5 liquid properties
TRANSCRIPT
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PETE 216RESERVOIR ROCK AND FLUID
PROPERTIES
PROPERTIES OF RESERVOIR LIQUIDS
SPRING 2012 2013
Dr. Mahmut Parlaktuna
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DEFINITION
Liquids have higher densities and viscosities than
gases.
l
>> g
, l
>>g
The density of a liquid is less affected by changes
in T and P.
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SPECIFIC GRAVITY OF A LIQUID
at the same T and P
In British system o 60/60 means that the densities of
both the liquid and water were measured at 60 F
and atmospheric pressure.
The petroleum industry also uses another gravity
term called API gravity,
w
oo
5.1315.141
o
API
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GAS SOLUBILITY
Solubility implies that there is some upper limitto the quantity of gas which can be dissolved in the
crude oil.
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GAS SOLUBILITY
The differencebetween the solubilityat the bubble pointand the solubility at
pressures below thebubble pointrepresents the amountof gas which hasalready evolved intothe pore space of thereservoir due to thereduction of pressurebelow bubble point.
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GAS SOLUBILITY
The gas-solubilityline is horizontal at
P>Pb because at
these pressures nogas is evolved in
the pore space and
the entire liquidmixture is
produced into the
wellbore.
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GAS SOLUBILITY
When the pressure
is reduced below
bubble point, gasbegins to form in
the reservoir and
less gas remains inthe liquid.
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LIQUID VISCOSITY
l is affected by P and T.
T l
P l
(provided that the only effect of pressure is tocompress the liquid)
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LIQUID VISCOSITY
A third parameter that affects liquid viscosity is:
A decrease in the amount of gas in solution in the
liquid causes an increase in viscosity and of course
the amount of gas in solution is a direct function of
pressure.
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LIQUID VISCOSITY
The decrease in l due to increase in T andincrease in l due to increase in P are offsetting.
So that the major effect on l is the decrease
attributed to the increase in the amount of gas insolution in the reservoir oil due to the increase in
pressure.
If the Pr > Pb (so that no additional gas enters intothe solution) the l due to the compression of
the liquid.
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LIQUID VISCOSITY
The effect of
reservoir pressure
on the viscosity ofthe reservoir oil at
constant reservoir
temperature
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LIQUID VISCOSITY
Pr > Pb initially.
As Pr is decreasedl decreases dueto expansion ofthe oil.
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LIQUID VISCOSITY
At Pb gas isliberated so l
starts to increase.
(i.e. lighterhydrocarbons start
to leave the
solution).
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LIQUID VISCOSITY
As an oil reservoir is depleted, not only does theproduction decreases due to decrease in
pressure available to drive the oil to the well,
but also because the has increased.
A 10-fold variation between the viscosity at the
bubble-point pressure and the viscosity at verylow pressure is not uncommon.
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OIL FORMATION VOLUME FACTOR
The volume of liquid that enters the stock tankat the surface is less than the volume of liquid
which leaves the reservoir due to,
Evolution of gas from liquid
Pressure reduction causes the remaining oil to
expand slightly.
Contraction of the oil due to the reduction oftemperature.
c in fact offsets b.
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OIL FORMATION VOLUME FACTOR
The change in liquid volume due to these 3factors is expressed in terms of formation
volume factor of oil which is defined as the
volume of reservoir liquid required to produce 1STB of oil.
STB
bblres
StocktankatoilofVolume
PandTreservoiratgasdissolvedoilofVolumeBo
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OIL FORMATION VOLUME FACTOR
Example: A sample of reservoir liquid whosevolume was 400 cc under reservoir conditions
was cooled to 60 F and the pressure was
released to 14.7 psia. The liquid volume wasreduced to 274 cc and 1.21 scf of gas were
released. Calculate the oil formationvolume
factor.
STBresbbl
cc
ccB
o46.1
274
400
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OIL FORMATION VOLUME FACTOR
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OIL FORMATION VOLUME FACTOR
As PR Bo due to expansion of liquid inthe reservoir.
Therefore Bo up to Pb.
A reduction PR below the Pb results in evolution of gasin the pore spaces of the reservoir. The liquidremaining in the reservoir has a smaller volume andconsequently Bo.
When Pr Patm, Bo 1. A reduction of temperatureto 60 F is necessary to bring Bo exactly to1.
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TOTAL FORMATION VOLUME
FACTORWhen reservoir pressure is below the bubble pointpressure of the oil, gas and liquid are present in thepores of the formation. Then total formation volumefactor (Bt) is used.
Bt = Bo + Bg(Rsb-Rs)
Bt sometimes called two-phase formation volumefactor
Bg(Rsb-Rs) volume of gas evolved from the liquid inthe reservoir.
Bg rbbl/SCF, Rs SCF/STB, Bo rbbl/STB
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TOTAL FORMATION VOLUME
FACTOR
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ISOTHERMAL COEFFICIENT OF
COMPRESSIBILITY
T
o
PV
VC
1
T
o
o
o
P
B
B
1C