Borehole Thermal Conductivity Profiling with Inverse Temperature Modeling
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Solution Overview
Problem
Current methods for determining thermal conductivity in subsoil for geothermal probes are limited by systematic measurement errors, high costs, and inability to accurately measure vertical variations, leading to inaccurate predictions of heat extraction capabilities and potential groundwater flow effects.
Innovation Solution
A method involving measuring undisturbed and regenerated temperature profiles using a wireless measuring device, followed by numerical simulation with inverse methods to calculate vertical thermal conductivity variations, reducing measurement time and costs while accounting for subsurface parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cable-connected borehole measuring probes are used in open boreholes, then temperature profiles can be measured, but systematic measurement errors occur due to borehole cooling and internal fluid circulation
Solution Approach 1:
The borehole is allowed to cool down completely before measurement begins. The method specifies waiting until the borehole temperature has returned to the initial geothermal gradient, eliminating systematic errors from residual heating and ensuring accurate baseline temperature profiles
Solution Approach 2:
The measurement process involves periodic temperature monitoring at multiple depths throughout the borehole cooling period and during the subsequent thermal response test. Temperature profiles are recorded at regular intervals to track the evolution from initial cooling through the heating phase, enabling separation of cooling effects from thermal conductivity signals
2Measurement precision
If wired borehole measurement technology is used, then temperature data can be collected, but weak measurement signals are masked by electromagnetically scattered interference signals
Solution Approach 1:
The patent replaces wired electrical measurement systems with wireless temperature sensors that transmit data via radio frequency or other non-electrical means. This substitution eliminates electromagnetic interference from cables and connectors, allowing weak temperature signals to be detected without masking by scattered electromagnetic signals
Solution Approach 2:
Wireless communication modules serve as intermediaries between the temperature sensors and the data collection system. These intermediaries transmit measurement data without requiring physical electrical connections through the borehole environment, thereby avoiding electromagnetic interference while maintaining data transmission capability
3Ease of manufacture
If geothermal probes are installed immediately after drilling to reduce costs, then borehole construction costs are minimized, but accurate thermal conductivity measurement becomes difficult
Solution Approach 1:
The thermal response test is performed as a preliminary action before geothermal probe installation. By measuring the thermal conductivity of the undisturbed ground in the open borehole first, the method captures accurate subsurface thermal properties without the complicating influence of probe materials, backfill, or spiral configuration that would be present after probe installation
Solution Approach 2:
The measurement process extracts thermal conductivity information from the natural ground conditions before the geothermal probe is installed. By separating the measurement phase from the installed probe phase, the method isolates the true subsurface thermal properties from artifacts introduced by the probe system itself
4Device complexity
If thermal response tests use conventional line source theory and model simplifications, then calculation is simplified, but accuracy of calculated thermal conductivity is greatly limited
Solution Approach 1:
The borehole is divided into multiple discrete measurement depths with temperature sensors positioned at specific intervals. By segmenting the continuous thermal field into discrete measurement points, the method captures vertical variations in thermal conductivity and groundwater flow effects that would be averaged out in conventional line source models, enabling more accurate representation of heterogeneous subsurface conditions
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 precise determination of thermal conductivity and mass transport variations, improving the accuracy of geothermal probe performance predictions and reducing measurement time from several days to under 72 hours, with significant cost savings.
Implementation Method 1
introducing a predetermined amount of heat into the borehole heat exchanger (2) by circulating a continuously heated fluid through the heat exchanger
Implementation Method 2
measuring with a wireless measuring device (30) the undisturbed temperature profile T1(z) as a function of depth z in the borehole heat exchanger (2) by means of at least two temperature sensors (20) for measuring the temperature of the circulating fluid at different depths
Data Source
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AI summary
The undisturbed temperature/depth profile T1(z) is measured. Hot fluid is circulated in the underground bore. The ground temperature regenerates over a given time interval, and a new temperature/depth profile T2(z) is then measured. A mathematical model is set up to calculate temperature profiles numerically, based on theoretical values of the subterranean ground parameters. Using inverse numerical methods, measured- and calculated profiles are brought into correspondence. A calculated, probable underground parameter profile is calculated from the results.