Chapter 12
The Structure and Hydrocarbon Traps of Sedimentary Basins
Roy H. Gabrielsen
12.1 Tectonic Regimes and Stress
Old knowledge told the early oil explorationist to focus
drilling on structurally high-standing areas because
hydrocarbons are trapped in positive structures like
folds and rotated fault blocks that, as such, define positive structural features and associated topographic
highs. Principally, however, three categories of traps
are recognised, namely the structural trap, the stratigraphic trap and the hydrodynamic trap.
Structural geology is significant in all stages of the
“value chain” of the exploration for and the exploitation of hydrocarbon resources, including the initial
exploration screening phase, the targeted exploration,
reservoir description and production (Gabrielsen &
Møller-Holst 1997). This involves studies that include
the basin-scale tectonic evolution, interaction between
structural evolution and sedimentation, maturation,
hydrocarbon migration, characteristics of trap type,
sealing potential and leakage. But generally, the most
common questions to ask a structural geologist in an
oil exploration environment concerns the trap itself.
Many types of traps exist, some of which are determined purely by the sedimentary development,
whereas the most common are due to structural development alone. Hence the purely stratigraphic trap is
due solely to sedimentary processes, such as the primary pinch-out of sedimentary units. Others may be
due partly to sedimentological and partly to structural
developments (e.g. some types of inconformity traps),
or purely structural (e.g. an anticline). To start with the
purely structural trap, this depends on the tectonic
environment (contraction, extension or strike-slip) in
which it was created (see Sect. 12.1.2).
On a worldwide scale, the structural trap is by far the
most common hydrocarbon trap type, but there is a
tendency for the two other trap types to be more relevant
in mature hydrocarbon provinces, because exploration
moves into a more detailed approach in such areas.
Structural traps are generated by tectonic, diapiric,
compactional or gravitational processes. They must
contain a reservoir constrained in three dimensions, a
cap, and be in communication with a reservoir unit. The
structure has a spill-point defining the volume available
in the trap, and commonly develops a gas/oil contact at
the top and oil/water contact at its base.
Geometrically speaking, the simplest structural trap
may be the anticline, or modifications hereof (Fig.
12.1a). Compressive tectonic regimes commonly
include a host of contractional folds and thrusts.
Good examples of such areas that are also hydrocarbon
provinces are the Zagros Mountains of Iran, the Caribbean of South America and the North American
Cordillera. To be of interest for the entrapment of
hydrocarbons, such structures must have a closure as
seen along the fold axis, implying that they should not
be strictly cylindrical. This is often the case for natural,
contractional folds, particularly in situations where
deformation took place above an uneven basement
topography and particularly so in areas where doublefolding (folding with to sets of cross-cutting fold-axes)
and halokinesis have occurred (Fig. 12.1d). The anticline must be thoroughly mapped in three dimensions.
The complexity and communication between contractional structures are, to a great extent, dependent on
R.H. Gabrielsen (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: roy.gabrielsen@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_12, # Springer-Verlag Berlin Heidelberg 2015
319
The Structure and Hydrocarbon Traps of Sedimentary Basins
Roy H. Gabrielsen
12.1 Tectonic Regimes and Stress
Old knowledge told the early oil explorationist to focus
drilling on structurally high-standing areas because
hydrocarbons are trapped in positive structures like
folds and rotated fault blocks that, as such, define positive structural features and associated topographic
highs. Principally, however, three categories of traps
are recognised, namely the structural trap, the stratigraphic trap and the hydrodynamic trap.
Structural geology is significant in all stages of the
“value chain” of the exploration for and the exploitation of hydrocarbon resources, including the initial
exploration screening phase, the targeted exploration,
reservoir description and production (Gabrielsen &
Møller-Holst 1997). This involves studies that include
the basin-scale tectonic evolution, interaction between
structural evolution and sedimentation, maturation,
hydrocarbon migration, characteristics of trap type,
sealing potential and leakage. But generally, the most
common questions to ask a structural geologist in an
oil exploration environment concerns the trap itself.
Many types of traps exist, some of which are determined purely by the sedimentary development,
whereas the most common are due to structural development alone. Hence the purely stratigraphic trap is
due solely to sedimentary processes, such as the primary pinch-out of sedimentary units. Others may be
due partly to sedimentological and partly to structural
developments (e.g. some types of inconformity traps),
or purely structural (e.g. an anticline). To start with the
purely structural trap, this depends on the tectonic
environment (contraction, extension or strike-slip) in
which it was created (see Sect. 12.1.2).
On a worldwide scale, the structural trap is by far the
most common hydrocarbon trap type, but there is a
tendency for the two other trap types to be more relevant
in mature hydrocarbon provinces, because exploration
moves into a more detailed approach in such areas.
Structural traps are generated by tectonic, diapiric,
compactional or gravitational processes. They must
contain a reservoir constrained in three dimensions, a
cap, and be in communication with a reservoir unit. The
structure has a spill-point defining the volume available
in the trap, and commonly develops a gas/oil contact at
the top and oil/water contact at its base.
Geometrically speaking, the simplest structural trap
may be the anticline, or modifications hereof (Fig.
12.1a). Compressive tectonic regimes commonly
include a host of contractional folds and thrusts.
Good examples of such areas that are also hydrocarbon
provinces are the Zagros Mountains of Iran, the Caribbean of South America and the North American
Cordillera. To be of interest for the entrapment of
hydrocarbons, such structures must have a closure as
seen along the fold axis, implying that they should not
be strictly cylindrical. This is often the case for natural,
contractional folds, particularly in situations where
deformation took place above an uneven basement
topography and particularly so in areas where doublefolding (folding with to sets of cross-cutting fold-axes)
and halokinesis have occurred (Fig. 12.1d). The anticline must be thoroughly mapped in three dimensions.
The complexity and communication between contractional structures are, to a great extent, dependent on
R.H. Gabrielsen (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: roy.gabrielsen@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_12, # Springer-Verlag Berlin Heidelberg 2015
319