From Complex Oil Distribution to Production Allocation: A Geochemical Surveillance Success in Ecuador's Fields

In Ecuador, Block 61 represents one of the country's most prolific hydrocarbon-producing areas, comprising 17 fields and seven principal reservoirs. Multi-zone production was evaluated as a means to accelerate hydrocarbon recovery and enhance asset value. However, realizing the full benefits of commingled production requires accurate and cost-effective quantification of reservoir contributions. Given the scale of the development and the extensive monitoring demands, conventional production back-allocation methods were not considered viable. Consequently, a field-wide geochemical fingerprinting campaign was launched in 2020 to assess its application as a production-allocation solution.

Geochemical fingerprinting provides a rapid, reliable, and cost-effective alternative to conventional production allocation methods. Key challenges for application of this methodology in Block 61 include the lack of reservoir-specific oil samples from target intervals in commingled producers and a complex oil distribution characterized by large variations in API gravity. To address this limitation, a structured sampling program was implemented to investigate fluid compositional variability across the asset and evaluate reservoir connectivity. Oil molecular and bulk compositions indicate varying levels of biodegradation as the primary control on observed compositional variations, with water washing and secondary charge contributing in some areas. This assessment enabled the identification of representative oils from neighboring wells that could be used as surrogate end-member samples in the allocation workflow.

A feasibility study based on laboratory calibration mixtures prepared from selected analogue end-members demonstrated the applicability of the geochemical allocation approach. Contributions from as many as four producing reservoirs were quantified through specialized geochemical allocation software that utilizes the statistical distribution of interparaffinic peak-ratio measurements. The methodology accounts for compositional changes that may occur in end-member fluids over time and incorporates uncertainty management within the allocation calculations. The resulting reservoir contribution estimates were independently verified through comparison with Production Logging Tool (PLT) data, providing confidence in the robustness of the allocation results.

More than 30 commingled wells across the block are currently monitored using this approach. The results demonstrate a substantial increase in production attributable to the multi-zone production strategy while minimizing completion costs. In addition, continuous production geochemical surveillance provides valuable reservoir insights that support improved reservoir characterization and data-driven reservoir management.