Assessment of Multiphase Metering Technology for Well Testing in Marginal Field Developments in Ondo State, South West Nigeria

Marginal field operators in Nigeria's South West zone require cost-effective production measurement solutions that can replace conventional test separator trains while maintaining fiscal metering accuracy standards. This study assesses multiphase metering technologies applicable to well testing programmes in marginal field developments in Ondo State. The performance of three commercial multiphase meter types, namely gamma-ray based, microwave tomography, and nuclear sensor systems, is evaluated against a conventional test separator baseline using historical production test data from four marginal fields in Ondo State where both measurement approaches were simultaneously deployed. Measurement uncertainty analysis is conducted using the ISO GUM framework for metrological evaluation. Results indicate that gamma-ray based multiphase meters achieve gas volume fraction measurements within plus or minus 3.5 percent of separator reference measurements across operating GVF ranges of 0.2 to 0.85, while oil and water flow rate accuracy varies between minus 4.1 and plus 6.2 percent depending on emulsion stability. The study identifies severe slug flow regimes as the primary operational condition degrading multiphase meter accuracy and recommends flow conditioning upstream of meter installations in slug-prone well strings. Economic analysis confirms that multiphase meters provide positive NPV over a four-year deployment cycle compared to separator-based testing for fields producing fewer than twelve wells simultaneously. Keywords: multiphase metering, well testing, marginal field, Ondo State, production measurement.