--> Abstract: Reservoir Characterisation and Stratigraphy of Lower Carboniferous Incised Valley Fill Sandstones in Western Libya, by Laurent O. Petitpierre, Jonathan Redfern, Sebastian Frohlich, Stephane Bodin, Paul Grech, and Simon Lang; #90082 (2008)

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Reservoir Characterisation and Stratigraphy of Lower Carboniferous Incised Valley Fill Sandstones in Western Libya

Laurent O. Petitpierre1, Jonathan Redfern1, Sebastian Frohlich1, Stephane Bodin1, Paul Grech2, and Simon Lang3
1North Africa Research Group, University of Manchester, Manchester, United Kingdom
2Woodside, Tripoli, Libya
3Woodside, Perth, WA, Australia

This study aims to better constrain the depositional environment and reservoir distribution of the Lower Carboniferous Marar Formation in the Murzuq and Ghadames Basins of Western Libya. This outcrop based regional scale study, integrated with subsurface well data, aims to characterize a potentially important hydrocarbon reservoir in the region. The Marar increases in thickness from 500m to 800m toward the North. The dominant lithofacies consists of mudstones with interbedded thin sandstones beds (cm up to 1m thick). Associated fauna (brachiopods, crinoids) suggest a marine depositional environment. Sedimentary structures include storm (HCS), wave or tidal (herring bone cross bedding) generated bedforms. These characteristics suggest a shallow marine wave and tide dominated deltaic depositional environment. The interval displays typical large scale shallowing-coarsening upward cycles. Outcrop spectral gamma ray measurements are used to established subsurface correlation with wireline logs from exploration wells in the vicinity. The main reservoir facies consists of fine grained sandstones deposited within discrete channelised bodies, that cut into the marine mudstones. The basal contacts of the channels are sharp, often exhibiting a conglomeratic base. The sandstone bodies are interpreted to be incised valleys, filled with fluvial and tidal sandstone. In the Jebel Aswad exposure (SW Ghadames basin), sedimentary logs, correlation panels and satellite image analyses have been used to quantify their size (10 to 50m thick and 100m to 2km wide) and to understand their stratigraphic distribution. We conclude that the incised valley fills are potentially present all over the studied area, but that the thicker reservoir facies occur at distinct stratigraphic horizons. The regional extent of the features suggest an important sea level control of the Marar Formation deposits.

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