oa Time–Lapse Geochemistry Using Tile-Based Fisher Ratio in Pre-Salt Crude Oils Under Enhanced Oil Recovery

Time-lapse geochemistry is a tool for understanding reservoir dynamics and optimizing oil production strategies, especially during enhanced oil recovery (EOR) operations. By analyzing chemical compositional changes in produced fluids over time, it is possible to detect molecular level variations before macroscopic indicators. This study applied a tile-based approach combined with the Fisher ratio (FR) to identify key molecular markers in pre-salt crude oils from eight wells in the Búzios field, Santos Basin (Brazil), before and after water-alternating-gas (WAG) injection. Samples collected at t0 (before WAG) and t1 (after WAG) were analyzed using GC×GC-TOFMS. Peak table-based analysis revealed increases in iso-alkanes, naphthenes, and aromatics in the C8–C11 range at t1. Applying the FR through ChromaTOF Tile enabled the detection of statistically significant molecular changes (96.90% variation in PCA), allowing the discovery of substances such as 1,2,4-trimethylbenzene and butylcyclohexane with distinctive behavior after WAG. These findings suggest that the tile-based FR approach can efficiently highlight key chemical changes during EOR, aligning well with traditional methods and enabling targeted monitoring. The combination of the GC×GC tool and innovative applications in data processing enhances understanding of in-reservoir oil behavior, aiding field management by indicating the movement of the miscible front.