Revisiting GBS CO2 Removal Optimization – First Step to NET ZERO

Abstract

Abstract Great Bongkot South (GBS) GHG emission is mainly contributed by permeate flare gas from CO2 removal membrane unit. Although GBS CO2 removal operation has been continuously optimized, the focus has never come with such high intensity the world demands today for GHG reduction. Higher CO2 in raw feed gas driven by economic values makes it even more challenging for GHG reduction. This is why GBS revisits our CO2 removal operation to contribute to PTTEP's Net Zero Goal. GBS CO2 removal optimization test designed for 3 phases. First, feed gas CO2 was varied between 34% to 39% to assess magnitude of higher hydrocarbon loss and permeate flow. Second, reduced permeate backpressure to minimum to get lowest possible CO2 content in raffinate product and utilize membrane unit bypass line to match sales specification, expecting less permeate flare through less membrane flow. GBS also explores bypassing whole CO2 removal pre-treatment and membrane units in order to extend service life of pre-treatment facilities. Lastly, membrane feed temperature is minimized beyond the original limit without adverse effects from liquid condensation. From optimization tests, it was found that 1% higher of CO2 in feed gas would increase hydrocarbon loss around 2 MMscfd. Although feed-to-sales gas ratio increases with higher feed CO2, the increasing rate becomes less sensitive when increasing feed CO2 beyond 37%. This means that permeate flare flow, which corresponds directly to GHG emission, increases but at a lower ratio when operating with higher feed CO2. Reducing permeate backpressure to minimum did not straightforwardly result in significant reduction of hydrocarbon loss and permeate flare flow. However, it allowed more operational flexibility to reduce membrane feed temperature which is the key to hydrocarbon loss optimization and GHG reduction. Membrane feed temperature reduction of 1°C can lower heating value of permeate flare around 5 BTU/scf. Since then GBS has reduced membrane feed temperature from 43 DegC to 40 DegC, lowering hydrocarbon loss by 2.5% and GHG emission by 3-4%. As GHG emission reduction becomes extremely important according to global trend, high CO2 gas fields are urged to revisit CO2 removal optimization scheme. The incremental GHG reduction from optimization always presents a quick-win benefits without the need of investment. This approach can be applied for any assets in PTTEP and subsidiaries including other oil and gas producers.