Pulsed Neutron Spectroscopy for Borehole Salinity Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Accurate measurement of borehole and formation water salinity is challenging due to its variable concentration over time and location, affecting hydrocarbon production estimates, as existing instruments like borehole resistivity sondes require knowledge of salinity to provide accurate water and hydrocarbon fraction estimates.
Innovation Solution
The method involves using pulsed neutron gamma-ray spectroscopy with a PNL tool, capturing and correcting near and far inelastic spectra, and employing a standard elements database to calculate apparent salinity ratios, allowing for the determination of borehole and formation salinity without requiring water saturation values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If borehole resistivity sonde is used to measure electrical resistivity, then water fraction can be determined, but measurement precision deteriorates due to sensitivity to salinity variations
Solution Approach 1:
The patent introduces salinity measurement as an intermediary parameter that mediates between the resistivity measurement and the water fraction calculation. By measuring salinity separately using neutron gamma-ray spectroscopy, the system can correct the resistivity-based water fraction calculation for salinity effects, thereby maintaining measurement precision despite salinity variations.
Solution Approach 2:
The patent replaces the direct resistivity-based measurement system with a combined system that uses neutron gamma-ray spectroscopy to measure salinity and combines this with resistivity data. This substitution allows the system to account for salinity effects mathematically rather than being directly affected by them, improving measurement precision.
2Measurement precision
If salinity measurement is performed at multiple depths and times, then production management accuracy improves, but device complexity increases
Solution Approach 1:
The patent employs a pulsed neutron gamma-ray spectroscopy tool that serves multiple functions: it measures salinity, determines water fraction, and provides depth-specific data. This multi-functional approach allows accurate salinity measurement at multiple depths and times without requiring separate specialized instruments for each measurement type, thereby managing device complexity while improving measurement precision.
Solution Approach 2:
The patent uses periodic pulsed neutron sources to obtain salinity measurements at different depths and times. The pulsed nature of the neutron source allows the tool to cycle through different measurement zones and conditions, providing comprehensive salinity data without requiring continuous operation of complex measurement systems.
3Measurement precision
If variable salinity conditions are accounted for in measurements, then hydrocarbon production estimates improve, but measurement time increases
Solution Approach 1:
The patent performs salinity measurement using neutron gamma-ray spectroscopy as a preliminary action before final hydrocarbon volume calculation. By obtaining salinity data in advance and storing it for later use in production management, the system avoids time-consuming iterative corrections and can quickly adjust hydrocarbon estimates as production conditions change, thereby improving accuracy without significant time loss.
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 approach enables accurate and efficient calculation of borehole and formation water salinity, optimizing hydrocarbon production by providing salinity data necessary for sensitive downhole measurement instruments, thus improving the management of hydrocarbon production.
Implementation Method 1
a pulsed neutron source
Implementation Method 2
pulsed neutron gamma-ray spectroscopy measurements
Implementation Method 3
two downhole gamma ray spectrometers (gamma ray detectors)
Implementation Method 4
near inelastic spectrum and the far inelastic spectrum
Implementation Method 5
near capture spectrum and the far capture spectrum
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present disclosure describes various embodiments related to methods for determining salinity of water in a borehole of a formation and the water in the formation. Various methods may use inelastic and capture gamma-ray spectra obtained from a pulsed neutron logging tool. Various embodiments may use a ratio of chlorine from a capture spectrum to oxygen from an inelastic spectrum for a near and a far detector to calculate apparent salinity ratios for water in a borehole and a formation. From the apparent salinity ratios, a borehole salinity and a formation salinity may be calculated using a tool characterization database and without using formation water saturation for the calculation. Other embodiments may be disclosed or claimed.