Petrographic coded correlations in petrophysics

Petrophysics refers to the research on the physical properties of rocks, their experimental and theoretical derivation and their correlations. Petrophysical applications are important in various geoscience, petroleum and geotechnical fields. Therefore a systematic study of various properties and influencing factors with a resulting matrix, where everything is combined for a further application is of great interest. The project should be a systematic study for the petrographic coded model concept and the influencing factors on the petrophysical properties. Within this project a ferrofluid based method for the derivation of the anisotropy of the pore space will be additionally evaluated. Therefore different petrophysical properties (electrical and elastic properties, porosity and permeability, thermal conductivity) are determined in the laboratory. For a systematic evaluation additional the mineral composition is identified and CT and SEM measurements will be carried out for a verification of the results. The first part of the project will be field work in Austria and sample preparation as well as the derivation of the orientation of the pores with the ferrofluid method. This method should be additionally improved and evaluated. The other petrophysical properties will be interpreted and a petrographic code will be determined. The result will be a deeper understanding of the influences on the properties. The relationship between physical defined model types and the petrographic code should be further investigated and stronger physically based by mixing rules for the host material. Combination of the new insights with standard formation evaluation for a more accurate interpretation and an extended output of borehole data should stand at the end. At that time requirements in petrophysics have changed. Needed is a good understanding of the various properties and a systematic matrix, where different geoscientist can get a quick idea of influencing factors on the different properties. Better understanding and therefore better correlations will result in improved applications. The result will be a unique systematic summary about the influencing factors on the individual properties, especially concerning pore space anisotropy and petrographic code.

Every risk analysis and feasibility study before e.g. a new tunnel- or geothermal energy- project needs input data about the rock properties in the subsurface. For this purpose, a systematic petrophysical database was compiled, which is now accessible for use in a variety of applications in geosciences and geotechnical engineering. The database contains comprehensive information about density, porosity and gas-permeability, as well as electrical, magnetic, thermal, radiometric and elastic properties of more than 150 sedimentary, metamorphic and plutonic rocks from the Eastern Alps and surrounding Basins in Austria. CT (computer tomography) technology, as well as optical and electron- microscopy was applied in order to attain information about the volume, orientation and internal surface of pores in the rocks. Statistical analyses yielded well-defined relationships of directional and non-directional petrophysical parameters for certain rocks, that were related with specific properties of the pore space and its anisotropy. A crucial factor is the preferred alignment of minerals and pores in the rock. The geometric arrangement of mineral grains controls elastic and thermal properties, while electrical properties and gas- permeability are determined by the geometrical arrangement of the pores. However, the mineral fabric and the pore fabric may have different orientations. Magnetic measurements of samples before and after impregnation with a magnetic ferro-fluid allowed the discrimination of the two textures. The new insights enable a more accurate and meaningful prediction of physical rock behaviour in the subsurface from laboratory and borehole measurements.