GEOL 404 Final Exam

Petroleum exploration needs huge up-front capital investment and has great risk of drilling dry holes which could lead to business failure. Risk analysis in petroleum geology to reduce such risks has the following five components:

source rock, reservoir rock, structural trap, seal and timing

The four levels of petroleum investigation proceed in the following order:

Sedimentary basin, petroleum system, play, prospect

Plate tectonics is important in petroleum system analysis, because it helps to determine ________.

sedimentary basin types, source property, reservoir types and structure types

To know the "Period" names and times of the Phanerozoic is very important because ______________.

the knowledge of the stratigraphic column is needed to calibrate the occurrence of the five system elements including the critical "timing"

______________ is mostly composed of granites, related igneous and metamorphic rocks, as well as sedimentary rocks.

continent crust

__________ is thicker than __________. _______ is denser than ______.

continent crust, oceanic crust; oceanic crust, continental crust

Higher a mountain, shallower its root.

False

Passive margins are usually formed during the stage of _____ in Wilson cycle.

sea floor spreading

Foreland basins are usually formed during the stage of _____ in Wilson cycle.

Continental Collision

Rocks tend to be more ductile as depth increases to the lower part of the crust or the upper mantle because _______.

both temperature and pressure increase

Sandstone usually has more fractures and faults than shale because ____

shale is more ductile than sandstone

Normal faults are produced by _____

tensional stress

Rocks tend to be more ductile as depth increases to the lower part of the crust or the upper mantle because _______.

both temperature and pressure increase

Sandstone usually has more fractures and faults than shale because ____

shale is more ductile than sandstone

Normal faults are produced by _____

tensional stress

For conventional hydrocarbon exploration, oil/gas reserves are trapped in __________.

anticlinal structures instead of synclinal ones

The San Andreas fault is ________________.

a right lateral fault.

__________ is to reveal the present position of rock strata and deformational features and uses the sea level as the datum.

Structural cross-section

__________ can use any regionally prominent bed as a relative datum to reveal the depositional history and features of the rock layers below the datum.

stratigraphic cross-section

__________ is to reveal the areal shapes of a formation top (surface).

structural map

An isopach map is a contour map of ______ whereas an isochore map is a contour map of ________.

true stratigraphic thickness; true vertical thickness

A net sand map is a contour map of ______ whereas a net pay map is a contour map of ________.

the sand:shale ratio of a formation; the gross pay : net pay ratio of a reservoir

Coarse-grained sand is deposited in _____________ environment.

high energy

Clay is deposited in _____________ environment.

low energy

Limestone is formed from calcite ______________.

transported by water and precipitated organically from solution.

Shale is formed from clay ______________.

transported by water as mineral grains.

Permeability is affected strongly by _________.

porosity and grain size as well as sorting

Channel bars are formed in _________ whereas point bars in _____.

braided stream systems; meandering river systems

Deposition of turbidites is usually found in _______.

deep-marine fan

A limestone called mudstone is usually formed ___________.

down the slope

During a core description work, you find a coarsening upward sequence which is a characteristic of ________.

sea level fall

During a core description work, you find a fining upward sequence which is a characteristic of ________.

sea level rise

Gravity survey can be used to map large-scale subsurface structures because it senses ___________.

the density difference between stratas

Magnetic survey can be used to map large-scale subsurface structures because it senses ___________.

iron content difference between stratas

Seismic survey can be used to map detailed subsurface structures because it senses ___________.

acoustic impedance difference between stratas

Mudcake is one of the four important zones in borehole environment. In which formation do expect thick layer of mudcake on the borehole wall?

porous sandstone

When you measure the conductivity of a solution in a container, you find its conductivity is very high, which lead yo to conclude: The most favorable scenario is that ___________.

its salinity is high and temperature is high

Conductivity of the formation in an uninvaded zone increases _________.

as the conductivity of the formation water, water saturation and porosity increase

Conductivity of the formation in an invaded zone increases _________.

as the conductivity of the mud filtrate, mud filtrate saturation and porosity increase

Sxo measures the mud filtrate saturation in the invaded zone which is ____________________, whereas Smo is _________.

water and movable hydrocarbon; movable hydrocarbon

From the spectral gamma ray log, the K-TH log gives a good indication of __________ whereas the very high U log reading means ___________.

clay content; high organic content.

Density log gives ____________, Pe log gives ____________, and neutron log gives _____________.

bulk density; matrix density; porosity

Which of the following statements is not true?

Seismic waves travel faster in the crust than in the mantle.

Which of the following statements is true?

Continental crust has high silica and aluminum content.

Which one of the following shows the correct order of the Wilson Cycle?

Continental rifting, seafloor spreading, ocean closing, arc-continent collision, continent-continent collision.

Which one of the following statements is true?

Shale is more ductile than sandstone.

Which of the following statements is true?

A reverse fault is produced by compression.

For conventional hydrocarbon exploration, oil/gas reserves are trapped in __________.

anticlinal structures instead of synclinal ones

A geologist walking across a plain observed the age change of the eroded outcrops in the following order: Permian, Triassic, Jurassic, Triassic, Permian. The geologist concluded that the eroded structure

a syncline.

Which of the following statements is true?

Isopach map shows contours of true stratigraphic thickness of a formation.

__________ is to reveal the shapes of a formation top (surface).

structural map

A net sand map is a contour map of ______ whereas a net pay map is a contour map of ________.

the sand:shale ratio of a formation; the gross pay : net pay ratio of a reservoir

Compared to clastic rocks, evaporites precipitated inorganically from solution are _________.

excellent seal rock.

When sediments are moved from the source to the ocean, _________________

coarse-sized grains are deposited nearer to the source than fine-sized grains.

Clay is deposited in _____________ environment, whereas organic matter is deposited in _____________ environment.

low energy; low energy

Limestone is formed from calcite ______________.

transported by water and precipitated organically from solution.

Shale is formed from clay ______________.

transported by water as mineral grains.

Permeability is affected strongly by _________.

porosity and grain size as well as sorting

In exploration, a thick coal deposit is found. A geologist concluded that the depositional environment is _________________.

terrestrial

What is the correct order of the following facies from land towards basin?

Beach, Lagoon, Reef, Slope

Deposition of turbidites is usually found in _______.

deep-marine fan

An unconformity is ______________________.

a surface in rock succession indicating a time gap caused by uplifting, folding and erosion or non-deposition

An oil reservoir has an average porosity 20%. The water resistivity Rw at the reservoir temperature is 0.02 ohm.m. Let both the cementation exponent (m) and the saturation exponent (n) be 2, tortuosity (a) be 1. If the true formation resistivity Rt measured from well logging is 50 ohm.m, calculate the oil saturation.

0.9

There are two reservoir units in an oil field. The upper unit is a sandstone reservoir and the lower unit is a carbonate reservoir. The water saturation estimated from well log data is 30% in both reservoir units. However, the saturation of movable fluid in the flushed zones of the sandstone reservoir is 45% whereas the saturation of movable fluid in the flushed zones of the carbonate reservoir is 35%. What is the recovery factor in the sandstone and carbonate reservoir respectively?

21% and 7%

Sound wave transmission in rocks is affected by _________.

lithology, fluid type and amount, pressure, porosity, rock structure

Compressional wave is related to _________ and shear wave is caused by ________.

volumetric and shape changes; shape change only

Sound wave travels faster in rocks of ________ porosity.

smaller

In electrical imaging logs, electric current is used to detect vuggs, fractures and other small-scale structures because ___________.

these structures usually contain conductive fluids whereas dense rocks are resistive to electric current

The T2 time in the NMR log is ________ in rocks containing more clay because _________.

smaller; water molecules are bounded to the grains and not easy to move

Clay particle in rocks is part of the __________________.

solid matrix

Connate water is _________________________.

water that can potentially freely move like meteoric water but is trapped by surrounding rocks

The state of hydrocarbon molecules in paraffins (i.e., gas, liqiud or solid), is determined by ______________.

the carbon number

By definition, "heavy oil" is ________ than water and "extra heavy oil" is _____________ than water.

lighter; heavier

During the burial of sediments and sedimentary rocks, compaction occurs in which __________

bulk rock mass gets more consolidated but the amount of solid mass does not change as the burial depth increases.

A rock at a depth is overpressured if ____________

its pore pressure is greater than the hydrostatic pressure at the same depth.

The temperature of a sedimentary basin is higher if ___________.

it thermal conductivity is smaller and it has more internal heat generation

Heat is conducted more efficiently in sedimentary rocks if they contain more _____.

a lot of low-porosity rocks with high quartz content.

The two processes in the definition of petroleum system are _____.

trap formation and petroleum generation-migration-accumulation

Trap formation and petroleum generation-migration-accumulation

that best shows the generation-migration-accumulation

Faulting is part of the ____________________.

basin-modifying tectonics

Sedimentary basins can have very different subsidence rate. That of passive margins usually is ______ than intracratonic basins and _____ than strike-slip basins.

faster; slower

According to Mann's basin classification, which basin type has most of the world's oil and gas?

Passive margins

The geothermal gradient of passive margins is usually _________.

below average

Strike-slip basins usually have _____ subsidence _______ deposition and ________.

very rapid; very rapid; very high facies variation

Natural gas produced from conventional reservoirs and shales is generated from kerogen type _______.

I and II

In the oil window, _________________ is produced.

more oil than natural gas

In the gas window, _________________ is produced.

very little or almost no oil

As a thermal maturation indicator, a vitrinite reflectance value of _______ marks the beginning of the oil window.

0.6

The depth of oil window varies in different basins because _______.

oil window is determined by temperature

Petroleum discovered and commercially produced so far originated from _______.

organic matter previously deposited in the sedimentary basins

Fossil fuel comes from only _________ of the organics in the carbon cycle

1 part per million

The best source of oil is from ________.

phytoplankton, spores and pine needles

The best conditions for organic matter accumulation are _______.

shallow marine, anoxia and intermediate sedimentation rate

After careful analysis, you found that your shale has a TOC of 3 % in weight percentage which means its hydrocarbon generation potential is __________.

very good

Kerogen is formed from _______.

lipid-rich solid organic compounds not consumed by bacteria

Among different kerogens, kerogen Type I has the _______________.

highest H-C ratio

Among different kerogens, kerogen Type III has ______________.

highest O-C ratio

Hydrocarbon generation rate depends on _______.

temperature, heating rate, kerogen amount and type

In the first-order kinetics of kerogen degradation, the reaction rate parameter in the Arrhenius law ______ as temperature increases.

increases

In a gamma ray log collected from a well drilled through an alternating sequence of shales and sands formed in a clastic environment, the GR reading of the cleanest sand unit is 50 API and the GR reading of the shaliest unit is 150 API. The GR reading of a thin sandy shale unit targeted for shale gas production is 90 API. Calculate the clay content (Vsh) of the thin sandy shale unit.

Vsh=0.40