Well Logging Response Characteristics And Evaluation Of Gas Hydrate In Qilian Mountain Permafrost

Geophysical well logging plays an important role in identifying and evaluating gas hydrate-bearing sediments. The physical properties of gas hydrate and the effects of its formation on the properties of gas hydrate-bearing rock raise physical parameters anomalies of gas hydrate-bearing sediments such as resistivity, sonic and density. These anomalies are the basis of application of well logging technology to prospect gas hydrate.This study mainly identifies and evaluates gas hydrate-bearing sediments, and simultaneously researches on characters of geothermal field in Muli drilling in Qilian Mountain Permafrost, based on the logging and laboratory data of gas hydrate. The logging date, including that of electrical resistivity, sonic, natural gamma, density, temperature, caliper and inclination, is obtained through routine coalfield wireline logging. Core laboratory experiment mainly measures the porosity of 39 sandstone core samples and litho-electricity of 16 core samples in the Key Lab for Hydrodynamics and Ocean Engineering Institute of Mechanics, Chinese Academy of Sciences.In this dissertation, based on the temperature logging data and the logging data which is anomaly for permafrost, the depth of permafrost bottom is ascertained and the geothermal gradient under the permafrost is calculated by linear regression analysis of the temperature logging data. The logging data of gas hydrate-bearing sediment is analyzed to summarize logging response characteristics of gas hydrate in Qilian Mountain Permafrost, then, the occurring horizon of gas hydrate in the drilling site with anomaly phenomenon of gas hydrate is inferred though the summary. On the basis of litho-electric experiment, the porosity of gas hydrate-bearing sediment is calculated by the log data of resistivity and density. Compared with the porosity derived from core analysis, the porosity derived from resistivity agrees with it. At the same time, in-situ gas hydrate saturation is estimated by Standard Archie and Modified Archie equation, then, compared in-situ gas hydrate saturation derived from Standard Archie equation with that derived from Modified Archie equation. However, this respect should be further researched in the future.