In exploration for natural gas hydrates, drilling, coring and well logging are the most important access to make deep understanding of the nature of hydrate reservoirs, besides the seismic prospecting methods. Because of the harsh conditions for hydrate stability and the complex of occurrence formations, the drilling and coring generally have a great difficulty and high cost. Therefore, the well logging becomes the priority method. The resistivity and sonic logging method, which were applied as the earliest logging method in the evaluation of hydrate reserviors, have been continuously applied ever since and the evaluation results derived from them have a relative accuracy and reliability. Other logging tools, such as borehole imaging, density, electromagnetic, nuclear magnetic resonance, etc. are also used to make integrated interpretation and evaluation for the hydrate reservoirs. Until now the applied porosity and hydrate saturation evaluation models are better suitable to the homogeneous reservoirs. However, they still need to be amended or improved for the anisotropism (e.g., fracture sediment) and shale-rich reservoirs. In addition, the external factors such as drilling fluid washout and invasion will also affect the well logging results. The combination of various well logging methods is an effective way to improve the accuracy of identification and quantification of hydrate reservoirs.

Finite element equations are introduced when the wet deformation is considered under Coupled Deformation and Seepage Fields. The principle of the initial stress increment method, by which the wet deformation can be calculated, is detailed dealt with. One earth-rock dam is stimulated by finite element method during water storage. By applying nonlinearity elastic model, give the discussions on the impact on stress field and displacement field by the wet deformation. The results show that the wet deformation weakens the uplift by buoyancy. Those results gained by numerical method may provide reference to engineering practice.

viscoelasto-plastic; double yield surface; equivalent sand wall; finite element; Abstract. Based on double yield elastoplastic model, one viscoelasto-plastic model is dealt with in detail. The method of transferring to equivalent sand wall is introduced when soft soil is treated by plastic drainage plate. The viscoelasto-plastic model and modified Cam-Clay model are applied into the finite element calculation of soft foundation treatment of a tailing dam. By comparison, it can be got that the displacement calculated by the viscoelasto-plastic model is closer to monitoring data than that calculated by modified Cam-Clay model. It demonstrates the reasonableness and efficiency of the viscoelasto-plastic model．