Search

The in-situ stress field in rock masses is a key aspect when a numerical analysis of a rock mass is carried out in any area of geo-engineering, such as civil, mining, or Oil & Gas. A method for the numerical generation of the in-situ stress state in the FE context, based on Airy stress functions was previously introduced. It involves two steps: 1) an estimate of the stress state at each Gauss point is generated, and 2) global equilibrium is verified and re-balancing nodal forces are applied as needed. In this paper, new developments towards improving the accuracy of the stress proposal are discussed. A real application example has been used to illustrate the results achieved with the new implementation.

Modeling of rock masses is of major importance to assess the Geomechanical behaviour of oil &gas reservoirs, especially for fractured tight reservoirs. The presence of discontinuities will significantly influence the general behavior of the rock masses, in particular introducing strength reduction, enhanced/reduction permeability, anisotropic behavior and a non-linear response. In the present study, Discrete and Equivalent continuum approaches have been used to simulate the mechanical behavior of jointed rock masses. Discrete approach uses the eXtended Finite Element Method (XFEM) and the Zero-thickness interface elements, while the Equivalent continuum approaches uses an elastic-viscoplastic constitutive model of the multilaminate type to represent the rock mass behavior. Advantages and limitations of each approach are identified and some hints for their practical use are given. Although the discrete approach is sometimes preferred for being based on a mature theory, the equivalent continuum analysis seems to be more often applicable for usual geomechanical analyses from engineering practice.

In spite of the significant developments seen in recent years,numerical modelin of Hydraulic Fracturing still poses major challenges due to the strong coupling between fluid flow and crack development,which is itself a strongly non-linear problem.The objective of this paper is to show advances in a line of work started by Segura and Carol,on the modelin of coupled H-M discontinuities via zero-thickness interface elements.In particular,this paper is focused on the 3D Applications of the approach,and the results obtained are compared to the existint GDK and PKN analytical solutions.For the comparison, two 3D models are described: a plate model for the GDK, and a block model for the PKN.In order to improve de modelling,both models are run withi nterfaces equipped with realistic non-linear materia llaws based on fracture energy. Results obtained show a good agreement with both analytical and numerical results.

Previous developments on zero-thickness interface elements for coupled Hydro-Mechanics problems are briefly described, followed by some new geomechanical applications, particularly to hydraulic fracture in rock. The results are compared satisfactorily to approximate formulas and previously published numerical results. Once verified, the model is applied to new cases to show the capabilities of the approach.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is an autosomal recessive disorder with a chronic progressive course. The gene, MLC1, has been localized on chromosome 22qtell and 26 different mutations have been described. We report two siblings of non-consanguineous parents who presented with characteristic features of MLC. They showed macrocephaly from the first months of life. After a short time, motor clumsiness, ataxia, seizures and psychomotor retardation were observed. During childhood, both patients had a coma that lasted several days following a minor head trauma. The eldest sister experienced a permanent deterioration of the clinical picture after the coma. Epilepsy and electroencephalographic alterations were chronic, tending to improve during adulthood. Cerebral biopsy showed normal or minor changes in the cortical grey matter, and in the white matter gliosis, increased extracellular spaces and decreased numbers of fibres with thin myelin sheets . We have followed the patients during 24 years, from the ages of 4 and 8 years to the their present ages of 28 and 32 years. Clinical and neuro-imaging follow-up showed a chronic course with more prominent progression of the white matter abnormalities than of the neurological features. A homozygous mutation of the MLC1 gene was found in both siblings. The eldest patient, 32 years-old, needs a wheel-chair but has a good contact with the family and surroundingpeople. The youngest, 28-years-old, shows mild ataxia, spasticity and motor clumsiness, but she is able to participate in activities of daily life.