The identification of "bright spot" anomalies on seismic sections is a traditional qualitative express-method for predicting the gas saturation of hydrocarbon traps. But it is known, that such anomalies are not always coincide with gas fields. Experience shows that, in addition to fluid saturation, they can be caused by lithological heterogeneities. So in doubtful cases it is necessary to use more "heavy" quantitative methods of seismic data interpreting for «bright spot» anomalies analysis. One of such methods is simultaneous inversion, since it transforms the seismic amplitudes of prestack data into elastic parameters. At first, such transformation makes it possible to predict the distribution of lithotypes in sedimentary basins.
This article deals with the experience gained from the analysis of "bright spot" dynamic anomalies in one of the small petroleum basins. There was structural gas field in the area, marked on seismic sections by a dynamic “bright spot” anomaly and a structural trap with a similar dynamic anomaly. Since unsuccessful wells had already been drilled in the area adjacent to the trap, the interpreters were tasked to find out the nature of the indicated dynamic anomaly. As a result of simultaneous inversion of the specially processed prestack data, it was determined that for the gas field a dynamic “bright spot” anomaly is caused by an abnormally low acoustic impedance of the upper section of the gas-bearing reservoir. For the structural trap, a similar anomaly is due to the lithological heterogeneities of the anhydrite seal overlying the reservoir. As a result of the investigation it was concluded that the gas potential of the identified structural trap is not essential, probably due to its small size and ineffective hydrocarbon migration.
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