Geological sequestration is a potential technology to reducelarge amount of greenhouse gas emissions which areessentially carbon dioxide (CO_2) released from stationaryindustrial sources such as petroleum extractive plants or fossilfiredpower plants. Sequestering CO_2 from a natural gasdevelopment involves separating CO_2 from hydrocarbongases, dehydrating and compressing CO_2, transporting it viapipeline to injection site, re-compressing if applicable,injecting it into geological reservoirs and monitoring itsmovement and behaviour after sequestration. Chemicalabsorption using amines is the most widely used technology todate for separating CO_2 from natural gas. Current researchesfocus on other technologies, especially membranetechnologies. Reservoir and geology studies are to optimizethe sequestration process and to predict the movement of theinjected CO_2 in the reservoirs. Monitoring the injected CO_2after sequestration is to ensure that CO_2 is retained inthe reservoirs.The costs of sequestration could vary from below US$5 toover US$20 per tonne of CO_2, which largely depends on theamount of CO_2, distance and reservoir properties. Economicresults are in favor of large CO_2 flow rate, short distance andhigh injectivity reservoirs. These costs exclude the separationcosts which are considered to be part of the natural gasprocessing because CO_2 must be reduced to a certain level(e.g. 2% by volume) before selling the natural gas even if nosequestration is needed. Cost per tonne of CO_2 sequesteredcould be translated into the incremental costs of producingnatural gas if we know the CO_2 volume fraction in raw naturalgas. For instance, as a rough estimate, sequestering the CO_2from a 25% CO_2 by volume raw natural gas field wouldincrease the costs of natural gas production by US￠9/Mcf toUS￠35/Mcf of processed natural gas.
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