Wellbore Cable Characterization for Stable Downhole Voltage
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Solution Overview
Problem
In wireline logging systems, maintaining a stable downhole voltage is challenging due to the long length of wireline cables, which makes it impractical to feed back the load voltage for accurate voltage regulation, leading to unacceptable voltage variations that can affect tool performance.
Innovation Solution
A method is developed to characterize the electrical cable by applying a voltage input at the earth surface and measuring the current response, allowing for the computation of cable parameters such as resistance, capacitance, and inductance, which are used to model the cable and maintain a stable downhole voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedback cable is added to carry the load voltage signal back to the surface, then voltage regulation accuracy is improved, but the system complexity and cost increase significantly
Solution Approach 1:
The patent introduces an intermediary electrical cable model that mathematically represents the cable's electrical characteristics (resistance, capacitance, inductance). This model acts as a mediator between the surface voltage source and the downhole load, allowing the system to predict and compensate for voltage drops without requiring a physical feedback cable to carry voltage signals back to the surface.
Solution Approach 2:
The patent creates a simplified electrical model (copy) of the actual cable that captures its essential electrical behavior. This model is used to predict voltage drops and guide compensation strategies, eliminating the need for complex physical feedback infrastructure while maintaining adequate voltage regulation.
2Length of moving object
If the wireline cable length is increased to reach deeper wells, then the operational capability is improved, but the voltage variation at the load increases
Solution Approach 1:
The patent applies preliminary action by measuring the cable's electrical parameters (resistance, capacitance, inductance) during installation and creating an electrical model before the logging operation begins. This pre-characterization allows the system to predict voltage drops for any given current draw and adjust the source voltage in advance to compensate for expected variations, maintaining stable downhole voltage even in long cables.
Solution Approach 2:
The patent implements a form of feedback by using the pre-established electrical model to continuously predict the relationship between source voltage, current draw, and load voltage. The surface voltage source adjusts its output based on these predictions and measurements of source voltage and current, effectively compensating for cable-induced voltage variations without requiring direct voltage feedback from the downhole load.
3Loss of energy
If the cable resistance is increased to reduce current draw, then power loss in the cable is reduced, but the power delivered to the load decreases
Solution Approach 1:
The patent applies dynamics by making the source voltage adjustable and adaptive rather than fixed. The system dynamically adjusts the source voltage based on the electrical model predictions and actual operating conditions (current draw, cable state). This allows the system to optimize the balance between cable power loss and load power delivery by selecting the appropriate source voltage for each operating condition.
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 efficient and accurate characterization of the electrical cable without the need for feedback cables, stabilizing the downhole voltage and improving data acquisition rates by modeling the cable's resistance and capacitance, thus addressing the issue of voltage variations.
Implementation Method 1
If the wireline cable is modeled as a simple resistive element
Implementation Method 2
computation of cable parameters such as resistance, capacitance, and inductance
Implementation Method 3
computation of cable parameters such as resistance, capacitance, and inductance
Data Source
AI summary
To characterize an electrical cable that is deployed in a well, a voltage input is applied to the electrical cable at an earth surface location, where the well extends from the earth surface location. A current response resulting from the voltage input is measured at the earth surface location. At least one parameter of the electrical cable is computed according to the measured current response.