Abstract
Depleted gas fields offer significant potential for CO₂ storage, but injecting CO₂ into such fields presents challenges due to cooling effects near the wellbore. This cooling arises from adiabatic expansion of CO₂ during pressure drop, which can lower temperatures below 10 °C and cause CO₂-hydrate formation. These hydrates can block pore space and reduce injectivity. Understanding hydrate formation and distribution in reservoir rock is essential for safe and efficient CO₂ injection.
We present results from a core-flooding experiment using X-ray microtomography (µCT) to visualize in-situ CO₂-hydrate formation under controlled cooling. A 24.7 cm Bleurswiller sandstone core was saturated with synthetic formation water (SFW) doped with CsCl to enhance contrast in µCT images. The core was then flooded with CO₂ at 100 bar, followed by stepwise cooling from 10 °C to −6 °C, with µCT scans taken at each step.
Hydrate formation was identified using “difference images” between consecutive temperature steps. Hydrates began forming significantly between 6 °C and 2 °C, coinciding with a back-pressure shutdown of the CO₂ pump. µCT images showed inhomogeneous hydrate distribution, with hydrates concentrated in the lower part of the core, correlating with higher local water saturations. Some channel structures showed limited hydrate presence, suggesting complex flow behavior.
This study demonstrates the feasibility of in-situ µCT imaging for CO₂-hydrate research, revealing the importance of local water saturation and highlighting the heterogeneous nature of hydrate formation during CO₂ injection.
We present results from a core-flooding experiment using X-ray microtomography (µCT) to visualize in-situ CO₂-hydrate formation under controlled cooling. A 24.7 cm Bleurswiller sandstone core was saturated with synthetic formation water (SFW) doped with CsCl to enhance contrast in µCT images. The core was then flooded with CO₂ at 100 bar, followed by stepwise cooling from 10 °C to −6 °C, with µCT scans taken at each step.
Hydrate formation was identified using “difference images” between consecutive temperature steps. Hydrates began forming significantly between 6 °C and 2 °C, coinciding with a back-pressure shutdown of the CO₂ pump. µCT images showed inhomogeneous hydrate distribution, with hydrates concentrated in the lower part of the core, correlating with higher local water saturations. Some channel structures showed limited hydrate presence, suggesting complex flow behavior.
This study demonstrates the feasibility of in-situ µCT imaging for CO₂-hydrate research, revealing the importance of local water saturation and highlighting the heterogeneous nature of hydrate formation during CO₂ injection.