Class 12A_Determination of Fluid saturation.pdf

reservoir

1. Determination of FLUID SATURATION
using preserved core samples
or rather plug-end trim of the
core plug
Direct approach
Indirect approach
Coreplugusedfor
measurementofcapillary
pressureonwhichthefluid
saturationaredetermined
Traditional well logging
techniques for indirect
measurement of
fluid saturation in-situ

2. RETORT DISTILLATION
volume of oil
So = ------------------
pore volume
volume of water
Sw = --------------------
pore volume
S
g+ S
o+ S
w= 1.0
Disadvantages
1. The rock samples is completely
destroyed
2. High temperature is required
Heating unit
Condenser unit
Receiver unit

3. PROBLEM OF USING HIGH TEMPERATURES
Atsuchhightemperaturethewaterofcrystallizationwithintherockisdrivenoffcausing
thewaterrecoveryvaluestobegreaterthanporewater.
Hightemperaturesmaycrackandcoketheoilcausingthecollectedoilvolumetonot
correspondtothevolumeofoilinitiallyintherocksample.
Inaddition,formationofoilwateremulsionthatdonotallowaccuratemeasurementsand
theabsenceofcleardemarcationbetweentheplateausofporewaterandthewaterof
crystallizationintroducinguncertaintiesinthemeasurementofwatervolume

4. DEAN-STARK EXTRACTION
Disadvantages
Time taken is very high
Only water saturation can be directly measured
WW –DW = M
g+ M
o+ M
w
V
g
g+ V
o
o= WW –DW -V
w
w --------Eq 1
PV = V
g+ V
o+ V
w
V
g + V
o= PV –V
w ------------------Eq 2
The difference between the wet weight and the
dry weight of the rock sample is equal to the weight
of the fluids in the rock samples
Eq 1 and Eq 2 can be solved to obtain the values of V
gand V
o
Vg Vo Vw
Fluid saturations Sg =-------, So = --------, Sw = -----------
PV PV PV
Long-neck round bottom flask

5. FACTORS AFFECTING FLUID SATURATION
•Effect of drilling mud: invasion of core sample by the mud or
or the mud filtrate during the coring process
•Effect of fluid expansion: shrinkage and expulsion of fluids from
the core material as the core is brought to the surface
Drilling mud–a particle suspension mixture of finely divided heavy material, barite,
bentonite blended with a liquid
water based
non-water based or oil based
Use: 1. to cool and lubricate the rotating bit
2. to hinder the penetration of reservoir fluid
into the well bore

6. Water based drilling mud –leading to higher water saturation
Oil based drilling mud –water saturation is almost likely unaltered

7. Effect of fluid expansion
1.When cores are cut and brought to
the surface –pressure depletion –
release of dissolved gases –escape
from the core with some mobile oil and
water
2.Thermalcontractionofanyoilandwater
presentintheporesystemmaybe
significantasthecorematerialcools
fromreservoirtemperaturetosurface
temperature
Pressure and temperature effects result in completely altered fluid saturation in
the core sample as compared to the actual reservoir

8. TYPICAL PRESSURE-TEMPERATURE DIAGRAM
OF TWO COMPONENT SYSTEM
•noliquidabovethis
temperature
•Maximum Tat
whichtwophasecan
existinequilibrium
•No gas above this pressure
•max. pressure at which two
phase can exist in equilibrium
Retrogradecondensation
occursattemperatures
betweenthecritical
temperature and
cricondentherm.

9. CR
Measuretheresistivityoftheformationbyinjecting
currentintotheformation
Current moves from
source to current return
Currentisfocusedsothatitdoesnottakethe
pathofleastresistancethroughthedrilling
mudtothecurrentreturn
RESISTIVITY MEASUREMENTS

10. SPACING: The
distance between
EMITTER and
RECEIVER
Generally, an increase in the distance between emitter and receiver results in an improved
depth of investigation at the expense of vertical resolution
The contributions from various zones, as
a function of distance from the sonde axis
DEPTH OF INVESTIGATION: The point at which
half of the signal comes from the invaded zone and
half from the uninvaded zone

11. FOCUSING LONG-
SPACING TOOLS
NON-FOCUSING SHORT-
SPACING TOOLS

12. TheLLdsystemusedremote
(surface)returnsforthemainand
buckingcurrents.So,thecurrent
wasflowingperpendiculartothe
tool.
TheLLssystemusedtheA
2-A’
2
electrodepairasthereturnforthe
buckingcurrentfromA
1-A’
1which
reducedtheeffectivenessofthe
focusingofl
0.Thiscausedthe
measuredcurrenttodivergemore
quicklyonceithadenteredthe
formation,thusproducinga
relativelyshallowdepthof
investigation.
DLL tool operated simultaneously at two frequencies: 35 Hz for the LLd
: 280 Hz for the LLs
LATEROLOGS

13. SPHERICALLY FOCUSED LOG (SFL)
Thetoolconsistsofa
central current
electrodeA0and
eightsymmetrically
placedelectrodes,
connectedinpairs
M
0-M’
0,A
0-A’
0etc.

14. MICROLATEROLOG
THE MICROLATEROLOG

15. THE MICRO-SFL (MSFL)

16. Resistivity log

17. DIL Versus AIT, HIDDEN ZONE IDENTIFICATION

18. EXAMPLE OF
INTERPRETATI
ON RESULTS
COMBINING
HDIL AND
OTHER LOG
DATA

19. Formation factor is defined as the ratio of the resistivity of
completely brine saturated rock to the resistivity of the
saturating brine
FORMATION FACTOR
R
o
F = -------
R
w

20.  = tortuosity (dimensionless) (La/L)
2
F = ----------L
a= effective path length through the pores
 L = length of the core, = porosity
TEXTURE OF THE ROCK
TheratioLa/Listheratioofthelengthofthetortuouspaththrough
therocktothelengthoftherockelement.Itiscommonlytermed
‘tortuosity’andinclean,uniformsandstonethesquareofthisvalue
isapproximatelyequaltothereciprocalofporosity

21. Theroleofmatrixisevident:
LessatlowvaluesofF(top)
GreaterathighvaluesofF(bottom)
La
La

22. Influenceoffracturesandnon-
connectedvugsonresistivity
measurementsandtheArchie’sfactor
m

23. Cementation Factor
To describe the relationship between the formation
factor and porosity.
A different form of equation is suggested by
introducing the cementation factor, m, where
R
o For sandstone a = 0.81
F = -------= aФ
-m
For carbonate a = 1
R
w and m ~2
This equation results in
F (Resistivity Factor) = infinite when Ф= 0
F = 0 when Ф= 1
Naturalformationsdon’thaveuniformpore
geometry.PlottingFasafunctionoftheporosityø,
commonexpressionis
F = aФ
-m

24. Resistivity Index
Inaporespacecontaininghydrocarbons(oilorgas),bothofwhich
arenonconductorsofelectricity,withacertainamountofwater,
resistivityisafunctionofwaterorbrinesaturation,Sw.
For a given porosity, at partial brine saturations, the resistivity of a rock is higher
than when the same rock is 100 % saturated with brine. Archie determined
experimentally that the resistivity factor of a formation partially saturated with
brine can be expressed by
R
o Ro = resistivity of the rock when saturated with 100% brine in m
-------= (Sw)
n
Rt = resistivity of the rock when in partially saturated with brine in m
R
t n = the saturation exponent
Theresistivityoftherockpartiallysaturatedwithbrine,
Rt,isalsoreferredtoastrueresistivityofformation
containinghydrocarbonsandformationwater.

25. R
o
F = -------= aФ
-m
R
w
R
o
------= (Sw)
n
R
t
Comparing the above two equation, Ro can be eliminated to obtain a generalized
relationship for water saturation
Ro FRw aRw
Sw = ( ------)
1/n
= (---------)1/n = (---------)
1/n
Rt Rt Ф
m
Rt
The ratio Rt/Ro is commonly referred to as the resistivity index, I
I = 1 for fully brine saturated rock
I> 1 for rock with partial saturation or HC are present
Ro
Sw= ( ------)
1/n
= (I)
-1/n
Rt

26. Constanta,mandnneedtobedeterminedfora
particularfieldorformationbeingevaluated.
Ro
Sw= ( ------)
1/n
= (I)
-1/n
Rt
Ro FRw aRw
Sw = ( ------)
1/n
= (---------)1/n = (---------)
1/n
Rt Rt Ф
m
Rt

27. EFFECTS OF CLAY ON ELECTRICAL
PROPERTIES
The effect of the clay on the resistivity of the rock is dependent upon
• the amount
• the type of clay
• the manner of distribution of the clay in the rock
Thecapacityof
claystoconduct
electricityvaries
between clay
speciesandseems
todependonthe
surface area
availableinthe
clay

28. Itisonlyatthesurfaceofclay-minerallayersthatthedissociation
occursandacurrentisabletobecarried.Clayislikeaninverted
electriccable:theinsideisnon-conductivewhiletheoutside
conductselectricity.Theoutsideconductinglayeriscomplex;
adsorbedwaterclingstotheimmediateclaylayerandthepositive
ions(Na+inasaltsolution)surroundedbyhydrationwaterforma
furtherouterlayer. This external water, called
bound water, is chemically
free but physically bound
Conceptualized model for clay bearing formation

29. o
wb
B
1
)S(1
G
N
VSTOIIP   hAV
b
 where:
V
b
= bulk volume of the reservoir rock, bbl
N/G = net/gross ratio of formation thickness, fraction
= porosity, fraction
S
w
= water saturation, fraction
B
o
= oil formation volume factor, rbbl/STB
STOIIP = stock-tank oil initially in place, STB
where: A = area of the reservoir, ft
2
h= thickness of the reservoir, ft
……..…. Eq. 1
……….….Eq. 2
Equation 2 is used to calculate bulk volume of the reservoir (V
b
)
initial fluid saturation leads to estimation of hydrocarbon reserves in place
WHY IMPORTANT

30. Oil-Water Relative
Permeability
40
0
20
400 1006020 80
Water Saturation (%)
Relative Permeability (%)
100
60
80
Water
k
rw@ S
or
Oil
Two-Phase Flow
Region
Irreducible
Water
Saturation
k
ro@ S
wi
Residual Oil
Saturation
dominates important flow properties due to the strong influence it
has on relative permeability functions

31. Oil-Gas Relative
Permeability40
0
20
400 1006020 80
Total Liquid Saturation -% of Pore Volume
Relative Permeability (%)
100
60
80
Gas
k
ro
Oil
k
rg
S
L= S
o+ S
wi

32. Interstitial wetting
phase saturation
0
20
40
60
80
100
0 20 40 60 80 100
DrainageImbibition
Wetting Phase Saturation, % PV
Relative Permeability, %
Residual non-
wetting
phase saturation
Drainagecurve
Wetting phase is displaced by the nonwetting phase, i.e., the wetting phase
saturation is decreasing
ImbibitionCurve
Non-wetting phase is displaced by wetting phase, i.e., the wetting phase saturation
is increasing
Effect of Saturation History

33. Natural Flow
PRIMARY RECOVERY Artificial Lift
Sucker Rod Pump
Gas Lift
Plunger Lift
Cavity Pump
Electrical Submersible Pump
Chamber Lift
Water Flood
SECONDARY RECOVERY Pressure Maintenance
(Water, Dry HC gas injection)
Thermal Recovery Process
TERTIARY RECOVERY Chemical Flooding
Miscible Flooding
Other (Microbial)
Primary production: natural energy
stored in the reservoir act as a
driving mechanism for production
Used to determine the target oil in place for secondary or tertiary
EOR project