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Lifetime oriented design of natural gas offshore processing for cleaner production and sustainability: High carbon dioxide content

de Carvalho Reis, Alessandra, de Medeiros, José Luiz, Nunes, Giovani Cavalcanti, Araújo, Ofélia de Queiroz Fernandes
Journal of cleaner production 2018
absorption, carbon dioxide, carbon dioxide production, financial economics, natural gas, oils, process design
Production of natural gas in deepwaters with high gas-to-oil ratio and high carbon dioxide (CO2) content challenges the design of offshore processing due to area and weight limitations. Furthermore, cleaner production and process sustainability impose sending the separated CO2 to early enhanced oil recovery, which has economic benefit but gradually increases %CO2 in raw gas, paralleled by decaying oil and gas flowrates. These conditions favor CO2 capture by membrane permeation (MP) for bulk removal and chemical absorption (CA) for polishing removal. Hybrid MP-CA has greater flexibility to face varying production and %CO2, demanding lifetime-oriented process design. CO2 production profile is estimated adopting %CO2 retained in source rock (0%, 60%) and gas flowrate predicted by empirical production decline curves. Under transient gas production MP area and operational conditions are optimized via non-linear programming at five points of process lifetime constrained by %CO2 in injected fluid above 75%mol. Treated gas reaches sale specification (%CO2 < 3%mol) in the CA unit placed downstream MP. The obtained best design matched targets, but was more impacted by decreasing flowrate of raw gas than by increasing %CO2.