Downhole Imaging Tool Impedance Segmentation
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Solution Overview
Problem
Current tools for imaging subsurface geological formations through non-conductive oil-based mud struggle with low sensitivity and resolution due to dominant mud impedance, particularly in formations with low resistivity, as they fail to adequately account for the electrical properties of rocks and muds.
Innovation Solution
A tool that measures complex impedance and determines the phase angle of the non-conductive medium, isolating the component of impedance orthogonal to the phase angle, using a configuration with imaging and mud buttons at different distances to differentiate and reduce mud influence, allowing for improved imaging in low resistivity formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current injection tools are used in non-conductive oil-based mud, then the tool can operate in the mud environment, but the mud impedance dominates the measured impedance and degrades imaging quality in low resistivity formations
Solution Approach 1:
The patent segments the impedance measurement into two independent components: a real component (resistive) and an imaginary component (reactive). By separating the measured complex impedance into these segments, the system can identify and isolate the mud impedance contribution (which is primarily imaginary) from the formation impedance (which is primarily real), thereby improving imaging quality while maintaining operation in non-conductive mud.
Solution Approach 2:
The patent extracts the mud impedance component from the total measured impedance by identifying and removing the imaginary (reactive) portion, which is dominated by mud impedance. This extraction leaves the real (resistive) component, which represents the formation impedance, thereby isolating the useful formation information from the harmful mud interference.
2Power
If the formation has low resistivity, then more current can be injected into the formation, but the mud impedance becomes even more dominant and degrades the signal
Solution Approach 1:
The patent converts the harmful dominant mud impedance into a beneficial filtering mechanism. By recognizing that mud impedance is primarily imaginary (reactive) while formation impedance is primarily real (resistive), the system uses the mud's electrical characteristics to its advantage in separating the two components, thereby improving signal-to-noise ratio even in low resistivity formations where mud impedance would normally be most problematic.
3Device complexity
If conventional current injection tools are used, then the tool structure is simple, but the resolution and sensitivity are insufficient due to mud impedance interference
Solution Approach 1:
The patent replaces complex mechanical filtering or signal processing hardware with a mathematical approach. Instead of using additional physical components to block or filter mud impedance, the system uses mathematical operations (separating real and imaginary components of complex impedance) to achieve the same goal, thereby maintaining simple tool structure while improving resolution and sensitivity.
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 enhances imaging accuracy by isolating the formation's impedance from the mud's, providing better resolution and sensitivity in low resistivity formations, overcoming the limitations of existing technologies.
Implementation Method 1
The impedance (voltage/current) seen by each button is indicative of the resistivity of a small volume of formation in front of each button
Implementation Method 2
Such tools inject AC current into the formation from one or more small electrodes (called 'buttons')
Implementation Method 3
operate at frequencies in the range 1-100 kHz where the formation generally has a resistive character and dielectric effects can be neglected except at very high resistivities
Data Source
AI summary
The invention is concerned with a tool and method for imaging a formation through a substantially non-conductive medium. The tool comprises first circuitry for injecting a current into the formation, wherein a complex impedance to the current is measured. Second circuitry for determining a phase angle of an impedance of the non-conductive medium and third circuitry for determining a component of the complex impedance that is orthogonal to the phase angle.