A method for building an enriched reservoir model

Abstract

It is disclosed a computer-implemented method for reservoir modelling, comprising: - Obtaining a structural model of the reservoir in the present-day state, comprising at least one initial horizon (H0, H1), corresponding to an iso- chronological surface associated to a determined absolute geological time, - Computing, from the structural model in the present-day state, a structural model of the reservoir in a deposit space, - computing an updated version of the structural model of the reservoir in the deposit space, comprising a plurality of additional horizons (Hi), where the additional horizons have been generated by forward sedimentary modelling, and - generating, from the updated version of the structural model in the deposit space, an updated version (P1) of the structural model of the reservoir according to the present-day state including the additional horizons (Hi).

Description

[0001] A METHOD FOR BUILDING AN ENRICHED RESERVOIR MODEL

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to the field of geological modeling, in particular to a computer-implemented method for building models of a geological reservoir according to a present-day state. The disclosure finds notable applications in the field of groundwater management, Carbon Capture and Storage (CCS) and / or hydrocarbon production.

[0004] BACKGROUND OF THE INVENTION

[0005] In the study of underground geological formations, it is necessary to have good knowledge of the geometry of the sedimentary structures and distribution of the geological and petrophysical properties of the underground. These properties enable for instance to better determine the geometry of a geological formation, for instance an oil or gas reservoir, estimate the quantity and distribution of oil and gas resources, or the volume of carbon that could be stored in depleted oil and gas reservoirs, aquifers, saline formations or the like.

[0006] In order to characterize a geological formation, it is well known to acquire on-site data for instance by campaigns or seismic reflections and / or by drilling exploration wells. This on-site data however only provides reduced, local, hindsight about the configuration of the reservoir, the geometry of horizons and the distribution of geological and / or petrophysical properties over the whole domain of interest.

[0007] Accordingly, according to standard geostatistical approaches, it is known to build a structural model of a reservoir, comprising a set of geological surfaces comprising horizons, corresponding to iso-chronological surfaces that are determined from the on-site data, and faults, which are also observable on-site.

[0008] Based on the structural model, a three-dimensional mesh is then built which conforms to the horizons and faults, and which is then populated by geological and / or petrophysical parameters, according to geostatistical algorithms. The geostatistical algorithms enable filling the mesh from the sparsely acquired, on-site data.

[0009] An important downside of these approaches is that the result is obtained without taking into account the complexity of geological phenomena having occurred successively during the formation of the reservoir. Hence the result is not necessarily related to geological chronology. Indeed, apart from the main horizons which are present in the structural model, and which are associated to relative, and sometimes absolute ages, there is no relationship, in the obtained model, between a cell and an age corresponding to that cell. As a consequence, the geological phenomena leading to the formation of the reservoir in its present-day state, and the causality between these phenomena, are ignored. It results in possible inconsistencies between the model and the corresponding existing structures, as well as errors in the geological and petrophysical parameters which populate the model, and hence the impossibility to validate such models by confronting them with field data.

[0010] DESCRIPTION OF THE INVENTION

[0011] The present disclosure aims at improving the prior art.

[0012] In particular, an aim of the present disclosure is enabling to build models of a reservoir having increased accuracy, and in particular with respect to geological representation. In particular, an aim of the present disclosure is enabling to build a structural model of a reservoir having a plurality of horizons in which each horizon is associated with a determined geological age.

[0013] Accordingly, it is disclosed a computer-implemented method for reservoir modelling, comprising:

[0014] - obtaining a structural model of the reservoir in the present-day state, comprising at least one initial horizon, corresponding to an iso-chronological surface associated to a determined absolute geological time,

[0015] - Computing, from the structural model in the present-day state, a structural model of the reservoir in a deposit space,

[0016] - computing an updated version of the structural model of the reservoir in the deposit space, comprising a plurality of additional horizons, where the additional horizons have been generated by forward sedimentary modelling, and

[0017] - generating, from the updated version of the structural model in the deposit space, an updated version of the structural model of the reservoir according to the present-day state including the additional horizons.

[0018] The reservoir may in particular be a real reservoir, and the structural model of the reservoir in the present-day state may be obtained from on-site data. In embodiments, computing the structural model of the reservoir in the deposit space comprises application, to the structural model of the reservoir in the present-day state, of a bijective transform function, and generating the updated version of the reservoir in the present-day state is performed by application, to the updated version of the model in the deposit space, of an inverse function of the transform function.

[0019] In embodiments, the additional horizons define a plurality of sedimentary layers, each sedimentary layer being defined between two consecutive horizons and having a respective thickness, and the relative thicknesses of the sedimentary layers in the updated version of the structural model of the reservoir according to the present-day state are constrained to fit the relative thicknesses of the sedimentary layers generated by the forward sedimentary modelling.

[0020] In embodiments, the structural model of the reservoir in the present-day state is defined in a Cartesian coordinates system, the structural model of the reservoir in a deposit space is defined in a parametric coordinates system, and generating the updated version of the structural model of the reservoir in the deposit space comprises:

[0021] - performing forward sedimentary modelling on a base iso-chronological surface of determined absolute geological age in a cartesian coordinates space, wherein the iso-chronological surface has an initial topography in said cartesian coordinates space, and performing forward sedimentary modelling comprises simulating deposition, on the iso-chronological surface, of a plurality of successive sedimentary layers, where each sedimentary layer corresponds to a determined period of time of sedimentation and the surfaces between consecutive layers of sediments form the additional horizons, and

[0022] - rescaling the generated horizons to fit in the structural model in the deposit space.

[0023] In embodiments, the parametric coordinates system comprises a vertical axis corresponding to relative geological time, and the generated horizons are rescaled to fit between minimum and maximum relative geological times along said vertical axis. In embodiments, the minimum relative geological time is the relative geological time corresponding to the absolute geological time value associated to the base iso- chronological surface.

[0024] In embodiments, the absolute geological time of the base iso-chronological surface is comprised between the respective absolute geological times of two initial horizons of the structural model of the reservoir in the present-day state, and the relative geological time corresponding to the base-iso-chronological surface is determined from the relative geological times corresponding to the initial horizons in the deposit space.

[0025] In embodiments, the maximum relative geological time value is determined from the maximum cumulative thickness of sediments between the generated additional horizons and the base iso-chronological surface.

[0026] In embodiments, determining the maximum relative geological time comprises:

[0027] Determining the maximum cumulative thickness between the generated additional horizons and the iso-chronological surface,

[0028] Determining coordinates of a reference point of the structural model of the reservoir in the present-day state that is spaced upwardly from the iso- chronological surface by a stratigraphic distance equal to the maximum cumulative thickness,

[0029] - Determining a corresponding relative geological time of the reference point in the deposit space, corresponding to the maximum relative geological time.

[0030] In embodiments, the method comprises determining coordinates of a reference point of a restricted version of the structural model of the reservoir in which all initial horizons extending above the iso-chronological surface are removed.

[0031] In embodiments, the method further comprises generating a three-dimensional meshed model of the reservoir from the updated version of the structural model of the reservoir in the present-day state.

[0032] In embodiments, the three-dimensional meshed model comprises a plurality of cells where each cell is assigned to at least one parameter chosen among a geological parameter, a mechanical parameter or a petrophysical parameter. In embodiments, the parameters associated to the cells are derived from the forward sedimentary modelling.

[0033] In embodiments, the geological surfaces of the structural model of the reservoir in the present-day state further comprise at least one fault extending transversely to the horizons, each fault separating areas of the reservoir having undergone a sliding displacement with respect to each other, and wherein computing the structural model of the reservoir in a deposit space comprises restoring each fault to an initial configuration where the relative displacement between the areas is null.

[0034] In embodiments, determining the coordinates of the reference point of the structural model comprises determining a point of the iso-chronological surface satisfying a defined criterion of distance relative to each fault, and the reference point is a point extending vertically above said point of the iso-chronological surface at a distance corresponding to the maximum cumulative thickness of the additional horizons.

[0035] In embodiments, the method further comprises, after modelling the deposition of successive layers of sediments, simulating at least one geological event selected among:

[0036] - a sedimentation event,

[0037] - a fracturation event, and

[0038] - a diagenesis event.

[0039] According to another object, a computer-program product is described, comprising code instructions for implementing the method according to the description above, when it is executed by a computer.

[0040] According to another object, a computing device is disclosed, comprising at least a computer and a memory, the computer being configured to implement the method according to the description above.

[0041] The disclosed method comprises building a model corresponding to a present-day state of a reservoir, wherein the model is derived from a model obtained by simulating the deposition of successive layers of sediments. Said simulation associates a period of time to each layer of sediments and hence, the layers forming the additional horizons of the structural model are associated with respective times. As the obtained model is derived from an initial structural model of the reservoir, which may be formed from sparse data acquired on site, the method enables completing the observable data with supplementary data derived from geological processes. The obtained model thus provides a better geological representation of a reservoir.

[0042] Moreover, the obtained model can also be meshed to obtain a three-dimensional grid populated with parameters such as petrophysical parameters, and this grid may further be constrained with experimental / on-site data. It thus makes it easier to correlate geological phenomena with actual data and obtain more accurate reservoir model.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals reference to similar elements and in which:

[0045] Figure 1 is a flow chart describing the main steps of embodiments of a method for building a model of a reservoir,

[0046] Figure 2a schematically represents an example of a structural model of a reservoir in a present-day state,

[0047] Figure 2b schematically represents a structural model of the reservoir of figure 2a in a deposit space,

[0048] Figure 2c schematically represents an updated version of the structural model of figure 2b in the deposit space, comprising a plurality of additional horizons, Figure 2d schematically represents an updated version of the structural model of the reservoir of figure 2a incorporating additional horizons.

[0049] Figure 3 schematically represents an embodiment for computing a structural model of the reservoir in a deposit space.

[0050] Figure 4 schematically represents an exemplary device for implementing the method.

[0051] Figure 5a shows an example of a structural model of a reservoir in a present day state, and figure 5b shows an example of a restricted version of the model in which horizons more recent than a determined geological time have been removed.

[0052] DETAILED DESCRIPTION OF AT LEAST AN EMBODIMENT With reference to the attached drawings, a method for building a model of a geological reservoir according to a present-day state will now be described.

[0053] With reference to figure 4, this method may be implemented by a device 10 comprises a computer, this computer comprising a memory 15 to store program instructions loadable into a circuit and adapted to cause circuit 14 to carry out the steps of the present invention when the program instructions are run by the circuit 14. The memory 15 may also store data and useful information for carrying the steps of the present invention as described above.

[0054] The circuit 14 may be for instance: a processor or a processing unit adapted to interpret instructions in a computer language, the processor or the processing unit may comprise, may be associated with or be attached to a memory comprising the instructions, or the association of a processor / processing unit and a memory, the processor or the processing unit adapted to interpret instructions in a computer language, the memory comprising said instructions, or an electronic card wherein the steps of the invention are described within silicon, or a programmable electronic chip such as a FPGA chip (for « Field- Programmable Gate Array »).

[0055] This computer comprises an input interface 13 for the reception of several data used for the above method according to the invention, for instance an initial structural model of a reservoir and parameters involved in simulating deposition of layers of sediments. This computer also comprises an output interface 16 for outputting the reservoir model.

[0056] The computer may also include a display 1 1 for displaying a three-dimensional representation of the model, or any data derived therefrom, such as for instance a 2D representation of a stratigraphic column, etc.

[0057] To ease the interaction with the computer, the device may also comprise human input means such as a keyboard 12, mouse, and / or a tactile screen which are connected to the computer circuit 14. The various components described above may be remotely connected to one another, i.e. the memory storing the data and / or the circuit implementing the method may be remotely located with reference to the user and accessible through any suitable network. A geological reservoir is a subsurface rock formation enabling the accumulation and storage of oil, natural gas, water or other types of resources. Modelling a geological reservoir may be performed in order to determine kea features of the actual reservoir, such as its geometry, its petrophysical properties, including porosity and permeability, and perform simulation of fluid flows within the reservoir, in view of assessing the potential for resource extraction from the reservoir, or storage in the reservoir (such as carbon dioxide).

[0058] As known to the skilled person, the formation of a geological reservoir is a phenomenon extending over millions of years, during which a succession of geological events may occur, including events of sedimentation, diagenesis, erosion, deformation, faulting, etc.

[0059] Regarding the very long time scales of these phenomena, the structure of a reservoir can be considered constant during periods of time ranging from at least 100 years to several thousand years. Therefore, the notion of “present-day state” of a geological reservoir refers to the geological structure of the reservoir that is observable by Man in modern times, and that may be analyzed with a view to operating that reservoir. In particular, the present-day state of a geological reservoir relates to a state that can be at least partly described by collecting experimental data, and performing fluid flow computations in order to simulate the actual behavior of the reservoir, if the latter was exploited. The experimental data that may be collected about the reservoir include data collectable either by observation of the geological formation (configuration of faults, dips etc.), by performing seismic acquisition campaigns, or by drilling exploration wells and extracting rock core samples enabling the establishment of stratigraphic logs.

[0060] The method disclosed herein enables building a model of a reservoir according to a present-day state, from an initial version of a structural model of the reservoir. The built model in particular comprises additional horizons not contained in the initial version of the structural model of the reservoir, said horizons being formed by forward sedimentary modelling.

[0061] A structural model is a numerical representation of the three-dimensional arrangement of rock structures forming the reservoir, which is defined at least by a boundary volume V, and a plurality of surfaces extending within said volume and partitioning the volume into a plurality of regions. The plurality of surfaces may include one or more horizons H, where each horizon is an iso-chronological surface associated to a determined absolute geological time T. In the present-day state, the one or more horizons of the structural model may be faulted or tilted due to tectonic forces or other geological processes.

[0062] The plurality of surfaces may also include one or more major faults F extending transversely to one or more horizons. A major fault may separate two regions of the reservoir which are thus enabled a relative displacement called slip.

[0063] In embodiments, the method comprises building a modified, enriched version of the structural model of the reservoir according to the present-day state, wherein the modified version includes at least additional horizons, which are the result of a simulation of the deposition of successive layers of sediments.

[0064] In other embodiments, the method comprises building, from the initial version of the structural model of the reservoir, a three-dimensional meshed model, including the additional horizons, and further including a plurality of three-dimensional cells. Each cell may be associated to at least one parameter, such as a physical, geological or petrophysical parameters. The latter may include at least one of a porosity value and a permeability value. The three-dimensional cells may be defined within each layer of sediments, i.e. each layer of sediments comprises at least one layer of three- dimensional cells.

[0065] With reference to figure 1 , the method comprises a first step 100 of obtaining an initial version of a structural model P0 of the reservoir according to the present-day state. A sectional view of an exemplary structural model according to the present-day state of reservoir is shown in figure 2a.

[0066] The initial version of the structural model of the reservoir that is obtained in step 100 comprises at least one, and more preferably at least two horizons H, each associated to a determined absolute geological time T. The initial version of the structural model of the reservoir may also include one or more surfaces F extending transversely to the horizons and representing major faults of the reservoir.

[0067] The represented reservoir may in particular be a real reservoir, and the initial version of the structural model of the reservoir (for instance, the number and disposition of faults and horizons) is obtained from data acquired with respect to this reservoir, which may include seismic data and / or well data.

[0068] In embodiments, the structural model PO of the reservoir according to the present-day state is defined in a cartesian space, where any point of the model can be defined by three coordinates (x,y,z), where x and y may be coordinates on perpendicular axes corresponding to a horizontal plane and z may be a coordinate on a vertical axis.

[0069] The structural model, in particular its dimensions and the definition and shape of each horizon and fault, may be defined by a user based on observations and data collected from the actual reservoir. During step 100, the structural model may be loaded from the memory 15, where it has been preliminarily stored.

[0070] The method then comprises computing, during a step 200, from the initial version of the structural model P0, a structural model of the reservoir in a deposit space DO.

[0071] In what follows, the “deposit space” refers to a configuration of the reservoir before occurrence of any deformation following the deposition of sediments constituting the reservoir, in particular folding, tilting, apparition of the faults and, as the case may be, relative displacement of the areas of the reservoir that are separated by the faults, called slip. Accordingly, in the deposit space, the horizons of the structural model of the reservoir according to the present-day state are assumed to be horizontal surfaces, and the slip of each major fault is brought back to zero.

[0072] With reference to figure 2b, is shown a sectional view of a the structural model of the reservoir of the model represented in figure 2a, in the deposit space wherein the faults have been removed, the slip is brought to zero, and the deformations of the horizons H have been removed.

[0073] In embodiments, the computation of the structural model in the deposit space DO from the present-day state P0 is performed by application of the Geochron model disclosed in the publication by [Mallet, 2004],

[0074] Employing the same notations as used in this publication, and referring to figure 3, the structural model of the present-day state of the reservoir corresponds to the G- space in the 3D Cartesian space. Any point belonging to that space is denoted x such that: x = x. X + y. Y + z. Z

[0075] Where (X,Y,Z) is a given right-handed orthogonal frame of unit vectors.

[0076] The structural model of the reservoir in the deposit space corresponds to the Geo- Chronological space and denoted G-space, which is defined in a parametric space (U,V,T) where T is orthogonal to the surface of the earth and oriented upwards, and corresponds to the direction of stacking of the sediments. T thus a relative geological time. Let Htbe the horizontal plane orthogonal to the vector T and corresponding to the surface of the earth at geological time t, Htis parallel to the pair of orthogonal unit vectors (U,V) which can thus be used as a frame for Ht. As a consequence, for any reference point p0belonging to Ht, the pair of vectors (U,V) induces a coordinate system (u,v) on Htsuch that :

[0077] Any particle of sediments observable today at a location x within the model of the present-day state of the reservoir, was deposited at some location (u,v) on a plane Htand can thus be characterized in a unique way by its coordinates (u,v,t) in the deposit space.

[0078] As a consequence, computing 200 the model of the pre-deformation state of the reservoir from the structural model of the present-day state of the reservoir corresponds to determining a transform function u defined as:

[0079] For which the norm of the gradient of t must be constant:

[0080] | |V(t) | | . N = C

[0081] The constant C can be arbitrarily defined. N is a vector field orthogonal to the horizons of the model in the present-day space, that points from the older horizon toward the most recent. An inverse function u’1exists for all points of the G space transformed into the G using u, such that : The method then comprises a step 300 of computing an updated version D1 of the structural model of the reservoir in the deposit space, comprising a plurality of additional horizons Hi, where the additional horizons have been generated by forward sedimentary modelling, on a determined base iso-chronological surface Sb corresponding to an absolute geological time.

[0082] Once this updated version D1 has been obtained in the deposit space, the method then comprises a step 400 of generating therefrom an updated version P1 of the structural model of the reservoir in the present-day state including the additional horizons Hi that have been generated by forward sedimentary modelling.

[0083] Therefore, this updated version P1 comprises the initial horizons present in the initial version PO of the structural model of the reservoir in the present-day state, where said horizons have returned to their initial, possibly folded or tilted, configuration. In other words, as these horizons have undergone a transformation from the present-day state to the pre-deformation state, an inverse transformation is applied to these horizons to bring them back to their initial configuration.

[0084] Further, this updated version P1 comprises all the faults present in the initial version, as well as the slip between the areas of the model separated by the faults.

[0085] Moreover, the additional horizons Hi generated in the structural model D1 in the deposit space are also present in this updated version P1 , with a geometry that results from the same inverse transformation that is applied to the horizons originally present in the model.

[0086] With reference to figure 2d, is schematically shown an example of an updated version of the structural model of a reservoir according to the present-day state SC2, where the additional horizons are deformed as compared to the pre-deformation state, and possibly crossed by faults.

[0087] Step 400 is implemented by applying, to the updated version of the structural model D1 in the deposit space, the inverse function u1of the restoration function u applied at step 200.

[0088] Back to step 300, a detailed implementation of this step will now be described. As explained below, this implementation enables constraining the relative thicknesses of the additional layers in the updated version of the model in the present-day state P1 to fit the relative thicknesses of these layers as generated by the forward sedimentary modelling, thereby respecting the sedimentary phenomena underlying the formation of the additional horizons.

[0089] In embodiments, step 300 of computing the updated version D1 of the structural model of the reservoir in the deposit space comprises a substep 310 of performing forward sedimentary modelling on a base iso-chronological surface Sb, in a cartesian coordinates system, and 320 rescaling the horizons generated by the forward sedimentary modelling to fit in the structural model in the deposit space.

[0090] Contrary to the initial horizons of the model PO, which are explicit surfaces of the model, the iso-chronological surface Sb may not be explicitly defined in the model PO of the present-day state of the reservoir, but may only be defined by its absolute geological time Tb. Said absolute geological time Tb of the base surface Sb is comprised between the respective absolute geological times To, Ti of two initial horizons Ho, Hi of the model in PO in the present-day state.

[0091] In order to perform forward sedimentary modelling, the base iso-chronological surface Sb is assigned a topography in cartesian coordinates (x,y,z). Performing 310 forward sedimentary modelling then comprises simulating deposition, on said base surface Sb, of a plurality of successive layers of sediments or sedimentary layer, where each layer of sediments Li corresponds to a determined period of time At of sedimentation, and the generated additional horizons Hi correspond to the surfaces between two consecutive deposited layers of sediments or, said otherwise, to the upper surface of each deposited layer of sediments.

[0092] Each layer of sediments is associated to a thickness, along z, which corresponds to a quantity of sediments deposited over the period of time represented by the layer. The thickness of a layer of sediments may be variable along said layer, as represented in the example of figure 2c. The duration of the period of time At represented by each layer of sediments may be fixed or set by the user.

[0093] Examples of forward sedimentary modelling methods suitable for implementing step 310 are disclosed in patent applications WO2020 / 229863 or WO2020 / 229866, PCT / FR2022 / 051397 or PCT / FR2022 / 051398, all filed by the applicant. Once the forward sedimentary modelling has been completed, a model M is obtained in a cartesian coordinates system comprising the base iso-chronological surface Sb and the additional layers Li of sediments deposited on said surface, forming at their respective interfaces the additional horizons Hi.

[0094] The method then comprises a rescaling step 320 to scale this model M in the deposit space, which is a unitary space where all coordinates rest between 0 and 1 and the vertical axis corresponds to a relative geological time.

[0095] The rescaling of the model is based on the ratio between the dimensions of the structural model in the deposit space DO and the dimensions of the model M.

[0096] In the t direction, the rescaling is performed to fit between minimum and maximum relative geological times Un and tmax, such that the later application (in step 400) of the inverse transform function u’1on the updated version of the structural model in the deposit space D1 returns a model P1 in the present-day state with a maximum thickness matching the maximum deposition thickness computed by the forward simulation. Thus, the relative thicknesses of the additional horizons in the model P1 are constrained to fit their thicknesses in the model D1 .

[0097] According to this rescaling, Un is the relative geological time corresponding to the base iso-chronological surface Sb, and is thus determined from the absolute geological time Tb associated to said surface, and tmax is determined from the maximum cumulative thickness of the deposited layers of sediments in the forward model.

[0098] Regarding Un, as the base iso-chronological surface Sb corresponds to an absolute geological time Tb comprised between the geological times To, Ti of two initial horizons of the structural model, the relative geological time tb associated to the base surface is determined from the relative geological times to, ti in the deposit space corresponding to the initial horizons Ho, Hi.

[0099] Using the constant gradient constraint of the relative geological time t in the deposit space, the value of n = tb is deduced by using a linear regression based on: The relative t0value in and the absolute time Toof the horizon below the iso-chronological surface (i.e. T0<Tb), - The relative ti value in (u,v,t) and the absolute time Ti of the horizon above the sedimentary deposit (i.e. Ti>Tb),

[0100] - The absolute time Tbof the base surface Sb.

[0101] The relative time tbof the base surface, corresponding to tmin, may be computed as follows:

[0102] On the other hand, the determination of tmaxfirst comprises determining the maximum cumulative thickness hdmaxobtained at the end of the forward sedimentary simulation, from the base surface Sb.

[0103] Then, the coordinates of a reference point of the structural model PO of the reservoir in the present-day state that is spaced upwardly from the iso-chronological surface Sbby a stratigraphic distance equal to the maximum cumulative thickness, are determined. The stratigraphic distance means a distance parallel to the direction of sedimentation, and hence the reference point is positioned upwardly according to a direction that is locally normal to the iso-chronological surface. As indicated above, the iso-chronological surface may not be explicitly defined in the initial version of the structural model PO in the present-day state. In that is the case, for the purpose of determining tmax, the iso-chronological surface may be defined, once its relative geological time tb has been defined, by computing an inverse transform of the surface of coordinates (u,v, t=tb) in the deposit space.

[0104] In embodiments, the point of the iso-chronological surface from which the coordinates of the reference point are determined is selected to be sufficiently distant from the faults crossing the base surface in the model PO. For instance, said point of the iso- chronological surface may be chosen as the farthest point from the faults. Alternatively, a point may be selected among a plurality of points located at a distance from each fault exceeding a predetermined threshold. This particular choice enables limiting the impact of the local transformation impacted by the transform function due to the fault throws.

[0105] In embodiments, and with reference to figures 5a and 5b, the coordinates of the reference point are determined in a restricted version of the structural model of the reservoir in the present-day state SrO, in which all horizons extending above the iso- chronological surface have been removed. Indeed, the more recent horizons can have an impact on the (u,v,t) transform, especially in case of erosion, an example of which is shown in figure 5a, where the (u,v,t) space is locally degenerated. Thus, removing these horizons allows obtaining a linear transform in the relative period above Sb, i.e. posterior to the absolute geological time Tb. The restricted version of the structural model also enables that all points in G have an image in G by application of IT1.

[0106] The reference point that has been identified is then converted into the deposit space to determine its associated relative geological time, and said time corresponds to tmax.

[0107] Once tmin and tmax have been determined, the model M obtained at the end of the forward sedimentary modelling is rescaled using the following equations:

[0108] Where Munitaryis the normalization of the model / Wto the dimensions of the structural model (boxmin and boxmax being 3D vectors corresponding respectively to the minimum and maximum dimensions of the structural model in the three directions),Mrescaiedisthe rescaling of Munitaryto it fit vertically between tmaxand fm,n, UsingMrescaiea the application of u-1allows to retrieve the present-day geometry of the forward sedimentary model M.

[0109] In embodiments, the following steps 100 to 400 are performed several times with various input parameters regarding the forward sedimentation modelling, to obtain a plurality of candidate models of the reservoir in the present-day state comprising additional horizons. The candidate models may in particular differ in the number of deposited layers to cover the period of time simulated by the forward modelling, or in the thickness and / or shape of each layer. One of the candidate models may then be selected according to a criterion of proximity between the uppermost deposited layer and a determined top horizon present in the initial version of the structural model in the present-day space. For instance, the candidate model where the uppermost deposited layer of sediments is closest to the top horizon, among all candidate models, may be selected.

[0110] Optionally, the method may further include simulating 400, on the model SP2 obtained at the end of step 300, at least one additional geological event, such as a diagenetic event, a faulting event or another sedimentation event. In particular, it is possible to simulate the occurrence of successive events according to a sequence that corresponds to a presumed sequence of events having occurred during the formation of the actual reservoir. Thus, the relative chronological order of each event is respected, which impacts the present-day structure of the reservoir. For instance, a sedimentary event posterior to a faulting event results in a fault that does not cross horizons formed by the posterior sediments.

[0111] In embodiments, as indicated above, the method may further comprise a step 500 of generating a three-dimensional meshed model of the reservoir from the updated version P1 of the structural model of the reservoir in the present-day state obtained at step 400. This three-dimensional meshed model may comprise, in addition to the horizons and faults of the structural model, a plurality of three-dimensional cells filling said structural models and having associated parameters, and may be formed by filling the structural model with a mesh according to methods known to the skilled person. In embodiments, a layer of cells may be defined between two consecutive horizons (whether initial horizons or additional horizons) of the structural model.

[0112] In embodiments, some parameters associated to cells of the meshed model may be derived from the forward modelling simulation. Notably, the additional horizons generated during the forward modelling simulation may be associated to parameters such as geological parameters (type of rock, facies, etc.), environmental parameters, petrophysical parameters (porosity, permeability), and said parameters may be assigned to the cells extending between an horizon and the previous horizon.

[0113] It is to be underlined that the updated version of the structural model of the reservoir, comprising additional horizons that are defined according to forward modelling, enables generating a mesh in which the cells are defined according to the orientation of the geological deposits. Hence, the mesh respects the sedimentary and stratigraphic heterogeneity and is readily of higher quality and relevance for later applications, such as fluid flow simulations, than the initial version of the structural model. This in turn enables improving the quality of the simulations run on the later model. In the case of hydrocarbon production or carbon capture and storage, it thus enables a better analysis of the reservoir, its production / storage potential, and a better determination of the number and locations of input / output wells. In the case of groundwater resource management, it also enables better computations of fluid flows and better management of the resource.

[0114] Accordingly, the method may further comprise a step 600 of performing at least one among the following applications:

[0115] Performing fluid flow computation within the obtained model of the reservoir,

[0116] - Extracting, from the obtained model, a stratigraphic column or a statistic distribution of at least one parameter populating the model, and comparing the stratigraphic column or statistic distribution to equivalents obtained from the actual reservoir by on-site data acquisition, Enhance the estimation of available resources, etc.

[0117] References:

[0118] [Mallet, 2004]: Jean-Laurent Mallet “Space-Time Mathematical Framework for

[0119] Sedimentary Geology”, in Mathematical Geology, Vol. 36, No. 1 , January 2004

Claims

CLAIMS1 . A computer-implemented method for reservoir modelling, comprising:- Obtaining (100) a structural model of the reservoir in the present-day state (PO), comprising at least one initial horizon (H), corresponding to an iso- chronological surface associated to a determined absolute geological time,- Computing (200), from the structural model in the present-day state, a structural model of the reservoir in a deposit space (DO),- computing (300) an updated version of the structural model of the reservoir in the deposit space (D1 ), comprising a plurality of additional horizons (Hi), where the additional horizons have been generated by forward sedimentary modelling, and- generating (400), from the updated version of the structural model in the deposit space, an updated version (P1 ) of the structural model of the reservoir according to the present-day state including the additional horizons.

2. The method according to claim 1 , wherein computing (200) the structural model of the reservoir in the deposit space comprises application, to the structural model of the reservoir in the present-day state, of a bijective transform function, and generating the updated version of the reservoir in the present-day state is performed by application, to the updated version of the model in the deposit space, of an inverse function of the transform function.

3. The method according to claim 1 or 2, wherein the additional horizons (Hi) define a plurality of sedimentary layers (Li), each sedimentary layer being defined between two consecutive horizons (Hi) and having a respective thickness, and the relative thicknesses of the sedimentary layers in the updated version of the structural model of the reservoir according to the present-day state are constrained to fit the relative thicknesses of the sedimentary layers generated by the forward sedimentary modelling.

4. The method according to claim 3, wherein the structural model of the reservoir in the present-day state is defined in a Cartesian coordinates system, the structural model of the reservoir in a deposit space is defined in a parametric coordinates system, and generating the updated version of the structural model of the reservoir in the deposit space comprises:- performing forward sedimentary modelling (310) on a base iso-chronological surface of determined absolute geological age in a cartesian coordinates space, wherein the iso-chronological surface has an initial topography in said cartesian coordinates space, and performing forward sedimentary modelling comprises simulating deposition, on the iso-chronological surface, of a plurality of successive sedimentary layers, where each sedimentary layer corresponds to a determined period of time of sedimentation and the surfaces between consecutive layers of sediments form the additional horizons, and- rescaling (320) the generated horizons to fit in the structural model in the deposit space.

5. The method according to claim 4, wherein the parametric coordinates system comprises a vertical axis corresponding to relative geological time, and the generated horizons are rescaled to fit between minimum and maximum relative geological times (tmin, tmax ) along said vertical axis.

6. The method according to claim 5, wherein the minimum relative geological time (tmin) is the relative geological time (tb) corresponding to the absolute geological time value associated to the base iso-chronological surface (Sb).

7. The method according to claim 6, wherein the absolute geological time (Tb) of the base iso-chronological surface is comprised between the respective absolute geological times (To, Ti) of two initial horizons (Ho, Hi) of the structural model of the reservoir in the present day state, and the relative geological time (tb) corresponding to the base-iso-chronological surface is determined from the relative geological times (to, ti) corresponding to the initial horizons (Ho, Hi) in the deposit space.

8. The method according to claim 5 to 7, wherein the maximum relative geological time value (tmax) is determined from the maximum cumulative thickness of sediments between the generated additional horizons and the base iso-chronological surface.

9. The method according to claim 8, wherein determining the maximum relative geological time (t max ) comprises:Determining the maximum cumulative thickness between the generated additional horizons and the iso-chronological surface,- Determining coordinates of a reference point of the structural model of the reservoir in the present-day state that is spaced upwardly from the iso- chronological surface by a stratigraphic distance equal to the maximum cumulative thickness,Determining a corresponding relative geological time of the reference point in the deposit space, corresponding to the maximum relative geological time.

10. The method according to claim 9, comprising determining coordinates of a reference point of a restricted version of the structural model of the reservoir in which all initial horizons extending above the iso-chronological surface are removed.

11. The method according to any of the preceding claims, further comprising generating (500) a three-dimensional meshed model of the reservoir from the updated version of the structural model of the reservoir in the present day state.

12. The method according to claim 11 , wherein the three-dimensional meshed model comprises a plurality of cells where each cell is assigned to at least one parameter chosen among a geological parameter, a mechanical parameter or a petrophysical parameter.

13. The method according to claim 12, wherein the parameters associated to the cells are derived from the forward sedimentary modelling.

14. A computer-program product comprising code instructions for implementing the method according to any of the preceding claims, when it is executed by a computer.

15. A computing device, comprising at least a computer and a memory, the computer being configured to implement the method according to any of claims 1 to

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