Abstract
The Early Cretaceous Biyadh and Shu'aiba formations form giant carbonate reservoirs with complex architectures and heterogeneous reservoir characteristics. This paper presents an integrated research where, core data, wireline logs, biostratigraphy and stable isotope data are integrated to constrain the stratigraphic architectures for reservoir characterization. The study also provides a new regional and global correlation that has significant implications on the evaluation of paleo climate and glacio-eustatic controls of the Lower Cretaceous systems. The Biyadh Formation consists of a composite sequence and four high-frequency sequences. S1 and S2 formed the TST with chalky mudstone facies that shallow up to skeletal grainstone of S3 and S4. The Shu'aiba Formation consists of a 2nd-order sequence, comprised of four 3rd-order sequences and ten high-frequency sequences. S1-S3 record the initial TST followed by the regional MFS (K70) and the deposition of an extensive Lithocodium/coral facies. S4-S6 marks the onset of rudist buildup that changed laterally to fore-bank, slope and basinal settings with basinward clinoform geometry, followed by HST of shallow lagonnal milliolids packstone facies of S7 and S8. S9 and S10 occured on the platform edge recording progradational systems formed during a major forced regression in the Late Aptian. They composed of a lowstand wedge of argillaceous mudstone that shallow upward to grainy marginal facies. A refined position of K70 and K80 and their relation with the global sea-level changes and perturbations in the Earth system have been proposed. Evidences of glacial events during the Aptian are recorded within the Shu'aiba sequences alternating with warming events associated with nannoconids crisis and Oceanic Anoxic Event (OAE 1a). The stratigraphic record in this study and their global correlation suggests that the Barremian stage was dominated by warm greenhouse interval, followed by rapid climate change of possibly more transitional interval in the Aptian associated with glacial events.