Lawrence Berkeley National Laboratory

iTOUGH2 (http://www-esd.lbl.gov/iTOUGH2) is a computer program for parameter estimation, sensitivity analysis, and uncertainty propagation analysis [Finsterle, 2007a,b,c]. It is based on the TOUGH2 simulator for nonisothermal multiphase flow in porous and fractured media. Most of the features of the TOUGH2 forward model used in iTOUGH2 are documented in Pruess [1991], with some added features described in Appendix A of the iTOUGH2 Command Reference [Finsterle, 2007b]. One of the added capabilities is to include heterogeneity by assigning element-specific permeabilities or permeability modifiers in block ELEME, Columns 41-50, or in block INCON.1, Columns 31-40 (see Finsterle [2007b], Appendix A.4). This approach requires that the permeability (or permeability-modifier) fields be generated externally and mapped onto the TOUGH2 mesh using some preprocessing software. This manual describes the added capability to internally generate heterogeneous, random, spatially correlated property fields (in particular heterogeneous permeability fields), and to map these fields onto the TOUGH2 mesh. The geostatistical simulation routines integrated into iTOUGH2 are taken from the widely-used Geostatistical Software Library GSLIB [Deutsch and Journel, 1992]. For this purpose geostatistical simulation routines from the widely-used Geostatistical Software Library GSLIB [Deutsch and Journel, 1992] have been integrated into iTOUGH2. The following interpolation and conditional geostatistical simulation methods are implemented: (1) GSLIB subroutine KTB3D, which allows for simple kriging, ordinary kriging, and kriging with various trend models; (2) GSLIB subroutine SGSIM, which allows for sequential Gaussian simulations; and (3) GSLIB subroutine SISIM, which allows for sequential indicator simulations. These geostatistical methods the can be used to generate permeability or permeability-modifier fields in linear or log space, conditioned on available data. The conditioning points of the geo