Low Dosage Chemical Assisted Enhanced CH4 Production and CO2 Storage in Porous Medium During Hydrate Swapping

Abstract:

In this study, we investigate the methane hydrate formation and CH₄/CO₂ exchange in unconsolidated porous media with and without surface-active chemicals such as surfactant and alcohol. CO₂ rich gas injection into natural gas hydrate reservoir is proposed as a novel technique to produce natural gas and simultaneously storage CO₂ without disturbing the geological settings. This method is limited by mass transport barrier created by hydrate film formed at the liquid/gas interface. The very low CO₂ diffusivity through these films causes a delay in CH₄/CO₂ exchange and lead to low recovery. A recent study using simulation suggests that in the presence of a low concentration of surface-active chemicals, CH₄-CO₂ exchange can be enhanced. Surface active chemicals could enhance the diffusivity of CO₂ through hydrate film by creating dispersed hydrate film. No experiment study has been conducted so far to study this phenomenon.

We formed CH₄ hydrate from gaseous CH₄ and in the present small concentration of different surface-active chemicals (surfactant, amino acid & methanol) to mimic the hydrate reservoir. Pure CO₂ was injected into this reservoir to initiate the CH₄/CO₂ exchange scenario. P-T and GC analysis was carried using a high-pressure cell with unconsolidated sand with particle size 0.9-1.6 mm. CH₄/CO₂ mixed hydrate formed at reservoir conditions (P = 50-65 bar and T = 1.0-3.0°C) at methane hydrate – CO₂ interface. After soaking period of 24 hours, GC analysis was carried out to measure the change in CO₂ and CH₄ mole concentration in the vapour phase at the start of injection and after soaking period to calculate liberated CH₄ moles and stored CO₂ moles. Effect of surface-active chemical, change in concentration, Initial hydrate saturation on methane recovery and CO₂ storage potential was also analyzed. The results showed that 5% methanol was the best-performing chemical among selected one to enhance methane production and CO₂ storage efficiency, as it boosted gas diffusion through hydrate film. The presence of methanol drastically reduced the risk of hydrate reformation compared to other hydrate formers, including SDS and Amino acids that increased the risk of hydrate reformation