Abstract
In this paper, we used a method of combining reservoir stimulation technique (RST) with depressurization to investigate the conversion efficiency of marine natural gas hydrate (NGH) reservoirs in the Shenhu area, on the northern slope of the South China Sea, which differ in intrinsic permeability and initial NGH saturation conditions. We also analyzed the influence of the variable-stimulation effect on marine NGH conversion efficiency in different accumulation conditions, providing a reference scheme for improving the NGH conversion efficiency in the Shenhu area. In this work, we performed calculations for the variations in CH4 production rate and cumulative volume of CH4 in different initial NGH saturation, intrinsic permeability, and stimulation effect conditions. Variance analysis and range analysis methods were used to analyze the significance of these key factors and their interaction. Furthermore, we investigated the sensitivity of stimulation effect on NGH conversion efficiency. The simulation results showed that the stimulation effect has a significant influence on NGH conversion efficiency, and the influence of interaction between these three factors was not obvious. Possibly most importantly, we clarified that the sparsely fractured networks (N = 3) had a better effect for higher NGH conversion efficiency under higher saturation conditions. For lower permeability cases, the influence between sparsely (N = 3) and densely (N = 5) fractured networks were similar.
Highlights
The main objective of this study is to investigate the influence of reservoir stimulation technique (RST) on the conversion efficiency of natural gas hydrate (NGH) under different accumulation conditions such as initial NGH saturation, intrinsic permeability, and variable-stimulation effect of the depressurization method
We considered the interaction of various factors and used the whole simulation experiments method (L27 (3)13 ) to analyze the significance of intrinsic permeability k, initial NGH
In this work, using CH4 cumulative volume Qcv to represent NGH conversion efficiency, the depressurization exploitation time was set to five years, because the CH4 production rates were stabilized at this time
Summary
Natural gas hydrates (NGH) are white and pale yellow, solid, ice-like cage type crystalline compounds [1]; formed by small-molecule gases such as light hydrocarbons, carbon dioxide, and water under low-temperature and high-pressure conditions. These are known as “combustible ice” [2]. NGH is an alternate energy resource with great reserves [3], very clean natural gas can be produced from NGH deposits, especially from sandy turbidites, from which conventional hydrocarbons can be produced [4]. It is estimated that natural gas from NGH in sands are >40,000 Tcf [5,6]. NGH should be Energies 2018, 11, 339; doi:10.3390/en11020339 www.mdpi.com/journal/energies
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