In recent years

exploration of the Paleogene ultra-deep gas reservoirs in the Qikou Sag has been fruitful. Yet no researches have been performed on the seismic response features of these gas reservoirs and relevant gas detection techniques

impeading exploration to some degree. In an attempt to solve these problems

a comparative study on various spectral decomposition methods was performed according to the typical frequency domain responses of the ultra-deep gas reservoirs

i. e. high-frequency attenuation and low-frequency resonation. In addition

according to the features of the ultradeep gas reservoirs

instantaneous wavelet absorption and amplitude to frequency ratio attribute were employed to detect gas-bearing intervals and their boundaries. The result shows that the spectral decomposition method is the basis of abnormal gas-bearing reservoir detection. The Short Time Fourier Transformation through Hanning time function with a time window length being two times of average distance between two through of seismic wavelets is suitable for detecting lowfrequency abnormaly of gas reservoir with high resolution both in time and frequency domains. The results of gas detection with these techniques match the drilling results of the new exploratory wells

verifying the effectiveness of these methods in ultra-deep gas reservoir detection in the Qikou Sag.