Distributed Thermal Response Multi-Source Modeling to Evaluate Heterogeneous Subsurface Properties.

Area of Science:

• Geotechnical Engineering
• Geothermal Energy Systems
• Environmental Science

Background:

• Accurate thermal property assessment is crucial for designing low-temperature borehole heat exchangers (BHEs).
• Heterogeneous subsurface conditions present challenges for traditional thermal property estimation methods.

Purpose of the Study:

• To evaluate the effectiveness of a distributed thermal response test (DTRT) for characterizing thermal properties in heterogeneous subsurface environments.
• To improve the accuracy of heat loss rate calculations and borehole temperature profile measurements in BHEs.

Main Methods:

• Conducted a DTRT combining distributed temperature sensing (DTS) and a conventional thermal response test (TRT) in a U-bend geothermal loop.
• Deployed fiber-optic cables within the geothermal loop and the borehole center for precise temperature monitoring.
• Developed and applied single-source and multi-source models based on the infinite line source method to analyze temperature data.

Main Results:

• The DTRT successfully estimated subsurface thermal conductivity by analyzing temperature responses of diverse geologic materials.
• Both single-source and multi-source models yielded comparable thermal conductivity values.
• Multi-source modeling demonstrated capability in predicting thermal conductivity for heterogeneous materials using borehole temperature profiles.

Conclusions:

• The DTRT, utilizing DTS, provides a robust method for assessing thermal properties in complex subsurface conditions.
• The developed modeling approaches enhance the understanding of thermal behavior within BHE systems.
• Accurate thermal conductivity data from DTRT supports optimized design and performance of geothermal energy systems.