Reservoir Characterisation of the Lower Devonian in the Ahnet – Timimoun Basin (Algeria)

Aldjia Djezzar¹ and Maarouf Brahim^2
1Sonatrach Algeria, Boumerdes, Algeria
²Sonatrach Algeria, Boumerdes, Algeria

The Ahnet -Timimoun basin is located in the Central Sahara of Algeria. Petroleum exploration allowed the discovery of 42 gas fields. The objective of this study is to analyze the distribution and continuity of the lower Devonian sands. From the sequence stratigraphy, three second order sequences can be distinguished. The Lower Devonian sediments consist of the two first sequences and first system tract of the third sequence. The basin architecture had an important control on the deposits distribution. Lower Devonian sands are developed to the east of the basin (125 to 200m). The Gedinnian constutes a multilayer reservoir, where interbedded shales can act as seals. Petrophysical characteristics: Gedinian: A good porosity values, mainly to the east of Ahnet (20%).The permeability increase slightly with porosity. In some regions, the permeability is enhanced by fracturation. Siegenian: A large porosity data set shows porosity values lower than 5%, however more than 20% can be observed. Permeability can vary from 0.01 to hundreds of md. Emsian: Porosity varies from 2 to 20%, the permeability can reach hundred of md. There is a clear relationship between the porosity and permeability. Sand distribution: The combined study of the cores, logs and tests resulted in the elaboration sand distribution maps for different reservoirs. Conclusion: The lower Devonian has good petroleum characteristics which are related to: •Important thickness of sandstone in the eastern margins and in the Djoua high. •Good reservoir qualities which yielded up to 590.000 m³/day. •Its position between the two best source rocks (Silurian, Frasnian).

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece