Analytical Study of Gas Well Performance Decline Mechanisms in Mature Fields of Imo State

Understanding the mechanisms driving production decline in mature gas fields is essential for designing effective well intervention and reservoir management programmes to sustain production from Nigeria's ageing gas assets. This study analytically investigates the production decline mechanisms affecting gas wells in mature onshore fields in Imo State, drawing on production history data, well test records, and completion information from 28 wells in the Oguta and Imo River basin fields. The research employs a diagnostic production analysis methodology combining Arps decline curve analysis, flowing material balance calculations, and water influx assessment using Carter-Tracy aquifer models. The study systematically distinguishes between reservoir-driven decline mechanisms (pressure depletion, water influx, and retrograde condensate dropout) and wellbore-related decline mechanisms (liquid loading, formation damage, and sand accumulation). A research gap addressed is the absence of published multi-mechanism decline characterisation studies specific to the Imo State producing environment, where the co-occurrence of water influx and liquid loading creates complex production behaviour not well represented by single-mechanism decline models. Findings reveal that liquid loading is the dominant current production decline mechanism in 60 percent of active wells, while water influx from adjacent aquifer formations is identified as the primary reservoir energy depletion driver in the remaining 40 percent. Combined well intervention scenarios modelled suggest potential production recoveries averaging 35 percent above current rates through plunger lift installation and wellbore cleanout operations. Recommendations include systematic well diagnostics programme implementation, prioritised plunger lift installations, and development of a field-wide water management strategy. Keywords: production decline, gas wells, Imo State, liquid loading, mature fields.