Stratigraphic sequential analysis, paleo- environment and oil interest of the Upper Silurian - Lower Devonian (F6 reservoir) of Southeastern Algerian Sahara: case of Hassi Mazoula field and its bordering regions (Illizi basin).

A. Belkacemi, A. Asses, R. Hamdidouche


Hassi Mazoula field is located in the Southeastern corner of the Algerian Sahara. It belongs to the meridional flank of Ahara spur which separate two big sedimentary basins: Berkine northwards and Illizi southwards.

The F6 Reservoir, of Upper Silurian-Lower Devonian Age, consists of sandstones, silts and shale. It’s divided into eight lithologic units; from bottom to top: M1, M2, A, B1, B2 units make the lower series and C1, C2, C3 units form the upper series. Caledonian unconformity separates them.

Key concepts in sequential stratigraphy involve understanding how certain geometric relationships between rock layers occur in its original deposition environment. Changes of deposition environments (due to climate, tectonics, subsidence and others) have economic importance when they cause significant lateral changes in sediment deposition patterns. The analysis of the spatio-temporal distribution of the deposits makes it possible to highlight the petroleum systems and locate the reservoir levels, the possible sources and the cover rocks.

Sequentially, the F6 Reservoir consists of five deposition sequences: three sequences in the Upper Silurian (S1, S2 and S3) and two sequences in the Lower Devonian (S4 and S5).

Paleo-environmental changes determine tract systems in each sequence; when we draw the limits of good sandstone bodies in each tract system, its leads to judging the possibilities of hydrocarbons in each sequence at the scale of this studied area.

In this case, lowstand systems tract of S4 and S4 sequences seem to constitute good petroleum targets.

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