1. A method for creating a modified realization of a geostatistical model of a subterranean hydrocarbon reservoir with the aid of a digital computer, wherein the modified realization is based on a current realization which is a function of a first uniform random number field, the method comprising the steps of: a) creating at least one further uniform random number field U i ; b) linearly combining the first uniform random number field and said at least one further uniform random number field U i together with combination coefficients r i to derive a modified non-uniform random number field V, wherein a sum consisting of a square of each combination coefficient of said combination coefficients is not limited to 1; c) performing in the computer a uniform score transformation procedure on the modified non-uniform number field V to derive a modified uniform random number field U mod ; and d) deriving the modified realization of the geostatistical model from the modified uniform random number field U mod .