Anisotropic Dielectric Properties of Fracture-Filling Hydrate Reservoirs in a Transversely Isotropic Background

Fracture-filling hydrate reservoirs represent a significant proportion of global gas hydrate resources, and dielectric methods have proven to be effective tools for hydrate evaluation in such reservoirs. However, for reservoirs where the host rock exhibits transverse isotropy (TI) and hydrate-bearing fractures are aligned, the anisotropic dielectric properties remain poorly understood, limiting the accurate assessment of hydrate saturation. We develop a theoretical model to address this gap by extending the Maxwell–Garnett mixing rule for aligned inclusions in an isotropic background to a TI background containing aligned penny-shaped fractures, incorporating the Eshelby tensor components for penny-shaped cracks in a TI medium. The model is validated against 3D finite-difference numerical simulations (R² > 0.99). Using this model, we systematically investigate the effects of hydrate distribution (floating vs. bridging), fracture porosity and fracture aspect ratio on the frequency-dependent anisotropic dielectric response. The results show that bridging hydrate causes a stronger reduction in dielectric constant and conductivity than floating hydrate. The effect of fracture porosity is significant at low hydrate saturations but negligible at high saturations. The effect of fracture aspect ratio depends strongly on both saturation and frequency, where at low saturations, decreasing the aspect ratio increases the dielectric constant at low frequencies but increases conductivity at high frequencies, whereas at high saturations, the effect is much weaker. The bridging hydrate consistently exhibits higher sensitivity to both fracture porosity and aspect ratio than the floating hydrate. The results provide a quantitative understanding of the effects of hydrate distribution on the anisotropic dielectric properties of fracture-filling hydrate reservoirs in a TI background, thereby contributing to a more reliable hydrate resource assessment in these complex formations.