Research And Application Of Component Elastic Parameters In Marine Gas Hydrate Exploration

The main work of this paper is use a new geophysical inversion method,which was proposed by Professor Niu Binhua--The Component Elastic Model Inversion Method,in gas hydrate exploration.Hydrate exploration mainly using geochemical method at the present stage.But in the first condition,the geochemical methods to obtain the data of pore free gas of drilling core and the characteristics of geochenmical indices must have a lot of drilling.At this present the geochemical methods only use in IODP and a few advanced countries because of its technical difficulties and high cost.And geophysical methods at this present stage tend to focus on the overall data,it is difficult to describe the distribution of geophysical parameters of hydrate fine.Therefore,there have a great significance to using the geophysical method which is more economical on exploration of the sea.The original data of this work is form the 5 sites of the expedition 311.Expedition 311 is located in a terrain height of the gas-hydrate ridge in southern accretionary wedge of Cascadia subduction zone out of Oregen,North America.This paper obtained 4 items of data such as overall density,velocity and porosity by drilling of expedition 311,inverting the 12 items of component elastic parameters such as density and velocity of framework and fluid through the component elastic parameters inversion.These elastic parameters reflect the basic information of the framework and fluid.First,search free hydrocarbon zone based on these elastic parameters.Then combined with the bottom simulating reflector(BSR)data to determine the lower bound of methane hydrate stability zone.And determine upper bounds of methane hydrate stability zone through the high value region of P-wave velocity.After all fine division to the methane hydrate stability zone reservoir,evaluate a approximate content of solid gas hydrate based on the result of compared with the framework density and standard framework rock density,standard hydrate density.But in fect,because of the special geological conditions,the seafloor rock are high porosity,low semi cemented,the analytical method which was used in the onshore drilling does not apply to the exploration of hydrate.A fter a lot of work on one site of expedition 311,we identify a effective analytical method which is suitable for the local geological condition.Compared and analyzed this result and the geochemical result to evaluate the feasibility of this method.After the above work,obtain the methane hydrate stability zone of the 5 sites of expedition 311.This result accord with geochemical result well,but still have a little discrepancy on some region,especially in the shallow strata,geophysical method is very difficult to find the occurrence of gas hydrate.So,we need more work to improved model and inversion calculation.Above all,the component elastic parameters inversion method applicate to the exploring deep ocean gas hydrate is feasible and have a further development.