Chapter 4
Sandstones and Sandstone Reservoirs
Knut Bjørlykke and Jens Jahren
4.1
Introduction
About 50% of all petroleum reservoirs are sandstones;
outside the Middle East, carbonate reservoirs are less
common and the percentage is even higher. The most
important reservoir properties are porosity and permeability, but pore geometry and wetting properties of
the mineral surfaces may also influence petroleum
production. Sandstones provide reservoirs for oil and
gas, but also for groundwater which is a fluid that
is becoming increasingly valuable. Sandstones are
deposited in many different sedimentary environments
by marine, fluvial and eolian (wind) processes.
The outer geometry and distribution of sand bodies is
determined by the depositional environment and the reservoir properties. The internal properties (porosity, permeability) are, however, critical for petroleum recovery.
The properties of sandstone reservoirs are functions
of the primary composition, which is controlled by the
textural and mineralogical composition (provenance)
of the depositional environment and by the diagenetic
processes near the surface and during burial.
Sand and sandstones are rocks which consist
largely of sand grains, i.e. sedimentary particles
between 1/16 and 2 mm in diameter. However,
sandstones also contain greater or lesser amounts of
other grain sizes and we find transitions to more siltand clay-rich rocks. Most sandstones have a welldefined upper grain-size limit with variable contents
of silt and clay. If they have a significant content of
coarser grains (pebbles) we call them conglomeratic
sandstones. Most classification systems are based on
the relationship between the relative quantity of sandsized grains, the composition of the sand grains, and
the clay and silt content (matrix).
If we use a four-component diagram we can distinguish between clay, and sand grains which consist
of quartz, feldspar and rock fragments (or unstable
rock fragments, U.R.F.) (Fig. 4.1). Rock fragments
consisting of microcrystalline (or cryptocrystalline)
quartz (including chert) are usually classified together
with the quartz mineral grains. Sandstones with more
than 25% feldspar and a low content of rock fragments
are called arkoses. If the percentage of rock fragments
is high, we speak of lithic sandstones which are normally derived from very fine-grained sedimentary
rocks or basalts and intrusive igneous rocks where
one sand grain often consists of several minerals.
Quartz arenite or orthoquartzite are the terms for
pure quartz sandstones which contain less than 5%
feldspar or rock fragments. Sandstones with moderate
feldspar contents (5–25%) are called subarkoses.
When granitic rocks and other coarse- to mediumgrained rocks are broken down by weathering or erosion, they form sand grains consisting for the most part
of single minerals, mostly quartz and feldspar.
The prerequisite for forming arkose is that not too
much of the feldspar in the source rock has been
weathered to clay minerals (e.g. kaolinite). Arkoses
are therefore formed if granites and gneisses are
eroded rapidly in relation to weathering, and the
sediments are buried in a basin after a relatively
short sediment transport. In the great majority of
cases arkose is therefore associated with sedimentary
rift basins formed by faulting in gneissic and granitic
K. Bjørlykke (*) J. Jahren
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no; jens.jahren@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_4, # Springer-Verlag Berlin Heidelberg 2015
119
Sandstones and Sandstone Reservoirs
Knut Bjørlykke and Jens Jahren
4.1
Introduction
About 50% of all petroleum reservoirs are sandstones;
outside the Middle East, carbonate reservoirs are less
common and the percentage is even higher. The most
important reservoir properties are porosity and permeability, but pore geometry and wetting properties of
the mineral surfaces may also influence petroleum
production. Sandstones provide reservoirs for oil and
gas, but also for groundwater which is a fluid that
is becoming increasingly valuable. Sandstones are
deposited in many different sedimentary environments
by marine, fluvial and eolian (wind) processes.
The outer geometry and distribution of sand bodies is
determined by the depositional environment and the reservoir properties. The internal properties (porosity, permeability) are, however, critical for petroleum recovery.
The properties of sandstone reservoirs are functions
of the primary composition, which is controlled by the
textural and mineralogical composition (provenance)
of the depositional environment and by the diagenetic
processes near the surface and during burial.
Sand and sandstones are rocks which consist
largely of sand grains, i.e. sedimentary particles
between 1/16 and 2 mm in diameter. However,
sandstones also contain greater or lesser amounts of
other grain sizes and we find transitions to more siltand clay-rich rocks. Most sandstones have a welldefined upper grain-size limit with variable contents
of silt and clay. If they have a significant content of
coarser grains (pebbles) we call them conglomeratic
sandstones. Most classification systems are based on
the relationship between the relative quantity of sandsized grains, the composition of the sand grains, and
the clay and silt content (matrix).
If we use a four-component diagram we can distinguish between clay, and sand grains which consist
of quartz, feldspar and rock fragments (or unstable
rock fragments, U.R.F.) (Fig. 4.1). Rock fragments
consisting of microcrystalline (or cryptocrystalline)
quartz (including chert) are usually classified together
with the quartz mineral grains. Sandstones with more
than 25% feldspar and a low content of rock fragments
are called arkoses. If the percentage of rock fragments
is high, we speak of lithic sandstones which are normally derived from very fine-grained sedimentary
rocks or basalts and intrusive igneous rocks where
one sand grain often consists of several minerals.
Quartz arenite or orthoquartzite are the terms for
pure quartz sandstones which contain less than 5%
feldspar or rock fragments. Sandstones with moderate
feldspar contents (5–25%) are called subarkoses.
When granitic rocks and other coarse- to mediumgrained rocks are broken down by weathering or erosion, they form sand grains consisting for the most part
of single minerals, mostly quartz and feldspar.
The prerequisite for forming arkose is that not too
much of the feldspar in the source rock has been
weathered to clay minerals (e.g. kaolinite). Arkoses
are therefore formed if granites and gneisses are
eroded rapidly in relation to weathering, and the
sediments are buried in a basin after a relatively
short sediment transport. In the great majority of
cases arkose is therefore associated with sedimentary
rift basins formed by faulting in gneissic and granitic
K. Bjørlykke (*) J. Jahren
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no; jens.jahren@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_4, # Springer-Verlag Berlin Heidelberg 2015
119