Experimental Study On Hydrate Saturation In Porous Media Based On Characteristics Of Impedance

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 not only is an effective technique to identify the formation and dissociation process of hydrate and to investigate its dynamic characteristics,but also could provide basis and calibration data for exploration and resource evaluation of hydrate in the field.Therefore,studying on the impedance characteristics of porous media containing hydrate has important scientific and practical significance.The AC impedance spectroscopy testing method is better than the simple ones which only test resistivity parameters,for it can be used to test the variation rules of impedance(e.g.resistivity and reactance)of the tested system in a certain range of frequency.And thus,the electrical characteristics of hydrate can be understood further.In this paper,a system used to test impedance spectroscopy of methane hydrate was designed.Methane hydrate-porous media-brine of 3.5% was prepared as the object in this study.Then,its impedance spectrum was tested during the formation and dissociation of hydrate in porous media and the fixed value problem of the relevant empirical parameters of Archie formula was briefly discussed.At the same time,the variation rules of characteristic parameters of impedance spectroscopy and frequency dispersion degree of reaction system with hydrate saturation were analyzed.It is shown that the results are not the same when using different frequency of excitation source signal to carry out the impedance test.When the test frequency is 1.1 Hz,there is no obvious relationship between the hydrate saturation and the impedance spectroscopy parameters of tested system.When the test frequency is 10 746 Hz,however,there is a monotonic increasing linear relationship between the hydrate saturation and the impedance spectroscopy parameters of the tested system within a certain range of allowable errors.And also,by selecting the appropriate test frequency(such as 1 114 Hz)to test the impedance spectroscopy parameters of the reaction system,the test results can be used to calculate the saturation value of the system.Namely,it can be used to develop the measurement and calculation method of hydrate saturation.Besides,the frequency dispersion degree which is calculated by ratio and variance proportions of the impedance amplitude and hydrate saturation satisfy the monotone decreasing linear relationship.The same is true for the frequency dispersion degree which is calculated by difference of the phase angle.And finally,Archie formula is established under ideal conditions and has certain limitations.But,in practical application,we can test the samples,so as to determine the most suitable Archie parameters for the specific reservoir conditions.