| Natural gas hydrate is a crystalline solid material by water and gas molecules formed in the low temperature, pressure conditions. It looks like ice, fire can burn, commonly known as the "combustible ice". Foreign research started earlier for natural gas hydrate, made a lot of achievements. And domestic started late, based on the reference of foreign research experience, we studied on the geological effect, reservoir models and physical characteristics of natural gas hydrate, also achieved initial results. But for the natural gas hydrate exploration technology of terrestrial permafrost region is still in the exploratory stage, especially for geophysical exploration.In this paper, under the guidance of geological structure theory, through the study of the thickness of permafrost zone, analysis of well logging data and reflection seismic data, established the geophysical method for the analysis of the formation conditions of natural gas hydrate, the seismic response characteristics and physical characteristic s in terrestrial permafrost regions. combined with the geological structure feature, fracture development system and natural gas hydrate storage type of study area(This area is the fracture type, pore type of supplement), through attribute analysis of the reflection seismic data, trace integral inversion and prediction of AVO and other special processing analysis, We obtained the following results and understanding:(1) The study area is a fault and fracture development zone, it can provide migration channel and storage space for the formation of natural gas hydrate.(2) Through the analysis and comparison of the long-term temperature data and high precision electromagnetic spectrum data, we can get that the frozen soil layer in the study area between 80m-130 m, conducive to the formation of natural gas hydrate stability zone, and with the natural gas hydrate formation temperature and pressure conditions, namely the temperature below 0?, the pressure is between 2Mp-6Mp.(3) According to the conventional analysis of the known well logging data, reflection seismic data attribute analysis and special processing, etc., the physical characteristics of natural gas hydrate bearing layer is obtained: Low density, high electrical resistivity, low speed(relative to surrounding rock), natural gamma value decreases relatively etc. Seismic response characteristics as follows: middle and low frequency, middle or weak amplitude and desultorily, low energy, etc.(4) For seismic acquisition and processing in the plateau region of the Qilian Mountains, small trace spacing, small shooting distance and high coverage system is adopted and it has the advantage of data imaging effect. In the aspect of static correction, first break picking accurately, optimization of static correction and special processing method for residual static correction is helpful to improve the quality of the data.(5) Through the analysis of AVO inversion and AVO prediction and frequency analysis can effectively detect hydrocarbon anomaly, we can delineate anomaly range of natural gas hydrate in the region; it can provide favorable evidence for drilling deployment in combination with control action of structure. Synthetically,reflection seismic exploration is one of effective methods for detection of gas hydrate. |
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