Study On Localization Of Porous Rocks

Rocks, which play an important role in a variety of applications and phenomena of societal activities, are widely used for building materials, foundations, tunnels and underground facilities. Meanwhile, they are related to most of the Earth's motion. These include natural disasters, such as landslides, volcanic eruptions and earthquakes. Porous rock is not only the major compositive part of the upper crust, but also the main stain place of petroleum and miners, directly effect the environment. Most of the world's energy now, and for the foresee able future comes from the upper crust and an understanding of rock behavior is essential to efficient and safe production and storage. Moreover, many of the by-products of energy production are reinjected to the upper crust. A relatively new but increasingly important application is geological sequestration of carbon dioxide, injection into the earth to mitigate harmful effects on the climate. In field and laboratory, Porous rock is observed to fail by the deformation of localization bands include shear bands, compaction bands and dilation bands. Many of these problems involve not only mechanical behavior but also its coupling with fluid flow, heat and chemistry. Therefore, research on the localization deformation of high porous rock is very important for studying the deformation of the upper crust and movement, which has become one of the main field of rock physics and mechanics.Shear bands form at an angle to the maximum compaction principal stress direction and have shear strain, with either compactant or dilatant strain normal to the band. Bands perpendicular to the direction of the maximum compaction principal stress, with pure compaction strain, are defined as compaction bands. Dilation bands form parallel to the maximum principal stress direction, with pure dilatant strain. Band formation has been suggested as a possible reason for sand production during drilling. Local changes in porosity and permeability within the band could affect fluid flow within the material. The faulting produced by shear localization is central to the solid earth sciences. Shear bands has been widely documented and studied for many years; Localized compaction in porous rocks is a recently recognized phenomenon that has been shown to reduce permeability dramatically. The presence of compaction bands in highly porous hydrocarbon reservoirs could adversely affect attempts to inject or extract fluids for energy storage or production. The vast majority of tests performed on rocks to determine constitutive behavior have been on cylindrical specimens loaded axially symmetrically. Such tests provided more information on the dependence of the behavior on the mean stress or confining stress but very limited information about the response for the range of deviatoric stress states. Recent experimental evidence indicates that the behavior of porous rock depends on the third stress invariant J3since it yields at a lower stress in extension, compared to loading under compression. In1975, Rudnicki and Rice develop the bifurcation theory to predicted the band orientation. In2002, Issen established two yield surface constitutive model to study the deformation of porous rocks. The first chapter of this paper introduce the cu双Rent laboratory research, theory research, field research and numerical research situation of localization deformation of rocks. The second chapter introduce the key definition used in this study. The third, fourth, fifth and sixth chapter reviewed the existing constitutive models, which depend only on two stress invariants, were modified and new constitutive models, which incorporate the J3dependence, were developed. Under non-axisymmetric stress states, when a single yield surface constitutive model is appropriate, including the J3dependence typically inhibits band formation, due to strongly negative critical hardening modulus hcr. For load paths where a two yield surface constitutive model is applicable, with J3dependence, shear bands were predicted. Compaction bands and dilation bands were predicted with a positive hcr, only under axisymmetric stress states. These results could be used to explain why these bands are rarely reported in the field, compared to shear bands. Although the vast majority of testing on brittle rock has been done in axisymmetric configurations, applications and field conditions are seldom purely axisymmetric. Consequently, there remain questions about the role of the intermediate principal stress in failure. Nowadays, most of the researches are focus on the prediction of localization band angle, which is the angle between normal to the band of localization and the largest compressive principal stress. The most famous prediction theory is Mohr-Coulomb condition posits behavior depending only the sum and difference of the largest and smallest principal stresses, which didn't consider the influence of the intermediate principal stress. The predictions results with Rudnicki and Rice two invariant model are smaller than the data. This paper uses the theorectical framework of shear localization as a bifurcationfrom homogeneous deformation to interpret observations of the inclination of the failure plane in true triaxial tests on Westerly granite and Dunham-Dolomite. Because the prediction theory of shear bands angle is strongly dependent on the type of constitutive relation used, the paper first discusses the framework for rate-independent, elastic plastic models and, especially the form for a class that depends on all three stress invariants. A particular form of yield function dependent on three invariants is used to infer parameters of the function from data on Westerly granite and use them to predict the failure angle. Based on the RR's model, we added a third invariant and established a three invariant model. We took the axisymmetric stress state data of Haimson's experiments on Westerly granite and Mogi's on Dunham-Dolomite as boundary condition to deduce the elastic-plastic parameter in the three invariants model, then to predict the band angle of the other deviatoric stress states. The results are compared with the data of Mogi's true trixial test on Dunham-Dolomite, and the agreement between the prediction and data are better than the two invariant model.