Lawrence Berkeley National Laboratory, Report LBNL-40042
## iTOUGH2 Sample Problems

*Stefan Finsterle*

Lawrence Berkeley National Laboratory, Earth Sciences Division

University of California, Berkeley, CA 94720

**Summary.**
iTOUGH2 is a program for parameter estimation, sensitivity analysis, and uncertainty
propagation analysis. It is based on the TOUGH2 simulator for non-isothermal multiphase
flow in fractured and porous media [Pruess, 1987, 1991]. The report
iTOUGH2 User's Guide
describes the inverse modeling framework, and provides the
theoretical background. The report
iTOUGH2 Command Reference
contains the syntax of all iTOUGH2 commands. The present report describes a variety of
sample problems solved by iTOUGH2.
Each sample problem focuses on a few selected issues. iTOUGH2 input features and the
usage of program options are described. Furthermore, interpretations of selected inverse
modeling results are given. Problem No. 1 is a multipart tutorial, describing basic
iTOUGH2 input files for the main iTOUGH2 application modes; no interpretation of results
is given. Problem No. 2 focuses on non-uniqueness, residual analysis, and correlation
structure. Problem No. 3 illustrates a variety of parameter and observation types, and
describes parameter selection strategies. Problem No. 4 compares the performance of
minimization algorithms and discusses model identification. Problem No. 5 explains how to
set up a combined inversion of steady-state and transient data. Problem No. 6 provides a
detailed residual and error analysis. Finally, Problem No. 7 illustrates the model character of
the estimated parameters.

All input and data files needed to run the sample problems are part of the iTOUGH2
distribution package. The TOUGH2 and iTOUGH2 input file names are sam# and sam#i,
respectively, where # stands for the problem number. Multipart problems have file names of
the form sam#p%i, where # is the problem number and % is the part number. Data files are
identified by a ".dat" file extension.

The key to a successful application of iTOUGH2 is (i) a good understanding of multiphase
flow processes, (ii) the ability to conceptualize the given flow and transport problem and to
develop a corresponding TOUGH2 model, (iii) detailed knowledge about the data used for
calibration, (iv) an understanding of parameter estimation theory and the correct interpretation
of inverse modeling results, (v) proficiency in using iTOUGH2 options. This report
addresses issues (iv) and (v).