Electrical Resistivity

An increase in resistivity results from the formation of gas hydrate, which partially fills the pore spaces. It is primarily the saline fluids within the pores that controls the resistivity. Thus, an allowance must be made for the in situ salinity of the pore water. We have shown (Hyndman et al. 1999) that hydrate concentration and in situ pore fluid salinity may be estimated simultaneously from log resistivities and from the pore fluid salinity and porosity measurements made on recovered ODP core samples. The in situ pore fluid resistivities are calculated to be about 80% of seawater; these low salinity fluids are probably produced at greater depths by hydrate dissociation as the base of the stability field has moved upward with time. The hydrate saturation in

Chlorinity (mM)

400 500 600

Chlorinity (mM)

400 500 600

Resistivity Permafrost

Figure 12. (a) Chloride concentration versus depth at Site 889/890. Average concentration at Site 888 represents the reference chlorinity. (b) Lower horizontal scale gives approximate concentrations of hydrate in pore spaces, estimated from chlorinity dilution.

Hydrate (%pore space)

Figure 12. (a) Chloride concentration versus depth at Site 889/890. Average concentration at Site 888 represents the reference chlorinity. (b) Lower horizontal scale gives approximate concentrations of hydrate in pore spaces, estimated from chlorinity dilution.

the 100 m interval above the BSR is calculated to be 25-30% (Fig. lib). Similar hydrate saturation values of 1726% were obtained from seafloor electrical sounding experiments (Yuan and Edwards, 2000).

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