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Reservoir Architecture + Nano-Scale Porosity Analysis of a Permian Age Tight Gas Field in NW Germany


1.

Research focussed towards unravelling the complexity of Permian (Rotliegendes) tight gas fields in Central Europe requires an integrated approach combining laboratory analysis, numerical modelling and field based analogue studies. The study of a tight gas field at ~4200 m depth in East Frisia, NW Germany, located at the south-western margin of the Southern Permian Basin (SPB), includes a geological framework model for the sedimentary facies distribution, volcanic influence and the structural grain. Fault induced topography served as a local sediment source and controlled sediment distribution. Palaeotopography, fault activity and the development of accommodation space through Permian Rotliegend and Zechstein times are reconstructed from sediment isopach maps, which are based on detailed seismic interpretation. The sedimentary environment and involved sedimentary processes are punctually reconstructed from core and log material. The field analogue study in Panamint Valley, California, was carried out to improve the understanding of the interactions between sedimentology, volcanic influence and tectonic processes. Both, the subsurface study area in north-western Germany and the Panamint Valley are characterized by synsedimentary transtensional tectonics, which provide accommodation space for sediments deposited in dune, wet and damp interdune environments and under ephemeral fluvial influence. A sedimentary model of the gas field in Germany includes the composition and distribution of aeolian sandstone reservoirs and their relation to fault induced topographies.

(AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011)

 

2.

We present first results of a high resolution petrographic study as part of a multidisciplinary research project focusing on the evolution of Permian tight gas reservoirs in the Southern Permian Basin in Northern Germany.The SEM-BIB (scanning electron microscopy - broad ion beam) technique enables pore visualization on polished surfaces down to nm-scale. The ion beam preparation thus provides unprecedented insights into pore geometries and morphologies of low porous rocks in general. In the first phase of this project, selected pores of Rotliegend tight gas samples were investigated. Initially, different phases of clay mineral growth (illite and chlorite) could be identified and the relative timing of crystallization was established. The focus lay on the analysis of clay mineral coatings of quartz grains. These play a major role during diagenesis, inhibiting porosity and permeability reduction through quartz overgrowth or pressure solution. Observations further revealed that chlorite crystallization may prevent the growth of illite which restricts porosity and permeability reduction by secondary illite to areas where chlorite is the dominant pore cementing phase. Results supported and refined our detailed sedimentary facies analysis from core material of the Upper Rotliegend II in aeolian reservoirs. In addition, possible stress indicators were identified, which might provide crucial information for future field development.

Future work will include a geometrical 3D analysis of selected samples and investigations of grain coatings in modern dune fields.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.


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