Production Allocation in Biodegraded Hydrocarbon Reservoirs: Overcoming Challenges with Incremental Linkage Hierarchical Cluster Analysis and Geochemical Fingerprinting

This study investigates a geochemical approach to quantifying fractional contributions of bio-degraded end-member crude in commingled production string. Bottom-hole samples from the 1A-B6 and 2A-B6 sands, as well as field-produced commingled samples, were analyzed to identify and quantify end-member contributions using Gas Chromatography-Mass Spectrometry (GC-MS). A major challenge was the striking similarity in the geochemical fingerprints of the end-member samples due to their pattern of biodegradation, which hindered differentiation using traditional geochemical methods. To address this, a selection of saturated biomarkers from the m/z 191 terpane group, which are known for their biodegradation resistance due to high molecular weight and complex ring structures, were combined with an Incremental Linkage Hierarchical Cluster (IHCA) model, using similarity linkage as the core principle for allocating contributions. This advanced approach improved the resolution and accuracy in distinguishing contributions within the commingled sample. The analysis revealed that End-member 1A-B6 contributed an average of 12.2%, 10.6%, and 9.9% to the field-produced commingled samples, while End-member 2A-B6 contributed 87.8%, 89.4%, and 90.1%, respectively. IHCA corroborated these findings, demonstrating a strong alignment between commingled samples and end-member 2A-B6. This study highlights that biomarker-based geochemical fingerprinting, combined with incremental linkage HCA, provides a robust and accurate method for production allocation.