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In the DF1-1 Gas Field in the Yinggehai Basin,South China Sea,the velocity-depth plot and velocity spectra show significant variations from a linear trend,exhibiting a distinct reversal phenomenon.Velocity parameters derived from velocity spectral analysis of the seismic data and sonic logs indicate that the interval velocity reverses below 2,100 m(2.2 s two-way time(TWT)) in the DF1-1 Gas Field.Some direct hydrocarbon indicators(DHIs) models developed for the shallow strata cannot be simply applied to the moderately to deeply buried strata for direct exploration target recognition because the velocity reversal has caused the middle-deep gas reservoirs to exhibit a moderate or weak seismic amplitude.The hydrocarbon indicator method of “Differential Interformational Velocity Analysis(DIVA)” with the aid of other hydrocarbon indicating techniques was employed to effectively identify DHIs in the middle-deep strata under velocity inversion.The result has shown that the DIVA technique can be effectively used as a DHI in both the shallow and the middle-deep strata in the study area with the shallow strata characterized by Type I DIVA anomaly and the middle-deep strata characterized by the Type II DIVA anomaly.
In the DF1-1 Gas Field in the Yinggehai Basin, South China Sea, the velocity-depth plot and velocity spectra show significant variations from a linear trend, exhibiting a distinct reversal phenomenon. Velocity parameters derived from velocity spectral analysis of the seismic data and sonic logs indicate that the interval velocity reverses below 2,100 m (2.2 s two-way time (TWT)) in the DF1-1 Gas Field. Home direct hydrocarbon indicators (DHIs) models developed for the shallow strata can not be simply applied to the moderately to deeply buried strata for direct exploration target recognition because the velocity reversal has caused the middle-deep gas reservoirs to exhibit a moderate or weak seismic amplitude.The hydrocarbon indicator method of “Differential Interformational Velocity Analysis (DIVA) ” with the aid of other hydrocarbon indicating techniques was employed to be effectively identified DHIs in the middle-deep strata under velocity inversion. The result has shown that the the DIVA technique can be effectively used as a DHI in both the shallow and the middle-deep strata in the study area with the shallow strata characterized by Type I DIVA anomaly and the middle-deep strata characterized by the Type II DIVA anomaly.