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Abstract

The Lower Devonian clastic reservoirs in the northern Zerafa block (Western Desert, Algeria) are relatively unexplored, while some of the existing discoveries seem to be tight gas reservoirs. The reservoir consists of shallow- marine clastic sequences dominated by fluvially and subordinately tidally influenced deltas. These units alternate with thick packages of non-reservoir, lagoonal and offshore marine sequences. The reservoir properties are typically poor to moderate due to burial and diagenetic overprint; this can result in some parts of the reservoirs being tight gas zones. Key uncertainties are the definition of net-versus-gross reservoir, productivity and connectivity. We will present the results and the process of a detailed study of the stratigraphy, sedimentology, facies types and their diagenetic overprint, structural setting and evolution, followed by integration of all other available reservoir quality and well test data. The facies types and associations of the Devonian reservoirs seem to point towards the identification of paleovalleys in which thicker and confined gross reservoir packages with better reservoir quality were deposited. These packages are probably genetically related to early transgressive systems tracts, estuarine-valley systems. However, lateral changes in seismic character of key reservoir horizons would suggest that lateral facies variability may be related to changes in depositional paleo-environment due to different responses to relative sea-level changes and related accommodation space. Possible relations between diagenesis, burial and depositional-stratigraphical setting and the reservoir properties will be discussed. Conceptual geological models have been translated into various 3-D static model realizations, which have been evaluated against different development concepts. The modeling results have been used to aid the design and decision-making for the ongoing appraisal campaign.

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/content/papers/10.3997/2214-4609-pdb.246.252
2008-01-03
2024-03-28
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