Sandstone intervals of the Lower Goru Formation of the Cretaceous age are proven reservoir intervals in the middle Indus Basin, Pakistan. However, based on seismic data interpretation, it is difficult to differentiate payable gas sand from non-payable gas sand. Various types of post-stacks seismic attributes are extracted and analyzed to differentiate payable gas sand from non-payable. The analysis reveals that average instantaneous frequency, peak spectral frequency, average instantaneous phase and sweetness seem to be more effective attributes along with energy half time. Sweetness attribute map shows two sweet spot below the targeted window which indicate to the presence of gas play. Statistical analysis is also carried out to find the associations between seismic attributes and thickness of gas layer values. Cross plots of these attributes were quantified through regression analysis. A good correlation with regression coefficient (R 2 ) [ 0.78 is found between seismic attributes and gas layer thickness except average instantaneous phase attribute, which lays the foundation for predicting the thickness of gas reservoir.
B and C sands of the Lower Goru Formation of Cretaceous are proven reservoirs in different parts of the Middle and Lower Indus Basin, Pakistan. Most of the discoveries in this basin have been made in structural traps. However, in Sawan gas field; structural inversion, deep burial depth and heterogeneity of reservoir intervals make it difficult to demarcate the sweetness zones through conventional seismic analysis. In this work, different data sets have been integrated through constrained sparse spike inversion to mark sweetness zones in B and C sands of this formation. C sand contains four sweetness zones; the main sweetness zone is located towards the east while three subtle sweetness zones were identified towards the west of Sawan fault. The location of producing and nonproducing wells within the sweetness and outside of sweetness zones confirms the credibility of this work. B sand includes three sweetness zones located towards the west of Sawan fault. Moreover, inverted porosity results not only show good agreement with the porosity log of blind well (Sawan-02) but also show good matching with the core porosities. Hence integration of different data sets leads to demarcate the accurate location, size and extent of the sweetness zones.
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