Chapter 1
Introduction to Petroleum Geology
Knut Bjørlykke
Petroleum geology comprises those geological
disciplines which are of greatest significance for the
finding and recovery of oil and gas. Since most of the
obvious and “easy to find” petroleum already has been
discovered it is necessary to use sophisticated methods
in the exploration of sedimentary basins. These
include advanced geophysical techniques and basin
modelling. There is also much more emphasis now
on enhanced recovery from the producing fields.
Petroleum technology has made great progress and
many new tools and modelling programs have been
developed, both in exploration and production.
It is however important to understand the geological processes which determine the distribution of different sedimentary rocks and their physical properties.
This knowledge is fundamental to being able to successfully apply the methods now available.
It is difficult to know where to start when teaching
petroleum geology because nearly all the different
disciplines build on each other.
This introductory chapter will provide a short and
rather simple overview of some aspects of petroleum
geology to introduce the subject and the problems.
Most of the other chapters will then expand on what
is presented here to provide a better background in
relevant subjects.
Since practically all petroleum occurs in sedimentary rocks, sedimentary geology forms one of the main
foundations of petroleum geology. Sedimentological
models are used to predict the location of different
facies in the sedimentary basins, and from that the
likely presence of source rocks with a high content
of organic matter, reservoir rocks and cap rocks. The
distribution and geometry of potential sandstone or
carbonate reservoirs requires detailed sedimentological models, and sequence stratigraphy has been a useful tool in such reconstructions.
The biostratigraphic correlation of strata encountered in exploration wells is achieved by
micropalaeontology (including palynology), a field
developed very largely by the oil industry. Due to the
small size of the samples obtained during drilling
operations one cannot rely on macrofossils; even in
core samples the chance of finding good macrofossils
is poor. By contrast a few grams of rock from the drill
cuttings may contain several hundred microfossils or
palynomorphs which are small remains of plants such
as pollen, spores etc. These also usually provide better
stratigraphic resolution than macrofossils.
Reservoir rocks are mostly sandstones and
carbonates which are sufficiently porous to hold significant amounts of petroleum. The composition and
properties of other rock types such as shales and salt
are also important.
The sedimentary environments (sedimentary facies)
determine the distribution of reservoir rocks and their
primary composition. Sediments do, however, alter
their properties with increasing overburden due to diagenesis during burial.
Diagenetic processes determine the changes in
porosity (compaction), permeability and other physical properties such as velocity, in both sandstone and
limestone reservoirs. Chemical processes controlling
mineral reactions are important.
K. Bjørlykke (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_1, # Springer-Verlag Berlin Heidelberg 2015
1
Introduction to Petroleum Geology
Knut Bjørlykke
Petroleum geology comprises those geological
disciplines which are of greatest significance for the
finding and recovery of oil and gas. Since most of the
obvious and “easy to find” petroleum already has been
discovered it is necessary to use sophisticated methods
in the exploration of sedimentary basins. These
include advanced geophysical techniques and basin
modelling. There is also much more emphasis now
on enhanced recovery from the producing fields.
Petroleum technology has made great progress and
many new tools and modelling programs have been
developed, both in exploration and production.
It is however important to understand the geological processes which determine the distribution of different sedimentary rocks and their physical properties.
This knowledge is fundamental to being able to successfully apply the methods now available.
It is difficult to know where to start when teaching
petroleum geology because nearly all the different
disciplines build on each other.
This introductory chapter will provide a short and
rather simple overview of some aspects of petroleum
geology to introduce the subject and the problems.
Most of the other chapters will then expand on what
is presented here to provide a better background in
relevant subjects.
Since practically all petroleum occurs in sedimentary rocks, sedimentary geology forms one of the main
foundations of petroleum geology. Sedimentological
models are used to predict the location of different
facies in the sedimentary basins, and from that the
likely presence of source rocks with a high content
of organic matter, reservoir rocks and cap rocks. The
distribution and geometry of potential sandstone or
carbonate reservoirs requires detailed sedimentological models, and sequence stratigraphy has been a useful tool in such reconstructions.
The biostratigraphic correlation of strata encountered in exploration wells is achieved by
micropalaeontology (including palynology), a field
developed very largely by the oil industry. Due to the
small size of the samples obtained during drilling
operations one cannot rely on macrofossils; even in
core samples the chance of finding good macrofossils
is poor. By contrast a few grams of rock from the drill
cuttings may contain several hundred microfossils or
palynomorphs which are small remains of plants such
as pollen, spores etc. These also usually provide better
stratigraphic resolution than macrofossils.
Reservoir rocks are mostly sandstones and
carbonates which are sufficiently porous to hold significant amounts of petroleum. The composition and
properties of other rock types such as shales and salt
are also important.
The sedimentary environments (sedimentary facies)
determine the distribution of reservoir rocks and their
primary composition. Sediments do, however, alter
their properties with increasing overburden due to diagenesis during burial.
Diagenetic processes determine the changes in
porosity (compaction), permeability and other physical properties such as velocity, in both sandstone and
limestone reservoirs. Chemical processes controlling
mineral reactions are important.
K. Bjørlykke (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_1, # Springer-Verlag Berlin Heidelberg 2015
1