The invention discloses a method for extracting
natural gas hydrate through CO2 / N2 underground replacement. The method includes that CO2 / N2 is injected into a
hydrate layer,
temperature and pressure in a well are controlled, replacement reaction is carried out to obtain
methane and CO2 / N2
hydrate, extracting of the
natural gas hydrate is achieved, through the horizontal abutting joint well technology and the fracturing technology, the contact area of the reaction is enlarged, and extracting efficiency is improved; first,
well drilling, well cementation and well completion of a horizontal abutting joint well are carried out, according to the
layer thickness and the range of the hydrate, the length and the layer number of a horizontal well section are confirmed; then the fracturing technology is carried out on a layer to be extracted in the mode of staged fracturing; and
fracturing fluid is removed, depressurizing extracting is carried out, after a period of time, extracting speed is reduced obviously, CO2 / N2 is injected in, the pressure in the well is controlled, and replacement extracting is carried out. Efficient replacement extracting of the
natural gas hydrate is achieved, environment benefits and economical benefits are remarkable, and the method can be used for large-scale extracting of the natural gas hydrate in a freeze soil area and the natural gas hydrate.