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A method for forming a 2D or 3D diffusive type model allowing simulation of multilithologic filling of a sedimentary basin over geologic periods. The model is based on the numerical simulation of the evolution of a sedimentary basin, from the past to the present, in a series of time intervals. In e

A method for forming a 2D or 3D diffusive type model allowing simulation of multilithologic filling of a sedimentary basin over geologic periods. The model is based on the numerical simulation of the evolution of a sedimentary basin, from the past to the present, in a series of time intervals. In each time interval, three major phenomena interact and are numerically modelled: basin deformation, sediment supply and transportation of these sediments in the deformed basin. To model sediment transportation, long-term permanent transportation (creeping, slow diffusion process, etc.), short-term transportation (due to rain and flood) and catastrophic transportation (notably due to cliff collapse) are taken into account using an exponential water velocity model.

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The invention claimed is: 1. A method for forming a diffusive type deterministic model for simulating multilithologic filling of a sedimentary basin, comprising: from known field data relative to an architecture of the basin and measured data or seismic data, forming a set of input data relative to

The invention claimed is: 1. A method for forming a diffusive type deterministic model for simulating multilithologic filling of a sedimentary basin, comprising: from known field data relative to an architecture of the basin and measured data or seismic data, forming a set of input data relative to an accommodation available through subsidence and eustasy, to a supply of fluvial or marine sediments and transportation thereof, and to physical parameters of lithologies, by an iterative process involving gridding the basin into grid cells of regular dimensions, modelling according to an explicit finite-volume scheme with constant time intervals, to simulate flow of each lithology deposited on each grid cell; and comparing simulation results with the data and modifying the set of input data step by step by inversion; and wherein for each time interval and for each lithology modelling by deterministic equations respectively a) a mean of a transportation processes acting on a permanent and continuous basis for a longer term, b) a mean of transportation processes acting on a permanent and continuous basis for a shorter term, and c) a mean of a transportation processes acting in a catastrophic way for a term less than the shorter term; and determining a resulting stratigraphy of the basin by accounting for the mass conservation. 2. A method as claimed in claim 1, comprising, in each time interval and for each lithology: modelling the longer-term flows of sediments carried by water by accounting for a model of a distribution of water flowing in the basin and of the sediment transportation capacity of the water flowing in the basin; modelling the shorter-term flows of sediments carried by water using an exponential model for estimating water velocity; and modelling catastrophic flows of sediments carried by water in unstable zones located by applying a critical slope criterion. 3. A method as claimed in claim 1, wherein in the longer-term flows are modelled by the relation as follows: description="In-line Formulae" end="lead"{right arrow over (Qlitho)}=λ{right arrow over (Q max,litho)}=-λ(Kgravity+K riverQwater) {right arrow over (grad)}z description="In-line Formulae" end="tail" where: Qmax,litho is transportation capacity of the lithology at any point of the basin; Qwater is a water stream flowing at the soil surface at a point; Kgravity is a diffusion coefficient related to permanent gravity processes; Kriver is a diffusion coefficient related to permanent river and ocean transportation; z is an altitude of the soil at a point; and λ is a weighting coefficient. 4. A method as claimed in claim 2, wherein in the longer-term flows are modelled by the relation as follows: description="In-line Formulae" end="lead"{right arrow over (Qlitho)}=λ{right arrow over (Q max,litho)}=λ(Kgravity+K riverQwater){right arrow over (grad)}z description="In-line Formulae" end="tail" where: Qmax,litho is transportation capacity of the lithology at any point of the basin; Qwater is a water stream flowing at the soil surface at a point; Kgravity is a diffusion coefficient related to permanent gravity processes; Kriver is a diffusion coefficient related to permanent river and ocean transportation; z is an altitude of the soil at a point; and λ is a weighting coefficient. 5. A method as claimed in claim 1, wherein the shorter-term flow of sediment carried by water is modelled by applying an exponential model for water velocity comprising: description="In-line Formulae" end="lead"U( M)=Ue+(Uo-Ue)e -ξ/Ledescription="In-line Formulae" end="tail" where Uo represents velocity at a reference point of the flow of sediment carried by water, Ue is a water equilibrium velocity, and ξ is a distance along the flow of sediment carried by water, the flows of sediment carried by water being estimated by a relation: where P(U) is a weighting coefficient of a velocity model depending on a velocity U of the flow of sediment carried by water, of a critical velocity Uc,litho from which each lithology can be transported. 6. A method as claimed in claim 2, wherein the shorter-term flow of sediment carried by water is modelled by applying an exponential model for water velocity comprising: description="In-line Formulae" end="lead"U( M)=Ue+(Uo-Ue)e -ξ/Ledescription="In-line Formulae" end="tail" where Uo represents velocity at a reference point of the flow of sediment carried by water, Ue is a water equilibrium velocity, and ξ is a distance along the flow of sediment carried by water, the flows of sediment carried by water being estimated by a relation: where P(U) is a weighting coefficient of a velocity model depending on a velocity U of the flow of sediment carried by water, of a critical velocity Uc,litho from which each lithology can be transported.