Multi-field and domain coupling numerical simulation of installation of suction buckets in methane hydrate bearing sands

Suction buckets demonstrate advantages such as simplified installation, low cost, and high construction efficiency, showing broad application prospects in deep-sea energy development. However, as methane hydrates (MHs) are widely distributed in seabed formations, the installation of suction buckets in marine hydrate bearing sediments will face engineering challenges caused by hydrate property variations. This study proposes a practical field-domain coupled numerical simulation method integrating multi-field coupling and discrete-continuum coupling, based on the commercial software PFC3D+FLAC3D and the multiphase flow analysis program TOUGH+HYDRATE for hydrate-bearing porous media. The method addresses suction penetration issues in methane hydrate bearing sands (MHBS). Firstly, the process of jacked and suction-assisted penetration in hydrate-free clean sands were simulated and compared with previous research outcomes to validate the coupling method. Subsequently, suction penetration processes in MHBS with an initial pore pressure of 8 MPa and hydrate saturation of 10% were simulated, with penetration characteristics analyzed. Key conclusions include: (1) During the penetration in MHBS, the soil mass inside the bucket exhibited "layered cracking", and the soil plug height showed a "stepped" increase with penetration depth, ultimately exceeding that in clean sands. (2) Penetration resistance, suction pressure, and drainage volume in MHBS significantly surpassed those in clean sand cases. Influenced by stratum cracking, both penetration resistance and suction pressure displayed notable fluctuations—peak values decreased while trough values increased with penetration depth. (3) Suction-induced variations in thermal-pressure-chemical fields and hydrate decomposition reduced the mechanical strength of MHBS. Compared to scenarios ignoring strength changes, penetration resistance and suction slightly decreased, while final soil plug height remained largely unaffected. (4) In MHBS, penetration rate positively correlated with penetration resistance and suction but showed weak correlation with soil plug height. This study provides valuable references for suction bucket construction in hydrate-bearing strata.