Methods and systems for estimating stress using seismic data
View Patent ↗A method for estimating principal stresses of a subterranean formation from seismic data. In one embodiment, rock strength parameters from seismic data of the formation is first determined to calculate the anisotropic elastic properties of the formation. The three principal stresses of the formation: vertical stress, minimum horizontal stress, and maximum horizontal stress, is determined using at least the calculated anisotropic elastic properties and the rock strength parameters of the formation. From the estimated principal stresses, the differential ratio of the maximum and minimum horizontal stresses can be determined to indicate optimal zones for hydraulic fracturing. In another embodiment, a tectonic strain term is introduced to calibrate the estimated principal estimated stress to a known reference point. In yet another embodiment, hoop stress is incorporated to estimate the fracture initiation pressures.
1. A method for estimating principal stresses of a subterranean formation using a computer system comprising:
determining, using the computer system, rock strength parameters from seismic data of the formation;
calculating, using the computer system, anisotropic elastic properties of the formation using at least said determined rock strength parameters; and
determining, using the computer system, principal stresses of the formation using at least the calculated anisotropic elastic properties and the rock strength parameters of the formation, wherein the principal stresses comprise a vertical stress, a minimum horizontal stress, and a maximum horizontal stress;
wherein the minimum horizontal stress is determined by a relation
σ
x
=
σ
z
v
(
1
+
v
)
1
+
EZ
N
-
v
2
between the vertical stress σ Z , Young's modulus E, Poisson's ratio ν, and normal compliance Z N .
2. The method of claim 1 wherein the vertical stress is determined by integrating a density log derived from seismic inversion.
3. The method of claim 1 wherein the maximum horizontal stress is determined by a relation
σ
y
=
σ
z
v
[
1
+
EZ
N
+
v
1
+
EZ
N
-
v
2
]
between the vertical stress σ Z , Young's modulus E, Poisson's ratio ν, and normal compliance Z N .
4. The method of claim 1 further comprising:
calculating a differential ratio of the maximum and minimum horizontal stresses to identify one or more optimal areas of a subterranean formation for hydraulic fracturing.
5. The method of claim 1 further comprising:
calibrating the determined minimum horizontal stress and maximum horizontal stress to a known reference point by adding a tectonic stress constant, wherein the tectonic stress constant is derived from in-situ stress logs of the reference point.
6. The method of claim 1 wherein the determination of the principal stresses includes a tectonic strain term and an overburden stress term.
7. The method of claim 1 further comprising:
incorporating hoop stress in the determination of the principal stresses to estimate the pressure required to initiate one or more fractures on the sides of a borehole.
8. A system comprising:
a first calculation logic that is operable to determine rock strength parameters from seismic data of a subterranean formation;
a second calculation logic that is operable to calculate anisotropic elastic properties of the formation using at least said determined rock strength parameters; and
a third calculation logic to determine principal stresses of the formation using at least the calculated anisotropic elastic properties and the rock strength parameters of the formation, wherein the principal stresses comprise a vertical stress, a minimum horizontal stress, and a maximum horizontal stress,
wherein the minimum horizontal stress is determined by a relation
σ
x
=
σ
z
v
(
1
+
v
)
1
+
EZ
N
-
v
2
between the vertical stress σhd z, Young's modulus E, Poisson's ratio ν, and normal compliance Z N .
9. The system of claim 8 wherein the vertical stress is determined by integrating a density log derived from seismic inversion.
10. The system of claim 8 wherein the maximum horizontal stress is determined by a relation
σ
y
=
σ
z
v
(
1
+
EZ
N
+
v
1
+
EZ
N
-
v
2
)
between the vertical stress σ z , Young's modulus E, Poisson's ratio ν, and normal compliance Z N .
11. The system of claim 8 further comprising:
a fourth logic to calculate a differential ratio of the maximum and minimum horizontal stresses to identify one or more optimal areas of a subterranean formation for hydraulic fracturing.
12. The system of claim 8 further comprising:
a fourth logic to calibrate the determined minimum horizontal stress and maximum horizontal stress to a known reference point by adding a tectonic stress constant, wherein the tectonic stress constant is derived from in-situ stress logs of the reference point.
13. The system of claim 8 wherein the determination of the principal stresses includes a tectonic strain term and an overburden stress term.
14. The system of claim 8 further comprising:
a fourth logic to incorporate hoop stress in the determination of the principal stresses to estimate the pressure required to initiate one or more fractures on the sides of a borehole.
15. A method for estimating principal stresses of a subterranean formation using a computer system comprising:
determining, using the computer system, rock strength parameters from seismic data of the formation;
calculating, using the computer system, anisotropic elastic properties of the formation using at least said determined rock strength parameters; and
determining, using the computer system, principal stresses of the formation using at least the calculated anisotropic elastic properties and the rock strength parameters of the formation, wherein the principal stresses comprise a vertical stress, a minimum horizontal stress, and a maximum horizontal stress,
wherein the maximum horizontal stress is determined by a relation
σ
y
=
σ
z
v
(
1
+
EZ
N
+
v
1
+
EZ
N
-
v
2
)
between the vertical stress σ Z , Young's modulus E, Poisson's ratio ν, and normal compliance Z N .
16. A system comprising:
a first calculation logic that is operable to determine rock strength parameters from seismic data of a subterranean formation;
a second calculation logic that is operable to calculate anisotropic elastic properties of the formation using at least said determined rock strength parameters; and
a third calculation logic to determine principal stresses of the formation using at least the calculated anisotropic elastic properties and the rock strength parameters of the formation, wherein the principal stresses comprise a vertical stress, a minimum horizontal stress, and a maximum horizontal stress,
wherein the maximum horizontal stress is determined by a relation
σ
y
=
σ
z
v
[
1
+
EZ
N
+
v
1
+
EZ
N
-
v
2
]
between the vertical stress σ z , Young's modulus E, Poisson's ratio ν, and normal compliance Z N .