The interpretation of geophysical data in exploration geophysics, well logging, engineering, mining and environmental geophysics requires knowledge of the physical properties of rocks and their correlations. Physical properties are a "key" for combined interpretation techniques. The study of rock physics provides an interdisciplinary treatment of physical properties, whether related to geophysical, geotechnical, hydrological or geological methodology.
Physical Properties of Rocks, 2nd Edition, describes the physical fundamentals of rock properties, based on typical experimental results and relevant theories and models. It provides readers with all relevant rock properties and their interrelationships in one concise volume. Furthermore, it guides the reader through experimental and theoretical knowledge in order to handle models and theories in practice.
Throughout the book the author focuses on the problems of applied geophysics with respect to exploration and the expanding field of applications in engineering and mining geophysics, geotechnics, hydrology and environmental problems, and the properties under the conditions of the upper Earth crust.
Physical Properties of Rocks, Second Edition, guides readers through a systematic presentation of all relevant physical properties and their interrelationships in parallel with experimental and theoretical basic knowledge and a guide for handling core models and theories
RocksâTheir Classification and General Properties
JĂŒrgen H. Schön MontanuniversitĂ€t Leoben, Austria
Abstract
Rocks are naturally occurring aggregates of one or more minerals. In the case of porosity or fracturing, they also contain fluid phases. With respect to their geological genesis and processes, rocks are divided into three major groups:
âigneous rocks (magmatites),
âmetamorphic rocks (metamorphites), and
âsedimentary rocks (sediments).
Rocks are characterized by their composition (minerals, fluids), texture, and structure.
Of specific interest are sedimentary rocks with respect to their reservoir properties. Clastic (sandstone) and carbonate (limestone, dolomite) rocks are the most common reservoir rocks. Clay and shale have a strong influence upon rock properties and are discussed.
Some core measurement techniques for laboratory determination are compiled.
Keywords
Igneous rocks
Metamorphic rocks
Sedimentary rocks
Clastic rocks
Sandstone
Shale
Carbonate rocks
Limestone
Dolomite
Core analysis
1.1 Introduction
Rocks are naturally occurring aggregates of one or more minerals. In the case of porosity or fracturing, they also contain fluid phases. With respect to their geological genesis and processes, rocks are divided into three major groups:
âąigneous rocks (magmatites),
âąmetamorphic rocks (metamorphites), and
âąsedimentary rocks (sediments).
Figure 1.1 shows the rock cycle. It starts with the magmatic rocks, formed by crystallization from the magma.
Figure 1.1 The rock cycle.
Chemical processes and processes of erosion, disintegration, and transportation create sedimentary rocks of different composition and texture.
Both types can be transformed into metamorphic rocks through the influence of pressure and temperature; a reworking by melting and recrystallization also occurs.
The following sections briefly describe the three rock types. Sedimentary rocks are discussed in more detail with respect to their importance to fluid reservoir exploration (e.g. hydrocarbons, water) and their abundance on the earth's surface. A detailed classification of rocks and their abundances on the earth is given by Best (1995) in âA Handbook of Physical Constants/AGU Reference Shelf 3â.
1.2 Igneous Rocks
Igneous rocks are formed by crystallization from a molten magma. Three types are characterized by their occurrence and position in the crust:
âąplutonic rocks crystallized in great depth and forming large rock bodies,
âąvolcanic rocks reaching the surface, in many cases forming layers of rocks like a pillow or blanket, and
âądikes with dominant vertical extension and a horizontal extension in one direction. They frequently separate geological units.
Igneous rocks can be classified according to their chemical or mineralogical composition. Chemical classification distinguishes acid, intermediate, basic, and ultrabasic rocks. Mineralogical classification uses the types (see also Fig. 1.2):
Figure 1.2 Mineralogical classification of common magmatic rock types. Modified http://en.wikipedia.org/wiki/File:Mineralogy-igneous_rocks.
âąfelsic or silicic rocks, examples are granite, rhyolite,
âąintermediate rocks, examples are granodiorite, diorite, dacite, andesite,
âąmafic rocks, examples are basalt, gabbro,
âąultramafic rocks, example is peridotite.
Mineral composition controls physical properties (e.g. density and seismic velocity increases from felsic to mafic rock types).
Table 1.1 shows the mean mineral composition of magmatic rocks.
Table 1.1
Approximate Average Mineral Composition (Volume Percent) of the Earth's (Upper) Crust and of Major Intrusive Rocks
Mineral
Crust
Granite
Granodiorite
Quartz-diorite
Diorite
Gabbro
Plagioclase
41
30
46
53
63
56
Alkali feldspar
21
35
15
6
3
Quartz
21
27
21
22
2
Amphibole
6
1
13
12
12
1
Biotite
6
1
13
12
12
1
Orthopyroxene
2
3
16
Clinopyroxene
2
8
16
Olivine
0.6
5
Magnetite, ilmenite
2
2
2
2
3
4
Apatite
0.5
0.5
0.5
0.5
0.8
0.6
After Wedepohl, 1969; see also Huckenholz (1982)
1.3 Metamorphic Rocks
âMetamorphic rocks are the result of metamorphism. Metamorphism is the solid-state conversion of igneous and sedimentary rocks under the pressureâtemperature regime of the crustâ (Huckenholz, 1982). During this process, the original mineral assemblages (magmatic or sedimentary) are converted into new assemblages corresponding to the thermodynamic conditions over a geologic time.
Through the different metamorphic processes (regional metamorphism, contact metamorphism, cataclastic metamorphism, etc.), the great variety of original rocks an...
