Paolo Berry

A GIS-based open source pre-processor for georesources numerical modeling

TOUGH2 is an integral finite differences numerical simulator for non-isothermal multiphase flow in fractured porous media, which can manage complex spatial discretizations. Numerical simulation accuracy is affected, among other things, by grid resolution. Increasing the grid resolution requires computational and operating costs depending on the number of nodes and variables processed. The complexity of the management of the model increases when unstructured grids and local refinement are used. In order to improve the management and optimize the activities to update the model, an open source pre-processor has been developed using the open source codes GRASS GIS, SQLite and AMESH. Operations such as domain discretization, rock type assignment and mesh file generation have been automatized. Graphical interfaces allow for a user-friendly utilization. Operating errors and time required by pre-processing activities to generate and update locally refined unstructured grids have been reduced. Productivity in numerical modeling has been substantially increased. A novel approach to generate TOUGH2 input file through GIS is presented.TOUGH2GIS automatically creates locally refined unstructured 3D grids.Rock types attribution to grid blocks is automatically and efficiently performed.Seamless integration into an available open-source GIS package.An application to a sample dataset shows method feasibility.

TOUGH2Viewer: A post-processing tool for interactive 3D visualization of locally refined unstructured grids for TOUGH2

Within the MAC-GEO research project, funded by Regione Toscana and addressed to the exploitation of high enthalpy geothermal systems, the authors worked on the utilization and customization of the open source numerical simulator TOUGH2, as implemented in the code dedicated to model calibration iTOUGH2. TOUGH2 is one of the most used numerical simulation software for non-isothermal flow of multicomponent, multiphase fluids in one, two and three-dimensional porous and fractured media. Lacking an official Graphical User Interface tool for post-processing operations, several commercial and academic software have been developed to manage and display TOUGH2 input and output data files. Almost all of these tools seem to have limits to visualizing parameter values of the numerical model, work only with a predefined binary version of TOUGH2, and only a few of them can manage locally refined unstructured grids (i.e. Voronoi grids). To overcome these limitations, the authors have developed and tested a dedicated software application (called TOUGH2Viewer) for reading and managing TOUGH2 output files, written in Java and able to provide an interactive 3D view of the numerical model. Several functionalities have been implemented for block query and searching, contour mapping and 3D surface mapping of TOUGH2 primary variables (i.e. pressure, temperature, etc.). TOUGH2Viewer is also able to display 2D and 3D views of mass and heat flow between blocks, for each time step in which the simulation proceeds. The application described in this paper is under development to improve its functionalities; nevertheless the current software release is a valid support tool for post-processing that significantly improves the possibility to inspect the simulated data coming from TOUGH2.

3D Voronoi grid dedicated software for modeling gas migration in deep layered sedimentary formations with TOUGH2-TMGAS

As is known, a full three-dimensional (3D) unstructured grid permits a great degree of flexibility when performing accurate numerical reservoir simulations. However, when the Integral Finite Difference Method (IFDM) is used for spatial discretization, constraints (arising from the required orthogonality between the segment connecting the blocks nodes and the interface area between blocks) pose difficulties in the creation of grids with irregular shaped blocks. The full 3D Voronoi approach guarantees the respect of IFDM constraints and allows generation of grids conforming to geological formations and structural objects and at the same time higher grid resolution in volumes of interest. In this work, we present dedicated pre- and post-processing gridding software tools for the TOUGH family of numerical reservoir simulators, developed by the Geothermal Research Group of the DICAM Department, University of Bologna. VORO2MESH is a new software coded in C++, based on the voro++ library, allowing computation of the 3D Voronoi tessellation for a given domain and the creation of a ready to use TOUGH2 MESH file. If a set of geological surfaces is available, the software can directly generate the set of Voronoi seed points used for tessellation. In order to reduce the number of connections and so to decrease computation time, VORO2MESH can produce a mixed grid with regular blocks (orthogonal prisms) and irregular blocks (polyhedron Voronoi blocks) at the point of contact between different geological formations. In order to visualize 3D Voronoi grids together with the results of numerical simulations, the functionality of the TOUGH2Viewer post-processor has been extended. We describe an application of VORO2MESH and TOUGH2Viewer to validate the two tools. The case study deals with the simulation of the migration of gases in deep layered sedimentary formations at basin scale using TOUGH2-TMGAS. A comparison between the simulation performances of unstructured and structured grids is presented. VORO2MESH is a 3D Voronoi gridding tool for TOUGH2.VORO2MESH allows generation of 3D Voronoi grids in compliance with the geological shape.TOUGH2Viewer is improved for 3D Voronoi grid visualization.

Nanomechanical Characterization of Brittle Rocks

After an introduction describing the indentation techniques traditionally applied to the study of micromechanical properties of minerals and rocks, phenomena induced by the diamond tip’s penetration into crystalline rocks are analyzed. Crystalline rocks are characterized by low values of the critical breakage load, i.e. the threshold load corresponding to the transition from a ductile to a brittle behavior. As a consequence, it seems more convenient to examine the mechanical behavior of crystalline rocks by using instrumented nanoindentations. Above the critical load, ranging from rock to rock, fractures occur, affecting the indentation results and thus invalidating the values of the rock mechanical properties obtained by indentation data processing. In order to determine the correct values of the hardness and elastic modulus of brittle rocks, an innovative measurement modality for rocks, i.e. Continuous Stiffness Measurement mode, is proposed. By providing the continuous evolution of the hardness and of the elastic modulus as a function of the indentation depth, it has proven particularly suited to analyze the effects of induced fracturing on the load versus displacement curve.