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GoThis paper presents the results of a laboratory investigation of the thermomechanical behaviour of anisotropic rock. The tests were performed on natural (Tournemire shale) using special triaxial cell able to control and to go to high temperature. The range of temperatures that were investigated is from 20 CÂ° to 250 CÂ°. (20, 100, 150, 200 and 250 CÂ°), and the range of confining pressures is from 0 MPa to 20MPa. (0, 5, 10, and 20 MPa). The influence of temperature on their mechanical behaviour was investigated for drained tests. Anisotropic elastic response and plastic deformation have been investigated. It seems that, the thermomechanical behaviour of the Tournemire shale is anisotropic and strongly depends on confining pressure and loading orientation at the applied temperature. Hydrostatic compressibility tests (in the perpendicular orientation

The group of sedimentary rocks, termed shales, represents a particular interest in oil industry. Experimental investigations are still necessary to have a better understanding of the thermomechanical behaviour of these materials. In the oil industry, the exploitation of heavy oil by the technical injection of vapour at high temperature, the rocks of the reservoir are subjected to coupled thermal and hydromechanical efforts. So it is necessary to study the thermo-mechanical behaviour of these materials subjected to variations of temperature in order to study the mechanical stability of the petroleum reservoirs.

The object of this study consists in carrying out new experimental study of the thermomechanical behaviour of the saturated stiff shales subjected to high temperatures (until 250 CÂ°) and to compressive stresses. The main aim was to carry out extensive laboratory experiments on the thermomechanical behaviour of Tournemire shale. The emphasis is given to investigating thermal effect on the elastic response, plastic flow and failure behaviour of the shale. Experimental results presented here provide a data base for the development of thermoelastoplastic modelling and failure criteria.

ISRM-SINOROCK-2009-140

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)

The issue of prescribing the support requirements for stratified roofs of no major discontinuities otherthanhorizontalbeddingplanesisherebyapproached ideallyaswellaspragmatically. Firstly, the unreinforced case is analytically defined; the solution acquired by elementary beam theory for a fixed beam under distributed load is compared to an Airy stress function solution for a fixed beam under its own weight based on Timoshenko beam theory. Finally, a finite difference numerical solution is performed and verified. The model is then used to investigate the behavior of a two-member stratified roof with contact plane governed by the angle of friction and tightened inordertomobilizetheshearingreactionforceatthediscontinuity.Parametric analyses to investigatethepossibleeffectsofelasticparameterssuchasthe modulusofelasticityandthe Poisson’s ratio and also the interbedding friction angle and its effect on the response of the model conclude thissection. The last part involves the numerical implementation of a bolting support system providingthe previously determinedforce andthe prescription ofits characteristics,i.e. length,spacing,diameterandpretensionofbolts.The impact of applying concentrated compressive forces instead of the theoretical distributed support is also outlined.

(Equation in full paper)

The maximum stress components σ

The modeled plane strain beam was of L/t=12.5, zero Poisson’s ratio, 1 m length, density 2400 Mg/m

ISRM-SINOROCK-2009-123

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)

Iwata, N. (Chuden Consultants Co.,Ltd.) | Sasaki, T. (Suncoh Consultants Co.,Ltd.) | Yosida, J. (Suncoh Consultants Co.,Ltd.) | Sasaki, K. (Suncoh Consultants Co.,Ltd.) | Yoshinaka, R. (Saitama University)

This paper describes the validity of the Multiple Yield Model (MYM) based on the comparison between the prediction by MYM analysis and the measurement results of two cases history about the large vertical excavation about 30m in depth and 100m in width for nuclear power plants. MYM is a kind of finite element method constituted the mechanical properties of intact rock and discontinuity systems in rock mass, and can be analyzed the non-linearity of deformation under loading and unloading stress paths. For analyzing, the geometrical model of rock mass were determined from test adit and borehole observations about the discontinuity conditions such as orientation, spacing, persistence, and the physical parameters were determined by laboratory test using core specimens and also considering scale effect. As the results of MYM analysis, both of the deformation mode and displacement were well corresponded to the measurement and we have been confirmed that the actual behavior of discontinuous rocks can estimate by MYM in practical accuracy"

As well known, the mechanical properties of discontinuous rocks are strongly influenced by the geometrical distribution and its mechanical properties of discontinuities which those strength and deformation behavior are non-linear. However, the practical parameters for design are generally setting by performing

(Equation in full paper)

Thus it is assumed that the joints are distributed periodically and the volume of each joint set is ignored in comparison with the volume of intact rock. And it is assumed that the stresses of the intact rock and joints coincide. The stiffness matrix of joint set I in the local coordinate system is transformed for the global coordinate system using the coordinate transformation matrix by equation (2).

ISRM-SINOROCK-2009-102

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

Comparison, deformation, deformation behavior, discontinuity, discontinuous rock, displacement, excavation, Horizontal, large-scale vertical excavation, model, numerical analysis, prediction, Reservoir Characterization, reservoir description and dynamics, rock, rock mass, shear, site, stiffness, Wellbore Design, wellbore integrity

SPE Disciplines:

Opening of fractures induced by shear dilation can be a significant source of fracture permeability change. In this study, the zones of fracture shear slip were examined through three-dimensional thermo-mechanical analysis of a nuclear waste repository model using the finite element method. Stress evolutions in selected locations revealed the main mechanisms of the generation of thermal stress important for fracture shear slip. The implications are that fractures of different orientations are vulnerable to shear slip at various locations throughout the lifespan of a geological repository. Stress paths obtained from the thermo-mechanical analysis were used as stress boundary conditions in order to investigate the effect of stress change on permeability. DFN-DEM (Discrete Fracture Network - Discrete Element Method) analysis showed that normal deformation dominated fracture closure/opening in four models and shear dilation dominated in the remaining two models. In the latter two models, modest permeability increases up to a factor of four were observed during thermal loading history. Permeability changes caused by shear dilation were not recovered after cooling of the repository, which was in contrast with the recovery of permeability changes for models in which normal fracture closure dominates.

The objectives of the current study are:

- to examine the contribution of thermal stress to the shear slip of fractures in mid- and far-field around the repository,
- to investigate the effect of the evolution of stress states on the permeability of repository settings, and
- to identify the shear slip potential through the entire lifespan of a KBS-3 type of a deep geological repository.

ISRM-SINOROCK-2009-185

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

change, deep geological repository, deposition, deposition hole, environmental law, evolution, flow in porous media, Fluid Dynamics, fracture, fracture shear, Horizontal, hydraulic fracturing, increase, location, model, permeability, repository, reservoir description and dynamics, shear, shear slip, shear slip potential, solid waste management, stress, thermal stress, Upstream Oil & Gas, View, well completion

Industry:

- Water & Waste Management > Solid Waste Management (1.00)
- Law > Environmental Law (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)

SPE Disciplines:

Liao, H.J. (Department of Civil Engineering, Xian Jiaotong University) | Han , J. (Department of Civil Engineering, Xian Jiaotong University) | Sugiyam, M. (Department of Civil Engineering, Tokai University) | Akaishi, M. (Department of Civil Engineering, Tokai University)

Most of the available constitutional equations indicating strain softening effect are based on stress space, but it is found that the elastic-plastic theory based on strain space is superior to stress space on solving the problem associate with large strain and softening. In this paper, a diatomaceous soft rock and its constitutive model are studied. A series of triaxial tests have been carried out on this soft rock. The constitutive equation of consolidated undrained triaxial stress state expressed in strain space is derived to simulate the stress-strain relationship of the results. It indicates that the elastic-plastic model based on strain space is applicable to express the strain softening effect of soft rock.

(Equation in full paper)

2.2 Hardening function

The selection of parameter К in the hardening function is very important. К determines the expansion mode of load surface during loading.

Considering the material softening effect, the hardening function is established now. The yield function that satisfies isotropic hardening in the stress space can be expressed as

(Equation in full paper)

Considering the stress-strain relationship curve of some direct shear tests shown in Fig.1, the hardening parameter К increases from point A to B, and then decreases and approaches constant after it reaches its maximum at point B if the material yield function satisfies equation (14).

(Equation in full paper)

(Table in full paper)

ISRM-SINOROCK-2009-088

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

axial strain, condition, consolidated undrained triaxial, consolidation, curve, equation, function, mechanics, plastic, Reservoir Characterization, reservoir description and dynamics, shear, soft rock, space, strain, strain space, strength, stress, stress space, stress-strain relationship, structural geology, tensor, test, Upstream Oil & Gas

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)

Weng, M.C. (Department of Civil and Environmental Engineering, National Kaohsiung University) | Liao, C.Y. (Department of Civil Engineering, National Taiwan University) | Jeng, F.S. (Department of Civil Engineering, National Taiwan University)

Weak sandstones possess deformational behaviors different from hard rocks; these phenomena, including shear dilation and degradation of deformational moduli, are much more significant. Therefore, a model capable of simulating major deformational characteristics of weak sandstones is essentially needed for engineering purposes. An innovative constitutive model is accordingly proposed. The proposed model was formulated based on the linear elastic model, and it accounts for the variations of moduli K and G through different loading conditions. In addition, an anisotropic factor

The proposed model was then incorporated into a finite element program and was used to analyze a squeezing tunnel case. Overall, this model can describe the deformation behavior for weak sandstones, especially on the significant shear dilation prior to the failure state. As a result, the proposed model shows the versatility in its applicability.

The western region of Taiwan is most populous and accompanied with active constructions of the transportation infrastructure. Many tunnel constructions currently in progress or in planning are, or to be, constructed in sedimentary strata of Tertiary Period. Due to this relatively young rock-geneses period, weathering and other factors, these sedimentary strata are mostly weak rocks. In the past, these weak rocks have caused several engineering difficulties such as squeezing of the tunnel under construction due to shear-induced deformations [1]. It was found that some typical weak rocks exhibit problematic characteristics such as substantial wet weakening, shear-dilation as well as creep deformation. Such behavior is often much less significant in hard rocks. In order to realize the deformation characteristics of weak sandstone, a series of laboratory tests including pure-shear triaxial tests and creep tests were performed by Jeng et al. [1], Weng et al. [2] and Tsai et al. [3]. According to the results of these researches, weak rocks typically exhibit the following behaviors:

- In the hydrostatic loading stage, the total strain possesses nonlinear behavior, which indicates that bulk modulus would increase as hydrostatic stress increases.
- In the shear loading stage, the initial shear modulus increases with increasing hydrostatic pressure applied.
- The volumetric strain induced by shear is initially contractive, and then gradually transits to be dilative upon increases of shear stresses.

Since squeezing phenomenon in tunnel constructions is inherently related to the aforementioned shear-induced deformation, proper assessments for the rock mass prone to such behavior is of interest in engineering practice. Therefore, it is needed to develop a constitutive model that can properly describe these deformational characteristics.

Incorporating the characteristics of deformation behavior of sandstone, especially for shear contraction/dilation, the compliance matrix in the principal stress coordinate is proposed accordingly based on Weng et al. [4] and Graham and Houlsby [5] as:

(Equation in full paper)

where K and G are tangent bulk modulus and shear modulus; β is the anisotropic factor;δσ

ISRM-SINOROCK-2009-079

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

anisotropic factor, Behavior, characteristic, constitutive model, deformation, deformational, degradation, dilation, increase, increment, model, moduli, Reservoir Characterization, reservoir description and dynamics, shear, shear stress, shear-induced volumetric deformation, Upstream Oil & Gas, variation, volumetric strain, weak sandstone

Thank you!