Stefano Bonduà

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.

How different data supports affect geostatistical modelling: the new aggregation method and comparison with the classical regularisation and the theoretical punctual model

ABSTRACT In geostatistical analysis, often the data have different support (volume). Data with different supports can be treated separately or together but in a consistent way. In many applications, data are considered as point variable averaged over the sample volume. Regularisation of data has a significant impact on variograms and geostatistical estimations. Two methods of managing data with different supports (“integrating”) are compared: regularisation and aggregation. This paper examines the consequences of the regularisation on sample variograms and proposes another procedure to integrate samples called “aggregation”. The variogram models of integrated data are compared with the theoretical punctual model. The point-support variogram presents some advantages, such as the possibility of utilizing samples without compositing their values. But, this implies to modify the classical kriging system. The ways of managing data with different supports are applied to a complex dataset of an iron ore body. The spatial variable analysis from the composited borehole samples demonstrates the impact of the integrating methods through cross validation. Results show the effect of the variogram model in the kriging system and the accuracy of the evaluation. Also evidenced are the sensitivity to the integration method, the selected parameters and the benefits of the theoretical punctual variogram.

Application of low frequency georadar antenna to fractures detection and 3D visualization in a new quarry bench

Recently, laser scanning systems (airborne and terrestrial mobile mapping systems) have been established as a leading technology for collecting high density 3D information from an objects surface. The availability of generated surface models is very important for various industrial, military, environmental, and public applications. The accuracy of the derived point cloud coordinates from a LiDAR system is affected by inherent systematic and random errors. The impact of random errors depends on the precision of the system’s measurements, which comprise position and orientation information from the GPS/INS unit, mirror angles, and ranges. On the other hand, systematic errors are mainly caused by biases in the mounting parameters (i.e., lever arm offset and boresight angles) relating the system components as well as biases in the system measurements (e.g., ranges and mirror angles). In order to ensure the geometric quality of the collected point cloud, the LiDAR systems should undergo a rigorous calibration procedure to estimate the system parameters that minimize the discrepancies between conjugate surface elements in overlapping LiDAR strips. The main objective of this paper is to look into an existing LiDAR system calibration technique, which is based on manual selection of overlapping regions between LiDAR strips and how to increase the efficiency of this technique by automatic selection of appropriate overlapping strip pairs, which should achieve the minimum optimal flight configuration that maximizes the impact of the discrepancies among conjugate surface elements in overlapping strips as well as automatic selection of regions within the appropriate overlapping strip pairs. The methodology of the proposed technique can be summarized as follows: first, the LiDAR strip pairs are grouped based on the flight configuration; second, appropriate overlapping strip pairs from each group is automatically selected; third, regions within the appropriate overlapping strip pairs are automatically selected based on their angles (slopes and aspects) and distribution; finally, the calibration procedure is applied. The experimental results have shown that the quality of the estimated parameters using the automatic selection is quite comparable to the estimated parameters using the manual selection while the proposed method is fully automated, and much faster.

Joints representation strategy: performance evaluation by a Finite Element code. A feasibility analysis of a tunnel infrastructure in the Carnian Alps

This study is part of a wider feasibility analysis of a new forestry road in the Dolomitic region. The investigated area is located in northeastern Italy, in the Carnic Alps complex geological context. The rock mass which would be crossed by the tunnel is a highly tectonized limestone characterized by a relatively high strength of the intact rock. The project focuses on the rock mass characterization and the modelling of its behavior by means of numerical simulations with a Finite Elements (FE) code. The generalized Hoek-Brown criterion is used, normal and shear stiffness of the joints are evaluated and different strategies for the representation of the rock mass discontinuities are adopted. The effects of two support systems, preliminary designed by a diffused simplified method, are evaluated focusing on the space around the tunnel, where the joints reach the critical state.