Application Of Acoustic Full Waveform Logging In The Interpretation Of Natural Gas Hydrate Reservoir

Natural gas hydrate is a new unconventional energy source with greatpotentialities, which is expected to be ideal alternative energy of oil and natural gas.Gas hydrate is mainly distributed on the sea bottom sediments and permafrost. Theseabed sediment mainly is the quaternary new deposits with mud, clay and siltyclay.Well logging is an indispensable geophysical method in gas hydrate researchbecause of its ability to identify natural gas hydrate reservoir and to estimatereserves. Acoustic full wave logging contains abundant acoustic information. Theparameters such as amplitude, energy attenuation and slowness of compressionalwave, shear wave and stoneley wave, can be widely used in the study of the elasticmechanics properties of reservoir and of oil and gas evaluation.In order to study the application of acoustic full wave logging in gas hydratereservoir, conventional logging and array acoustic logging data in Cascadia hydratereservoir have been gathered, velocity of longitudinal wave and shear wave hasbeen extracted, and then the elastic properties of hydrate reservoirs has beenstudied. It includes the following several aspects in detail:(1) calculate the elasticparameters of the formation and summarize the change rule, then createtemplates identifying gas hydrate reservoir by elastic parameters;(2) study themodel applying for unconsolidated sandstone(Hashin-Shtrikman-Hertz-Mindlinmodel and cement model),construct the relationship between gas hydrate saturationand elastic parameters such as bulk modulus, shear modulus and Poisson’s ratio;(3)process the logging date from study area by Hashin-Shtrikman-Hertz-Mindlinmodel and cement model, calculate the gas hydrate saturation and compare to theresult from Archie’s formulas. It turned out that the saturation from cement modelis more agreement with that from Archie’s formulas when the gas hydratesaturation is low, whereas the result from contact mode and floating mode is betterwhen he gas hydrate saturation is high. The results provide an effective method for identifying gas hydrate reservoir,and verify the applicability of the elastic modulus model in the interpretation of gashydrate reservoir.