Borehole density measurement using pulsed neutron tool
Systems and methods employed measure borehole density by neutron induced gammas using a pulsed neutron tool. Traditional nuclear density methods only measure a bulk average density of the surrounding material. As discussed below, methods to measure only the borehole density excluding the contamination from the formation are disclosed. Specifically, the proposed methods use unique signatures from each geometric region to directly measure the borehole density or compensate for the contamination from formation. This method may be achieved by a borehole density measurement using differential attenuation of capture gamma from casing iron, a borehole density measurement using differential attenuation of inelastic gamma from oxygen, a differential attenuation of any induced gamma from any element from borehole and formation, or any combination thereof.
1. A method for determining borehole density comprising:
disposing a pulsed-neutron logging tool into a borehole, wherein the borehole has a wellbore casing;
emitting a neutron from a neutron source on the pulsed-neutron logging tool into the wellbore casing, wherein the wellbore casing includes iron;
capturing one or more gammas expelled from iron in the wellbore casing in response to the neutron from the neutron source; and
determining borehold density utilizing the captured one or more gammas based at least in part on a production intensity, wherein the production intensity is constant.
2. The method of claim 1 , further comprising formulating the production intensity of 7.6 MeV for the one or more gammas using I γ=7.6 MeV=T Fe *σ*φ, wherein T Fe is an iron atomic density in a material, σ is a capture cross section of iron, and φ is a neutron flux at given point.
3. The method of claim 2 , further comprising finding a count rate using Count Rate=I γ e −μρx , wherein μ is a mass attenuation coefficient at 7.6 MeV, and ρ is a bulk material density, and x is a material thickness for the attenuation of the one or more gammas.
4. The method of claim 3 , further comprising integrating over two or more coordinates using
CR
7.6
MeV
=
∫
0
2
π
∫
0
R
∫
0
π
(
S
σ
T
Fe
4
π
D
e
-
r
L
S
r
e
-
μρ
x
)
d
θ
dr
d
φ
.
5. The method of claim 4 , further comprising taking a ratio between multiple detectors of the count rate to identify a borehole density.
6. A method for determining borehole density comprising:
disposing a pulsed-neutron logging tool into a borehole;
emitting a neutron from a neutron source on the pulsed-neutron logging tool into the wellbore casing;
capturing one or more gammas expelled from the borehole; and
determining borehole density utilizing the captured one or more gammas based at least in part on a production intensity, wherein the production intensity is constant.
7. The method of claim 6 , further comprising formulating a production intensity of 7.6 MeV for the gamma using I γ=7.6 MeV=T Fe *σ*φ, wherein T Fe is an atomic density of the oxygen, the carbon, or the silicon in a material, σ is a capture cross section of iron, and φ is a neutron flux at given point.
8. The method of claim 7 , further comprising finding a count rate using Count Rate=I γ e −μρx , wherein μ is a mass attenuation coefficient at 7.6 MeV, and ρ is a bulk material density, and x is a material thickness for the attenuation of the gamma.
9. The method of claim 8 , further comprising integrating over two or more coordinates using
CR
7.6
MeV
=
∫
0
2
π
∫
0
R
∫
0
π
(
S
σ
T
Fe
4
π
D
e
-
r
L
S
r
e
-
μρ
x
)
d
θ
dr
d
φ
.
10. The method of claim 9 , further comprising taking a ratio between multiple detectors of the count rate to identifying a borehole density.
11. A system for determining borehole density comprising:
a pulsed-neutron logging tool comprising:
a neutron source configured to emit a neutron into a wellbore casing; and
a neutron detector configured to capture a gamma expelled from the wellbore casing due to the neutron from the neutron source; and
an information handling system for:
identifying an attenuation and a borehole density; and
formulating a production intensity of 7.6 MeV for the gamma of iron using I y=7,6 MeV =T Fe *σ*φ wherein T Fe is an iron atomic density in a material, σ is a capture cross section of iron, and φ is a neutron flux at given point.
12. The system of claim 11 , wherein the information handling system further finds a count rate using Count Rate=I y e −μpx , wherein μ is a mass attenuation coefficient at 7.6 MeV, and p is a bulk material density, and x is a material thickness for the attenuation of the gamma.
13. The system of claim 12 , wherein the information handling system further integrates over two or more coordinates using
CR
7.6
MeV
=
∫
0
2
π
∫
0
R
∫
0
π
(
S
σ
T
Fe
4
π
D
e
-
r
L
S
r
e
-
μρ
x
)
d
θ
dr
d
φ
.
14. The system of claim 13 , wherein the information handling system further takes a ratio between multiple detectors of the count rate to identify the borehole density.
15. The system of claim 11 , wherein the information handling system further formulates a production intensity of 7.6 MeV for the gamma OF oxygen, carbon, or silicon using I γ=7.6 MeV=T Fe *σ*φ, wherein T Fe is an atomic density of the oxygen, the carbon, or the silicon in a material, σ is a capture cross section of iron, and φ is a neutron flux at given point.
16. The system of claim 15 , wherein the information handling system further finds a count rate using Count Rate=I γ e −μρx , wherein μ is a mass attenuation coefficient at 7.6 MeV, and ρ is a bulk material density, and x is a material thickness for the attenuation of the gamma.
17. The system of claim 16 , wherein the information handling system further integrates over two or more coordinates using
CR
7.6
MeV
=
∫
0
2
π
∫
0
R
∫
0
π
(
S
σ
T
Fe
4
π
D
e
-
r
L
S
r
e
-
μρ
x
)
d
θ
dr
d
φ
.
18. The system of claim 17 , wherein the information handling system further takes a ratio between multiple detectors of the count rate to identifying a borehole intensity.
19. The system of claim 11 , wherein the information handling system further identifies if a gas is present in a wellbore from the attenuation and the borehole density.