Transport Mechanisms for CO2-CH4 Exchange and Safe CO2 Storage in Hydrate-Bearing Sandstone

CO 2 injection in hydrate-bearing sediments induces methane (CH 4 ) production while benefitting from CO 2 storage, as demonstrated in both core and field scale studies. CH 4 hydrates have been formed repeatedly in partially water saturated Bentheim sandstones. Magnetic Resonance Imaging (MRI) and CH 4 consumption from pump logs have been used to verify final CH 4 hydrate saturation. Gas Chromatography (GC) in combination with a Mass Flow Meter was used to quantify CH 4 recovery during CO 2 injection. The overall aim has been to study the impact of CO 2 in fractured and non-fractured samples to determine the performance of CO 2 -induced CH 4 hydrate production. Previous efforts focused on diffusion-driven exchange from a fracture volume. This approach was limited by gas dilution, where free and produced CH 4 reduced the CO 2 concentration and subsequent driving force for both diffusion and exchange. This limitation was targeted by performing experiments where CO 2 was injected continuously into the spacer volume to maintain a high driving force. To evaluate the effect of diffusion length multi-fractured core samples were used, which demonstrated that length was not the dominating effect on core scale. An additional set of experiments is presented on non-fractured samples, where diffusion-limited transportation was assisted by continuous CO 2 injection and CH 4 displacement. Loss of permeability was addressed through binary gas (N 2 /CO 2 ) injection, which regained injectivity and sustained CO 2 -CH 4 exchange.