Effect of permeability anisotropy on depressurization‐induced gas production from hydrate reservoirs in the South China Sea

Abstract

The permeability anisotropy (ie, horizontal, kr, to vertical, kz, permeability ratio) of gas hydrate reservoirs may be a significant factor that affects hydrate dissociation and gas production. Here, site SH2, a candidate for field testing comprising a clayey silt gas hydrate reservoir in the Shenhu area in the South China Sea, was chosen to investigate the effect of permeability anisotropy on gas production behavior through numerical simulations. The spatial distribution of physical fields (ie, pressure, temperature, and saturation) and the evolution of gas and water recovery are comparatively analyzed. The simulation results show that permeability anisotropy has a significant impact on gas extraction, especially when the horizontal permeability is higher than the vertical one. The sensitivity analyses indicate that permeability anisotropy in both medium‐permeability (10‐100 mD) and low‐permeability (1‐10 mD) sediments are conducive to hydrate dissociation and that a higher horizontal permeability is more favorable for gas production. Comparatively, permeability anisotropy in low‐permeability sediments is not beneficial for improving production efficiency. In addition, our work also suggests that heterogeneous hydrate saturation in a reservoir‐scale model should be employed in future predictions because the gas production potential will be overestimated in a homogeneous reservoir under the same conditions. These findings contribute to a clear understanding of the influence of reservoir properties on gas hydrate dissociation processes and provide a reference for future field trials and commercial production.

Numerical simulations of depressurization‐induced gas production from hydrate reservoirs at site GMGS3‐W19 with different free gas saturations in the northern South China Sea

“…Therefore, we specify different values of r rz for the reservoir (ie, r rz = 1, 5 and 10) in our modelling to analyze the effect of permeability anisotropy on gas production, which are consistent to the field permeability anisotropy values obtained from laboratory tests 43,72,74 and the general assumptions adopted in most numerical simulations. 44,46,49 Consequently, the absolute isotropic/anisotropic permeability of the hydrate layer ranges from 10 mD to 100 mD, and the absolute isotropic/anisotropic permeability of the gas layer is mainly between 2 mD and 20 mD. Case 2 and Case 4 are preferred as the corresponding reference cases.…”

“…This outcome is consistent with the gas production behavior predicted in a low-permeability Class III hydrate reservoir. 44 Therefore, increasing horizontal permeability as much as possible may lead to better gas production performance during long-term production.…”

“…42,43 Permeability anisotropy influences the fluid flow behaviors, pressure propagation, and heat transfer in the reservoir during production. 44 Specifically, increasing horizontal permeability is conducive to hydrate dissociation and fluid migration in the lateral direction, which are essential to longterm gas production. [45][46][47][48] Feng et al 49 investigated the effect of permeability anisotropy on gas production behavior using a horizontal well by depressurization in a sand-dominated hydrate reservoir in the eastern Nankai Trough.…”

Types and Quantitative Characterization of Microfractures in the Continental Shale of the Da’anzhai Member of the Ziliujing Formation in Northeast Sichuan, China

“…Fracture studies in the shale gas exploration stage can therefore provide a reference for the optimal areas for shale gas exploration [6][7][8][9]. In the development stage of shale gas reservoirs, the effectiveness and permeability anisotropy of fractures directly affects the pattern of the deployment of the extraction wells and the reservoir fracturing reformation [10][11][12][13], which is an important reference for horizontal well deployment and geosteering [14]. In addition, the existence of shale cracks provides storage space for shale gas [15][16][17].…”

Gas Production from Methane Hydrate Reservoirs in Different Well Configurations: A Case Study in the Conditions of the Black Sea

“…2,3 About 97−99% of methane hydrates exist in the marine environment. 4,5 According to the reserves estimations made between the 1970s and the 2010s, the amount of CH 4 in all CH 4 hydrates in the world ranges from 2.0 × 10 2 to 7.6 × 10 6 standard trillion cubic meters (tcm). 6 Even at pessimistic estimations, the amount of technically recoverable CH 4 from CH 4 hydrates is in the range of 300 tcm.…”