Abstract：It is always a difficult problem to accurately identify the formation condition of gas hydrates in fluid inclusions in conventional ways. The present paper introduces a new method to get the formation condition of methane hydrate in natural fluid inclusion by in situ Raman spectroscopy. The researched fluid inclusion is in a CH4-H2O system identified by Raman spectroscopy at room temperature. In order to obtain the Raman spectra of methane hydrate,the experimental temperature was controlled in three ways,and the Raman spectra of methane hydrate and ice were obtained at -170 ℃ in the third way. The results of in situ Raman spectroscopy show that the temperature of methane hydrate forming in the authors’ interested inclusion is 7.5 ℃. According to the equilibrium between water and methane hydrate in the CH4-H2O system,the authors’ computed the pressure for the methane hydrate formation to be 5.587 3 MPa. The authors study shows that the in situ Raman spectroscopy is an effective method to obtain the formation condition of gas hydrates in fluid inclusions.
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