US 2024/0175355 A1 · METHOD FOR EVALUATING PRODUCTIVITY OF VERTICALLY HETEROGENEOUS GAS RESERVOIR CONSIDERING INTERLAYER CROSSFLOW

Abstract

A method for evaluatingproductivity of a vertically heterogeneous gas reservoir considering interlayer crossflow is disclosed in the invention, and includes: (1) dividing a heterogeneous gas reservoir into multiple thin layersvertically; (2) obtaining the productivity of each thin layer according to data obtained through wireline formation test; (3) superimposing the productivity of all thin layers based on the water-electricitysimilarityprinciple to obtain the superimposed productivity of the heterogeneousgas reservoir; and (4) using an interlayer crossflow correction coefficient considering influence caused by the interlayer crossflow to obtain the corrected productivity of the heterogeneousgas reservoir. Specific to the vertically heterogeneous characteristics of the gas reservoir, a gas reservoir section is divided into several different flow units, such that a reservoir with strong heterogeneity is converted into relatively homogeneous reservoir sections, and the productivity thereof is determined using the data obtained through wireline formation test, considering the influence of the interlayer crossflow in a vertically heterogeneous reservoir on productivity prediction, which has more accurate prediction results.

A method for evaluating productivity of a vertically heterogeneous gas reservoir considering interlayer crossflow, comprising the following steps:

(1) dividing a heterogeneous gas reservoir into multiple thin-layers vertically;
(2) obtaining the productivity of each thin-layer according to data obtained through wireline formation test;
wherein, the productivity of the reservoirs is calculated according to the calculation formula (1):
q
s
⁢
c
=
-
A
+
A
2
-
4
⁢
B
⁡
(
ψ
⁡
(
p
w
⁢
f
)
-
ψ
⁡
(
p
e
)
)
+
C
2
⁢
B
where
,
A
=
6
.
3
⁢
6
⁢
7
×
1
⁢
0
-
4
⁢
T
⁢
e
(
-
b
⁡
(
p
e
-
p
_
)
)
K
0
⁢
h
⁢
ln
⁢
(
r
e
r
w
)
where
,
B
=
1.0795
×
1
⁢
0
-
10
⁢
γ
g
⁢
T
⁢
e
(
-
b
⁡
(
p
e
-
p
_
)
)
K
1.5
⁢
h
2
⁢
μ
¯
⁢
(
1
r
w
-
1
r
e
)
C
=
λ
⁡
(
p
e
+
p
w
⁢
f
2
)
⁢
(
r
e
-
r
w
)
⁢
e
(
-
b
⁡
(
p
e
-
p
¯
)
)
μ
¯
⁢
Z
¯
qsc is the gas production rate under standard conditions, in the units of m3/d;
ψ
⁡
(
p
)
=
∫
p
0
p
p
⁢
e
(
-
b
⁡
(
p
e
-
p
¯
)
)
μ
⁢
Z
is the pseudo-pressure function of single-phase gas;
T is reservoir temperature;
pe, P, Pwf, p are respectively original reservoir pressure, mean reservoir pressure, bottom hole flowing pressure, and pressure at any point in formation, in the units of MPa;
K and K0 are respectively reservoir permeability at pressure of p and permeability at the original reservoir pressure, in the units of mD;
h is reservoir thickness, in the units of m;
re and rw are respectively discharge radius and shaft radius, in the units of m;
Yg is the relative density of natural gas;
b is a stress sensitivity coefficient, in the units of MPa−1;
μ and μ are respectively natural gas viscosity and mean natural gas viscosity, m the units of mPa·s;
2 is starting pressure gradient, in the units of MPa m;
and
Z and Z are respectively a deviation coefficient and a mean deviation coefficient;
(3) superimposing the productivity of all thin layers based on the water-electricity similarity principle to obtain the superimposed productivity of the whole heterogeneous gas reservoir;
Wherein the superimposed productivity of the gas reservoir is that of all thin-layers, namely:
Q
t
⁢
o
⁢
l
=
∑
i
=
1
n
q
i
Q
m
=
α
*
⁢
Q
t
⁢
o
⁢
l
where Qtol is the superimposed productivity of the gas reservoir;
qi is the productivity of the i(th) reservoir section of the gas reservoir;
a is the correction coefficient of the layer cross flow;
and
Qm is the corrected comprehensive productivity of the gas reservoir;
wherein the interlayer crossflow correction coefficient is specifically obtained by the following method:
calculating corresponding flow coefficients of various thin-layers according to the permeability, effective thickness, and gas viscosity of various small heterogeneous gas reservoir;
arranging the flow coefficients into a sequence from small to large;
calculating the cumulative percentages of flow coefficients and effective thicknesses of the various thin layers, respectively;
plotting Lorenz curve on a rectangular coordinate paper;
calculating a ratio of an envelope area SADCA to a triangle area SABC as a flow variation coefficient β;
using a relation curve of an interlayer interference coefficient γ and a flow variation coefficient β to calculate the interlayer interference coefficient γ;
and then calculating the interlayer crossflow correction coefficient according to formula α=1−γ;
and
(4) using an interlayer crossflow correction coefficient considering influence caused by the interlayer crossflow to obtain the corrected comprehensive productivity of the whole gas reservoir.

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Method for evaluating productivity of vertically heterogeneous gas reservoir considering interlayer crossflow

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Method for evaluating productivity of vertically heterogeneous gas reservoir considering interlayer crossflow

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Abstract

Claims9