A METHOD FOR UPSCALING OF RELATIVE PERMEABILITY OF THE PHASE OF A FLUID
The invention relates to a method for upscaling data of a reservoir model, the method being implemented by a computer, and comprising the steps of: —defining a reservoir model comprising a volume of dimensions D H , D v along respectively two distinct directions H,V, —receiving statistical data relative to the volume, comprising: relative proportions of at least two rock types, wherein each rock type corresponds to a permeability value and respective curves of relative permeability with water saturation of two phases of a fluid within the rock type, one of the phases being water, and a variogram of absolute permeability defined by correlation lengths L H , L v , along the two directions H,V, and, —computing, equivalent relative permeability values of a phase of the fluid within the volume, comprising: at least an equivalent relative permeability value according to the first direction H, and at least an equivalent relative permeability value according to the second direction V, wherein each equivalent relative permeability value of a phase of the fluid according to a direction d chosen among H,V is computed based on relative permeability values of the phase of the fluid within each rock type, and on a coefficient depending on the anisotropy of the volume and on non-ergodicity parameters ε H , ε v relative to each direction H,V, the non-ergodicity parameters depending on the volume dimensions along said directions and on the variogram of absolute permeability.
1 . A computer-implemented method for upscaling data of a reservoir model, comprising:
defining a reservoir model comprising a volume of dimensions D H , D V along respectively two distinct directions H,V,
receiving statistical data relative to the volume, comprising:
relative proportions of at least two rock types, wherein each rock type corresponds to a permeability value and respective curves of relative permeability with water saturation of two phases of a fluid within the rock type, one of the phases being water, and
a variogram of absolute permeability defined by correlation lengths L H , L V , along the two directions H,V, and,
computing, equivalent relative permeability values of a phase of the fluid within the volume, comprising:
at least an equivalent relative permeability value Kr eq,H according to the direction H, and
at least an equivalent relative permeability value Kr eq,V according to the direction V,
wherein each equivalent relative permeability value of a phase of the fluid according to a direction d chosen among H,V is computed based on relative permeability values of the phase of the fluid within each rock type, and on a coefficient depending on the anisotropy of the volume and on non-ergodicity parameters ε H , ε V relative to each direction H,V, the non-ergodicity parameters depending on the volume dimensions along said directions and on the variogram of absolute permeability.
2 . A method according to claim 1 , wherein the computing of an equivalent relative permeability value of a phase according to the direction d is based on a mean power formula:
K
r
,
eq
,
d
=
∑
i
(
K
i
.
K
r
,
i
)
ω
d
ω
d
∑
i
(
K
i
)
ω
d
ω
d
where K i is the permeability value of a rock type i, K r,i is a relative permeability value of a phase of a fluid within the rock type i, K r,eq,d is an equivalent permeability value of the phase of the fluid according to the direction d, and ω d is a power coefficient, applicable for the direction d, defined, for the direction H being a horizontal direction, by:
ω
H
=
Arc
tan
α
π
-
Arc
tan
α
and for the direction V being a vertical direction, by:
ω V =−2ω H +1
where α is the coefficient depending on the anisotropy of the volume and on non-ergodicity parameters, defined by:
α
′
=
L
H
L
V
×
K
V
K
H
ϵ
H
ϵ
V
where
k
V
k
H
and
L
H
L
V
are petrophysical and geostatistical anisotropies depending on the statistical data, and ε H , ϵ V are the non-ergodicity parameters relative respectively to each direction H, V.
3 . A method according to claim 2 , wherein the computation of an equivalent relative permeability value of a phase according to a direction is performed for a determined value of water saturation of the phase of the fluid, based on equivalent relative permeability values of the phase within each of the rock types for the same determined value of water saturation.
4 . A method according to claim 2 , wherein the computation of an equivalent relative permeability value of a phase according to a direction is performed for a determined value of fractional flow of the phase of the fluid, based on equivalent relative permeability values of the phase of the fluid within each of the rock types for the same determined value of fractional flow.
5 . A method according to claim 3 , comprising computing values of equivalent relative permeability of a phase of the fluid according to a first direction for determined values of water saturation, and computing values of equivalent relative permeability of the phase of the fluid according to a second direction for determined values of fractional flow.
6 . A method according to claim 1 , wherein each non-ergodicity parameter ε d relative to the direction d is also a function of a mean m and a variance σ of the reservoir absolute permeability values, the mean m and the variance σ depending on the statistical data.
7 . A method according to claim 1 , wherein each non-ergodicity parameter εd relative to a direction d is expressed as a function:
ε d =ƒ( X d )
wherein X d depends on the ratio (D d /L d ) of a dimension d of the volume to the correlation length of the dimension d, and on the limiting value (D d /L d ) loss of the ratio, and wherein the function
ε d −ƒ( X d )
satisfies the condition:
lim
D
d
L
d
→
(
D
d
L
d
)
l
o
s
s
ɛ
d
=
1
8 . A method according to claim 7 , wherein
X
d
=
1
-
(
D
d
L
d
)
(
D
d
L
d
)
l
o
s
s
And the function
ε d −ƒ( X d )
Is of the polynomial type:
ɛ
d
=
1
+
∑
i
=
1
…
a
i
X
d
i
9 . A method according to claim 8 , comprising determining the distribution of each non-ergodicity parameter ε d using an analytical model.
10 . A computer program product, comprising code instructions for implementing the method according to claim 1 , when it is executed by a computer.
11 . A non-transitory computer readable storage medium encoding a computer executable program for executing the method according to claim 1 .
12 . A method according to claim 4 , comprising computing values of equivalent relative permeability of a phase of the fluid according to a first direction for determined values of water saturation, and computing values of equivalent relative permeability of the phase of the fluid according to a second direction for determined values of fractional flow.