Pulsed Neutron Capture Tool Cement Identification
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Solution Overview
Problem
Current methods for locating induced subterranean fractures and cement placement in boreholes are complex, time-consuming, and often provide misleading results due to logistical and mechanical challenges, and require expensive equipment or radioactive materials.
Innovation Solution
A pulsed neutron capture (PNC) tool is used to determine the location and height of fractures by comparing pre-fracture and post-fracture data sets, utilizing a proppant doped with a thermal neutron absorbing material like gadolinium oxide, which alters the capture to inelastic gamma ray count ratio, allowing for accurate identification of proppant placement without the need for radioactive tracers or complex data processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If radioactive tracers or complex logging methods are used to identify cement and fractures, then identification accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex mechanical and radioactive logging systems with a simplified pulsed neutron capture tool that measures gamma ray ratios. The system uses a neutron source and gamma ray detector to measure capture gamma rays and inelastic gamma rays, calculating their ratio to identify cement and fractures without requiring complex radioactive tracers or multiple logging runs.
Solution Approach 2:
The patent changes the measurement parameter from absolute gamma ray counts to a ratio of capture gamma rays to inelastic gamma rays. This ratio parameter is insensitive to variations in neutron source strength, borehole conditions, and tool position, providing accurate identification while simplifying the measurement system and reducing the need for complex calibration and correction procedures.
2Reliability
If multiple logging runs or complex data processing are performed, then identification reliability is improved, but loss of time increases
Solution Approach 1:
The patent performs identification in a single continuous logging run without requiring multiple separate operations. The pulsed neutron tool continuously measures capture and inelastic gamma rays while being pulled through the wellbore, calculating the ratio in real-time to identify cement and fractures immediately, eliminating the time required for multiple logging runs and complex post-processing.
Solution Approach 2:
The system uses the formation and cement themselves as the measurement target, requiring no external tracers or additives. The natural gamma ray responses from the formation and cement are measured and ratioed to provide identification, making the system self-sufficient and eliminating time-consuming preparation and interpretation steps associated with other methods.
3Difficulty of detecting and measuring
If radioactive materials are used for tracing, then detection capability is improved, but harmful factors increase
Solution Approach 1:
The patent replaces long-lived radioactive materials with a pulsed neutron source that generates neutrons on-demand for brief measurement intervals. The neutron source is activated only during logging operations and produces no residual radioactivity, eliminating radiation hazards while maintaining detection capability through the transient measurement of capture and inelastic gamma rays.
Solution Approach 2:
The patent converts the potential harm of neutron radiation into a benefit by using the neutron-induced gamma ray emissions as the measurement signal. The capture gamma rays and inelastic gamma rays produced by neutron interactions with formation and cement provide the identification information needed, turning a potentially harmful radiation source into a useful detection mechanism.
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
This method provides deeper investigation depths, avoids hazards associated with radioactive materials, and is cost-effective, enabling precise identification of fractured zones and cement placement with minimal logistical complexity, enhancing hydrocarbon production planning and remedial operations.
Implementation Method 1
emitting neutron pulses from the neutron source into the borehole and the subterranean formation and detecting capture and inelastic gamma rays generated by the neutron pulses
Implementation Method 2
detecting capture and inelastic gamma rays generated by the neutron pulses
Data Source
AI summary
Methods are provided for determining the location and height of cement in a subterranean borehole region using pulsed neutron capture (PNC) logging tools. The methods include obtaining a pre-cementing data set, placing in the borehole region a cement slurry that includes a liquid a thermal neutron absorbing material, obtaining a post-cementing data set, comparing the pre-cementing data set and the post-cementing data set to determine the location of the cement, and correlating the location of the cement to a depth measurement of the borehole to determine the location and height of the cement placed in the borehole region.