Physical Properties of Rocks

Fundamentals and Principles of Petrophysics

Juergen H. Schön

• Publisher: Elsevier
• Year: 2015
• ISBN:
  9780081004234
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Geophysics

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

Chapter 1

Rocks—Their Classification and General Properties

Jürgen H. Schön Montanuniversität 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:

– igneous rocks (magmatites),

– metamorphic rocks (metamorphites), and

– sedimentary 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:

• igneous rocks (magmatites),

• metamorphic rocks (metamorphites), and

• sedimentary 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 “A Handbook of Physical Constants/AGU Reference Shelf 3”.

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:

• plutonic rocks crystallized in great depth and forming large rock bodies,

• volcanic rocks reaching the surface, in many cases forming layers of rocks like a pillow or blanket, and

• dikes 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.

• felsic or silicic rocks, examples are granite, rhyolite,

• intermediate rocks, examples are granodiorite, diorite, dacite, andesite,

• mafic rocks, examples are basalt, gabbro,

• ultramafic 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

“Metamorphic rocks are the result of metamorphism. Metamorphism is the solid-state conversion of igneous and sedimentary rocks under the pressure–temperature regime of the crust” (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...