Identifying the Presence of Water Finger and Assessing Influence of WBM Filtrate Invasion in a Fractured Zone of Brazilian Presalt Carbonates

The present study investigates the complex phenomenon of water-based mud (WBM) filtrate invasion and its implications in a fractured carbonate reservoir within the Brazilian Pre-Salt Campos Basin. During the drilling of a vertical production well in the Coqueiros Formation, a zone significantly above the oil-water contact exhibited unexpectedly low resistivity and higher water saturation, despite being far from the expected water zone. Initial hypotheses attributed these anomalies to WBM filtrate invasion, exacerbated by fractures identified in image logs. However, the well ultimately produced 100% water, leading to its abandonment, suggesting that the formation water saturation was due to unexpected field injection water fingering. To investigate those possibilities, the research employed advanced numerical simulations using the UTAPWeLS platform to model WBM filtrate invasion and resistivity logs, alongside fracture aperture analysis. Various scenarios of initial water saturation and invasion conditions were tested to evaluate their impact on resistivity and water saturation estimates. Results revealed that pure WBM invasion could not fully explain the observed resistivity behavior, suggesting the presence of movable water prior to drilling. The study highlights the critical role of fractures in fluid flow dynamics and the importance of integrating invasion modeling with resistivity log interpretation to improve reservoir evaluation and decision-making in complex carbonate systems.