Nano-Scale Porosity Analysis of a Permian Tight Gas Reservoir

Antrett, Philipp ¹; Vackiner, Anna A.¹; Hilgers, Christoph ²; Wollenberg, Uwe ¹; Kukla, Peter ¹; Urai, Janos ³; Stollhofen, Harald ⁴
(1)Geological Institute, RWTH Aachen University, Aachen, Germany. (2) Reservoir Petrology, RWTH Aachen University, Aachen, Germany. (3) Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Aachen, Germany. (4) North Bavarian Center of Earth Sciences, FAU Erlangen-Nuernberg, Erlangen, Germany.

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.