Prismatic Grid Inversion for Borehole-Formation Fluid Separation
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Solution Overview
Problem
Pulsed-neutron logging faces challenges in differentiating borehole fluid content from formation fluid content, particularly in distinguishing between oil, water, and gas, which complicates accurate hydrocarbon reserve estimation and production optimization.
Innovation Solution
A physics-based comprehensive data visualization and inversion framework using a prismatic grid representation to analyze fluid volumetrics in real-time, leveraging carbon-to-oxygen ratios and inelastic count rates from near and far detectors to accurately differentiate between borehole and formation fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulsed-neutron logging measurement is used to determine formation properties, then valuable data on formation carbon-oxygen ratio and porosity can be obtained, but it becomes challenging to isolate and differentiate the contributions from borehole fluid content versus formation fluid content
Solution Approach 1:
The patent segments the pulsed-neutron logging signal into distinct components: borehole fluid contribution and formation fluid contribution. By separating these overlapping signals through mathematical modeling and inversion techniques, the method enables independent analysis of each component, thereby resolving the difficulty of differentiating borehole holdup from formation oil saturation.
Solution Approach 2:
The patent introduces additional measurement dimensions by utilizing multiple detector types (neutron detectors and gamma ray detectors) and multiple measurement modes (elastic scattering, inelastic scattering, and capture gamma rays). This multi-dimensional approach provides sufficient independent equations to solve for multiple unknowns (borehole holdup, formation oil saturation, water saturation), transforming an underdetermined problem into a solvable system.
2Measurement precision
If traditional pulsed-neutron logging analysis is used, then carbon-oxygen ratio data can be obtained, but accurate determination of borehole holdup content and differentiation from oil content presents significant challenges
Solution Approach 1:
The patent employs mathematical inversion models and computational algorithms as intermediaries to bridge the gap between raw pulsed-neutron logging measurements and accurate fluid content determination. These computational tools process the combined borehole-formation signals, applying physical constraints and iterative optimization to extract accurate borehole holdup and formation saturation values that cannot be obtained through direct measurement alone.
3Measurement precision
If pulsed-neutron logging is used to estimate hydrocarbon reserves, then formation porosity and saturation data can be obtained, but the combination of signals from borehole and formation complicates the analysis
Solution Approach 1:
The patent performs preliminary separation of borehole and formation signals before proceeding with hydrocarbon reserve estimation. By first determining borehole holdup content and subtracting its contribution from the total measurement, the method prepares cleaned formation-only data that can then be reliably used for reserve calculations, avoiding the errors that would result from analyzing mixed signals.
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
Enhances the accuracy and efficiency of formation evaluation by providing robust fluid characterization, enabling reliable interpretation of fluid identification and quantification in flowing wells, thereby improving reservoir characterization and production strategies.
Implementation Method 1
In elastic neutron-scattering, the neutron bounces off the bombarded nucleus without exciting it or destabilizing it
Implementation Method 2
In inelastic neutron scattering, the neutron bounces off the nucleus, but excites it into quickly giving off what are called inelastic gamma rays
Implementation Method 3
In neutron absorption, the nucleus absorbs the neutron and becomes excited, typically emitting delayed gamma rays
Implementation Method 4
The excited target nucleus relaxes to its ground state by emitting characteristic gamma radiation
Implementation Method 5
Hydrogen, with the mass of its nucleus equal to that of a neutron, is very good at slowing down neutrons. With each elastic interaction, the neutron loses energy
Data Source
AI summary
A method of determining downhole formation oil saturation and three-phase holdup is described. The method includes lowering a pulsed-neutron logging tool downhole with a near detector and a far detector. The method further includes measuring a carbon to oxygen ratio from the near detector, measuring a carbon to oxygen ratio from the far detector, measuring a ratio of inelastic count rates, and plotting the measured ratios in a prismatic grid. The method further includes visualizing the fluid volumetrics around the pulsed-neutron logging tool.