Geological sequestration is a potential technology to reduce large amount of greenhouse gas emissions which are essentially carbon dioxide (CO2) released from stationary industrial sources such as petroleum extractive plants or fossil-fired power plants. Sequestering CO2 from a natural gas development involves separating CO2 from hydrocarbon gases, dehydrating and compressing CO2, transporting it via pipeline to injection site, re-compressing if applicable, injecting it into geological reservoirs and monitoring its movement and behaviour after sequestration. Chemical absorption using amines is the most widely used technology to date for separating CO2 from natural gas. Current researches focus on other technologies, especially membrane technologies. Reservoir and geology studies are to optimize the sequestration process and to predict the movement of the injected CO2 in the reservoirs. Monitoring the injected CO2 after sequestration is to ensure that CO2 is retained in the reservoirs.
The costs of sequestration could vary from below US$5 to over US$20 per tonne of CO2, which largely depends on the amount of CO2, distance and reservoir properties. Economic results are in favor of large CO2 flow rate, short distance and high injectivity reservoirs. These costs exclude the separation costs which are considered to be part of the natural gas processing because CO2 must be reduced to a certain level (e.g. 2% by volume) before selling the natural gas even if no sequestration is needed. Cost per tonne of CO2 sequestered could be translated into the incremental costs of producing natural gas if we know the CO2 volume fraction in raw natural gas. For instance, as a rough estimate, sequestering the CO2 from a 25% CO2 by volume raw natural gas field would increase the costs of natural gas production by US¢9/Mcf to US¢35/Mcf of processed natural gas.