Numerical investigation of natural gas hydrate production performance via a more realistic three-dimensional model

Numerical simulation plays a crucial role in the prediction of natural gas hydrate production performance. However, most existing models are two-dimensional or three-dimensional with idealized geometries and uniform parameter assignments, which cannot depict the effects of stratigraphic undulation and spatial variability of reservoir physical parameters on gas production. Therefore, a convenient method to convert the image information (more accessible) into parameter attribute values (required for model construction) was proposed in this study. Using the converted data of reservoir depth, thickness, and porosity, a more realistic three-dimensional model was innovatively constructed. Then, the influences of reservoir fluctuations and spatial variability of physical parameters on production performance were quantitatively analyzed. It was found that placing the production well in an elevated area can facilitate gas production. Specifically, Well 1 (located in the highland) had a 34.1% higher normalized gas production rate (i.e., production rate per unit well length) and a 14.9% lower normalized water production rate than Well 3 (located in the flat area) in the free gas layer. In addition to reservoir fluctuations, the exploitation efficiency of the gas hydrate-bearing layer was also affected by the thickness. The spatial variability of hydrate saturation and that of gas saturation in the study area were not very prominent, and the gas production rate obtained by the heterogeneous scheme was approximately 10% different from that of the homogeneous scheme. However, although the spatial variability of porosity was also not great (no more than 2%), when the cubic law was used to calculate the corresponding permeability, the gas production rate obtained by the heterogeneous scheme was nearly 20% different from that of the homogenous scheme. This study demonstrates the need to use a more realistic three-dimensional model for gas hydrate production performance prediction and is expected to provide an important reference for well location selection.