Pulsed Ultrafast Neutron Logging Tool Depth of Investigation
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Solution Overview
Problem
Existing neutron logging tools for hydrocarbon reservoirs have limited depth of investigation and pose health, safety, and security risks due to radioactive sources, failing to provide a representative sample of the reservoir formation beyond near-borehole regions.
Innovation Solution
A pulsed ultrafast neutron logging tool that emits a pulse of neutrons with kinetic energy greater than 20 MeV, detected by gamma ray detectors at varying distances, allowing for deeper investigation and reducing radiation emission when not activated, thereby enhancing the depth of investigation and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional radioactive neutron sources (252Cf, 241Am-9Be) are used, then neutron generation is achieved, but health, safety, and security risks increase due to continuous radiation emission
Solution Approach 1:
The patent employs pulsed neutron generation instead of continuous emission. The neutron source operates in periodic pulses, emitting neutrons only during measurement intervals and remaining inactive during storage and transport. This periodic operation eliminates continuous radiation exposure risks while maintaining neutron generation capability when needed.
Solution Approach 2:
The patent separates the neutron generation function from continuous radiation emission. By using particle acceleration to generate neutrons only during pulsed operation rather than relying on continuously decaying radioactive isotopes, the harmful radiation background is extracted and eliminated while preserving the useful neutron generation function.
2Measurement precision
If conventional neutron logging tools are used, then saturation measurement is achieved, but depth of investigation is limited to 6-12 inches preventing sampling of unaltered reservoir regions
Solution Approach 1:
The patent changes the energy parameter of the neutron source from conventional levels to ultrafast energies exceeding 20 MeV. This parameter change increases the neutron mean free path and penetration depth, enabling investigation beyond the conventional 6-12 inch limit into deeper, unaltered reservoir regions while maintaining saturation measurement precision.
Solution Approach 2:
The patent extends the measurement capability from near-borehole regions into the deeper radial dimension of the formation. By using ultrafast neutrons, the tool accesses the third radial dimension (deeper into the formation) that was previously inaccessible, allowing sampling of reservoir regions beyond the altered near-borehole zone.
3Object-affected harmful factors
If pulsed neutron tools with lower energy (14 MeV) are used, then radiation safety is improved, but depth of investigation remains limited
Solution Approach 1:
The patent changes the neutron energy parameter from 14 MeV to ultrafast energies exceeding 20 MeV. This parameter increase extends the depth of investigation by increasing neutron penetration depth while maintaining the pulsed operation mode that ensures radiation safety during storage and transport.
Solution Approach 2:
The patent creates a neutron source that simultaneously achieves multiple functions: it maintains radiation safety through pulsed operation, extends depth of investigation through ultrafast neutron energies, and provides representative reservoir sampling. The system is designed to fulfill multiple conflicting requirements through the combination of pulsed operation and high energy neutrons.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The tool achieves a deeper depth of investigation, providing a more representative sample of the reservoir formation and reducing health and safety risks by minimizing radiation emission when not in use, thus improving hydrocarbon reservoir management.
Implementation Method 1
a source of ultrafast neutrons mounted in the logging tool housing that emits a pulse of ultrafast neutrons into an irradiated portion of a formation surrounding the borehole
Implementation Method 2
one or more gamma ray detectors located at increasing distances from the source of ultrafast neutrons that detect a flux of stimulated gamma rays generated within the irradiated portion of the formation
Data Source
AI summary
A method, including emitting from a source of ultrafast neutrons within a logging tool deployed in a borehole, a pulse of ultrafast neutrons into an irradiated portion of a formation surrounding the borehole. The method further includes detecting, with one or more gamma ray detectors located at increasing distances from the source of ultrafast neutrons, a flux of stimulated gamma rays generated within the irradiated portion of the formation by the pulse of ultrafast neutrons; and determining, from the detected flux of stimulated gamma rays, one or more petrophysical properties of the irradiated portion of the formation.