Review of Crude Oil Properties
Specific gravity
Solution gas-oil ratio
Density of oil- Calculation from composition (C3
+)- Calculation from composition (C1 ~ C3
+)- Calculation if composition is not known
Bubble point pressure
Formation volume factor
Isothermal compressibility
Viscosity
Formation Volume Factor BO
Definition (FVF, BO ):
BO > 1- temperature high in reservoir- Gas is dissolved in oil under reservoir conditions.
Shrinkage factor: 1/Bo
ro
sc
VBV
Vr : Volume of oil at reservoir T and PVsc : Volume of oil at standard condition
(14.7 psia and 60F)Units: barrels of oil at reservoir conditions per barrel of stock-tank oil (res bbl/STB), always at 60F
Formation Volume Factor, Bo
Above bubble point pressure, …
Below bubble point pressure, …
Chart #22Estimation from Correlation Chart
You need: Gas-oil ratio Gas gravity Tank oil gravity Temperature
Ex. 2.11: Estimation of Bo from Correlation ChartWe have an oil with the following properties:g =0.786, o =40.7API, T=220F, read Bo values from
correlation chart under various Rs conditions.
Solution: Estimation from chart #22
Rs = 600 SCF/STB, Bo = 1.35
Rs = 1000 SCF/STB, Bo = 1.52
Two Phase (Total) Formation Volume Factor, Bt
Definition: Volume in barrels one stock tank barrel and its initial complement of dissolved gas occupies at reservoir condition (res bbl / STB).
Bo : single phase formation volume factorBg : gas formation volume factorRsoi : initial solution gas-oil ratio in reservoirRso : solution gas-oil ratio
( )t o g soi soB B B R R
Two Phase Formation Volume Factor, Bt
Above bubble point pressure,
Rsoi = Rso , Bt = Bo
Below bubble point pressure
Bt > Bo
( )t o g soi soB B B R R
Estimation of Bt from Correlation Charts
Chart #20
You need: Gas-oil ratio Gas gravity Tank oil gravity (API) Temperature Pressure
Ex. 2.12, Estimation of Bt from Correlation Chart
We have an oil with the following properties: g = 0.786, o =40.7API, T = 220F, P = 2000 psia. Read Bt values under various Rs conditions from correlation chart.
Solution:
Estimation from chart #20
Rso = 600 SCF/STB, Bt = 1.50
Rso = 1000 SCF/STB, Bt = 2.00
Isothermal Compressibility
1o
T
dVcV dp
co : oil compressibility
v: volume
p: pressure
Definition: change of volume per change of pressure under constant temperature condition.
Simplified calculation:
2 1
2 1
1o
V VcV p p
V: V1 , V2 , or the average
Isothermal Compressibility
p < pb : Villena-Lanzi correlation for black oil
p > pb : Vasquez and Beggs correlation
,
ln( ) 0.664 1.430ln( ) 0.395ln( ) 0.390ln( )0.455ln( ) 0.262ln( )
o b
sob o API
c p p TR
6 6
,
31.0(10) ( ) 6600(10) , 500 ( ) 5300, 763 ( ) 5300, 78 ( ) 3301.5 , ( / ) 1947, 6.0 ( ) 52.0, 0.58 1.20
o b
o API g
c psia p psig p psig T FGOR gas oilratio SCF STB API
5,(5 17.2 1180 12.61 1433) /( 10 )o sob g o APIc R T
,
126 ( ) 9500, 1.006 ( / ) 2.2269.3 , ( / ) 219915.3 ( ) 59.5, 0.511 1.351
o
o API g
p psig B bbl STBGOR gas oilratio SCF STB
API
Viscosity
Above pb , viscosity increases with p
Below pb , viscosity decreases with p
Viscosity ~ f(T, P, composition)
Viscosity Estimation Correlation
p < pb , dead oil (No solution gas):
p < pb , live oil (with solution gas)
10 10 ,
od
log [log ( 1)] 1.8653 0.025086 0.5644log( )where dead oil viscosity, cp, T = temperature, deg F
od o API T
0.515 0.338so
o,API
where A= 10.715(R 100) , 5.44( 150)conditions:0<p(psig)<5250, 70<T( F)<295, 16< ( ) 5820<GOR, gas-oil ratio (SCF/STB)<2070
Bo od
so
A
B R
API
pour ,Conditions: 59 < T( F) < 176, -58 < T ( F) < 59, 5.0 < < 58.0o API
Viscosity Estimation Correlation Chart
Chart #19
Dead oil Live oil
Viscosity Estimation Correlation
p > pb
1.187 -5
o,API
( / )
where m= 2.6p exp[-11.513-8.98(10) p]oil viscosity at the bubble point pressure, cp
conditions:126< p(psig) <9500, 15.3< ( ) 59.50.511 1.351
9.3<GOR, gas-oil ratio (SCF/
mo ob b
ob
g
p p
API
o
STB)<21990.117< ( ) 148.0cp
Type of Oil
Black oil
Volatile oil
Black Oil
Pressure path in reservoir
Separator
Black Oil
Contain more relatively heavier components
Critical T is far away from reservoir T
Rso < 2000 scf/STB
Bo < 2.0 res bbl/STB
Not always black, but usually dark colors
Volatile Oil
Pressure path in reservoir
Separator
Comparison: Black and Volatile Oil
Pressure path in reservoir
Separator
Volatile Oil
Contain more intermediate components (ethane to hexane)
Critical T is close to reservoir T
2000 < Rso < 3300 scf/STB
Bo > 2.0 res bbl/STB
2. Fluid and Rock Properties
2.1 Rock properties2.2 Gas properties2.3 Liquid properties
Oil properties:
Specific gravity
Bubble point pressure
Formation volume factor
Solution gas-oil ratio
Density
Total Formation volume factor
Isothermal compressibility
Oil viscosity, …
Gas properties:
z factor
Formation volume factor
Gas viscosity
Specific gravity, …
Questions: How do we obtain raw data on these properties?
Reservoir Sample Collection
Bottom-hole sample or subsurface sample
Put in figures
Reservoir Sample Collection
Put in figures
Separator samples, surface samples, recombination samples
2. Fluid and Rock Properties
2.1 Rock properties2.2 Gas properties2.3 Liquid properties2.4 Reservoir fluid properties – PVT study
Reservoir Fluid Studies – PVT study
Oil Properties
Gas properties
Quantities of separator gas, stock- tank gas, and stock-tank oil
Important properties in material balance equation
Reservoir Fluid Studies – PVT study
Oil properties:
Bubble point pressure
Formation volume factor
Solution gas-oil ratio
Total Formation volume factor
Isothermal compressibility
Oil viscosity, …
Gas properties:
z factor
Formation volume factor of gas
Gas viscosity
Specific gravity, …
PVT Study Procedures
Composition measurement
Flash vaporization
Differential vaporization
Separator tests
Viscosity measurement
Composition Analysis
Usually determine the composition of C1 - C6 , and lump all others to heptanes plus.
Heptanes plus composition
We get: mole fraction of each component.
Flash Vaporization
Put in figures
p decrease gradually
p1 >pb , Vt,1 p2 >pb, Vt,2 p3 , Vt,3 p4 , Vt,4p5 , Vt,5
Flash Vaporization
Put in figures
Start at Tr , Pr >= Pb Pressure is reduced gradually. Agitation to keep liquid-gas equilibrium. No gas or liquid is removed from the cell.
Also called: flash vaporization, flash liberation, pressure-
volume relations, constant composition expansion, flash expansion.
What we Get from Flash Vaporization?
Put in figure 10-2Determination of: pb Vsat specific volume = Vsat / mass relative volume:
V / Vsat , (Vt /Vb )F:
Ex. 2.13: The data from a flash vaporization on a black oil at 220 deg F is given below. Determine the bubble point pressure and prepare a table of pressure and relative volume for the reservoir fluid study.
Solution:1. Plot pressure against total volume, determine
pb = 2620 psig, Vb = 63.316 cc2. Determine relative volume = Vt / Vb
Ex. 2.13: The data from a flash vaporization on a black oil at 220 deg F is given below. Determine the bubble point pressure and prepare a table of pressure and relative volume for the reservoir fluid study.
Differential Vaporization
p decrease gradually until atmospheric P
p1 >=pb , Vo,1 p2 , Vo,2 p3 , Vo,3
Differential Vaporization
Start at Tr , P >= Pb Pressure is reduced gradually. Agitation to keep liquid-gas equilibrium. Gas expelled from cell while keeping p constant. Gas quantity and properties determined. Vo determined at each p until atmospheric p residual oil at T = 60 deg F and P = Pa Called: differential liberation, differential expansion
What we Get from Differential Vaporization
r r sc
sc sc r
V p TzV p T
Vo at various p (Reservoir conditions) Vresidual oil (standard condition): Vo,scRelative volume = Vo / Vresidual oil (= BoD )
Oil:
Gas:
Vg at cell condition (Reservoir conditions): Vr Vg at standard condition: Vg,scAlso know: pr , psc , Tr , Tsc z factor Bg
cu ft0.0282scf
rg
r
zTBp
How is Gas-oil Ratio (Rso ) Determined?
,
,
g scsD
o sc
VR
V
,
,
(entire process)g scsDb
o sc
VR
VBubble point
gas-oil ratio:
How is Relative Total Volume Determined?
( )tD oD g sDb sDB B B R R
PVT Study Procedures
Composition measurement
Flash vaporization
Differential vaporization
Separator tests
Oil viscosity measurement
What we Get from Flash Vaporization?
Put in figure 10-2Determination of: pb Vsat specific volume = Vsat / mass relative volume:
V / Vsat , (Vt /Vb )F:
What we Get from Differential Vaporization
r r sc
sc sc r
V p TzV p T
Vo at various p (Reservoir conditions) Vresidual oil (standard condition): Vo,scRelative volume = Vo / Vresidual oil (= BoD )
Oil:
Gas:
Vg at cell condition (Reservoir conditions): Vr Vg at standard condition: Vg,scAlso know: pr , psc , Tr , Tsc z factor Bg
cu ft0.0282scf
rg
r
zTBp
,
,
g scsD
o sc
VR
V
,
,
(entire process)g scsDb
o sc
VR
VBubble point
gas-oil ratio:
( )tD oD g sDb sDB B B R R Total relative volume:
Gas-oil ratio:
Ex.2.14: The data from a differential vaporization on a black oil at 220 deg F are given below. Prepare a table of solution gas-oil ratios, relative oil volumes, and relative total volumes by this differential process. Also include z-factor and formation volume factors of the increments of gas removed.
Ex.2.14 Solution
,sD -6
,
All calculation will be shown for pressure at 2100 psig. 1. Calculate gas-oil ratio:
(0.21256 0.02265 0.01966) scfR 684 scf/residual bbl(39.572 cc residual oil)(6.29 10 bbl/cc)
1'. Calcul
g sc
o sc
VV
,sDb -6
,
oD
ate gas-oil ratio at bubble point:( ) 0.21256 scfR 854scf/residual bbl
(39.572 cc residual oil)(6.29 10 bbl/cc)2. Calculate relative oil volume:
59.952 reservoir ccB39.572 residual c
g sc
o sc
V allV
-6R R sc
sc sc R
res bbl1.515 c residual bbl
3. Calculate z-factorV p T (4.292 cc)(35.315 10 cu ft/cc)(2114.7 psia)(520 R)z= 0.851V p T (0.01966 scf)(14.65 psia)(680 R)
4. Calculate formation volume factor of gas
B
g
g
tD oD g
cu ft cu ft0.0282 0.0282 0.851 680 / 2114.7 0.00771scf scf
(another way of calculating B ?)
5. B B B ( )
res bbl 0.00771 cu ft/scf scf1.515 + (854 684)residual bbl 5.615 cu ft/bbl residual o
r
r
sDb sD
zTp
R R
tD
il bblres bblB 1.748
residual bbl
Ex.2.14 Solution
Separator Tests
Reservoir T, P >= Pb
Separator T, P
Stock tank T, P
Separator Tests
Volume of liquid expelled from the cellVolume of liquid arriving in the stock tankoSbB
Volume of separator gas +volume of stock-tank gasVolume of liquid in the stock tanksSbR
Selection of Separator Conditions
Optimum separator pressure: the pressure that
produces the maximum amount of stock-tank fluid.
minimum RsSb , BoSb , maximum API
Typical range: 100 to 120 psig
Ex 2.15. Given the following separator test data of a black oil, calculate gas-oil ratio and formation volume factor. Volume of oil at bubble-point pressure and reservoir temperature = 182.637 cc; volume of separator liquid at 100 psig and 75 deg F = 131.588cc; volume of stock-tank oil at 0 psig and 75 deg F = 124.773 cc; volume of stock-tank oil at 0 psig and 60 deg F = 123.906; volume of gas removed from separator = 0.52706 scf, volume of gas removed from stock tank = 0.07139 scf.
sSb
-6
182.637 cc 1.474 res bbl/STB123.906 ccvolume of gas from separator + volume of gas from stock tankR
volume of gas from stock tank0.52706 scf + 0.07139 scf
123.906 cc (6.29 10 bbl/cc)767.9
oSbB
scf/STB