Phase-field simulation of fluid inclusion migration due to underground excavation in rock salt
Abstract
Due to stress redistribution induced by underground excavation, an Ed/DZ (excavation disturbed/damaged zone) is known to be generated in the vicinity of an opening, which may significantly alter the hydraulic and mechanical properties of the rock in the near-field. Fluid inclusions, e.g. hydrocarbon found along grain boundaries in rock salt, which are quasi-randomly distributed in rock and sometimes can only be observed with ultraviolet light, can even be mobilised and migrate at potentially significant speed towards the excavation (Paul et al., 2015).
To simulate the coupled hydro-mechanical processes driving fluid inclusion migration, a research team is intensively working on the development and application of different numerical approaches within the international cooperative project DECOVALEX-2019. A multi-scale modelling strategy has been developed (Shao et al., 2019). Macroscale coupled hydro-mechanical modelling of an underground excavation serves to determine hydraulic and time-dependent deviatoric stress conditions, taking creep behaviour of the rock salt into account. Under these constraints, a variational phase-field method (Bourdin et al., 2012) is used to simulate the pathway dilation along the halite grain boundary and to quantify the microscale change in permeability for flow migration. In phase-field models, sharp interfaces such as cracks are regularized using a phase-field order variable (Bourdin et al., 2012). Following this formalism, fluid migration is simulated as crack propagation along weak interfaces (grain boundaries) which is driven by both the high pressure of the locally distributed hydrocarbon and the time-dependent stress development caused by creeping of the rock salt. Figure 1 shows that a small volume of fluid inclusion initially located at the fourfold junction of halite grain boundaries can migrate under a deviatoric stress condition. The finite element mesh is based on the information extracted from a colour raster from a CT (Computer Tomography) image. Keywords: Fluid inclusion, microscale pathway dilation, phase-field modelling, hydromechanical coupling, OpenGeoSys References Bourdin B., Chukwudozie C., Yoshioka K., 2012. A Variational Approach to the Numerical Simulation of Hydraulic Fracturing. SPE 146951, ATCE. Kolditz O., Bauer S., Bilke L., Böttcher N., Delfs J.O., Fischer T., Görke U. J., Kalbacher T. Kosakowski G, McDermott C. I., Park C. H., Radu F., Rink K., Shao H., Shao H.B., Sun F. Sun Y. Y., Singh A. K. Taron J., Walther M., Wang W., Watanabe N., Wu Y., Xie M., Xu W., Zehner B. 2012. OpenGeoSys: An Open-Source Initiative for Numerical Simulation of Thermo-Hydro-Mechanical/Chemical (THM/C) Processes in Porous Media. Environmental Earth Sciences 67 (2): 589-99. Bilke, L., Bernd F., Kalbacher T., Kolditz O., Helmig R., Nagel T. 2019. Development of Open-Source Porous Media Simulators: Principles and Experiences. Transport in Porous Media. https://doi.org/10.1007/s11242-019-01310-1. Paul B., Shao H., Hesser J., Ostertag-Henning Ch., Lege Ch. 2015. In-Situ Quantification of Hydrocarbon in an Underground Facility in Tight Salt Rock, Engineering Geology for Society and Territory - Vol. 6, PP 893 - 896, Springer, 2015. Shao H., Wang Y.F., Kolditz O., Nagel T., Brüning T. 2019. Approaches for the multi-scale analysis of mechanically and thermally driven migration of fluid inclusions in salt rock, Journal of Physics and Chemistry of the Earth, DOI: 10.1016/j.pce.2019.07.003- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T31F0322Y
- Keywords:
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- 5104 Fracture and flow;
- PHYSICAL PROPERTIES OF ROCKS;
- 8178 Tectonics and magmatism;
- TECTONOPHYSICS