A flexible sequential Gaussian simulation program: USGSIM

Sequential Gaussian simulation is a widely used algorithm for the stochastic characterization of properties from various earth science disciplines. Many variants have been developed to deal with the increasing complexity of modeling applications. The program described in this paper is a flexible, tested, and documented implementation. Multiple variables can be cosimulated within different rock types simultaneously. The stepwise transform is integrated into the program as are collocated cokriging, collocated cokriging with the intrinsic model, and cokriging with a linear model of coregionalization for the cosimulation of multiple variables. Multiple secondary data can be incorporated using locally varying means, collocated cokriging, and Bayesian updating. The search options and other parameters are flexible within rock types. Fortran source code and a compiled executable are provided.

► Sequential Gaussian simulation is a robust and widely used algorithm and can be adapted for a variety of modeling techniques.
► Many of the available methods for geostatistical modeling in a sequential Gaussian simulation framework are summarized.
► A flexible program is developed allowing practitioners to experiment with the techniques.