PETROLEUM GEOLOGY

4.5 billion years

age of Earth based on radioactive dating of the oldest available rock samples

• inner core

• mantle

• crust

Earth’s interior is subdivided into:

core

consists of crystalline inner core and molten outer core

• electrical and magnetic properties of the Earth

• density of the core

Evidence for iden fying the metal as an alloy of iron and nickel:

iron

dominant constituent

mantle rocks > crust rocks

densities of rock

Mantle

contains primarily basalt (a dark volcanic rock)

Basalt

composed of magnesium and iron silicates

Semimolten basalt

found at the surface of the mantle and this layer is known as asthenosphere

granitic continental crust

composed of silica and aluminum.

oceanic crust

contains silica and magnesia.

layer of basalt

Underlying the continental and oceanic crusts is a

Mohorovicic discontinuity or Moho

The boundary between the crustal basalt and the semimolten basalt of the mantle

lithosphere

The combina on of crust and solid basalt above the Moho

asthenosphere

below lithosphere

Asthenosphere

contains the part of upper mantle, which is duc le.

Lithosphere-asthenosphere boundary (LAB)

Lithosphere and asthenosphere are separated by the

semimolten asthenosphere

the lithosphere (consists of rigid plates) is floating on the

Continental Drift

proposed by Alfred Wegener (1915)
explains the movement of continental plates over time

Convergent plate boundaries

form when two plates collide which can result in crea on of mountain ranges like Himalayas.

Subduction Zones

occur when one plate moves beneath another, which may descend through the Moho into the asthenosphere.

Seafloor spreading

separa on of two plates by the extrusion of material which creates new oceanic plates and seafloor (e.g. mid-Atlan c Ridge)

Plate tectonics

is the theory describing the movement of Earth's lithospheric plates and has shaped Earth's landmasses over millions of years.

Pangaea

All Earth's landmasses were once united in a supercontinent called

eons, eras, and periods.

The Earth's history is categorized using the geologic me scale:

MYBP

millions of years before the present

Rocky mountains

formed by the subduction of plates beneath the western edge of the North American plate

Laramidia and Appalachia.

Fossils of marine life found in the region indicate that it was once submerged under the Western Interior Seaway, which divided North America:

Igneous

Formed from the cooling and solidification of magma or molten rock.

sedimentary

Formed from the accumulation, compaction, and cementation of sediments.

metamorphic

Created when existing rocks undergo physical and chemical changes due to heat, pressure, or chemical processes.

magma formation

Begins in the Earth's mantle and rises to the surface due to convection currents.

• mineral composition

• grain size and shape

• color and structure

Key attributes used for classification of sedimentary rocks:

mineral composition

The chemical and crystalline structure of the minerals within the rock.

Grain size and shape

Influenced by the transport and depositional environment.

Color and structure

Indicators of geological processes and conditions.

Grains

are created by weathering at the Earth's surface and transported to deposition sites.

Sharp-edged grains

Suggest transport in a low-energy environment (e.g., slow-moving stream).

rounded grains

Indicate high energy transport (e.g., fast moving stream) and tend to form rocks with higher permeability than flat or sharp edged grains.

Sorting

Refers to the uniformity of grain size in rocks:

Well-sorted rocks

Uniform grain sizes, better fluid flow, higher permeability.

Poorly sorted rocks

Varied grain sizes, lower fluid flow and permeability.

permeability

A rock property that describes its ability to allow fluid to flow through it.

Data

is collected and plotted in spatial locations, helping to determine property values at any point within a volume.

Discontinuities in contours

may indicate geologic features like faults or unconformities.

Hand Contouring

for geological interpretation that automated methods may miss

Formation

basic descriptive unit for a sequence of sediments, which is mappable rock unit deposited under dominant conditions over time and may contain multiple rock types.

members

Distinct rock types within a formation.

Stratum

Individual sedimentary layers within a formation, distinguishable by their unique characteristics.

Stratigraphic column

Represents the sequence of layers (oldest at the bottom, youngest at the top). Gaps can occur due to erosion or missing deposits.

Structure map

Shows the depth to the top or base of a stratum using contour lines.

Isopach map

Displays the thickness of a rock unit.

Fluvial Environment (Rivers):

Deposits rocks over great distances in meandering patterns.

Deltaic Environment (Deltas)

Deposits rocks in more compact locations.

sedimentary basin

a crustal region underlain by thick sedimentary rock sequences.

source rock

Sedimentary layers rich in organic matter capable of generating petroleum.

Transformation ratio

The ratio of petroleum formed to the organic material available for its generation.

Traps

structures that prevent the movement of hydrocarbons, allowing their accumulation in reservoirs.

Structural traps

Formed by the geometry of the reservoir, which blocks fluid movement.

Stratigraphic traps

Formed by changes in the characteristics of a formation that blocks fluid flow.

tectonic activity

Results from the movement of lithospheric plates.

regional activity

Includes growth of structures like salt domes, leading to diapiric traps.

diagenesis

refers to processes in which the lithology of a formation is altered at relatively low pressures and temperatures when compared with the metamorphic formation of rock

Combination traps

Result from a mix of structural and stratigraphic features.

Hydrocarbons can exist as solid, liquid (oil), or gas.

hydrocarbon states

• Source rock

• Carrier rock

• Trap (reservoir)

Key factors for a Hydrocarbon Reservoir:

source rock

Contains decaying organic material that forms hydrocarbons.

Carrier rock

A permeable flow path that enables hydrocarbons to migrate from the source rock to the reservoir rock.

Trap (reservoir)

A structure that confines hydrocarbons and allows economic production

• porosity

• permeability

• timing

Characteristics of traps

Porosity

Determines the volume of fluid that can be stored

Permeability

Determines the rate at which fluids can be produced.

Timing

The trap must exist when hydrocarbons migrate; otherwise, no hydrocarbons will be captured.

Sandstones

Compacted sediment, including consolidated rock (cemented grains), unconsolidated rock (uncemented grains), conglomerates (pebbles/boulders).

Carbonates

Formed by chemical and biochemical processes

Shales

Laminated sediment formed from consolidated mud or clay