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

Abstract

CO2 injection in hydrate-bearing sediments induces methane (CH4) production while benefitting from CO2 storage, as demonstrated in both core and field scale studies. CH4 hydrates have been formed repeatedly in partially water saturated Bentheim sandstones. Magnetic Resonance Imaging (MRI) and CH4 consumption from pump logs have been used to verify final CH4 hydrate saturation. Gas Chromatography (GC) in combination with a Mass Flow Meter was used to quantify CH4 recovery during CO2 injection. The overall aim has been to study the impact of CO2 in fractured and non-fractured samples to determine the performance of CO2-induced CH4 hydrate production. Previous efforts focused on diffusion-driven exchange from a fracture volume. This approach was limited by gas dilution, where free and produced CH4 reduced the CO2 concentration and subsequent driving force for both diffusion and exchange. This limitation was targeted by performing experiments where CO2 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 CO2 injection and CH4 displacement. Loss of permeability was addressed through binary gas (N2/CO2) injection, which regained injectivity and sustained CO2-CH4 exchange. OPEN ACCESSEnergies 2015, 8 4074

Simulation Study on the Effect of Fracturing Technology on the Production Efficiency of Natural Gas Hydrate

“…NGH should be converted in situ to its constituent gas and water. A number of conversion methods exist, but early production testing and modeling indicate that depressurization will be the ideal method to use [14][15][16][17][18].…”

“…Thermal stimulation and fracturing combine to exploit NGH [27,37], as hot fluid enters NGH concentrations through the crack network and directly heats NGH to increase the mining radius and reduce heat loss. For CO2 replacement [17], CO2 enters NGH concentrations through the crack networks. The large contact area between CO2 and NGH increases replacement efficiency by CO2.…”

“…The combination of fracturing technology and existing methods to exploit natural gas hydrates would solve some of the problems of existing methods [17,27,37,38]. Fracturing technology is the primary mechanical solution for increasing porosity, interconnecting artificial cracks and natural cracks, and forming a mutual interconnected crack network in NGH concentrations, in order to enhance the conductivity of NGH concentrations.…”

Formulating formation mechanism of natural gas hydrates

“…Finally, a new equilibrium is established. This guest gas basically forms a thermodynamically preferred gas hydrate and replaces the methane molecule within the hydrate cavity 6 . During the solid-liquid-solid transition, there is no apparent dissociation noticed, which indicates that the geomechanical stability remains unaffected 7 .…”

“…As indicated, in addition to CH 4 production, this swapping phenomenon is used for stable long term CO 2 storage 8 . This, in turn, leads to maintain structural integrity and reduce seepage since CO 2 hydrate itself acts as an additional sealing layer 6 . At this point, it is interesting to note that the P-wave velocity (i.e., compressional wave velocity) is measured to have the information of the stiffness evolution of hydrate-bearing sediments that is related to the reservoir stability 9 .…”