A New Approach to Manage CO2 Hydrates During Geological Carbon Sequestration

Abstract

Abstract CO2 storage into reservoirs aims to reduce global Green House Gas emission. CO2 is injected into the reservoir in supercritical conditions and undergoes expansion when reaching the lower pressures of the depleted reservoir. During start-up, or restart, rapid CO2 expansion at the near wellbore region induces a significant temperature drop in the near wellbore. In presence of water, CO2 hydrate can form, precipitate, and degrade well injectivity. To prevent hydrate formation during start-up, or after a long shut-down, mitigation measures should be implemented. Contrary to CH4 hydrates, there is a lack of CO2 hydrate formation in reservoir conditions in literature. This innovative study assessed the use of Kinetic Hydrate Inhibitor (KHI) to avoid CO2 hydrate formation during start-up sequences. The impact of fluid composition, process parameters and reservoir conditions on the possible implementation of the mitigation measure have been mapped to support the selection and use of an appropriate KHI. This study proposes to assess the use of Kinetic Hydrate Inhibitor (KHI) and Thermodynamic Hydrate inhibitors (THI) to avoid CO2 hydrate formation during start-up sequences. Laboratory tests were conducted by reproducing reservoir conditions inside an autoclave set-up. The impact of various parameters, such as water composition (salinity), mineralogy of the reservoir (especially the clay content), CO2 purity (H2S, CO, H2 and CH4 impurities) have been studied on KHI efficiency. Autoclaves tests were conducted to assess the performance of several KHI chemistries to delay CO2 hydrates formation. Adsorption tests were conducted to better understand interactions of KHI chemistries and reservoir mineralogy. Lab results point out the impact of the salinity on KHI performance and a correlation has been highlighted between KHI efficiency and KHI composition (polymer based vs. alcohol based). Results indicate that reservoir samples containing the highest clay content, lead to the lowest KHI efficiency when keeping a constant salinity level. Indeed, KHI efficiency drops when increasing clay content in the reservoir mineralogy and decreasing KHI concentration in water phase. Results suggest that the inhibitor chemicals are adsorbed by the clay and plays an important role in KHI efficiency.