Conventional approaches in time-lapse studies often ignore seismic transmission effects such as attenuation. For example, gas injection may produce changes in the factor Q. Consequently, amplitude and phase variations in time-lapse seismic data may be wrongly interpreted To correct such spectral distortion, we present a cross-equalisation technique based on differential Q-controlled calibration. The methodology should be applied in a 4D context when frequency attenuation variation occurs inside a reservoir or in the overburden. <br>The spectral characterisation of the data is tested for two different techniques: Multi-taper and Wavelet decomposition. We present the advantages and the disadvantages specifically for time-lapse studies. <br>The cross-equalisation is defined as "attribute-driven-processing". Using the constant Q definition, an attribute, called 4DQ, is computed simultaneously on the base and monitor with linear fitting of the logarithmic spectral ratio.<br> The calibration, controlled by the 4DQ attribute, removes the effect of the absorption variation. <br>The methodology is tested on real data. The measured 4DQ attribute shows a clear spatial correlation with the reservoir in production, but its direct interpretation seems to be critical. Furthermore, the calibration process and a single-Q compensation are applied providing a high-resolution 4D signature.


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