Carbon capture and high-capacity supercritical fluid processing with supersonic separator: Natural gas with ultra-high CO2 content

Abstract

Some deep-water offshore fields produce oil with high gas/oil ratios and ultra-high %CO2 (>60%mol) with the onus of processing low-grade gas simultaneously handling huge CO2 dispatch goals. Thus, processing solutions are needed to make feasible such high-capacity gas rigs hundreds of kilometers offshore. Feasibility relies on the choices for CO2 capture and adjustment of water and hydrocarbon dew-points of such high flow rate gas. This problem was approached adopting supersonic separators for dew-point adjustments and for CO2 capture on a floating-hub processing 50 MMsm³/d of CO2 ultra-rich gas, reinjecting 96% of treated CO2-rich gas for enhanced oil recovery, while reserving 4% as fuel-gas after CO2 abatement to 20%mol for power production. Process alternatives were assessed in terms of power demand and profitability comparing supersonic separator with membrane-permeation for CO2 removal. Results show that 1st supersonic separator for dew-point adjustments of raw gas recycling condensate to the oil-gas-water separator and 2nd supersonic separator for CO2 removal avoiding CO2 freeze-out, give optimum net present value and minimum CO2 emissions. On one hand, these facts are consequences of less compressor investment as 2nd supersonic separator ejects pressurized CO2 condensate requiring 5% less compression power for enhanced oil recovery relatively to the power required by the low-pressure CO2-rich permeate from the membrane-permeation alternative. On the other hand, the best net value of supersonic separator alternative also reflects its highest revenues derived from recycling condensate from 1st supersonic separator entailing 18% higher oil production.