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Objectives:
Oil quality linked to viscosity, density, and wettability varies significantly in Al Shaheen oil field, impacting the oil recovery and production forecast. The objective of the study was to identify the alteration process causing oil quality variation and quantify oil API specific gravity (an oil quality proxy) at a high resolution along the wells.
Procedure:
The organic geochemical parameter phytane/nC18 was measured from oil samples and was calibrated to a measured oil API to obtain a predictive regression curve.
Carbon Isotopic data were used in conjunction with phytane/nC18 to identify the main alteration type causing oil API variation.
The drilling cuttings were used to measured phytane/nC18 and inferred a predictive oil API along the wells at a high resolution.
Results:
The oil alteration was identified as bacterial alteration in reservoir namely Biodegradation. The oil quality varied with true-vertical depth as the first order variation, however faulted zones showed local and sharp decrease of oil quality.
Conclusions:
The spatial high resolution of oil quality prediction revealed a correlation with geological and structural features. The data have been used in static and dynamic models and can be used for appraisal and field development strategies.