Measurement of the Spatial Distribution of Heat Exchange in a Geothermal Analog Bedrock Site Using Fiber Optic Distributed Temperature Sensing

Abstract

Highly channelized flow in fractured geologic systems has been credited with early thermal breakthrough and poor performance of geothermal circulation systems. An experiment is presented here in which the effect of channelized flow on fluid/rock heat transfer is measured. Hot water was circulated between two wells in a single bedding plane fracture and the elevation of rock matrix temperature was measured using fiber optic Distributed Temperature Sensing (DTS). Between wells with good hydraulic connection, heat transfer appeared to follow a classic dipole sweep pattern. Between wells with poor hydraulic connection, heat transfer was skewed toward apparent regions of higher transmissivity (or larger aperture). These results are consistent with hydraulic and tracer tests, as well as ground penetrating radar imaging, that shows a heterogeneous distribution of transmissivity. Although these results are preliminary and still qualitative, they suggest that flow channeling can have a significant impact on heat transfer efficiency even in single planar fractures.