Abstract
Over the past 10 years, more than 300 trillion kg of carbon dioxide (CO2) have been emitted into the atmosphere, deemed responsible for climate change. The capture and storage of CO2 has been therefore attracting research interests globally. CO2 injection in submarine sediments can provide a way of CO2 sequestration as solid hydrates in sediments by reacting with pore water. However, CO2 hydrate formation may occur relatively fast, resulting decreasing CO2 injectivity. In response, nitrogen (N2) addition has been suggested to prevent potential blockage through slower CO2-N2 hydrate formation process. Although there have been studies to explore this technique in methane hydrate recovery, little attention is paid to CO2 storage efficiency and geomechanical responses of host marine sediments. To better understand carbon sequestration efficiency via hydrate formation and related sediment geomechanical behaviour, this study presents numerical simulations for single well injection of pure CO2 and CO2-N2 mixture into submarine sediments. The results show that CO2-N2 mixture injection improves the efficiency of CO2 storage while maintaining relatively small deformation, which highlights the importance of injectivity and hydrate formation rate for CO2 storage as solid hydrates in submarine sediments.
Highlights
CO2 emission from burning fossil fuels and industry processing traps heat in the atmosphere, which has grown from 30.4 Gigatonnes (Gt) in 2010 to 33.3 Gt in 2019 resulting global concern of climate change [1]
It is interesting to note that the heave occurs almost immediately after fluid injection, but with time, the sediment slowly compresses, which can be seen by the increase in the vertical strain. This is caused by the slow process of CO2 hydrate formation as shown in Fig. 10, which presents the development of CO2 hydrate in the vicinity of the injection well
To consider the CO2 storage efficiency and geomechanical response of host sediments, two cases of CO2 and CO2-N2 injection (90-10 mol%) into marine sediment are simulated with the implementation of gas mixture and hydrate mixture in the coupled formulation
Summary
CO2 emission from burning fossil fuels and industry processing traps heat in the atmosphere, which has grown from 30.4 Gigatonnes (Gt) in 2010 to 33.3 Gt in 2019 resulting global concern of climate change [1]. Different CO2 sequestration concepts are brought up including CO2 injection into deep geological formations of low permeability and carbon mineralization via reaction with metal oxides. The former may involve leakage issue due to the mobility of CO2 fluid and the latter usually requires long time for producing stable carbonates, limiting CO2 storage efficiency [4]. When injected CO2 is mixed with free water in marine sediments, CO2 hydrates can form under suitable conditions of pressure and temperature. To investigate gas hydrate-based carbon storage efficiency and associated geomechanical response, this paper presents two cases of pure CO2 injection and CO2N2 mixture (90-10 mol%) injection into water saturated marine sediments. Model geometry and the initial conditions are presented before discussing the advantage of CO2-N2 mixture injection in detail
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