Integration of well logs for seismic-guided sand mapping in the Barail coal-shale sequence of Geleki Field

Abstract

Sandstones associated with Oligocene Barail coal-shale sequences form good reservoir facies and are oil producers in many wells of India's Geleki Field and adjoining areas. Mapping these sands using seismic attributes may lead to data that are difficult to interpret because sand-coal and shale-coal interfaces generate similar attributes. In such cases, seismic attributes may show the depositional geometry but with ambiguous lithology. The lithologic ambiguity may further be worsened by carbonaceous shales, which often occur in coal-shale sequences, and that shales may appear similar to sandstones in some log (e.g., gamma ray, resistivity, etc.) and interface properties. Integration of logs with seismic data improves lithologic discrimination and reservoir characterization. The log motifs (patterns) reinforce the interpretation of depositional environments and processes and log properties (magnitude) reduce the ambiguity in lithologic prediction. Seismic attributes and log properties can be integrated by finding interrelationships between these two types of data at control (wells) points. The interrelationships are used for seismic-guided prediction of log properties beyond the wells and generation of property volumes. The predicted volumes are interpreted in terms of lithology and other reservoir parameters (porosity, saturation, etc.).