1. A method of producing hydrocarbons from an underground deposit of hydrocarbons containing organosulfur compounds, comprising: i. determining an amount of hydrogen sulfide (H 2 S) produced by aquathermolysis induced by a thermal processing including steps of: a) using a computer to describe the hydrocarbons with a compositional representation using at least the H 2 S and fractions of saturated compounds, aromatics, resins and asphaltenes; b) using a computer to construct an elementary reaction scheme representative of a material balance for elemental sulphur based on the compositional representation of the hydrocarbons, and pseudo-stoichiometric coefficients related to pseudo-stoichiometric constituents and other constituents; c) using a computer to construct a kinetic model based on a system of reactions simulating generation of the H 2 S and the elementary reaction scheme; d) using a computer to construct a thermodynamic model based on the compositional representation; and e) using a computer to determine an amount of the H 2 S to be produced, by performing a compositional reservoir simulation by using a compositional and a reactive thermal simulation employing the kinetic model and the thermodynamic model; ii. determining exploitation conditions of the underground deposit as a function of an amount of H 2 S therein; and iii. producing the hydrocarbons as a function of the amount of H 2 S to be produced by applying the exploitation conditions so than an amount of H 2 S actually produced with the hydrocarbons from the underground deposit is below a maximum legal limit.