Analysis of direct hydrocarbon indicators in the case of Pannonian sandstones Miklós Kóbor Department of Geophysics & Space Sciences, Eötvös Loránd University, Budapest

Outline Introduction Aims Direct Hydrocarbon Indicators Seismic attributes Qualitative analysis Crossplots Conclusions

Introduction Attributes are simply defined as information extracted or computed from seismic data. Seismic attributes are often used as tools for direct hydrocarbon indication. OpendTect 4.0 was applied for the investigation. 2 study area 1.: Identified reservoirs with 2 gas producing wells (T-1, T-2) 2.: Possible hydrocarbon (gas) prospects with 2 drilling target (C-1, C-2)

Aims Use the seismic data of already producing wells to investigate the effectiveness of the various attributes. Use the observations as analogy for other possible hydrocarbon prospects in similar lithological settings, where well log data are not yet available. Combination of two different types of attributes to investigate and visualise on crossplots. Distinguish the hydrocarbon bearing rocks on the crossplots.

Direct Hydrocarbon Indicators Bright spot Dim spot Flat spot Low frequency shadow below the suspect reservoir Polarity change T-2, gas producing reservoir T-1, gas producing reservoir C-1, drilling target C-2, drilling target

Seismic Attributes Instantaneous Phase Instantaneous phase makes strong seismic events clearer. Θ(t): instantaneous phase trace q(t): quadrature seismic trace r(t): real seismic trace Complex seismic trace, Taner et al., 1979

Seismic Attributes 2) Event peakedness Event peakedness is the ratio between the Extremum value and distance between next and previous zero crossings (ZC). Useful tool to quantify the quality of a horizon in seismic data. Helpful for users to find the distance between two events. Basic sketch of single trace Event attributes

T-1, Producing gas reservoir, Energy Qualitative Analysis T-1, Producing gas reservoir, Energy 18 various attributes were computed (Energy, Frequency attributes, Instantaneous attributes, Event attributes, etc.) Visualized on seismic volumes The anomalies were classified in 4 categories: - Excellent -Significant -Observable - No anomaly The observations were summarized in a table

Qualitative Analysis C-1, Drilling target, Energy Mintaszöveg szerkesztése Második szint Harmadik szint Negyedik szint Ötödik szint

Qualitative Analysis -Significant -Observable - No anomaly C-2, Inst. Ampl. 2nd derivative, Discoverable C-2, Average Frequency, No anomaly T-1, Event peakedness, Significant T-1, Energy, Projecting 18 various attributes were computed (Energy, Frequency attributes, Instantaneous attributes, Event attributes, etc.) Visualized on seismic volumes The anomalies were classified in 4 categories: - Excellent -Significant -Observable - No anomaly The observations were summarized in a table Attribute T-1 T-2 C-1 C-2 Instantaneous phase Observable No anomaly X Event peakedness Significant

Crossplots Event Peakedness vs. Intantaneous Phase T-1, gas producing reservoir Mintaszöveg szerkesztése Második szint Harmadik szint Negyedik szint Ötödik szint

Crossplots Event Peakedness vs. Intantaneous Phase T-2, gas producing reservoir Mintaszöveg szerkesztése Második szint Harmadik szint Negyedik szint Ötödik szint

Crossplots Event Peakedness vs. Intantaneous Phase C-1, drilling target Mintaszöveg szerkesztése Második szint Harmadik szint Negyedik szint Ötödik szint

Crossplots Event Peakedness vs. Intantaneous Phase C-2, drilling target Mintaszöveg szerkesztése Második szint Harmadik szint Negyedik szint Ötödik szint

Conclusions Seismic attributes are useful tools to visualize hydrocarbon prospects. Attribute vs. Attribute crossplots give more reliable information than single attributes. On the crossplots we can distinguish gas bearing sandstones.

Acknowledgements MOL Hungarian Oil and Gas Company Budapest, Hungary László Pollner MOL Hungarian Oil and Gas Company Budapest, Hungary Endre Dombrádi Department of Geophysics & Space Sciences, Eötvös Loránd University, Budapest Márta Pócsik