oil and gas Flashcards
reserves
the amount of the resource that can be extracted at a profit using existing technology
primary recovery
oil initially gushes out to the surface under natural pressure and is then pumped out
secondary recovery
water is injected below or natural gas injected above the oil to maintain pressure
travel time
the time taken for a pulse to travel to a boundary and back again
oil shale
fine grained sedimentary rock containing kerogen that did not mature into oil
name and explain two key properties rocks require to be good reservoir rocks
high porosity to store significant amounts of oil and natural gas. High permeability to allow them to migrate into the rock
sapropel
the unconsolidated, dark-coloured, organic-rich deposit which becomes the source rock
fossil fuel
made from the remains of once living organisms and are coal, oil and natural gas
caprock
the impermeable rock above the reservoir rock preventing further upwards migration of petroleum
describe the maturation process
on burial, the source rock is subjected to compaction and an increase in temperature. over time the organic matter breaks down to kerogen and then to petroleum
what types of rock form caprocks?
fine grained, clay, mudstones and evaporites
What causes the loss of oil and natural gas?
destroyed at 200 degrees due to deep burial, regional metamorphism or heat from an igneous intrusion or volcanic activity. it may also be lost from a trap by erosion and removal of caprock or by migration along an unsealed fault plane.
how are seismic survey carried out?
seismic waves are generated by a ‘thumper’ or air gun which travel into the earth and are reflected at layer boundaries. the reflected waves travel back to the surface and are detected by geophones or hydrophones.
how are gravity surveys carried out?
Gravimetres are mounted to road vehicles, helicopters or planes to cover large areas. the data is corrected for latitude, altitude and topography to give the Bouguer anomaly which indicates variations in the underlying rock.
what does a positive gravity anomaly indicate?
results from an excess of mass. this may be due to an anticline or an uplift fault block which could be a potential trap structure.
what does a negative gravity anomaly indicate?
results from a deficit in mass. this may be due to a low-density salt dome. the exploration target would be around the edge of the salt dome at the zero milligal line.
Source rock
Organic rich mudstone or shale which contained abundant plankton that formed in low energy, anoxic, marine environments
Migration
The movement of petroleum from a source rock to a reservoir rock
Reservoir rock
Highly porous and permeable rock capable of storing and yielding significant amounts of petroleum
Trap
A geological situation that concentrates petroleum in one place
What methods are used in secondary recovery to recover more oil? X4
Water flood drive
Gas cap drive
Detergents
Bacteria digesting method
What temperature creates oil?
50-100 degrees C
What temperature creates natural gas?
100-200 degrees C
What kind of fields are found in the Northern North Sea Basin?
Oil
What is the source rock in the northern North Sea basin?
Kimmeridge clay
What are the reservoir rock in the northern North Sea basin?
Marine sandstone
Fractured chalk
What is the cap rock in the northern North Sea basin?
Clays
What kinds of fields are found in the southern North Sea basin?
Gas
What is the source rocks in the southern North Sea basin?
Coals
Organic shales
What is the reservoir rock in the southern north sea basin?
Permian dune sandstone
What is the cap rock in the southern North Sea basin?
Permian evaporites
Why is there only one hydrocarbon type in the southern North Sea basin?
The coal did not contain the marine plankton needed for oil formation
Why are older rocks unlikely to hold oil?
Buried too deep- out of oil window
Oil migrated to surface
What is the deposition an environment required of source rocks for oil and natural gas?
Low energy
Anoxic
Marine environment
How much of a reserve can be recovered using primary methods?
20 to 30%
Name 3 unconventional sources of oil and gas
Oil shales
Tar sands
Frozen gas hydrates
