Forward Modeling Neutron Gamma-Ray Density Logging
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Solution Overview
Problem
Current downhole nuclear logging methods, particularly in non-trivial geometries like high-angle/horizontal wells and thinly bedded formations, face challenges due to the computational intensity of Monte Carlo simulations, and lack accurate forward models for measuring formation density based on neutron-induced gamma-ray emission.
Innovation Solution
A method and system employing forward models to derive synthetic detector measurements from neutron-induced gamma-ray emission, allowing for the inference of geological formation properties such as bulk density, by comparing synthetic and actual detector measurements, and using a characteristic formation parameter defined by a combination of fundamental nuclear properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Monte Carlo method is used for modeling neutron-induced gamma-ray emission, then measurement accuracy is improved, but computational time and resource requirements increase significantly
Solution Approach 1:
The patent creates a simplified forward model that copies the essential physics of neutron-induced gamma-ray emission without the full complexity of Monte Carlo simulations. This forward model uses analytical solutions to reproduce the key measurement responses, enabling rapid interpretation while maintaining adequate accuracy for complex logging geometries.
Solution Approach 2:
The invention changes the mathematical parameters and approaches used in modeling - transitioning from stochastic Monte Carlo methods to deterministic forward models with analytical solutions. This parameter change fundamentally alters the computational characteristics while preserving the ability to interpret neutron-induced gamma-ray measurements in complex geometries.
2Productivity
If forward models are used for gamma-gamma density and neutron porosity measurements, then computational speed is improved, but measurement accuracy and physical completeness decrease
Solution Approach 1:
The patent performs preliminary development and validation of forward models specifically for neutron-induced gamma-ray emission measurements. By pre-establishing the forward model framework, sensitivity functions, and interpretation algorithms, the system enables rapid real-time interpretation without sacrificing the physical completeness needed for accurate measurements in complex geometries.
Solution Approach 2:
The forward model serves as an intermediary between the complex Monte Carlo physics and the practical measurement interpretation. It translates the fundamental neutron-gamma-ray interaction physics into a computationally efficient form that can be used for real-time logging while maintaining the physical relationships needed for accurate bulk density determination.
3Adaptability or versatility
If measurement zone encompasses regions with different properties, then adaptability to complex geometries is improved, but interpretation uniqueness deteriorates
Solution Approach 1:
The patent segments the measurement response into contributions from different formation regions using sensitivity functions. By analyzing how the measurement responds to property variations at different depths and locations, the forward model can deconvolve the mixed signal and provide unique interpretation even when the measurement zone encompasses multiple regions with different properties.
Solution Approach 2:
The invention introduces additional dimensional information through the forward model's ability to account for three-dimensional geometry effects, borehole conditions, and depth-of-modulation variations. This additional dimensional analysis enables unique interpretation by resolving ambiguities that arise from measuring mixed signals from multiple formation regions.
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
Enables faster and more accurate measurement of bulk density and other formation properties, improving interpretation in complex logging geometries and aiding in well control decisions.
Implementation Method 1
The neutron source is configured to emit neutrons into the formation to induce gamma-ray emission from the formation. The gamma-ray emission can result from inelastic interaction of neutrons with the formation.
Implementation Method 2
at least one radiation detector spaced from the neutron source in axial direction, wherein the at least one radiation detector is configured to detect gamma-rays emitted from the formation as a result of the interaction of the neutrons with the formation
Data Source
AI summary
A method and system for determining at least one property of a geological formation employs at least one forward model to derive at least one synthetic detector measurement that relates to neutron-induced gamma-ray emission from geological formation. The forward model is also used to infer at least one property of the geological formation including bulk density of the geological formation.