Sensitivity Analysis of Multi–phase Seepage Parameters Affecting the Clayey Silt Hydrate Reservoir Productivity in the Shenhu Area

Abstract

Natural gas hydrate (NGH) is an important future resource in the 21^st century and strategic resource with potential for commercial development in the third energy transition. It is of great significance to accurately predict the productivity of hydrate bearing sediments (HBS). The multi–phase seepage parameters of HBS include permeability, porosity which is closely related to permeability, and hydrate saturation which has a direct impact on hydrate content. Existing researches show that these multi–phase seepage parameters have a great impact on HBS productivity. Permeability directly affects the transmission of pressure–drop and discharge of methane gas, porosity and initial hydrate saturation affect the amount of hydrate decomposition and transmission process of pressure–drop, and also indirectly affect temperature variation of the reservoir. Therefore, in this paper, considering the spatial heterogeneity of multi–phase seepage parameters, a depressurization production model with layered heterogeneity was established based on the clayey silt hydrate reservoir at W11 station in Shenhu Sea area. And then the Tough+Hydrate software was used to calculate, the process of gas production and seepage parameters evolution under different multi–phase seepage parameters were obtained, and the sensitivity analysis of the parameters affecting the clayey silt hydrate reservoir productivity was conducted. The research found that: (a) The HBS model with layered heterogeneity can better describe the transmission process of pressure and thermal compensation mechanism of hydrate reservoir. (b) Considering the multi–phase seepage parameters heterogeneity, the influence degrees of the parameters on HBS productivity was permeability, porosity and initial hydrate saturation in order from large to small, and the influence of permeability was significantly greater than that of other parameters. (c) The production potential of the clayey silt reservoir should not be determined only by the hydrate content or seepage capacity, but also by the comprehensive effect of the two. (d) Time scales need to be concerned when studying the effects of changes in multi–phase seepage parameters on HBS productivity.