The Use of Infrared Thermography on the Measurement of Microstructural Changes of Reservoir Rocks Induced by Temperature

Abstract

A variation of temperature produces a change in the microstructure of the rock due to the mineral thermal expansion and its residual strain. Depending on the temperature cycle and texture, microstresses may lead to the development of preexistent cracks or the creation of a new and irreversible cracking. The effect of temperature on reservoir rocks is an important topic since it conditions the permeability and the fluid flow. Two main questions arise from this: the first is if an irreversible cracking threshold is attained in the reservoir rocks at low temperature geothermal systems (around 100 °C); the second one is about the influence of thermal fatigue by the repetition of heating–cooling cycles on the different rock types. To answer these questions, four reservoir rocks (chalk, sandstone, fresh granite, and weathered granite) were submitted to two different thermal regimes. The first test was conceived to detect the irreversible cracking threshold, and for that, the rocks were submitted to progressive heating (90°, 100°, 110°, 120°, and 130 °C). The second test consisted of doing cycles of fast heating of the samples up to 200 °C. The microstructure variation was assessed by means of a scanning electron microscope, mercury porosimetry, and capillary water uptake combined with passive infrared thermography. Infrared thermography is an emerging tool in the field of rock study, used to detect water masses or determine thermal properties. The water transfer during the capillary tests of the rocks, before and after the tests, was monitored with this technique. In addition, the cooling rate index, a non-destructive parameter to detect cracking development, was calculated. The results made it possible to differentiate the behaviours in relation to the rock type, with a chalk and a weathered granite less susceptible to thermal stresses than a fresh granite and sandstone. In addition, infrared thermography resulted in being a very useful indirect technique to detect the changes on the surface, although they do not always correlate to the bulk microstructural changes.

Rock Emissivity Measurement for Infrared Thermography Engineering Geological Applications

“…IRT was further employed to characterize landslides, even in combination with other remote survey or geophysical techniques, e.g., [32][33][34], and for the detection of rock bridges within rock mass cracks [35]. Further applications refer to the study of rock behavior under stress, where IRT can highlight the unstable crack propagation and/or flaw coalescence [36], to the evolution monitoring of excavation damaged zones [37], and to the detection of microstructural changes of reservoir rocks [38].…”

Evaluation of Natural Stone Weathering in Heritage Building by Infrared Thermography

“…Thanks to its potential, IRT is currently used in numerous activities and scientific branches also involving the characterization of rocks. In particular, it is applied to the study of rock fracturing in rock masses, e.g., [16,22,23], or for the characterization of intact rock properties and related variations under specific conditions, e.g., [12,[24][25][26][27]. In the frame of cultural heritage preservation, IRT has already proved useful in detecting biocolonization on natural stones [28], studying sulfated crusts [29] and, more in general, for investigation of chemical degradation processes in historical buildings, e.g., [30][31][32].…”

Evaluation of InfraRed Thermography Supported by UAV and Field Surveys for Rock Mass Characterization in Complex Settings

“…The use of infrared thermography was also extended to geotechnical applications: for instance, the relation between the cooling index of rocks and the compressive strength of rock blocks was identified by coupling IRT and Schmidt Hammer tests [32]. In addition, methods to estimate the porosity of rock samples [33], to predict cracks development [34], wedge indentation [35] and to detect microstructural changes [36] at the laboratory scale were recently proposed.…”