Method and tool for determination of fracture geometry in subterranean formations based on in-situ neutron activation analysis
View Patent ↗A method for determining fracture geometry of a subterranean formation from radiation emitted from a fracture in the formation, including measuring gamma-radiation emitted from the fracture; subtracting background radiation from the measured gamma-radiation to obtain a peak-energy measurement; comparing the peak-energy measurement with a gamma-ray transport/spectrometer response model; and determining formation fracture geometry of the fracture in accordance with values associated with the response model.
1. A method of determining fracture geometry of a subterranean formation from radiation emitted from a fracture in said formation, comprising:
a) measuring gamma-radiation emitted from the fracture;
b) subtracting background radiation from said measured gamma-radiation to obtain a peak-energy measurement;
c) comparing said peak-energy measurement with a gamma-ray transport/spectrometer response model; and
d) determining formation fracture geometry of said fracture in accordance with values associated with said response model.
2. The method of claim 1 , wherein fracture geometry includes the height and width of a fracture formation.
3. The method of claim 1 , further comprising generating said gamma-ray transport/spectrometer response model by applying a Monte Carlo simulation to gamma-ray buildup/decay profile data.
4. The method of claim 3 , wherein said Monte Carlo simulation comprises a Monte Carlo N-Particle Transport Code.
5. The method of claim 3 , wherein said gamma-ray buildup/decay profile data is obtained by integrating neutron transport data.
6. The method of claim 5 , wherein said integrating is performed using a Euler method.
7. The method of claim 6 , wherein said Euler method is an implicit Euler method.
8. The method of claim 6 , wherein said Euler method is a backward Euler method.
9. The method of claim 6 , wherein said neutron transport data is obtained by applying neutron source parameters and subterranean formation parameters to a Monte Carlo simulation.
10. The method of claim 9 , wherein said neutron source parameters include neutron source, tool composition, tool geometry, and said subterranean formation parameters include borehole fluid composition and formation composition.
11. The method of claim 9 , wherein said Monte Carlo simulation comprises a Monte Carlo N-Particle Transport Code.
12. A method for modeling geometrical parameters of a subterranean formation fracture detected by collecting gamma-radiation data stimulated by a neutron source, comprising:
a) obtaining neutron transport data by applying neutron source detector parameters and subterranean formation parameters to a Monte Carlo simulation;
b) obtaining gamma-ray buildup/decay profile data by integrating said neutron transport data;
c) generating a gamma-ray transport/spectrometer response model by applying a Monte Carlo simulation to said gamma-ray buildup/decay profile data; and
d) creating a gamma-ray transport/spectrometer response database correlating gamma-radiation spectra with subterranean formation fracture geometry parameters.
13. The method of claim 12 , wherein said Monte Carlo simulations comprise a Monte Carlo N-Particle Transport Code.
14. The method of claim 12 , wherein said neutron source parameters include neutron source, tool composition, tool geometry, and said subterranean formation parameters include borehole fluid composition and formation composition.
15. The method of claim 12 , wherein said integrating is performed using a Euler method.
16. The method of claim 15 , wherein said Euler method is an implicit Euler method.
17. The method of claim 15 , wherein said Euler method is a backward Euler method.
18. A method of determining fracture geometry of a subterranean formation from radiation emitted from a fracture in said formation, comprising:
a) measuring gamma-radiation emitted from the fracture using a logging tool having two radiation detectors, wherein one of said two radiation detectors is used to measure background radiation emissions;
b) subtracting background radiation from said measured gamma-radiation to obtain a peak-energy measurement;
c) comparing said peak-energy measurement with a gamma-ray transport/spectrometer response model; and
d) determining formation fracture geometry of said fracture in accordance with values associated with said response model.
19. A method as set forth in claim 18 , wherein peak-energy of gamma radiation is received by said detectors as a result of activation of a radiation susceptible material in said fracture, and said one of said two radiation detectors receives radiation present in said subterranean formation before and after said activation.
20. A method as set forth in claim 19 , wherein said activation is performed by bombardment of said radiation susceptible material with neutrons from a neutron source attached to said detectors.