Multiscale modelling of compaction bands in porous rocks

PRABSTRACTM3340-N: Compaction bands in porous rocks are tabular zones with concentrated compaction and the ensuing reduction of permeability play an important role in geophysical and geo-engineering applications. Same laboratory experiments on field samples were carried out, which confirmed principally the formation and propagation of compaction bands under compressive stress. h^owever, some discrepancies between filed observations and laboratory experiments come to light. Moreover, occurrence of compaction band is found to depend not only on porosity and pressure, but also on stress state and loading history. Afurther issue is the hidden link between microscopic property and macroscopic behavior. Numerical models may help bridge the gap between laboratory tests and field observations, and bring the hidden micro-macro relationships to light. The main objective is revealing the multiscale localized failure mechanism of compaction bands in porous rocks, which includes: (1) Enhancement of hypoplastic constitutive model with fabric tensor evolution equation. (2) Development of the hypoplastic peridynamic model for modelling the inception and propagation of compaction bands in porous rocks. (3) Building a hierarchical multiscale computational framework accelerated by CPU-GPU heterogeneous computing architecture to shed light on the multiscale localized failure mechanism of compaction bands in porous rocks. The hypoplastic constitutive model with a fabric tensor captures the salient behaviour of porous rocks such äs pressure sensitivity, nonlinearity, dilatancy, inherent and induced anisotropy. The fabric tensor with the evolution equation links the microscopic fabric to the macroscopic behaviour of porous rocks. In the state-based peridynamics, the field equations are formulated by integral/integral-differential equations instead of PDEs, which allows the strong and weak discontinuities to handle continuous and discontinuous media. The hierarchical multiscale framework including FEM, DEM and peridynamics is built to bridge the gap and bring the hidden interplay between microstructural deformation mechanisms and macro-scale localized failure behaviors of compaction bands into light. The novelties ofthe project consist of: (1) hlypoplastic constitutive model is forthe first time enhanced by a fabric tensor capturing the salient behavior of porous rocks to predict the onset of compaction bands. (2) Hypoplasticity is for the first time incorporated into peridynamics to simulate the inception and propagation of compaction bands in porous rocks. (3) The hierarchical multiscale framework that is composed of FEM at macro-scale, DEM at granulär scale and peridynamics at micro- scale is for the first time built to simulate nucleation and propagation of compaction bands. Project leader:_V^CtO^J \^^^Co-applicant:_^_^_ ^ ` Pate: (8/0/2^; pate: ^. ^ 2ö2-( "7-^ IX. ^U^E^^ ^AN^ UN`N, P^f. P^. 1^6(. ^6i ^U.

Narrow bands with highly concentrated deformation are often observed in geological materials like soils and rocks. These deformation bands can be classified into dilation bands, shear bands, shear-enhanced compaction bands and compaction bands. Compaction bands are tabular zones with concentrated compaction and negligible shear off set under predominantly compressive stress. Compared with shear bands, there are relatively few field evidences for compaction bands. Since the 1990s, it is the fact that compaction bands have been observed in very few sites in the world, such as Navajo Sandstone in Utah, Aztec Sandstone in Nevada, Orange area in France. However, compaction bands in porous rocks and the ensuing reduction of permeability not only play an important role in a number of geophysical and geo-engineering applications, such as geothermal engineering, oil and gas production, CO2 storage in aquifer, but also provide vitally loading history to illustrate geological formations. Therefore, understanding the localized failure mechanism of compaction bands in porous rocks is a major challenge for modern geomechanics