Study on the Production of Gas Hydrates and Underlying Free Gas by Horizontal Well Under Different Directions of Hydraulic Fracturing

Abstract

In most of gas hydrates reservoirs, the low permeability of sediments limits the commercial production of gas hydrates. Hydraulic fracturing is a good way to improve the permeability. However, how to choose a suitable hydraulic fracturing direction during hydrate production is still unknown. In this study, the depressurization induced gas hydrates and free gas production by a horizontal well under different directions of hydraulic fracturing was numerically studied in a 3D model. Results showed that, compared to no hydraulic fracturing, the increase range of hydrate dissociation volume and gas production was largest when the hydraulic fracturing was applied in YZ plane. Although the hydraulic fracturing in YZ plane obtained the highest gas production volume, the connection of the production well with the upper and lower strata was earlier, which reduced the final gas to water ratio. For hydraulic fracturing in XY plane, the connection of the production well with the upper and lower strata was delayed, thereby obtaining the highest gas to water ratio. Furthermore, the existence of the underlying free gas layer could reduce the hydrate dissociation rate at the bottom boundary of hydrate layer. This study could provide some guidance for gas hydrates production by hydraulic fracturing.

Keywords: Hydraulic fracturing direction, Gas hydrates, depressurization, Free gas layer, Horizontal well