterogeneities are visualised, whose understanding directly influences the planning and development of an accumulation (for example, in the definition of the production wells grid and water or steam injection in case of application of secondary recovery methods). Additionally, a methodology was developed to quantify the production capacity of the rocks using a Reservoir Quality Index (RQI). This RQI was validated with field production data. RQI strongly correlated with accumulated production (R2 = 0.9578 for cold production and R2 = 0.8103 for production after steam injection). A key observation is that the minimum accumulated production after the first steam injection cycle is almost three times the cold production values.