The characteristics and its implications of hydraulic fracturing in hydrate-bearing clayey silt

Abstract

As a reservoir stimulation technique, hydraulic fracturing is expected to be used in gas hydrate production to overcome the glaring challenge of low gas production rate. Several experimental studies have been carried out in hydrate-bearing sand, which confirmed the frackability of this kind of geomaterial. But for the fine-grained hydrate reservoir, which spreads more widely, contains the majority of the total hydrate resource, and is more difficult to exploit, there is no explicit research studying the fracturing behavior in it. To investigate the characteristics of hydraulic fracturing in fine-grained hydrate-bearing sediments (HBS), we carried out hydraulic fracturing experiments using hydrate-bearing clayey silt specimens with and without confining pressure. Tetrahydrofuran (THF) was used to synthesize hydrate in sediment. The breakdown pressure and its mechanical implications were analyzed. The failure process was visually presented, and the internal structure of the fractured specimen was revealed by X-ray computed tomography (CT). The results indicate that hydrate-bearing clayey silt can also be fractured effectively, and the failure process can be divided into the initial tensile failure stage and the following erosion stage. According to the experimental results, hydraulic fracturing was considered to be an effective stimulation method in gas production from fine-grained hydrate reservoirs but should be implemented with other production countermeasures to ensure long-term and efficient gas production.