Abstract

Partitioning and preservation of facies at the reservoir-scale are two main problems that have been widely discussed in petroleum geology. However, the parametres that control these two processes have been poorly studied. This work deals with Hettangian siliciclastic deposits located at Chemery in the Sologne region (southwestern part of the Paris basin). These sediments consist of continental facies, largely influenced by fluvial processes. Reservoir sandstones are observed in many well-logs of the Chemery area, which is being utilised by Gaz de France for the purpose of gas storage in underground aquifers. A very large data base is available to study the architecture of reservoir bodies at high resolution scale. The analysis of their geometry has permitted clarification of the effects of the different parameters that control the location and preservation of reservoir sediments at various time scales. The main result is that reservoir bodies are organised in small stratigraphic units totaling 100 to 400 ky, controlled by high-frequency, relative sea-level changes. Facies partitioning within these units is directly influenced by local conditions (e.g. topography, fault activity, stratigraphic balance during fluvial transport, etc). Moreover, eustatism or the regional component of subsidence control the morphological and volumetric preservation of sediments, and may force volume partitioning of reservoir sediments through time.

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