Distribution of horizontal permeability coefficient of the cover layer of HBS at Site W18/19 of Shenhu area

Horizontal permeability coefficient (HPC) of the cover layer of hydrate bearing sediment(HBS) is one of the crucial factors that affect engineering design for marine hydrate production test. Based on the piezocone penetration test (CPTU) data obtained from the calcareous cover layer of hydrate formation at site W18/19 of the Shenhu area, different HPC estimation models based on the dislocation theory were analyzed, together with their corresponding adaptability to calcareous cover clay in the Shenhu area of northern South China Sea. Finally, the vertical distribution of HPC value for the calcareous cover clay of HBS at the site of W18/19 was predicted and analyzed using the above prediction models. The research results show that the Elsworth (2005) method is not adapt for HPC evaluation at site W18/19. Totally, HPC value at site W18/19 ranges from 0.1×10^-8~4×10^-8m/s and increase gradually with depth. In the interval shallower than 30mbsf, HPC values are vastly fluctuated because of some disturbance. In the interval below 30mbsf, of which the HPC values range from 0.1×10^-8~0.6×10^-8m/s, however, the gaps from different prediction models come closer. Prediction results indicate that pore-pressure diffusion model and diffusion function are two basic factors that lead to the gaps among HPC values obtained from different models.