Review of Crude Oil Properties Specific gravity Solution gas-oil ratio Density of oil - Calculation from composition (C 3 + ) - Calculation from composition (C 1 ~ C 3 + ) - Calculation if composition is not known Bubble point pressure Formation volume factor Isothermal compressibility Viscosity
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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.
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
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:
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