Abstract
We apply thermoporoelasticity and a sequentially coupling technique for modeling thermally-driven coupled Thermo-Hydro-Mechanical (THM) processes in tight claystone. A THM benchmark case with a corresponding analytic solution for thermoporoelasticity under a constant heat loading verifies the model. Thereafter, two in situ heating experiments are simulated for model validation: a smaller-scale heating experiment (TED experiment) and a larger-scale experiment (ALC experiment) in Callovo-Oxfordian (COx) claystone at the Meuse/Haute-Marne underground research laboratory in France. The model exhibits good performance to match the observed temperature and pore pressure evolution for the smaller-scale TED experiment. For the larger-scale ALC experiment, general trends of thermal-pressurization are captured in the modeling, but pressure is underestimated at some monitoring points during cool-down. This indicates that the THM response in the field may be affected by the variability of rock’s properties or irreversible or time-dependent mechanical processes that are not included in the current thermoporoelastic model. The main contributions of this work are as follows: (1) we verify and validate the numerical simulator, TOUGH-FLAC, to be a valuable coupled THM modeling tool; (2) prove that the laboratory determined material parameters can be used as reference values for upscaling experiments. However, to better identify and quantify THM processes with modeling of in situ tests, more emphasize should be dedicated to obtaining high-quality mechanical deformation data.
Highlights
Claystone is currently considered as a potential host material in nuclear waste disposal
A number of in situ heating experiments to study coupled THM processes in claystone have been conducted at several underground research laboratories over the past decades
The current version of TOUGH-FLAC includes a sequential coupling scheme corresponding to a fixed stress-split method (Kim et al, 2011; Blanco-Martín et al, 2017), which is here applied to investigate thermally-driven coupled THM in tight claystone
Summary
Claystone is currently considered as a potential host material in nuclear waste disposal. Braun et al (2019) proposed tests involving thermal and mechanical loading to measure drained and undrained parameters of COx claystone Such experimental work and in situ studies at the MHM URL has led to substantial knowledge about the THM behavior of COx claystone and a set of proposed material parameters for coupled processes modeling of the MHM URL heating experiments in COx claystone (Armand et al, 2013, 2017a,b; Conil et al, 2020). We apply a modular approach originally proposed by Settari and Mourits (1998) for linking an existing reservoir simulator (fluid flow and heat transport) with a geomehanical simulator This method has been mostly investigated and applied for modeling coupled HM processes through a carefully derived pore-volume coupling, or porosity correction (Kim et al, 2011). We conclude and provide recommendations for further studies to improve the state of knowledge and our abilities of making confident model predictions of coupled THM processes in tight claystone
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