In most cases of seismic processing and interpretation, elastic isotropy is assumed. However, velocity anisotropy is found to exist in most subsurface media. Hence, there exists a fundamental inconsistency between theory on the one hand, and practice on the other. If not recognised, this can invalidate interpretation of seismic data. In this thesis, inversion methods for elastic parameters are developed to quantify the degree of velocity anisotropy of multi-layered transversely isotropic media. This primarily involves examining the velocity fields of layered media using anisotropic elastic wave propagation theory, and developing inversion programs to recover elastic parameters from those velocity fields. The resolved elastic parameter information is used in carrying out further studies on the effects of seismic anisotropy on normal moveout (NMO). Mathematical analyses, numerical simulations, and physical modelling experiments are used in this research for verification purposes before application to field survey data. Numerical studies show the transmission velocity field through layered media appears to be equivalent to that through a single-layered medium, within the practical offset limits in field surveys. The elastic parameters, which describe the property of such equivalent single-layered media, can be used as apparent elastic parameters to describe the collective mechanical property of the layered media. During this research, Snell's law was used in ray tracing to determine ray paths through the interface between any two component layers. By analyzing the signals recorded by any receiver in a walkaway VSP survey, the apparent transmission velocity field for the layered media above this receiver depth was inverted. / Software was developed to recover the apparent elastic parameters for the layered media above this receiver depth using the transmission velocity field as input. Based on a two-layered model, another method was developed to recover the interval elastic parameters for an individual layer of interest, using the signals recorded by receivers on the upper and lower surfaces of this layer. The recovered elastic parameters may be considerably different from the real values if a transversely isotropic medium with a tilted symmetry axis (TTI) is treated as a transversely isotropic medium with a vertical symmetry axis (VTI). A large angle of tilt of the symmetry axis significantly influences the recorded velocity field through the medium. An inversion program was written to recover the value of the tilt angle of a TTI medium, and the elastic parameters of the medium. Programs were also developed to combine information from P, SV, and SH-waves in an inversion procedure. This capability in inversion programs enables us to use the additional information provided by a multi-component VSP survey to obtain accurate estimates of the elastic parameters of geological formations. Software testing and development was carried out on numerically generated input data. Up to 10 milliseconds of random noise in travel time was added to the input to confirm the stability of the inversion software. Further testing was carried out on physical model data where the parameters of the model were known from direct measurements. Finally the inversion software was applied to actual field data and found to give plausible results. / In software testing in the physical modelling laboratory, other practical problems were encountered. System errors caused by the disproportionately large size of the transducers used affected the accuracy of the inversion results obtained. Transducer performance was studied, and it was found that reducing the size of transducers or making offset corrections would decrease the errors caused by the disproportionately large transducer dimensions. In using the elastic parameters recovered, it was found that the elastic parameter δ significantly influences the seismic records from a horizontal reflector. The normal moveout velocity was found to show variations from the zero-offset normal moveout velocity depending on the value and sign of elastic parameter δ. New approximate expressions for anisotropic normal moveout, phase and ray velocity functions at short offsets were developed. The value of anisotropic parameter δ was found to be the major factor controlling these relations. If the recovered parameter δ has a large negative value, analytical and numerical studies demonstrated that the new expression for moveout velocity developed herein should be used instead of Thomsen's normal moveout equation.

It has been proven by J.C.Criscione that constitutive relations(mixed approach) based on a set of five strain invariants (Beta-1, Beta-2, Beta-3, Beta-4, Beta-5) are useful and stable for experimentally determining response terms for transversely isotropic material. On the other hand, Rivlin’s classical model is an unsuitable choice for determining response terms due to the co-alignment of the five invariants (I1, I2, I3, I4, I5). Despite this, however, a mixed (Lagrangian and Eulerian) approach causes unnecessary computational time and requires intricate calculation in the constitutive relation. Through changing the way to approach the derivation of a constitutive relation, we have verified that using an Eulerian approach causes shorter computational time and simpler calculation than using a mixed approach does. We applied this approach to a boundary value problem under specific deformation, i.e. finite extension and torsion to a fiber reinforced circular cylinder. The results under this deformation show that the computational time by Eulerian is less than half of the time by mixed. The main reason for the difference is that we have to determine two unit vectors on the cross fiber direction from the right Cauchy Green deformation tensor at every radius of the cylinder when we use a mixed approach. On the contrary, we directly use the left Cauchy Green deformation tensor in the constitutive relation by the Eulerian approach without defining the two cross fiber vectors. Moreover, the computational time by the Eulerian approach is not influenced by the degree of deformation even in the case of computational time by the Eulerian approach, possibly becoming the same as the computational time by the mixed approach. This is from the theoretical thought that the mixed approach is almost the same as the Eulerian approach under small deformation. This new constitutive relation by Eulerian approach will have more advantages with regard to saving computational time as the deformation gets more complicated. Therefore, since the Eulerain approach effectively shortens computational time, this may enhance the computational tools required to approach the problems with greater degrees of anisotropy and viscoelasticity.

No description available.

Hydraulic fracturing of transverse isotropic reservoirs is of major interest for reservoir stimulation and in-situ stress estimation. Rock fabric anisotropy not only causes in-situ stress anisotropy, but also affects fracture initiation from the wellbore. In this study a semi-analytical method is used to investigate these effects with particular reference to shale stimulation. Using simplifying assumptions, equations are derived for stress distribution around the wellbore's walls. The model is then used to study the fracture initiation pressure variations with anisotropy. A sensitivity analysis is carried out on the impact of Young's modulus and Poisson's ration, on the fracture initiation pressure. The results are useful in designing hydraulic fractures and also can be used to develop information about in-situ rock properties using failure pressure values observed in the field. Finally, mechanical and permeability anisotropy are measured using Pulse Permeameter and triaxial tests on Pierre shale.

No description available.

The estimation of anisotropic parameters in the shallow subsurface becomes increasingly important for 4C seismic data processing in order to obtain accurate images in both time and depth domain. I focus on two approaches to evaluate anisotropy in seismic data: using P-wave data and PS-converted (C-wave) data. To gain better insight into the accuracy and sensitivity of anisotropic parameters to for instance layering and compaction gradients, I undertake numerical modelling studies and verify the results with full-wave modelling as well as findings from the real data from a 4C data set from the Alba field. The focus of this thesis is on vertical transverse isotropy (VTI) which widely occurs in marine sediments and cannot be neglected in seismic processing. P-wave data alone cannot constrain the vertical velocity and the depth scale of the earth model for a VTI medium. Therefore, the joint inversion of non-hyperbolic P- and converted wave (C-wave) or S-wave data from long offsets has been suggested. I carried out a detailed analysis of the resolution and accuracy of non-hyperbolic moveout inversion for P-, S- and C-waves for a single VTI layer in two parts. First, I introduce the concept of the inherited error delta inh as a measure of the possible resolution of the moveout approximations for the different wave types. The range of this error stays constant regardless of the magnitude of the anisotropic parameter for each wave type. Second, I analyse the accuracy of non-hyperbolic moveout inversion. I find that for anisotropy parameter eta the error of estimation from C-wave data is in most cases about half that from P-wave data. Inversion of non-hyperbolic S-wave moveout data does not resolve the anisotropy parameter due to the presence of cusps in the data. The study is then extended to a multilayered medium considering only P- and C-waves. The results confirm the findings from the single layer case. Furthermore, I investigate phase effects on parameter estimation for P- and C-waves. It is suggested that eta estimated from C-wave data gives a better description of the anisotropy found in a medium than the eta values picked from P-wave data. To verify the above findings near-surface effects are studied on the 4C data from the Alba field and accompanied by a full-waveform modelling study. I find that the picked eta values from P-wave data are distinctly larger than the eta values from C-wave data and also larger than the eta values from VSP data. The full-wave modelling study shows that picked eta values from P-wave data may account for influence of structure such as velocity gradients in the near-surface and are influenced by high velocity ratios and phase reversals. Finally, I have carried out an integrated analysis of the Alba 4C data to demonstrate how seismic anisotropy can be estimated from 4C seismic data and how such information can be used to improve subsurface imaging. The results are presented in two parts. The first part deals with non-hyperbolic moveout analysis for estimating anisotropic parameters to gain improved stacked sections. The second part describes migration model building and final imaging. The models are evaluated by comparison with VSP data results and with a synthetic modelling study for three events of the overburden. The evaluation confirms that the anisotropy parameter obtained from C-wave moveout corresponds better with the VSP data than the values directly estimated from P-wave data.

In this preprint, we look onto the theory of linear thermoelasticity. At the beginning, this theory is shortly repeated and afterwards applied to transversely isotropic materials. Then, the corresponding weak formulation is derived, which is the starting point for a FE-discretisation. In the last part, we explain how we added this material behaviour to an adaptive Finite-Element-code and show some numerical results.

In this preprint, we look onto the theory of linear thermoelasticity. At the beginning, this theory is shortly repeated and afterwards applied to transversely isotropic materials. Then, the corresponding weak formulation is derived, which is the starting point for a FE-discretisation. In the last part, we explain how we added this material behaviour to an adaptive Finite-Element-code and show some numerical results.:1 Introduction 2 Theoretical Background 3 Special Cases of Linear Thermoelasticity 4 Weak Formulation 5 Implementation 6 Numerical Examples A. Results of the Computation

En raison de l'exigence de protection de l'environnement, les briques d'argile cuites sont face à une nouvelle tendance de développement. Briques d'argile cuites ne sont pas seulement satisfaits de la mécanique force mais aussi augmentation de l'utilisation de l'énergie. La conductivité thermique est un paramètre très important mesurer l'utilisation de l'énergie. Sur le principe de garantir essentiellement propriétés mécaniques, la réduction de la conductivité thermique a été l'un des développements importants objectifs dans l'industrie du bâtiment.Basé sur l'analyse de la microstructure, les pores microscopiques ont un effet sur la macroscopie constantes élastiques et conductivité thermique. Micropores parallèles résultant de la production les méthodes provoquent l'isotropie transversale des briques d'argile cuites. Cependant, ce n'est pas clair que l'influence des micropores sur les propriétés macroscopiques. Bien que certains modèles étudié l'effet de la porosité sur les propriétés mécaniques des briques d'argile cuite, ces modèles sont empiriques et ont ignoré de nombreuses informations microscopiques. Un des buts de la thèse est d'analyser l'influence de la forme, l'orientation et la distribution spatiale de microscopique facteurs sur les propriétés mécaniques et la conductivité thermique afin de fournir une référence optimiser la micro-structure des briques d'argile cuites. / Due to the environmental protection requirement, fired clay bricks are facing new development tendency. Fired clay bricks are not only satisfied with mechanical strength but also rising energy utilization. Thermal conductivity is a very important parameter to measure the energy utilization. On the premise of guaranteeing the basically mechanical properties, reducing thermal conductivity has been one of important development goals in building industry.Based on the analysis of micro-structure, microscopic pores have an effect on macroscopic elastic constants and thermal conductivity. Parallel micropores resulting from producing methods cause the transverse isotropy of fired clay bricks. However, it is not clear that the influence of micropores on the macroscopic properties. Though some models studied the effect of porosity on mechanical properties of fired clay bricks, these models are empirical and ignored many microscopic information. One of the goals of the thesis is to analyze the influence of shape, orientation and spatial distribution of microscopic factors on mechanical properties and thermal conductivity in order to provide a reference to optimize the micro-structure of fired clay bricks.

Une connaissance plus approfondie du comportement des roches argileuses, et plus particulièrement de leur tenue, s'avère aujourd'hui indispensable dans le cadre de plusieurs thèmes de recherche d'importance croissante : comme couverture des réservoirs pétroliers pour la production d’hydrocarbures et la séquestration de CO2, ou en tant que roche hôte pour le stockage des déchets nucléaires en couches géologiques profondes. Ces roches sont particulièrement difficiles à caractériser expérimentalement du fait de leur très faible perméabilité et de leur sensibilité à l'eau. L'objectif de cette thèse est d'améliorer la compréhension des couplages hydromécaniques intervenant dans ces matériaux. Tout d’abord, une contribution à la caractérisation de l’évolution de la structure des roches argileuses soumises à un chargement mécanique est apportée. A cet effet, un essai de compression uniaxiale sur l’argilite de Tournemire associant des observations au MEB et une méthode de corrélation d’images numériques est proposé. Par la suite, des simulations numériques des essais œdométriques ont été réalisées pour appréhender l'influence des propriétés poromécaniques, en particulier de la faible perméabilité sur le comportement de l'échantillon. L’étude des équations de diffusion et les simulations numériques effectuées nous permettent de proposer une méthode de détermination de la perméabilité intrinsèque de ces matériaux. Dans la dernière partie, une étude du comportement d’une roche couverture d’un réservoir pétrolier à grande échelle est réalisée sur un cas synthétique 3D. L’objectif de ce chapitre est d’étudier les variations du champ de contrainte au sein de la couverture au cours de la production du réservoir / Knowledge of shale poromechanical behavior is essential for various environmental issues such as CO2 deep geological storage, high level radioactive waste storage, oil field abandonment… Furthermore, due to their good confinement properties, there are considered as potential host rocks for high level radioactive waste storage. However, their experimental characterization is very complex because of their very low permeability and their saturating fluid sensitivity. The main objective of this study is to improve knowledge of hydromechanical coupling of such a material. To study the structure of argillites under stress, SEM in-situ uniaxial compression test is performed on parallelepiped sample; compression orientation is perpendicular to bedding planes direction. Correlation techniques are used to estimate strain distributions. Second part underlines the key points of shale experimental characterization using the framework of Biot’s mechanics of fluid saturated porous solids. Shales are well known as a more or less transverse isotropy material. The complete methodology to conduct œdometric tests on such sensitive and weakly permeable material is described. Measurements realized on Tournemire argillite are proposed and a comparison with the poroelastic parameters of Meuse / Haute-Marne is given. Furthermore, to investigate hydromechanical coupling, a transverse isotropic poroelastic model is used to estimate the influence of anisotropy on diffusion characteristic time. The experimental data are used in numerical simulations to estimate the intrinsic permeability of the samples. In the last part, the caprock behavior of a petroleum field is studied at large scale with a 3D synthetic model (finite element analysis). The purpose of this last chapter is to study changes in stress field during the oil production