Spontaneous imbibition in hydrate-bearing sediments under creep

Abstract

During hydrate exploitation, water generated by the phase transition of natural gas hydrate (NGH) invades the pore space of hydrate-bearing sediments (HBS) through spontaneous imbibition (SI), restricting the depressurization-based extraction. Besides, the creep behaviors of HBS complicate the SI process. Therefore, it is crucial to understand SI behaviors in HBS under creep. This study presents a theoretical model considering the effects of creep behaviors of HBS due to effective stress, as well as occurrence patterns and saturation of NGH. Moreover, fracture networks generation due to hydration in HBS, wall roughness, gravity, and dynamic contact angle are considered. The proposed model is adequately validated by available experimental data. In addition, based on the derived model, parameter sensitivity analysis is carried out. The results demonstrate that the porosity and wall roughness of HBS significantly enhance the SI capacity of HBS. Moreover, when other parameters are fixed, the SI capacity decreases with the increase of hydrate saturation (or retained water saturation). In addition, during the creep process, the SI capacity decreases with time. The derived model not only helps to better understand and predict the SI kinetics in gas hydrate reservoirs, but also provides guidance for the hydrate exploitation process.