Integrating Petrophysics, Digital Image Analysis and Magnetic Methods in Reservoir Characterization: A Case Study from the Triassic of Northern Germany

Maerz, Sven ¹; Zeug, Matthias ¹; Frijia, Gianluca ¹; Szurlies, Michael ¹; Mutti, Maria ¹
(1) Institute of Earth and Environmental Science, Potsdam University, Potsdam-Golm, Germany.

The Buntsandstein (Early Triassic) sedimentary succession is the third most important gas producing interval in Germany. However, the pore system of these sandstones and carbonates is yet not fully understood. In this study we have used an innovative approach by integrating petrophysics, digital image analysis and magnetic methods to improve characterization of reservoir properties.

A total of 280 samples has been analysed from fluvio-lacustrine fine- to coarse-grained sandstones and interbedded oolitic limestones deposited in playa lakes. For determination of the bulk 3D grain orientation in the samples, magnetic grain fabric analysis has been used. Magnetic method allows re-orienting drill cores and quantifying preferred grain and pore orientation. The latter geometries can be used as indicators for preferred paths of pore fluid flow through sandstones intervals. Moreover, this technique has allowed us to estimate the degree of sinuosity of the Buntsandstein fluvial system through time as derived from recorded variability of grain fabric. In order to refer the obtained directional properties to geographic North, the plug samples have been re-oriented by the paleomagnetic method, which is based on the fact that sediments acquire a viscous magnetism that points in the direction of the recent geomagnetic field. Consequently, it can be used to define the direction of geographic north in drill cores.

Petrophysical properties have been analyzed using a combination of He-injection porosimetry and digital image analysis (DIA). The DIA is a relatively new method for predicting reservoir quality through a quantitative analysis of pore size, geometry, distribution and abundance, which cannot be calculated using classic He-injection porosimetry. In order to quantify the total porosity and pore parameters, we have developed a rapid and accurate DIA routine based on optical and scanning electron microscope photographs. With DIA we were able to differentiate between micro and macroporosity as well as calculate various important pore parameters in the studied samples, (pore perimeter, pore area, pore shape and pore orientation) and to quantify the homogeneity of pore-distribution by calculating a porosity-distribution factor. The main outcome of our integrated approach is a considerable improvement in characterizing petrophysical parameters in the Buntsandstein reservoir rocks and their lateral variability, which are important for developing fluid flow directions.

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