A Sequence Stratigraphic Analysis of Fluvio-Deltaic Deposits using Facies Characterization and Wireline Logs Correlation: Case of the Upper Devonian Tahara Formation, Ghadamis Basin, Libya

The correlation between wireline logs and sedimentological data can provide a better understanding of reservoir architecture and sandstone interconnectedness. In this paper, we present the application of wireline log correlation and core results for sequence stratigraphic analysis to the Upper Devonian Tahara Formation, Ghadamis Basin. Sequence stratigraphic analysis indicates that the Tahara Formation is characterised by transgressive and regressive phases of deposition in response to changes in relative sea level. The overall succession stacks into two partial sequences separated by a Type 1 sequence boundary. The lower sequence below the sequence boundary represents a coarsening-upward prograding shoreline comprising sediments deposited as part of a highstand systems tract. Above the sequence boundary, the incomplete sequence 2, includes the Tahara sandstones. These are believed to have been deposited as part of a transgressive systems tract bounded at the top by a maximum marine flooding surface. The succession includes marine flooding surfaces of different hierarchical level which record a deepening of the depositional environment in response to sea-level rise. Both preserved sequences form part of a third-order cycle which in the upper part includes fourth-order higher frequency cycles. The deposition and distribution of facies within the sequences are controlled by different factors including rate of relative sea-level change, rate of subsidence and sediment supply. Gamma ray log shapes in the Tahara sandstones vary from funnel to roughly cylindrical shapes. The lower Tahara sandstone shows a serrate cylindrical gamma ray log shape in well CI-49 and AST2, and a funnel gamma ray log shape in well K1-1, A1-NC151 and AST1. The upper Tahara sandstone shows a funnel gamma ray log shape in well CI-49, a complex gamma ray log shape in well K1-1 trend, and a serrate cylindrical gamma ray log shape in wells A1-NC151 and AST2.