Wet gas flow measuring method and apparatus
A wet gas flow measuring method, wherein measuring total flow differential pressure value ΔP of wet gas in a pipeline by a differential pressure flow measuring device ( 201 ), measuring section gas contents of the wet gas in the pipeline by at least two phase fraction meters respectively ( 202 ), obtaining optimized section gas content value GVFopt by a flow calculating module based on the section gas contents respectively measured by the at least two phase fraction meters ( 203 ); and calculating gas volume flow rate Qg and liquid volume flow rate Ql by the flow calculating module based on the total flow differential pressure value ΔP of the wet gas and the optimized section gas content value GVFopt ( 204 ). As the section gas content of the wet gas in the pipeline is detected by the redundant phase fraction meters, the gas volume flow rate Qg and the liquid volume flow rate Ql can be measured accurately, which meets the requirements on production measurements of oil and gas field and facilitates management improvement and production optimization of oil-gas reservoir. A wet gas flow measuring apparatus is also provided.
1. A method for measuring wet gas flow, characterized in that the method comprises the steps of:
(a) measuring the total flow differential pressure value ΔP of wet gas in a pipeline via a differential pressure type flow measuring device disposed on the pipeline;
(b) measuring gas void fraction of the wet gas in the pipeline via at least two phase fraction meters disposed on the pipeline downstream from the differential pressure type flow measuring device, respectively;
(c) obtaining optimized gas void fraction GVF opt by a flow calculating module based on the gas void fractions respectively measured by the at least two phase fraction meters; and
(d) calculating the gas volume flow rate Q g and the liquid volume flow rate Q l by the flow calculating module based on the total flow differential pressure value ΔP and the optimized gas void fraction GVF opt of the wet gas;
characterized in that:
the step (c) comprises the following steps:
(c1) calculating the short-term local reliability function F( ) of the gas void fraction Xi measured by each phase fraction meter: F(X i )=D(X i )=E([X i −E(X i )] 2 ), wherein
Xi denotes the time sequence of the gas void fraction measured by the phase fraction meter i, 1≤i≤N;
N denotes the number of phase fraction meters;
D( ) denotes a variance function; and
E( ) denotes an expectation function;
(c2) constructing a long-term whole reliability function LF( ) for the gas void fraction Xi measured by each phase fraction meter:
S i [0]=X i [0],
S i [m]=αS i [m− 1]+(1−α) X i [m],
LF ( S i )= D ( S i ),
wherein 0≤α≤1, and 0≤m≤M−1, where M denotes the number of the gas void fractions included in the time sequence, and X i [m] denotes the m th gas void fraction in the time sequence of the gas void fraction measured by the phase fraction meter i;
(c3) constructing a comprehensive reliability function NICE( ) for the gas void fraction Xi measured by each phase fraction meter by utilizing the short-term local reliability function F( ) and the long-term whole reliability function LF( ):
NICE
(
X
i
)
=
1
F
(
X
i
)
+
L
F
(
S
i
)
;
and
(c4) obtaining the optimized gas void fraction GVF opt by utilizing the comprehensive reliability function NICE( )
G
V
F
opt
[
m
]
=
∑
i
=
1
N
X
i
[
m
]
NICE
(
X
i
)
∑
i
=
1
N
NICE
(
X
i
)
,
wherein GVF opt [m] denotes the m th optimized value in the time sequence of the optimized gas void fraction GVF opt .
2. The method according to claim 1 , characterized in that: the axial lines of said at least two phase fraction meter are respectively intersected with and perpendicular to the axial direction of the pipeline.
3. The method according to claim 1 , characterized in that: the step (d) comprises the following steps:
(d1) calculating the mixed density ρ mix of the wet gas according to the optimized gas void fraction GVF opt ;
(d2) calculating the total volume flow rate Q of the wet gas according to the total flow differential pressure value ΔP and the mixed density ρ mix ; and
(d3) calculating the gas volume flow rate Q g and the liquid volume flow rate Q l according to the total volume flow rate Q and the optimized gas void fraction GVF opt .
4. The method according to claim 3 , characterized in that: the step (d 1 ) comprises utilizing the equation ρ mix =ρ gas GVF opt +ρ liquid (1−GVF opt )to calculate the mixed density ρ mix of the wet gas, wherein ρ gas denotes the gas density, and ρ liquid denotes the liquid density.
5. The method according to claim 3 , characterized in that the step (d2) comprises utilizing the equation
Q
=
K
Δ
P
ρ
min
to calculate the flow volume flow rate Q of the wet gas, wherein the parameter K is a systematic parameter.
6. The method according to claim 3 , characterized in the step (d3) comprises the steps of:
calculating the gas volume flow rate Q g by utilizing the equation Q g =Q×GVF opt ; and
calculating the liquid volume flow rate Q l by utilizing the equation Q g =Q×(1−GVF opt ).
7. A wet gas flow measuring apparatus, comprising a pipeline, a differential pressure type flow measuring device, at least two phase fraction meters, and a flow calculating module, wherein the differential pressure type flow measuring device is disposed on the pipeline and said at least two phase fraction meters are disposed on the pipeline downstream from the differential pressure type flow measuring device and wherein:
the pipeline is used to convey the wet gas;
the differential pressure type flow measuring device is used to measure the total flow differential pressure value ΔP of wet gas in the pipeline;
the at least two phase fraction meters are respectively used to measure the gas void fractions of wet gas in the pipeline; and
the flow calculating module is used to calculate the optimized gas void fraction GVF opt based on the gas void fractions respectively measured by the at least two phase fraction meters; and the flow calculating module is used to calculate the gas volume flow rate Q g and the liquid volume flow rate Q l based on the total flow differential pressure value ΔP and the optimized gas void fraction GVF opt ;
characterized in that the flow calculating module calculates the short-term local reliability function F( )of the gas void fraction Xi measured by each phase fraction meter: F(X i )=D(X i )=E([X i −E(X i )] 2 ), wherein
Xi denotes the time sequence of the gas void fraction measured by the phase fraction meter i, 1≤i≤N;
N denotes the number of phase fraction meters;
D( ) denotes a variance function; and
E( )denotes an expectation function;
the flow calculating module constructs a long-term whole reliability function LF( )for the gas void fraction Xi measured by each phase fraction meter:
S i [0]=X i [0],
S i [m]=αS i [m− 1]+(1−α) X i [m],
LF ( S i )= D ( S i ),
which 0≤α≤1, and 0≤m≤M−1, where M denotes the number of the gas void fractions included in the time sequence, and X i[m] denotes the m th gas void fraction in the time sequence of the gas void fraction measured by the phase fraction meter i;
the flow calculating module constructs a comprehensive reliability function NICE( )of the gas void fraction Xi measured by each phase fraction meter by utilizing the short-term local reliability function F( )and the long-term whole reliability function LF( ) wherein
NICE
(
X
i
)
=
1
F
(
X
i
)
+
L
F
(
S
i
)
;
and
the flow calculating module utilizes the comprehensive reliability function NICE( )to obtain the optimized gas void fraction GVF opt:
G
V
F
opt
[
m
]
=
∑
i
=
1
N
X
i
[
m
]
NICE
(
X
i
)
∑
i
=
1
N
NICE
(
X
i
)
,
wherein GVF opt [m] denotes the m th optimized value in the time sequence of the optimized gas void fraction GVF opt.
8. The wet gas flow measuring apparatus according to claim 7 , characterized in that the axial lines of said at least two phase fraction meters are intersected and perpendicular to the axial direction of the pipeline.
9. The wet gas flow measuring apparatus according to claim 7 , characterized in that the flow calculating module calculates the mixed density ρmix of wet gas based on the optimized gas void fraction GVF opt ; and, the flow calculating module calculates the total volume flow rate Q of wet gas based on the total flow differential pressure value ΔP and the mixed density ρ mix of wet gas; and, the flow calculating module calculates the gas volume flow rate Q g and the liquid volume flow rate Q l based on the total volume flow rate Q and the optimized gas void fraction GVF opt .
10. The wet gas flow measuring apparatus according to claim 9 , characterized in that the flow calculating module utilizes the equation ρ mix =ρ gas GVF opt +ρ liquid (1−GVF opt ) to calculate the mixed density ρ mix of the wet gas, wherein ρ gas denotes the gas density, and ρ liquid denotes the liquid density.
11. The wet gas flow measuring apparatus according to claim 9 , characterized in that the flow calculating module utilizes the equation
Q
=
K
Δ
P
ρ
min
to calculate the total volume flow rate Q, wherein the parameter K is a systematic parameter.
12. The wet gas flow measuring apparatus according to claim 9 , characterized in that the flow calculating module utilizes the equation Qg=Q×GVFopt to calculate the gas volume flow rate Qg and utilizes the equation Ql=Q×(1−GVFopt) to calculate the gas volume flow rate Ql.
13. The wet gas flow measuring apparatus according to claim 7 , characterized in that said at least two phase fraction meters are installed on the same one section of the pipeline.
14. The wet gas flow measuring apparatus according to claim 7 , characterized in that said at least two phase fraction meters are installed on different sections of the pipeline.