Helmut Dürrast

Physical and Mechanical Properties of Rocks

Since early antiquity dimension stones have been used as building materials due to their natural beauty and availability, and the diversity of their applications has increased ever since. As any other building material, dimension stones today have to fulfill the physical and technical requirements demanded by architects. This chapter focuses on the physical and mechanical properties of dimension stones, while emphasizing that stones are an old, but still modern building material. Among the parameters discussed here are water absorption, thermal conductivity and expansion, hygric and hydric properties, strength, abrasion, the more modern aspect of breaking load at the dowel hole, and ultrasonic wave velocities. Extensive data sets and a variety of case studies reveal relationships between the physical properties and the internal fabric elements of the dimension stones, such as sedimentary layering, metamorphic foliation, pores, and microcracks. In addition, these fabric elements are often responsible for the weathering behavior of the dimension stones, which not only affects the heritage but also the safety of modern buildings. This is illustrated through laboratory experiments and case studies.

P‐wave velocity and permeability distribution of sandstones from a fractured tight gas reservoir

Fractures are an important fabric element in many tight gas reservoirs because they provide the necessary channels for fluid flow in rocks which usually have low matrix permeabilities. Several sandstone samples of such a reservoir type were chosen for a combined study of rock fabric elements and petrophysical properties. Geological investigations of the distribution and orientation of the fractures and sedimentary layering were performed. In addition, laboratory measurements were carried out to determine the directional dependence of the permeability and P‐wave velocities. Higher permeability values are generally in the plane of the nearly horizontal sedimentary layering with regard to the core axis. With the occurrence of subvertical fractures, however, the highest permeabilities were determined to be parallel to the core axis.Compressional wave velocities were measured on spherical samples in more than 100 directions to get the VP symmetry without prior assumptions. Below 50 MPa confining pressure, all ...

Limestones in Germany used as building stones: an overview

Abstract Germany has an enormous number of different carbonate rock units, which vary widely in their geological age and sedimentary depositional environment. Limestones quarried from these exposures have a wide range of usages and applications, such as dimension and ornamental stones, floor tiles and panelling, and for use as paving stones and massive stones. Since antiquity, limestones were used as building materials in areas where they were naturally available and abundant. Limestones exhibit a relatively good weathering resistance, which is mainly controlled by the mineralogical composition and the rock structure. The susceptibility of limestones to weathering and alteration is only secondarily related to the stones contact with rainwater and its exposure to frost. In this situation the pore space is the main controlling factor. Industrialization and the subsequent increase in air pollutants, which started at the end of the nineteenth century, led to the formation of dark and unsightly crust deposits on the limestones surfaces. These crusts, being the result of man-made activities, are the main weathering problem for carbonate dimension stones.

Anisotropy of Seismic Wave Propagation, Permeability And Electrical Conductivity In Carbonate Reservoir Rocks Caused By a System of Aligned Cracks

The present abstract considers the relationship between cracks and other rock fabric elements (i. e. major constituents, like fossils, ooides, peloides, crystals, etc., pore types and stylolites) and the complex petrophysical properties of carbonate reservoir rocks. A core sample from the oil and gas reservoirs of the NW German basin was chosen as an example for this study. Detailed fabric analyses and texture investigations were carried out as well as laboratory measurements of density, porosity, permeability, electrical conductivity and seismic compressional and shear wave velocities. The results clearly show that the directional dependencies of the petrophysical properties are fairly related to the anisotropies of the rock fabrics, especially the orientation and distribution of the open cracks. The knowledge gained from such correlations may lead to an improved interpretation of geophysical borehole measurements for hydrocarbon exploration and therefore to advanced reservoir characterizations.