Geochemical Monitoring as an Operational Tool: A Case Study from the Middle Magdalena Valley Basin– VMM, Colombia

Optimizing enhanced oil recovery processes through water injection requires tools capable of understanding the evolution of produced fluids, identifying compositional changes, and quantifying the contribution of different producing units. In this context, petroleum geochemistry extends beyond its traditional role as a characterization tool and becomes a dynamic reservoir monitoring mechanism.
This study presents a geochemical monitoring strategy developed for a producing field in the Middle Magdalena Valley Basin (VMM), Colombia, based on the construction of a compositional baseline using three complementary analytical scales. The first scale corresponds to the overall fluid composition determined through SAR fractionation by MPLC-MKW, which was used to evaluate crude oil quality, thermal maturity, and compositional variability. The second scale incorporates the molecular fingerprint obtained from Whole Oil analysis by GC-FID, enabling the establishment of chromatographic patterns, the identification of differences among producing units, and the estimation of production contributions through production allocation techniques. Finally, the third scale integrates aromatic biomarkers determined by GC-MSD, providing high-resolution molecular tracers for fluid differentiation and the monitoring of compositional changes associated with reservoir intervention.
The results reveal oils of marine origin deposited under anoxic conditions, derived from Type II organic matter and within the oil generation window. The integration of these analytical approaches enabled the establishment of a robust geochemical baseline characterized by strong genetic affinity among fluids and subtle but sufficiently sensitive compositional differences to discriminate contributions from individual producing units. In addition, production allocation models identified dominant contributions from the main producing unit and enabled the quantification of fluid mixtures with a high degree of accuracy.
GC-MSD analysis established a molecular baseline using several families of aromatic compounds, including benzohopanes, methylphenanthrenes, methyl dibenzothiophenes, dimethylphenanthrenes, methylated triaromatic steroids, and monoaromatic steroids, among others. These compounds will serve as sensitive tracers for evaluating compositional variations in crude oil samples following water injection operations. The integration of the three analytical scales resulted in a highly consistent baseline, reaffirming the geochemical affinity of the fluids while identifying key discrimination parameters. The incorporation of aromatic biomarkers expanded the molecular resolution of the system, substantially increasing monitoring sensitivity. Furthermore, the development and implementation of proprietary in-house algorithms automated the selection and evaluation of these geochemical attributes, enhancing traceability and supporting operational control applications.