oa Sequence Stratigraphy and Reservoir Characterization of the Lower Devonian in the Southwest of Algeria

Lower Devonian reservoirs in Southwest Algeria are included in a stratigraphic interval between the so called “Caledonian Unconformity”, at the Silurian/Devonian (Lochkovian) limit, and a major regional flooding surface at the Emsian top. Three lithostratigraphic units are identified and correlated over hundreds of kilometers in outcrops and through Reggane basin. The Lochkovian/Gedinnian A & B reservoir units have been respectively deposited in tidal and foreshore environment. The Pragian/Siegenian C & D and Emsian reservoir units correspond to shoreface sandstones separated by offshore shales. In terms of sequence stratigraphy framework, they are equivalent to five 3rd Order Sequences (Vail et al., 1978), called De 1, 2, 3 4 and 5. A progressive decrease of the sand-shale ratio is expected from the SE to the NW of Reggane basin in every reservoir unit according to the overall progradation of the system and increasing marine influences. In spite of the extremely good correlation of these units around the whole area, internal heterogeneities exist due to facies associations and additional diagenetic processes.