Identification of Tuning Effects Using Analytically Computed Tuning Curves – Case Study

Hydrocarbon reservoir prospecting within pinching-out layers is difficult. DHI analysis can lead to false conclusions. Seismic image depends not only on lithology of reservoir layers, porosity and hydrocarbon saturation but also on their thickness. Interference of reflected signal from top and bottom of a layer can result in increase or decrease of amplitude. This phenomena is observed in a wide range of thickness. The paper presents procedure interpretation of seismic amplitude anomalies caused by pinching-out layer using analytically calculated tuning curve. The curve was computed on the basis of wavelet shape and distribution of the reflection coefficient at the top and bottom of a single layer. In first stage the curve was compared with a curve obtained on the basis of the convolutional model of the seismic trace (synthetic section of the wedge model). Positive results were obtained what allowed to apply the procedure to amplitude maps derived from recorded data. Analysed seismic data include pinching-out Cenomanian sandstones creates base of the central part of the Carpathian Foredeep toward the east of Cracow (Poland). Procedure application resulted in identification anomalies caused by tuning effect. The lack of gas saturation was also determined in the analyzed area.