The present work carried out an experimental study of the Roman travertine carbonate with a focus on the anisotropic geomechanical behavior in two directions (normal and parallel to the sedimentary bedding) under similar confinement stress values with those that occur in Brazilian carbonate reservoirs. For this purpose macro and microscopic analyzes were performed, besides chemical analysis. Two kind of mechanical tests were made–tensile tests and axisymmetric triaxial tests. Then, rock strength was compared with index properties, especially the porosity, analyzed geomechanical behavior and rock strength envelope was plotted in two failure criteria following a porosity degree.
Looking for a better geomechanical behavior comprehension of the carbonate rocks, this work utilized the Roman travertine, a rock commonly used as analogous rock to Brazilian carbonate reservoirs. So a brief geological preview of the source area was carried out. Macroscopic and microscopic descriptions, chemical analyzes and laboratory index properties, in particular porosity and density, were made for analysis and comparisons with the results of the mechanical tests. Two kinds of mechanical tests were made–tensile tests and compression tests. The first one by Brazilian test methodology. The second one by axisymmetric triaxial tests with confining stresses from 0 to 40 MPa. The results were plotted in stress vs total porosity and stress vs strain graphs, where it was possible to evaluate the geomechanical behavior according porosity degree, as well as total porosity’s influence in strength. Finally, two failure criteria were applied. Mohr-Coulomb, widely used, and Lade & Kim, much common in the petroleum area.
The studied Roman travertine came from a quarry of Tivoli, Central Italy, in the Acque Albule sedimentary basin. According to Faccenna (1994), the geological context can be summarized in an intercalation of Meso-Cenozoic travertines and marlstone with marine and volcanic deposits, in most of the Quaternary. The Basin was developed along Pleistocene Post-Orogenic Framework.
