Development of a Low-Cost Compact Separator Unit for Small-Scale Associated Gas Recovery in Nigerian Marginal Oilfield Operations

Associated gas flaring at Nigerian marginal oilfields constitutes a persistent environmental and economic challenge, with approximately 7.7 billion standard cubic metres (scm) of gas flared annually across the Niger Delta region. Existing gas recovery infrastructure is predominantly designed for large-scale operations and remains economically inaccessible to marginal field operators, who typically manage wellhead production rates below 5,000 barrels of oil per day (BOPD). This study presents the design, fabrication, and experimental evaluation of a low-cost compact three-phase separator unit specifically optimised for small-scale associated gas recovery in marginal oilfield settings. The separator was designed using established two-film theory and droplet settling velocity principles, incorporating a horizontal vessel configuration with a diameter of 0.6 m and a seam-to-seam length of 2.4 m. Structural integrity was assessed using finite element analysis (FEA), and pressure drop characteristics were modelled via computational fluid dynamics (CFD) simulations. Laboratory testing was conducted at inlet gas-oil ratios (GOR) ranging from 200 to 800 scm/m³ and operating pressures of 0.5 to 1.5 MPa. Experimental results demonstrated a liquid carryover of less than 0.04 mL/m³, gas carryunder below 0.5%, and an overall separation efficiency exceeding 97.8% under all tested conditions. Material selection prioritised locally available low-alloy carbon steel (ASTM A516-70) to minimise capital expenditure, with total fabrication cost estimated at USD 18,500, representing a cost reduction of approximately 65% relative to conventional equivalent units. The findings confirm that purpose-engineered compact separators can deliver technically adequate performance at commercially viable cost thresholds for marginal field operators in sub-Saharan Africa.