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PETROLEUM SYSTEMS QUESTIONS
1. Of all the environments in which large volumes of
hydrocarbons are found, ice-like gas hydrates are thought tocontain
some of the largest volumes of gas both onshore in permafrost and
offshore on cold continental shelves,but they cannot be tapped
commercially today. Which of the following is the main cause of
that?a. the reservoirs are too deep,b. they contain the wrong type
of gas,c. the concentration of the gas is too low,d. it is
difficult to melt the hydrate,
e. it is too expensive to drill the wells.
. !he top of the oil generation window can be found at depths
ranging from "1###m to $###m but is generallyreached between
###-%###m below surface. Which of these is the main reason why this
variation is found?a. changes in tectonic uplift and &or
downwarp,b. changes in organic material,c. changes in thermal
conductivity,d. changes in heat flow,e. changes in
structuration.
%. 'ost source rocks are fine grained( shales or micrites. )et
coal, which is hosted in fine grained mud, is not ama*or source for
gas or oil +ignore its ability to be a minor source of coal bed
methane. Which of the following isthe most important reason for
this?
a. too much moisture,b. too much wood,c. too much oxygen,d. too
much sulphur,e. too much mud.
. !he worlds oil is mostly found in /retaceous and !ertiary
strata. Which of these is the main cause of that?a. temperature,b.
pressure,c. timing,d. sediment,e. organic matter.
$. 0eservoirs of oil can be found at depths ranging between
surface and more than kilometres but generally###-%###m below
surface. 'ost reservoirs can be tapped with current technology yet
most of the oil is left in thereservoir after production with
commonly only #-%#2 being produced. Which of the following is the
main reasonwhy so much oil is left behind?a. reservoir pressure is
too low,b. boreholes have a short lifespan,c. water preferentially
flows from the reservoir,d. gas flows preferentially from the
reservoir,e. the ground shrinks too much.
3. !he oil industry taps conventional sources of oil worldwide
to feed the worlds economy. )et the price of oil hasrisen five-fold
over the past 1# years and the world reportedly faces a crisis
dubbed the 4end of oil5 amid fears thatwe will soon run out of oil.
)et the world barely taps tar sands which contain orders of
magnitude more oil than
conventional oil sources. Which of the following is the main
reason why that is the case?a. too many engineers are needed,b. too
slow a production rate,c. too expensive to transport to market,d.
too much energy needed produce the oil,e. too much water needed to
steam the oil.
6. !he main method of finding structures that might contain
hydrocarbons is the reflection seismic method inwhich sound waves
are sent into the ground and the sound waves reflect from
geological boundaries. 7mpedancecontrasts due to differences in
velocity and density characterise geologic boundaries allowing for
the constructionof a seismic section through the earths surface. 7t
is not uncommon to find indications of gas reservoirs from
theircontacts +bright spots, flat spots but rare to find that for
oil reservoirs. Which of the following is the main reasonfor the
inability of seismic data to reliably image oil in reservoirs?a.
bad seismic data,b. gas is more common,c. oil density and fluidity
in the reservoir is similar to that of water,d. gas is too diffuse
in the reservoir,e. water is too salty.
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. !he 8etroleum 9ystem concept is a way of interpreting geologic
data to determine if an area or basin is likely tocontain oil or
gas before it has been extensively drilled. !he concept relies on $
main factors that need to be inplace in order for oil or gas to be
found. Which of the following is the correct set of criteria?a.
seismic interpretation, reservoir engineering, geochemistry,
palaeontology and palaeobotany.b. evaporites, mass flows,
vulcanism, granite intrusion, lava domes.c. structure, seal,
charge, reservoir, preservation.d. maturation, generation,
migration, seepage, leakage.
e. time, source, charge, migration, gas flow.
:. 'any of the wells drilled over the past 1## years with the
express intention of finding commercial volumes of oilwere
reportedly unsuccessful. )et it is not uncommon for to encounter
old wells that were drilled through an oilreservoir but it was not
recognised. !oday many small companys profit by rediscovering that
oil through carefulstudy of the original drilling and log data.
Which of the following is the main reason why it is possible to
miss theoil?a. the volumes were thought too small,b. the log data
were not properly interpreted,c. the well was drilled with too
dense a mud,d. the oil or gas migrated into the structure after the
first well,e. the gas or oil was the wrong type to be
commercial.
1#. 'any gas fields have been found over the past 1## years of
exploration but not developed. ;ow companiesare re-considering
those wells because they host commercial volumes of gas. asin been
selected by foreign and local companies as the focus area for
okkeveld shales and unknowns can be good,
+b because >okkeveld shales have proven their ability to flow
gas,+c because there is known oil in the area,+d because the
Whitehill shale is known to have high carbon contents+e the
Whitehill is heavily fractured?
1. arge volumes of gas without oil has been found off 'o@ambiAue
and =enya whereas large volumes of oilwith minimal gas has been
found in Bganda. Which of the following is the main reason for
this?+a Bganda has a tropical climate,+b because onshore areas
generally have oil deposits,+c because offshore areas generally
have gas deposits,+d because gas-prone organic material has been
concentrated in offshore areas and oil-prone in the graben,+e
because all the gas has escaped from the Bganda deposits?
1%. Cas fracking has become a highly emotive phrase, both in the
B9
