Evaluating hydraulic permeability of hydrate-bearing porous media based on broadband electrical parameters: A numerical study

Monitoring of the reservoir permeability in hydrate exploitation process is of great significance to the dynamic optimization of production strategy. A new methodology for evaluating the effective permeability (kh) of hydrate-bearing porous media was proposed based on broad-frequency-band (mHz – MHz) electrical parameters. Finite-element models were established for acquiring the electrical and hydraulic parameters numerically. The influences of hydrate saturation (Sh) and pore growth habit on the high-frequency complex permittivity (ε∗) were analyzed. The Sh and absolute permeability (k0) without hydrates were estimated from the high-frequency ε∗ spectrum and low-frequency quadrature conductivity (σ''), respectively. The models of normalized permeability (kn) were introduced to establish the kh models. It has been demonstrated that: (1) the σ'' cannot be used to discriminate variations of Sh for grain-coating (GC) hydrate cases, while the ε∗ spectra from 104 to 106 Hz covering the hydrate polarization frequency can be used to quantify the Sh for both the pore-filling (PF) and GC hydrates; (2) the proposed two-step mixing procedure is effective to reproduce the high-frequency ε∗ spectra of porous media composed of skeleton particles, hydrate and pore water based on classical dielectric mixing models; the Sh estimation models can be derived by combining the Bruggeman and Bruggeman-Hanai models and combining the Maxwell Garnett and Bruggeman-Hanai models, and the maximum relative error (ER) of model predicted Sh is 5.67 % and 10 % for PF and GC hydrates, respectively; (3) the k0 can be estimated from the σ'' in the frequency range dominated by electrical double layer polarization; the kh models can be obtained by combining the Sh, k0, and kn models; the ER of model computed kh is within ±25 and ± 30 % for PF and GC hydrates, respectively. The proposed methodology provides a theoretical foundation for developing permeability monitoring techniques of hydrate reservoirs. •Novel method for evaluating effective permeability of hydrate-bearing porous media based on broadband electrical parameters was proposed.•Low-frequency quadrature conductivity was used for estimating absolute permeability of hydrate-free porous media.•High-frequency spectrum of complex permittivity including hydrate polarization mechanism was used for estimating hydrate saturation.•Two-step dielectric mixing procedures were proposed for modelling dielectric responses of three-component porous m