Studies On The Complex Resistivity Characteristics And Saturation Calculation Model Of Natural Gas Hydrate Bearing Porous Media

Because of its extremely strong gas storage capacity,natural gas hydrate is considered to be a new kind of energy mineral resource with huge potential.Experimental study on electrical properties of natural gas hydrate could provide basis and calibration data for exploration and resource evaluation of hydrate in the field.Electrical testing technique not only is an effective technique to identify the formation and dissociation process of hydrate and to investigate its dynamic characteristics,but also plays an important role in the exploitation of natural gas hydrate and analogue experiment.The widely used resistivity parameter is unable to characterize the electrical properties of hydrate bearing sediments comprehensively during electrical simulation experiment,while the complex resistivity testing method can realize the measurement of electrical parameters within a wide range of frequency.Improve the accuracy of hydrate saturation calculation to provide data base for hydrate exploitation.Based on the system used to test impedance spectroscopy of methane hydrate,the complex resistivity parameter was obtained based on the measured impedance spectroscopy of the methane hydrate-porous medium-brine of 3.5% NaCl.The complex resistivity variation process of methane hydrate decomposition.The frequency dispersion characteristics of complex resistivity and the effects of hydrate saturation were analyzed.Several commonly used complex resistivity models were discussed.The parameters of the several models were fitted through experimental data,based on which the applicability of the models were evaluated and compared.Finally a model of complex resistivity was proposed for hydrate saturation estimation suitable for porous media system containing methane hydrate.It has been demonstrated that complex resistivity of porous media system containing hydrate can effective identify saturation change of hydrate decomposition process.The complex resistivity of porous medium containing methane hydrate exhibits remarkable frequency dispersion characteristics within the range of 0.1 Hz~1 MHz.There is a close relationship between the methane hydrate saturation and characteristic parameters of frequency dispersion.The frequency dispersion characteristics of complex resistivity becomes more significant with the decrease of hydrate saturation.The amplitude,real part and imaginary part of complex resistivity vary linearly with the test frequency in the double logarithmic coordinate within the range of 0.1Hz~10Hz,and there is a nearly linear relationship between the absolute values of fitting straight line slope and hydrate saturation.The percent frequency effect of the amplitude and real part of complex resistivity decreases linearly with an increasing hydrate saturation within the range of 10 Hz~1 MHz.Warburg model can be used for complex resistivity data interpretation of hydrate-bearing porous The empirical parameters(cementation index m and saturation index n)of the empirical formula of Archie are affected by the frequency of testing,and the dispersion phenomenon is obvious.Under the test conditions in this study the impedance spectroscopy of porous medium containing hydrate can be fitted through an equivalent circuit model with a resistor and capacitor in series,and the resultant complex resistivity model can be used to calculate the gas hydrate saturation.