Pulsed Neutron Tool for Formation Water Salinity
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Solution Overview
Problem
Conventional methods for measuring formation water salinity from within a borehole are prone to errors due to sparseness of data, especially in mature reservoirs with mixed salinity conditions, where salinity can vary over time and space, affecting the accuracy of interpretations from instruments sensitive to salt presence.
Innovation Solution
The use of pulsed neutron gamma-ray spectroscopy with at least two detectors to determine formation and borehole apparent salinities through a cross-plot of spectroscopically determined yields of hydrogen and chlorine, allowing for the calculation of water saturation and oil holdup, and subsequently the determination of formation water salinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods (fluid samples, produced fluids, or measurements from different wells) are used to obtain formation water salinity, then the measurement process is simple, but the accuracy and reliability of salinity data are compromised due to sparseness, mixed salinity conditions, and temporal-spatial variations
Solution Approach 1:
The patent divides the measurement task into multiple energy component analyses (gamma-ray, neutron, density, sonic) with each detector type segmenting the overall measurement process. Each detector measures specific properties independently, and the results are integrated to calculate formation water salinity, thereby improving measurement accuracy through divided functional responsibilities
Solution Approach 2:
The patent employs a composite measurement approach combining multiple physics principles (gamma-ray spectroscopy, neutron capture, density measurement, sonic logging) into a single integrated system. This composite methodology leverages the strengths of each measurement technique to overcome the limitations of individual methods, achieving higher salinity measurement accuracy in mixed salinity conditions
2Productivity
If water injection is performed to maintain reservoir pressure, then reservoir pressure is maintained and oil displacement is improved, but formation water salinity becomes mixed and variable in time and space, compromising measurement accuracy
Solution Approach 1:
The patent implements continuous measurement capabilities using multiple detectors that continuously monitor formation properties. The gamma-ray, neutron, density, and sonic detectors continuously gather data, allowing the system to track temporal-spatial salinity variations caused by water injection and maintain accurate salinity measurements despite mixed salinity conditions
Solution Approach 2:
The patent incorporates feedback mechanisms where measurement results from multiple detectors are continuously integrated and used to update salinity calculations. The system uses the feedback from various measurement components to adjust and refine the formation water salinity determination, accounting for variations introduced by water injection operations
3Measurement precision
If formation tester sample method is used to obtain accurate formation water salinity, then salinity measurement accuracy is improved, but the operation becomes expensive and time-consuming, requiring workover rig and being limited to uncased boreholes
Solution Approach 1:
The patent enables the measurement system to obtain formation water salinity data directly through the existing borehole infrastructure using downhole detectors. The system performs self-contained measurements within the borehole using gamma-ray, neutron, density, and sonic detectors, eliminating the need for external workover rigs or complex sampling operations, thereby reducing operational complexity and cost while maintaining accuracy
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 more accurate and continuous measurements of formation water salinity, reducing errors associated with conventional methods and accounting for spatial and temporal salinity gradients, thereby enhancing the interpretation of borehole measurements sensitive to salt.
Implementation Method 1
using measurements of formation characteristics acquired from a pulsed neutron tool having at least two detectors
Implementation Method 2
A cross-plot is generated forming a quadrilateral from a database of ratios of spectroscopically determined yields of hydrogen (H) and chlorine (Cl) from a near spaced detector and a far spaced detector
Data Source
AI summary
Methods and systems are described for using pulsed neutron ?-ray spectroscopy to measure formation water salinity from within a borehole. Through generating a cross-plot of database values of ratios of spectroscopically determined yields of hydrogen (H) and chlorine (Cl) from two detectors, deriving apparent salinities therefrom, formation and borehole water salinities can be determined.