Chapter3 Phase state of Reserviors Hydrocarbons and Gas-Liquid Equilibrium(59)
The characteristic of phase behavior
The equilibrium gas and liquid phases
The dissolution(溶解 ) and separation(分离) of system
Terminology:
Phase behavior: 相态 Bubble point :泡点
Critical ponit :临界点 Two phase region :两相区Phase diagram: 相图 Dew point :露点
Phase envelope :相包络线 Quality lines: 等液量线Cricondentherm: 临界凝析温度 Cricondenbar: 临界凝析压力Locus :轨迹 Shrinkage :压缩 Condensate gas :凝析气Curve :曲线 Volatile :挥发性的 Depletion :衰竭,降低Retrograde gas condensate: 反凝析油 Separator :分离器Equilibrium ratio :平衡比
• Reservoirs may be radically different from each other in fluid composition.
diversified forms: gas reservoir
oil reservoir
oil reservoir with gas-cap
3.1.1Phase and the descriptive approaches of phase相态及其表示方法
Theoretically based on the thermodynamics( 热力学 ) and the physical chemistry,the theory of reservoir-fluid-phase usually takes a ”system”
as the object of study.
The term ”system” refers to the object which is artificially divided from the others for study and
conceived as a space enveloped( 包围 ) by boundaries.
3.1 Phase behavior of reservoir hydrovarbon fluids
For a constant(常量,不变的 ) composition system, the relationship between pressure, temperature and volume can be represented by EOS ( equation of state)
f(P , v , T) = 0
Phase diagram is the graphic display of EOS.
( 将状态方程以图示法表示就是相图 )
3.1.1.1 3D phase diagram(P - V - T)
( 三维相图)
2 、 2D diagram 二维相图( or Plane phase diagram 平面相图)
The P-T diagram is most convenient
P-V( 压力 - 比容图 ) and P-T( 压力 - 温度图 ) phase
diagram are generally used in petroleum industry.
2D phase diagram of propane( 丙烷的二维相图 )
C 1 , %
C 2 , %
C 3 , %
C 4 , %
C 5 , %
C 6 , %
C 7 , %
4 8 .8 3
2 .7 5
1 .9 3
1 .6 0
1 .11 5
1 .5 9
4 11 5
6 4 .3 6
7 .5 2
4 .4 7
4 .1 2
2 .99 7
1 .3 8
1 4 .9 1
8 7 .0 1
4 .3 9
2 .2 9
1 .0 8
0 .88 3
0 .6 0
3 .8 0
9 5 .8 5
2 .6 7
0 .3 4
0 .5 2
0 .00 8
0 .1 2
0 .4 2
合计, % 1 0 0 .0 0 1 0 0 .0 0 1 0 0 .0 0 1 0 0 .0 0
C 7+ 分 子 量3 3气油比, m / m
3地 面 液 体 密 度 , g / cm
液体颜色
225
111
0 .8 5 3 4
绿色
181
356
0 .7 7 9 2
桔黄色
112
3240
0 .7 3 5 8
浅稻草色
157
18690
0 .7 5 9 9
无色
3.1.1.3 Triangle phase diagram ( ternary diagram ) 三角相图 (P61)
组 分 黑 油 轻质油 凝析油 干 气
M1 M2 M3 ?
3.1.2Phase behavior of single/two-component system(P62)
3.1.2.1 The characteristic of single component system单组分体系的相态特征
1 、 Key parameters
(1)Bubble point pressure( 泡点压力 ): refers to pressure atwhich the first bubble occurs under constant temperaturewhen pressure decreases
(2)Dew point pressure( 露点压力 ) : refers to pressure atwhich the first liquid dew occurs under constanttemperature when pressure increases
(3)Saturated vapor pressure curve( 饱和蒸汽压线 ) :refers to the line showing that vapor and liquid phase
coexist for single component system
(4)Critical point( 临界点 ) : refers to the end of saturated
vapor pressure curve (point C).
(5)Critical temperature (Tc) , critical pressure (Pc) :refers to the corresponding temperature and pressure at
the critical point
a 压 力 , MPa
P-T diagram for ethane
C5 Pc
超临界区(气相区)F 。
液相区
4
3
2
1
0
-150 -100 -50 0 50 100 150
D 。。。BE
。A
蒸汽区Tc
温度, C
图 3—3 乙烷的 P-T 相图
(30C, 4.88MPa)
H2 SCO2
N2 CH4 C2 H6
C3 H8 C4 H1 0 C5 H1 2
a 压 力 , MPa
3 、 P-T diagram for different pure system
109876543210
-200 -100 0 100 200 300
温度,℃
图 3—5 几种烷烃和非烃的饱和蒸汽压线
1.2 The characteristic of binary(二元的 ) component system双组分体系的相态特征
1 、 Key parameters(1)Bubble point curve( 泡点线 ): is defined as the line
separating the liquid phase region from the two phase region
(2)Dew point curve( 露点线 ):is defined as the line separating
the vapor phase region from the two phase region
(3)Cricondentherm( 临界凝析温度 ): is defined as the maximum
temperature above which liquid can not be formed regardless
of pressure.
(4)Cricondenbar( 临界凝析压力 ): is defined as the maximum
pressure above which no gas can be formed regardless of
temperature.
(5)Phase envelope ( 相包络线 ): the region enclosed by the
bubble-point curve and the dew-point curve, wherein gas and
liquid coexist in equilibrium, is defined as the phase envelope
of the hydrocarbon system.
(6)Quality lines( 等液量线 ): refers to the dash lines within the
phase diagram. They describe the pressure and temperature
conditions for equal volumes of liquids.
cricondenbar
2 、 P-T diagram for binary system
cricondentherm
3 、 Typical P-T diagram for a binary system
1) The two-phase region is between the saturated vapor line ofindividual pure substance.
2) The Pc is higher than one of pure substance, while Tc is betweenthat of both pure substance.
3) Point C will migrate to the side closer to the heavy substance withthe content increase of heavy one, accompanied with the P-T driftingto the saturated vapor pressure curve of heavy substance
4)The two phase region is larger if the proportion of both componentis close, contrary to the bigger proportion
1.3 The characteristic of multi-component hydrocarbon system(P66)
1 、 The key points:
1.Three phase regions: liquid
region, vapor region, two phase
region
2.Three points: cricondenbar,
critical point, cricondentherm
3. Three lines: bubble point
curve, dew point curve, quality
lines
4.Two iso-regions: isothermal
P - T diagramdecompression retrograde
region( 等温降压反凝析区 ),isobaric cooling retrograde
region( 等压降温反凝析区 )
Critical point( 临界点 ) : intersection of bubble point curve
and dew point curve.
The Pc is the maximum pressure above which no gas can
be formed regardless of temperature (cricondenbar),
The Tc is defined as the maximum temperature above which
liquid cannot be formed regardless of pressure
(Cricondentherm).
isothermal decompression retrograde region( 等温降压反凝析区 )
isobaric cooling retrograde region( 等压降温反凝析区 )
2 、 The particular (P68)
isothermal decompression
retrograde region( 等温反凝析区 )
3 、 Judgment of reservoir types
GasVolatile oil Condensate gasBlack oil
Oil reservoirs—If the reservoir temperature T is less than the criticaltemperature Tc of the reservoir fluid, the reservoir is classified as an oilreservoir.Gas reservoirs—If the reservoir temperature is greater than the critical
temperature of the hydrocarbon fluid, the reservoir is considered a gasreservoir.
4 、 Phase behaviors of Typical reservoirs(P70)
1. Under-saturated oil
reservoir.
2. Saturated oil reservoir.
3. Gas-cap reservoir.
1 ) Phase diagram of conventional heavy oil reservoir( low shrinkage oil)
常规黑油油藏(低收缩油藏)相图1. The quality lines are closely
spaced near the dew-point curve,
2. The gas oil ratio is generally
lower than 90 m3/m3, and the
relative density is higher than 0.876.
The color of this type of oil is
generally black or dark brown.
3. The dash line simulates the path
of pressure and temperature
variation from wellbore to surface.
Oil accounts for about 85% at the
condition of separator.
2) Phase diagram of light oil reservoir (high shrinkage)
1. The phase diagram of
轻质油藏(高收缩油藏)相图
volatile oil reservoir is similarto that of black oil. But thequality lines are close togethernear the bubble-point and aremore widely spaced at lowerpressures.
2. The relative density is lowerthan 0.78, and gas oil ratio islower than 1800 m3/m3
3. Oil accounts for about 65%at ,.the condition of separator
5 、 Gas reservoirs
On the basis of their phase diagrams and the
prevailing reservoir conditions, natural gases can
be classified into four categories:
-Retrograde gas-condensate
-Near-critical gas-condensate
-Wet gas
-Dry gas
1 ) Phase diagram of retrograde condensate gas reservoir(P72)
反凝析气藏相图1. The initial reservoir pressureis higher than critical pressure ,but its temperature is betweencritical temperature andcricondentherm
2. The gas oil ratio ofcondensate gas reservoir couldreach 12600 m3/m3. The relativedensity of condensate oil couldreach 0.74. The color is light andtransparent.33. liquid accounts for about 25%under the condition of surfaceseparator. The produced liquid iscalled as condensate oil
2 ) Phase diagram of near critical gas condensate reservoir
近临界凝析气藏相图
1. The initial reservoir
temperature is near the
critical temperature
2. All the quality linesconverge ( 会聚 / 聚合 )at the critical point,
3.a rapid liquid buildup willimmediately occur below the
dew point as the pressure is
reduced to point 2.
3)Phase diagram of wet gas reservoir( 湿气气藏相图 )
1.The reservoir temperature isabove the cricondentherm ofthe hydrocarbon mixture, and itwill always keep gas statuswhen pressure decreases frompoint 1 to point 2.
2.It will be in two phase regionunder separator condition,therefore, there will be somelight oil in separator.
3.The relative density of lightoil is lower than 0.78, and thesurface gas oil ratio is lowerthan 18000 m3/m3.
4)Phase diagram of dry gas reservoir( 干气气藏相图 )
1.The natural gas withhigh methane content(70
% ~98 % ) is referred asdry gas.
2.The reservoirtemperature andseparator temperature areoutside two phase region.There is no liquidreleased in undergroundand surface condition.The gas oil ratio is higherthan 18,000 m3/m3.
3.2 Gas-liquid phase equilibrium ( P73)汽 - 液相平衡
1 、 Ideal solution(溶液)
1) complete mixed between different constituents of
solutions;
2) no chemical reaction during mixing;
3) particle volume of each constituent is equal (that is , the
repulsion force and attractive force between different
particle are equal)
2 、 Raoult’s Law ( 拉乌尔定律 ) :The equilibrium partial pressure of any component in a multi-
component system is the product of its mole fraction xi in the
liquid phase and the vapor pressure of the pure component
pi:
pi xi pvi
where :pi = partial pressure of ith component.
pvi = vapor pressure of ith pure component.
xi= mole fraction of ith component in the liquid.
3 、 Dalton’s Law ( 道尔顿定律 )
The partial pressure pi of any component is the productof it’s mole fraction yi in the vapor phase and the total
pressure of the system p
pi yi p
where : yi—mole fraction of component i ;p- total pressure of the system.
k
4 、 Vapor-liquid phase equilibrium of ideal solution理想溶液汽 - 液平衡计算
1) The equilibrium ratio
Raoult's and Dalton's law may be combined and written as
yi p xi Pvi
yi
xi
Pvi
Pk
f Li
f gi
yi
xi
Real solution at high pressure
yi ( f gi ) pure xi ( f Li ) pure
fugacity 逸度
The equilibrium ratio k:
The equilibrium ratio occurs underequilibrium conditions between vaporand liquid at any specified temperatureand pressure.
zi Ki∑yi ∑
2) Development of equations for calculating equilibrium relations
z j n x j nL y j ng
zi xi L yiV
xi zi
L KiV∑xi = 1 ∑yi = 1
zi
i
n n
1
Where : i 1 i 1 VKi L
L = moles of liquid at equilibrium V = moles of vapor at equilibriumzi xi yi = mole fraction of the ith component in the total/ liquid/ vapor phaseKi = yi/xi = equilibrium ratio of the ith component at the pressure andtemperature of the system
组分 组成,摩尔分数
丙烷丁烷戊烷
0.610
0.280
0.110
合计 Sum 1.000
Ex. 3-1: The composition of ideal liquor is listed in table
3-1, calculate the composition of vapor and liquid phase
under 65.5 (150 ) and 200 psia.℃ ℉
表 3-1
组分 组成Zj , mole fraction
Pv j ,
Psia
yj ,
mole fraction
xj ,
mole fraction
C3 0.610 350 0.771 0.441
n-C4 0.280 105 0.194 0.370
n-C5 0.110 37 0.035 0.189
sum 1.0 y j 1 . 000 x j 1 .000
Solution:Step 1: Based on thechart of vapor pressure vs.T, presented thecomponent vapor
表 3-2
pressure, list at the 3thcolumn;;
组分 组成Zj , mole fraction
Pv j ,
Psia
yj ,
mole fraction
xj ,
mole fraction
C3 0.610 350 0.771 0.441
n-C4 0.280 105 0.194 0.370
n-C5 0.110 37 0.035 0.189
sum 1.0 y j 1 . 000 x j 1 .000
∑j 1 y j ∑j 11 nL (
indicated that ∑y j 1
Step 4: The composition of each∑j 1
x j ∑1 ng (
m m
1−1)
z j
p
pvjj
Step 2: Assumed that nL=0. 487, use theequation yi to trial calculate, list at the4th;Step 3: If trial calculation is satisfied,
1
−1)
m
j 1
m
m
j 1
component in liquid xi is obtained.z j
pvj
p
表 3-2
zi∑y ∑ LV
zi Ki∑
∑z K
zi xi
Ki
pb ∑zi pvi
3) Calculate the bubble pressure
At the bubble-point pressure, p=pb ,it is consideredas a single phase liquid. L=1,V≈0
Based on the vapor equation :
i①
1
② pvi
pb
Ki
n
i 1 VKi L
i i 1
n n
i 1 i 1
n
i 1
n
i 1
组分 组成, zj
Fractlon mole
饱和蒸汽压Pvj,Psia
zj Pv j
C3 0.610 350 213.5
n-C4 0.280 105 29.4
n-C5 0.110 37 4.1
Pb=247Psia
Ex. 3-2: Calculate the bubble point pressure of the above-
mentioned mixture (regarding as ideal liquor).
表 3-3
zi
∑i 1 xi ∑i 1 VK L 1
∑z / K
Ki
pd zi∑
4) Calculate the dew pressure
At the dew-point pressure, p=pd ,it is considered as asingle vapor phase. V=1,L≈0
Based on the vapor equation :
n n
①i
zi yi
②
1
pvi
pd
ii
n
i 1n
1
i 1 pvi
组分 组成, zj fraction mole
饱和蒸汽压 ,
Pvj, Psia
zj / pvj
C3 0.610 350 0.00174
n-C4 0.280 105 0.00267
n-C5 0.110 37 0.00297
sum 1.000 0.00738
Ex. 3-3: Calculate the dew point pressure of the above-
mentioned mixture (regarding as ideal liquor).
最后 1
0 .00738136 Psia 。Pd
Calculating steps for saturated pressure
Yes
Given assumed Pb
Ki is obtained at Pb
No
calculatingΣniki=1
Yes
Output Pb
Given assumed Pd
Ki is obtained at Pd
No
Σni/ki=1
Output Pd
体 积
p5 p4 3
3 The solution and liberation of hydrocarbonsystem 油气体系中气体的溶解与分离 (P88)
3.1 liberation of system
p p2 p1
1 、 Flash liberation 闪蒸分离V5
V4
V3 Vb
V2
V1
pb
压力
The solution gas that is liberated from an oil sample during a stepdecline in pressure stays in the cell by contact with the oil, andthe change in the total hydrocarbon volume Vt is measured foreach pressure increment. (CCE)
1 、 Flash liberation 闪蒸分离
(CCE Constant Composition Expansion)
• Saturation pressure (bubble-point or dew-point pressure)
• Isothermal compressibility coefficients of the single-
phase fluid in excess of saturation pressure
• Compressibility factors of the gas phase
• Total hydrocarbon volume as a function of pressure
2 、 Differential liberation微分分离
The solution gas that is
liberated from an oil摩尔
液体
摩尔气体
液体
摩尔
液体
sample during a declinein pressure iscontinuously removedfrom contact with the oil,and before establishingequilibrium with the
( b ) ( c )( a )total hydrocarbonsystem. (CVD)
2 、 Differential liberation微分分离
(CVD Constant Volume Depletion)
• Amount of gas in solution as a function of pressure
• The shrinkage in the oil volume as a function of pressure
• Properties of the evolved gas including the composition of the
liberated gas, the gas compressibility factor, and the gas
specific gravity
• Density of the remaining oil as a function of pressure
3 、 multi-stage liberation (or separator)
多级分离
The solution gas that is liberated from an oil sample during a stepdecline in pressure is removed from contact with the oil, and thecell is constant.
A scheme using three stage separation at a fixed temperature
Optimum separation conditions
• A maximum stock-tank
API gravity
• A minimum oil
formation volume factor
(i.e., less oil shrinkage)
• A minimum producing
gas–oil ratio (gas
solubility)
Schematic illustration of n separation stages.
4 、 Comparison between flash liberation andmulti-stage separator 一次脱气与多级脱气的比较
reservoirs( oil sample at the
gas oil ratio m3 / m3 Gas volumeincrement in
bottom hole ofproducing well )
罗马什金次布仁斯克
新季米特里耶夫斯克
Flash
59.683.0175.4
Multi-stage
41.471.5144.5
different mothod
V ,%
30.613.917.6
In the flash (equilibrium) separation, the liberated
gas remains in contact with oil until its instantaneous
removal at the final separation pressure. A maximum
proportion of intermediate and heavy components is
attracted into the gas phase by this process, and this
results in a maximum oil shrinkage and, thus, a lower
oilil recovery.
In the differential separation, or multi-stage
separator, the liberated gas (mainly composed of lighter
components) is removed from contact with the oil as
the pressure on the oil is reduced. The maximum
amount of heavy and intermediate components will
remain in the liquid, minimum shrinkage of the oil will
occur, and, therefore, greater stock-tank oil recovery
will occur.
The gas volume released from oil sample by flash
liberation is more than by multi-stage separation, that
is the more gas oil ratio measured
The specific gravity of gas liberated from oil sample
by flash liberation is higher because of the more
molar fraction of light oil
3.2 The gas solution
1 、 Solubility
The gas solubility Rs is defined as the number of
standard cubic feet of gas which will dissolve in one
stock-tank barrel of crude oil at certain pressure and
temperature. The solubility of a natural gas in a crude
oil is a strong function of the pressure, temperature,
API gravity, and gas gravity.
2 、 influential factor about gas solubility
1) Temperature factor
Gas solution volume
reduces as the temperature
is increased, especially at
high pressure.
2) Pressure and API oil gravity factor
•Gas solution volume increases
as the pressure is increased
•With the increase of API oil
gravity, gas solution increases,
because of the composition of
hydrocarbon liquid is extremely
dynamic as P and T change.
3) Gas gravity (or component) factor
•Gas solution volume increases
as gas gravity is increased
4 、 The relationship between solution and liberation
1)The processes of solution and
liberation are opposite
and uniform. These two
processes occur at a specified
condition.
liberation curve and solution
curve by flash liberation are①all the same
Solution curve and②liberation curve by differential③liberation , two lines do not
coincide with each other
2) Two process lines of light component are
nearly the same whereas lines of heavier
component are just the opposite, especially
at low pressure.