Pulsed Neutron Logging Tool for Cement Annulus Evaluation
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Solution Overview
Problem
Current methods for assessing cement and gravel-pack quality in wellbores are inefficient, often requiring separate logging passes and are sensitive only to casing/cement contact, leading to increased time and cost, and struggle with irregular borehole shapes and trapped fluids.
Innovation Solution
The use of specific ratios of gamma-count measurements from a pulsed neutron logging tool, specifically the NLIC/NCAP and NNIC/LCAP metrics, to assess the completeness of cement and gravel-pack annuli, which can be determined during standard formation-evaluation logging operations without increasing complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate logging passes are used to assess cement and gravel-pack quality, then measurement reliability is improved, but loss of time and productivity decrease
Solution Approach 1:
The patent combines cement quality assessment and gravel-pack quality assessment into a single logging pass by integrating multiple measurement capabilities (acoustic/ultrasonic measurements for cement, gamma-ray and neutron measurements for gravel-pack) into one tool string, eliminating the need for separate logging operations while maintaining measurement reliability
Solution Approach 2:
The logging tool is designed with multi-functionality to perform both cement evaluation and gravel-pack evaluation simultaneously, along with standard formation evaluation measurements, making a single pass sufficient for multiple assessment purposes
2Device complexity
If acoustic/ultrasonic measurements are used for cement assessment, then device complexity is reduced, but measurement precision deteriorates due to low radial depth
Solution Approach 1:
The patent segments the measurement functions by using different measurement techniques for different assessment needs: acoustic/ultrasonic measurements for basic cement presence detection, and gamma-ray/neutron measurements for detailed gravel-pack and cement quality assessment, with each method contributing to overall measurement precision without requiring a single complex system
Solution Approach 2:
The logging tool employs a composite measurement approach, combining multiple physical measurement principles (acoustic, gamma-ray, neutron) in a single integrated system, allowing each measurement type to compensate for the limitations of others and achieve comprehensive assessment precision
3Measurement precision
If conventional pulsed neutron tools are used with activation of silicon nuclei, then measurement precision is improved, but loss of time increases due to separate logging passes
Solution Approach 1:
The patent merges the pulsed neutron measurement capability with other logging tools into a single integrated tool string that can perform formation evaluation, cement assessment, and gravel-pack quality assessment simultaneously in one logging pass, eliminating the time loss associated with separate passes while maintaining the precision of neutron-based measurements
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
Provides a new source of information for evaluating cement and gravel-pack quality, ensuring complete annulus filling and reducing the need for additional logging passes, thereby overcoming the limitations of prior art methods.
Implementation Method 1
Measurements using pulsed neutron tools are conventionally based on the activation of silicon nuclei (i.e., the generation of unstable silicon isotopes) in the cement or gravel by high-energy neutrons
Implementation Method 2
spectral measurements of the gamma rays created during the decay of these isotopes
Implementation Method 3
specific ratios of gamma-count measurements from a pulsed neutron logging tool, specifically the NLIC/NCAP and NNIC/LCAP metrics
Data Source
AI summary
Disclosed are apparatus, systems, and methods for determining the completeness of the cement sheath or gravel-pack annulus of a borehole based on gamma counts or count rates measured with a pulsed neuron tool deployed in the borehole in conjunction with a quantitative relationship between certain gamma count (rate) ratios and a parameter of completeness. In various embodiments, the determination utilizes the ratio of the net long inelastic count (rate) and the near capture count (rate), or the ratio of the net near inelastic count (rate) and the long capture count (rate). Additional apparatus, systems, and methods are disclosed.