5 Liquid Properties

7/30/2019 5 Liquid Properties

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PETE 216RESERVOIR ROCK AND FLUID

PROPERTIES

PROPERTIES OF RESERVOIR LIQUIDS

SPRING 2012 2013

Dr. Mahmut Parlaktuna

[email protected]


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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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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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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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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

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5 Liquid Properties