Downhole Electromagnetic Salinity Detection Using Multifrequency Permittivity
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Solution Overview
Problem
Current methods for determining formation water salinity in shaly sands are limited by their reliance on correlations with different physical principles than conductivity, are time-consuming, and costly, and often fail to accurately measure salinity at low or high levels, especially when using higher frequency dielectric data.
Innovation Solution
Measuring multifrequency permittivity data at frequencies below 1 MHz from downhole electromagnetic measurements, processing this data to estimate salinity using calibration equations that relate the slope of permittivity change to frequency, and using these estimates to determine other formation properties like water saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher frequency (20 MHz to 1 GHz) dielectric data is used to measure formation water salinity, then measurement speed is improved, but measurement precision deteriorates at low and high salinity levels
Solution Approach 1:
The patent changes the frequency parameter of electromagnetic measurements from higher frequencies (20 MHz to 1 GHz) to lower frequencies (below 1 MHz). This parameter change enables accurate salinity measurement across the full range of salinity levels, resolving the precision deterioration that occurs at low and high salinity when using higher frequencies.
2Measurement precision
If downhole fluid sampling methods are used to measure formation water salinity, then measurement precision is improved, but loss of time and productivity deteriorate
Solution Approach 1:
The patent replaces the mechanical sampling system (physical collection and transport of formation water samples to laboratories) with an electromagnetic measurement system that performs salinity determination in-situ downhole. This substitution eliminates time losses associated with sampling, transport, and laboratory analysis while maintaining measurement precision through electromagnetic property measurements.
3Productivity
If higher frequency dielectric measurements are used, then productivity is improved, but reliability deteriorates due to shallow measurement depth
Solution Approach 1:
The patent changes the frequency parameter to lower values (below 1 MHz), which increases the penetration depth of electromagnetic signals into the formation. This parameter change ensures that measurements are taken from deeper, more representative formation zones rather than shallow near-borehole regions, thereby improving reliability while maintaining productivity.
4Device complexity
If conventional electromagnetic induction tools are used, then device complexity is reduced, but measurement precision deteriorates due to inability to detect clay volumes and salinity accurately
Solution Approach 1:
The patent introduces dynamic multifrequency measurements (measuring at multiple frequency points below 1 MHz) rather than single-frequency measurements. This dynamic approach enables the detection of frequency-dependent permittivity changes that are characteristic of clay minerals and formation water, thereby improving measurement precision for clay volume and salinity while maintaining relatively simple tool design.
Solution Approach 2:
The patent adds the frequency dimension to electromagnetic measurements by performing measurements at multiple frequency points below 1 MHz. This dimensional expansion enables the detection of dispersive effects that provide additional information about clay volumes and formation water salinity, improving measurement precision without significantly increasing device complexity.
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 provides nondestructive, highly sensitive measurements of formation water salinity and other properties, effectively addressing the limitations of existing methods by accurately detecting clay volumes and salinity levels across various conditions.
Implementation Method 1
measuring, from downhole electromagnetic measurements at multiple frequencies below 1 MHz, multifrequency permittivity data of a subsurface formation
Implementation Method 2
The multifrequency permittivity data is processed to estimate salinity of the formation water of the subsurface formation
Data Source
AI summary
Methods and systems are provided for characterizing formation water salinity of subsurface formation using multifrequency permittivity data over a range of frequencies below 1 MHz. The multifrequency permittivity data is processed to determine salinity of formation water contained in the subsurface formation. Other useful formation properties (such as formation water saturation) can be determined based on the formation water salinity.