High Resolution Resistivity Measurement on Core Plugs
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Solution Overview
Problem
Current resistivity measurement techniques, such as the four-electrode method, provide insufficient axial resolution and depth of investigation, often missing rock inhomogeneities due to fixed electrode spacing, which is too coarse for accurately determining resistivity variations within the core sample.
Innovation Solution
A system with multiple voltage electrodes arranged closer together than traditional methods, allowing for higher resolution resistivity measurements by varying electrode pair combinations to achieve different depths of investigation, enabling detection of small resistivity anomalies within the core sample.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard four-electrode measurement with fixed electrode spacing is used, then measurement simplicity is maintained, but axial resolution is insufficient (approximately 1 inch) causing rock inhomogeneities to be overlooked
Solution Approach 1:
The invention divides the measurement system into multiple discrete voltage electrodes (at least three) positioned at different axial locations along the core sample, between which current electrodes are placed. This segmentation allows multiple measurements to be taken at different axial positions, thereby achieving high axial resolution resistivity profiling without requiring a single complex high-resolution electrode assembly.
Solution Approach 2:
The invention transitions from a single-plane two-dimensional measurement (standard four-electrode method with fixed electrode spacing) to a three-dimensional measurement arrangement where voltage electrodes are distributed along the axial dimension. This dimensional extension enables resolution along the entire length of the core sample by taking measurements at multiple axial positions, effectively adding the axial dimension to the measurement space.
2Measurement precision
If voltage electrodes are placed closer together to improve axial resolution, then detection of small resistivity anomalies is enhanced, but depth of investigation is reduced
Solution Approach 1:
The invention segments the voltage measurement into multiple discrete electrode positions along the axial direction. By placing at least three voltage electrodes between the current electrodes at different axial locations, the system performs multiple measurements with different effective spacing configurations. This segmentation allows the system to achieve both high axial resolution (through closely spaced electrodes) and adequate depth of investigation (through the cumulative effect of multiple measurement positions).
Solution Approach 2:
The invention uses more voltage electrodes than the minimum required for a single measurement (at least three voltage electrodes between current electrodes). This excessive action creates multiple overlapping measurement zones that collectively provide both high axial resolution and sufficient depth of investigation. The redundant measurements at different axial positions compensate for the reduced depth of any single measurement pair.
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 allows for detailed resistivity profiling along the core sample length with high axial resolution, detecting otherwise overlooked inhomogeneities and providing precise resistivity data, enhancing the ability to characterize rock heterogeneity.
Implementation Method 1
An electric current is passed through the sample. The measurement device is used to make a first set of electrical measurements that involve a first pair of voltage electrodes and to make a second set of electrical measurements that involve a second pair of voltage electrodes.
Implementation Method 2
The resistance of the sample is calculated using Ohm's law. Given the geometry (e.g., length, cross-sectional area) of the core sample 110, the resistivity of the core material can be determined from the resistance.
Data Source
AI summary
A tool having two current electrodes, three or more voltage electrodes, and a measurement device capable of making electrical measurements is provided, along with a sample. With electrical connectivity to the sample, one current electrode is disposed at one location on the sample while the other current electrode is disposed at another location on the sample, and the three or more voltage electrodes are disposed on the sample intermediate the two current electrodes. An electric current is passed through the sample. The measurement device is used to make a first set of electrical measurements that involve a first pair of voltage electrodes and to make a second set of electrical measurements that involve a second pair of voltage electrodes. The first set of electrical measurements is compared to the second set of electrical measurements. It is inferred whether the sample has heterogeneous electrical properties using the compared electrical measurements.