Sweetness analysis of Lower Goru sandstone intervals of the Cretaceous age, Sawan gas field, Pakistan

Abstract

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 non-producing 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.