US2014352949A1PendingUtilityA1
Integrating rock ductility with fracture propagation mechanics for hydraulic fracture design
Est. expiryMay 29, 2033(~6.8 yrs left)· nominal 20-yr term from priority
E21B 49/00E21B 47/0006E21B 43/26
37
PatentIndex Score
0
Cited by
0
References
0
Claims
Abstract
The invention relates to the calculation of parameters to inform hydraulic stimulation of non-conventional hydrocarbon-bearing rock formations, such as shales. Unlike conventional formations, non-conventional formations tend to display elastic-plastic behavior and have stress-strain characteristics which with substantial non-linear regions. A parameter which has been termed Elastic Index (EI) is proposed, together with a demonstration of how this parameter, when coupled with principles of fracture mechanics, may be used to extract meaningful calculated or estimated values for e.g.; total required volume of fracturing fluid; treating pressure; fracturing fluid viscosity; proppant size; and proppant concentration.
Claims
exact text as granted — not AI-modified1 . A method of calculating one or more parameters for performing hydraulic fracturing of a well in a non-conventional subterranean hydrocarbon reservoir, the method comprising:
a) taking a core sample from the reservoir; b) performing a tri-axial compressive test on said core sample; c) determining from the tri-axial test:
i) the axial poro-elastic stress, if a poro-elastic region is present;
ii) the axial yield stress; and
iii) the axial failure stress;
d) calculating an elastic index value (EI), defined as:
EI
=
[
(
axial
yield
stress
-
poro
-
elastic
stress
,
if
present
)
(
failure
stress
-
poro
-
elastic
stress
,
if
present
)
]
or its mathematical equivalent;
(e) calculating an average fracture width D ductile for a propagating crack using the equation:
D
ductile
D
brittle
=
(
1
EI
)
E
ductile
E
brittle
or its mathematical equivalent,
where E ductile is the secant modulus and E brittle is the tangent modulus, and where D brittle is an average fracture width value; and
(f) using said calculated value of D ductile to derive or estimate one or more of:
(i) fracturing fluid viscosity;
(ii) total required volume of fracturing fluid;
(iii) treating pressure;
(iv) proppant size; and
(v) proppant concentration.
2 . The method according to claim 1 , wherein in step (f) a value for treating pressure P prop(ductile) is derived by applying the equation:
P
prop
(
ductile
)
=
4
(
1
-
v
2
)
K
Ic
2
D
max
E
s
Ωπ
(
EI
)
or its mathematical equivalent, where ν is Poisson's ratio, K Ic is the mode-I critical stress intensity factor for brittle rock, D max is equal to D ductile , E s is equal to E ductile and Ω is a crack geometry factor.
3 . The method of claim 2 wherein K Ic is derived using the expression σ√(πa) where a is half the estimated crack length and σ is the yield stress.
4 . The method according to claim 1 , wherein in step (f) a value for total required volume of fracturing liquid is estimated by deriving a value for fracture volume by applying the equation:
V
prop
=
κ
K
IC
(
1
-
v
2
)
E
8
π
L
3
/
2
H
Ω
or its mathematical equivalent, where E is the ductile (secant) modulus, L and H are estimates of fracture length and height and κ is a value converting the maximum opening displacement to the average opening displacement.
5 . The method according to claim 4 wherein κ has a value of between 0.5 and 1.0.
6 . The method according to claim 5 wherein crack geometry is assumed to be elliptical and κ has a value of between 0.75 and 0.79.
7 . The method according to claim 6 wherein crack geometry is assumed to be elliptical and κ has a value of about 0.78.
8 . A method of designing a hydraulic fracturing procedure for a well in a non-conventional subterranean hydrocarbon reservoir, the method including calculating one or more parameters derived or estimated by a method comprising:
a) taking a core sample from the reservoir; b) performing a tri-axial compressive test on said core sample; c) determining from the tri-axial test:
i) the axial poro-elastic stress, if a poro-elastic region is present;
ii) the axial yield stress; and
iii) the axial failure stress;
d) calculating an elastic index value (EI), defined as:
EI
=
[
(
axial
yield
stress
-
poro
-
elastic
stress
,
if
present
)
(
failure
stress
-
poro
-
elastic
stress
,
if
present
)
]
or its mathematical equivalent;
(g) calculating an average fracture width D ductile for a propagating crack using the equation:
D
ductile
D
brittle
=
(
1
EI
)
E
ductile
E
brittle
or its mathematical equivalent, where E ductile is the secant modulus and E brittle is the tangent modulus, and where D brittle is an average fracture width value; and
(h) using said calculated value of D ductile to derive or estimate one or more of:
(vi) fracturing fluid viscosity;
(vii) total required volume of fracturing fluid;
(viii) treating pressure;
(ix) proppant size; and
(x) proppant concentration.
9 . The method according to claim 8 , wherein in step (f) a value for treating pressure P prop(ductile) is derived by applying the equation:
P
prop
(
ductile
)
=
4
(
1
-
v
2
)
K
Ic
2
D
max
E
s
Ωπ
(
EI
)
or its mathematical equivalent, where ν is Poisson's ratio, K Ic is the mode-I critical stress intensity factor for brittle rock, D max is equal to D ductile , E s is equal to E ductile and Ω is a crack geometry factor.
10 . The method of claim 9 wherein K Ic is derived using the expression σ√(πa) where a is half the estimated crack length and σ is the yield stress.
11 . The method according to claim 8 , wherein in step (f) a value for total required volume of fracturing liquid is estimated by deriving a value for fracture volume by applying the equation:
V
prop
=
κ
K
IC
(
1
-
v
2
)
E
8
π
L
3
/
2
H
Ω
or its mathematical equivalent,
where E is the ductile (secant) modulus, L and H are estimates of fracture length and height and κ is a value converting the maximum opening displacement to the average opening displacement.
12 . The method according to claim 11 wherein κ has a value of between 0.5 and 1.0.
13 . The method according to claim 12 wherein crack geometry is assumed to be elliptical and κ has a value of between 0.75 and 0.79.
14 . The method according to claim 13 wherein crack geometry is assumed to be elliptical and κ has a value of about 0.78.
15 . A method of performing a hydraulic fracturing procedure on a well in a non-conventional subterranean hydrocarbon reservoir, the method including designing said procedure with reference to one or more parameters derived or estimated by a method comprising:
a) taking a core sample from the reservoir; b) performing a tri-axial compressive test on said core sample; c) determining from the tri-axial test:
i) the axial poro-elastic stress, if a poro-elastic region is present;
ii) the axial yield stress; and
iii) the axial failure stress;
d) calculating an elastic index value (EI), defined as:
EI
=
[
(
axial
yield
stress
-
poro
-
elastic
stress
,
if
present
)
(
failure
stress
-
poro
-
elastic
stress
,
if
present
)
]
or its mathematical equivalent;
(i) calculating an average fracture width D ductile for a propagating crack using the equation:
D
ductile
D
brittle
=
(
1
EI
)
E
ductile
E
brittle
or its mathematical equivalent, where E ductile is the secant modulus and E brittle is the tangent modulus, and where D brittle is an average fracture width value; and
(j) using said calculated value of D ductile to derive or estimate one or more of:
(xi) fracturing fluid viscosity;
(xii) total required volume of fracturing fluid;
(xiii) treating pressure;
(xiv) proppant size; and
(xv) proppant concentration.
16 . The method according to claim 15 , wherein in step (f) a value for treating pressure P prop(ductile) is derived by applying the equation:
P
prop
(
ductile
)
=
4
(
1
-
v
2
)
K
Ic
2
D
max
E
s
Ωπ
(
EI
)
or its mathematical equivalent, where ν is Poisson's ratio, K Ic is the mode-I critical stress intensity factor for brittle rock, D max is equal to D ductile , E s is equal to E ductile and Ω is a crack geometry factor.
17 . The method of claim 16 wherein K Ic is derived using the expression σ√(πa) where a is half the estimated crack length and σ is the yield stress.
18 . The method according to claim 15 , wherein in step (f) a value for total required volume of fracturing liquid is estimated by deriving a value for fracture volume by applying the equation:
V
prop
=
κ
K
IC
(
1
-
v
2
)
E
8
π
L
3
/
2
H
Ω
or its mathematical equivalent, where E is the ductile (secant) modulus, L and H are estimates of fracture length and height and κ is a value converting the maximum opening displacement to the average opening displacement.
19 . The method according to claim 18 wherein crack geometry is assumed to be elliptical and κ has a value of between 0.75 and 0.79.
20 . The method according to claim 19 wherein crack geometry is assumed to be elliptical and κ has a value of about 0.78.Join the waitlist — get patent alerts
Track US2014352949A1 — get alerts on status changes and closely related new filings.
We store only your email — no account needed. See our privacy policy.