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 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.

3D static reservoir modelling to evaluate petroleum potential of Goru C-Interval sands in Sawan Gas Field, Pakistan

“…Basement induced NNW to SSE wrench faults cut the whole sedimentary section till Cretaceous (Kazmi, 1979;Kazmi and Rana, 1982). These faults form as a single rooted system within the basement and changes character to a multiple fault system (making negative flower structures) near the Upper Goru formation until terminating against the tertiary unconformity (Azeem et al, 2018). Uplifting of Jacobabad-Khairpur high happened in the Late Tertiary which controlled the sedimentation of the reservoir units of Lower Goru Formation (Berger et al, 2009;Azeem et al, 2016;Khan and Khan, 2018).…”

Controls on Reservoir Heterogeneity of a Shallow-Marine Reservoir in Sawan Gas Field, SE Pakistan: Implications for Reservoir Quality Prediction Using Acoustic Impedance Inversion

“…The lower zone of the LGF is also distributed into D, C, B, and A-intervals ( Figure 1c). The C-sand interval and B-sand interval of the Cretaceous age of the LGF acts as the primary and secondary reservoirs within the study area [32]. The principal lithologies of the LIB are shelf clastics and non-clastics, and marine-shales [47].…”

“…The results of the inversion analysis highlighted substantial vertical and lateral heterogeneity within the LGF. The deposition of the shallow-marine LGF is feasibly related to the presence of the narrower basement-rooted NNW-SSE wrench faults [32,33]. Hence, various shaly-sand and shale facies were conserved in the reservoir sands.…”

“…Recent studies conducted in the LGF of the SGF were performed to highlight the possible gas-bearing sweet zones [31,32]. Various authors performed multiple post-stack inversion methods to calculate the reservoir parameters [33,34].…”

“…Various authors performed multiple post-stack inversion methods to calculate the reservoir parameters [33,34]. However, their studies were based only on attributes [27,28,31], inversion techniques [32][33][34], or well logging [29,35]. None of those studies have provided comprehensive research to incorporate all the necessary methods to present thorough research for classifying the reservoir thickness, quantitative and qualitative assessments of facies heterogeneity, and the factors controlling the reservoir heterogeneity of the Lower Goru sands (LGS).…”