Thermal Acoustical and Mechanical Characterization of Rock under in-situ conditions

TL;DR

This study presents a novel experimental setup to measure rock thermal conductivity under in-situ pressure and temperature conditions, revealing how pressure and temperature jointly influence thermal properties and micro-structural evolution.

Contribution

It introduces a multi-anvil cubic press for simultaneous thermal, acoustic, and mechanical measurements of rocks under controlled in-situ conditions, providing new insights into micro-structural effects.

Findings

Thermal conductivity decreases by about 5.9% per 50°C at low pressure.

Increased confining pressure enhances thermal conductivity.

Pressure reduces the rate of thermal conductivity decrease with temperature.

Abstract

Data on the coupled influence of pressure and temperature on rock thermal conductivity remain limited. This study adapts a multi-anvil cubic press to enable steady-state thermal conductivity measurements under controlled in-situ conditions. The setup concurrently records P- and S-wave velocities along three orthogonal directions, providing unique real-time constraints on micro-structural evolution. Beyond the expected temperature dependence, preliminary tests on two sandstones reveal a twofold pressure effect: increasing confining pressure enhances thermal conductivity through microcrack closure and better grain contacts, while simultaneously reducing the rate at which conductivity decreases with temperature. Initial results align closely with published datasets, supporting the reliability of the developed methodology. Quantitatively, the thermal conductivity of the studied sandstones was found to decrease by an average of approximately 5.9% per 50 {\deg}C at the lowest confinement (12 MPa), compared with about 4.2% per 50 {\deg}C at the highest confinement (100 MPa). In addition, an average increase of roughly 1.4% per 10 MPa of applied confining pressure was observed for both samples.