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| Titel |
Application of an extended finite element method for modeling fully coupled hydromechanical processes in discrete fracture-rock matrix systems |
| VerfasserIn |
Norihiro Watanabe, Wenqing Wang, Haibing Shao, Joshua Taron, Olaf Kolditz |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051260
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| Zusammenfassung |
| Analysis of mechanics related coupled processes in fractured rock, such as hydromechanical
(HM) processes, is important in assessment of deep geothermal reservoirs, because of their
strong influence on flow and subsequent transport systems in subsurface. Various numerical
HM models, e.g. interface elements (IE) approach, have been developed and applied to
geotechnical applications (Jing 2003, Rutqvist & Stephansson 2003 and Segura & Carol
2008). However, a challenge still remains in explicit representation of complex fracture
geometries in a computer model.
In this study, we propose a numerical method partially using an enrichment technique, i.e.
an extended finite element method (XFEM), to include pre-existing fractures for modelling
coupled HM processes. The XFEM theory has been developed for crack analysis (Belytschko
& Black 1999) and it treats the discontinuities directly in an approximation space with jump
functions. Hence there is no need to represent them in a mesh. This significantly reduces a
cost for remeshing when geometry changes. The XFEM has been applied to rock mechanics
such as a tunnel stability analysis (Belytschko et al. 2001, Deb & Das 2010). To author’s
knowledge, there are few studies to apply it for modeling coupled HM processes in fractured
rock.
Our proposed method is based on an XFEM theory presented by Belytschko et al. (2001)
which has capability of handling arbitrary discontinuities. Modeling a fully coupled
HM model becomes possible by (1) representing fractures as lower dimensional
elements, (2) applying enrichment only at the fracture elements and (3) modeling
mechanical behaviour of fractures as spring systems. Although the XFEM does not
require including fracture geometries into a mesh, we do it to use a same mesh
for both flow and mechanical processes. This is feasible because we concern only
pre-existing fractures and assume no fracture growth. We introduce a spring model so
as to be able to include well-known fracture closure laws such as Barton-Bandis
model.
For verification of the method, we have conducted simulations of a 2D fluid
injection problem into a single fracture where fracture aperture varies depending on
fluid pressure. The study shows that the proposed method can produce very similar
results as the semi-analytical solution. Ongoing works are solving more complex
fracture geometries such as fracture intersection and higher-dimensional spaces. |
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