A method for modelling a fractured geological reservoir comprising fault zones

Abstract

It is disclosed a computer-implemented method for modelling a reservoir comprising fault zones, comprising: - Obtaining an initial model of the reservoir (100) and ground data (200), - Implementing (300) at least one set of fault zones generation in the initial model, comprising receiving input parameters (310), and, based on the received ground data and input parameters: o generating at least one core zone (322) of a fault zone, and a damage zone extending around the core zone, and o Generating a plurality of fault segments (324) within the damage zone.

Description

[0001] A METHOD FOR MODELLING A FRACTURED GEOLOGICAL RESERVOIR COMPRISING FAULT ZONES

[0002] TECHNICAL FIELD

[0003] The present disclosures relates to a computer-implemented method for modelling a geological reservoir incorporating fractures, in particular fault zones. The disclosure finds notable applications in the fields of hydrocarbon production, Carbon Capture and Storage (CCS), or water resource management.

[0004] TECHNICAL BACKGROUND

[0005] In geology, there is an ongoing need of proposing computer modelling methods that enable accurately representing real geological reservoirs. Such models are indeed used to simulate various scenarios and predict how a reservoir might behave under different conditions.

[0006] In the field of hydrocarbon production, a good understanding of the actual geometry and petrophysical properties of a reservoir are essential for forecasting fluid flow patterns, and determining oil and gas recovery strategies. In the field of carbon capture and storage, it is equally important to rely on accurate representations of the reservoir in order to forecast the storage potential of a reservoir, the most appropriate locations of injection wells, and anticipate risks of leakage. Also in the field of water resource management, relying on an accurate reservoir representation enables simulating the movement and behavior of groundwater in aquifers, enabling prediction of water availability, as well as potential flooding or pollution risks.

[0007] One element that can strongly influence the behavior of a reservoir relates to the existence and disposition of fractures within the reservoir. Indeed, fractures creates local heterogeneities in the behavior of a reservoir, in particular with respect to permeability and hence to fluid flows within the reservoir.

[0008] Furthermore, the generic term of “fractures” actually encompasses a large variety of geological structures, exhibiting different geometries, respective chronologies of formation and hence different impacts as to the petrophysical properties of a geological reservoir. Geologists thus have established a typology of fractures, according to features such as the mode of deformation of the fractures, or their specific chronology of formation. One may for instance refer to [Peacock, 2016]. In the field of hydrocarbon production, an accurate representation of the disposition of fractures is essential for forecasting production, whereas in the field of CCS, fractures may cause leaks and thus adversely affect the efficiency of carbon storage. There is therefore a need for a good knowledge of fractures present within a reservoir in order to accurately represent said reservoir and use it for the above-mentioned applications.

[0009] However, the available ground data is too scarce to accurately represent the fractures within a reservoir. Regarding ground data that is obtained through campaigns of seismic reflections, it only enables detecting major fractures, but fails to provide any information on fractures of lesser size. As to ground data that is obtained by drilling exploration wells and analyzing the wells, it provides detailed but local information, and fails to provide an extensive hindsight about the number, disposition and relationship between fractures within all the considered domain.

[0010] In this perspective, computer modelling methods enabling the generation of fractures have been developed. Simulation of fractures is commonly achieved by generating a Discrete Fracture Network (DFN), which is a numerical representation of fractures, in which fractures are represented as discrete features associated with specific properties, including orientation, length, aperture and connectivity.

[0011] In particular, it is known from [Libby, 2019], an algorithm for modelling fractures, according to which fractures are grown according to a sequence of fracture sets. Within each set, fractures grow from a seed point stochastically located in space, until it reaches its target size, terminates against a previous fracture, or until a target fracture intensity is reached. Exclusion zones are defined around each fracture that prevent nucleation of new fractures of the same set within the exclusion zones. Moreover, for a considered fracturing set, a user may configure the geometrical parameters (size, orientation) of the fractures, as well as rules of interaction between fractures of a same set. This algorithm thus enables modelling fractures with varying orientations, sizes and types of intersection.

[0012] However, this algorithm still does not enable accurate representation of the diversity of fracture types within a reservoir, as well as the interactions between them. First, in this algorithm, all fractures are generated stochastically based on density data, and no fracture which location is based on hard data may be integrated. Second, despite changes in sizes and orientations of the generated fractures, all fractures are generated according to the same process, and the algorithm does not manage different rules of intersection between fractures of different fracturing sets. To the contrary, as all fractures and generated and represented according to the same process, the rules of intersection between fractures are also always the same. Therefore the resulting network of fractures does not accurately reflect reality, and hence the resulting upscaling and / or fluid flow simulations that will be performed might be flawed.

[0013] SUMMARY OF THE INVENTION

[0014] An aim of the present disclosure is to improve the situation.

[0015] In particular, an aim of the present disclosure is to provide a method for modelling a reservoir including fractures, which more accurately reflects the disposition of the fractures of the reservoir, the actual geological phenomena that have led to the formation of the fractures, and the impact of these fractures on the petrophysical properties and behavior of the geological reservoir when said fractures are fault zones.

[0016] Another aim of the present disclosure is to provide a method enabling accurately modelling the formation of fault zones. Another aim of the present disclosure is to provide a method enabling modelling a chronological sequence of fracturing sets, where a subsequent fracturing set takes into account the fractures generated during an earlier fracturing set.

[0017] To this end, it is disclosed a computer-implemented method for modelling a reservoir comprising fault zones, comprising:

[0018] Obtaining an initial model of the reservoir and ground data,

[0019] Implementing at least one set of fault zones generation in the initial model, comprising receiving input parameters, and, based on the received ground data and input parameters: o generating at least one core zone of a fault zone, and a damage zone extending around the core zone, and o Generating a plurality of fault segments within the damage zone.

[0020] In embodiments, the ground data comprises at least one of: - a localization of the fault zone,

[0021] - geometric parameters of the fault zone,

[0022] - a density of fault segments within the damage zone, and

[0023] - a chronology of the formation of fractures.

[0024] In embodiments, wherein the core zone is a single fault.

[0025] In embodiments, generating the at least one core zone comprises generating a plurality of core zone seeds, by implementing a probabilistic process based on a determined distribution.

[0026] In embodiments, generating a plurality of fault segments within the damage zone comprises generating a plurality of fault segments seeds within the damage zone, and generating fault segments from at least part of the segments seeds.

[0027] In embodiments, the generation of a fault segment comprises managing intersection with a previously generated fault, wherein:

[0028] When the current fault segment intersects a previously generated fault segment, the two fault segments cross, and

[0029] When the current fault segment intersects the core zone, the current fault segment abuts against the core zone.

[0030] In embodiments, each set of fault zones generation further comprises selecting a fault zone type among a plurality of pre-determined fault zone types, and each fault zone type is associated with at least one of:

[0031] A range of values of a dip angle of the core zone, and

[0032] A relative size of damage zone on each side of the core zone.

[0033] In embodiments, the method further comprises assigning a null permeability to the core zone.

[0034] In embodiments, the method further comprises a step of computing two equivalent fractures on each side of the core zone, where each equivalent fracture is computed from all the generated fault segments on the part of the damage zone located on the respective side of the core zone. In embodiments, computing an equivalent fracture from a plurality of fault segments comprises computing an equivalent permeability of the fault segments, and generating an equivalent fracture having geometrical parameters inferred from geometrical parameters of the core zone, and having an assigned permeability inferred from the equivalent permeability.

[0035] According to another object, a computer program product is disclosed, comprising code instructions for implementing the method according to the description above, when it is executed by a computer.

[0036] According to another object, a non-transitory computer-readable storage is disclosed, having stored thereon code instructions which, when executed by a computer, cause said computer to implement the method according to the description above.

[0037] According to another object, a computer is disclosed, configured for implementing the method according to the description above.

[0038] The disclosed method enables modelling the formation of fault zones, which are complex fracture networks, in a manner that is not computationally intensive and which enables accurately modelling the impact of such fracture network on the petrophysical properties of a reservoir, notably in terms of fluid flow.

[0039] A fault zone may thus be represented by a single fracture with a null permeability representing the core zone, and a plurality of fault segments having respective permeabilities within the damage zone.

[0040] In embodiments, the fault segments of the damage zone may also be replaced by the computation of a pseudo-equivalent fracture, which enables limiting the memory and processing resources for storing and processing the obtained model in later applications.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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:

[0043] Figures 1 a and 1 b are flow charts describing the main steps of a possible embodiments of a method for modelling a reservoir,

[0044] Figure 2 schematically represents an example of a geological calendar, Figure 3 schematically represents geometrical parameters of a fracture, Figure 4 schematically represents a fault zone generation process according to a possible embodiment,

[0045] Figure 5 is a possible embodiment of a device for implementing the method according to the disclosure

[0046] Figures 6a and 6b schematically represent the computation of pseudoequivalent fractures to represent a plurality of fault segments, in the case of a fault zone.

[0047] DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0048] A method for modelling reservoirs incorporating fractures according to embodiments of the present disclosure will now be described.

[0049] The method may be carried out by a computer system 1 , schematically represented in figure 5. In preferred embodiments, the computer system 1 comprises one or more processors 10 (which may belong to a same computer or to different computers) and storage means 20 (magnetic hard disk, optical disk, electronic memory, or any computer readable storage medium) in which a computer program product is stored, in the form of a set of program-code instructions to be executed in order to implement all or part of the steps of the method. Alternatively, or in combination thereof, the computer system can comprise one or more programmable logic circuits (FPGA, PLD, etc.), and / or one or more specialized integrated circuits (ASIC), etc., adapted for implementing all or part of said steps of the processing method. In other words, the computer system comprises a set of means configured by software (specific computer program product) and / or by hardware (processor, FPGA, PLD, ASIC, etc.) to implement the steps of the method.

[0050] The computer system may comprise an input interface 30 for the reception of input data, in particular ground data regarding a reservoir that is to be modelled by application of the method. The input interface may be an interface with a storage device storing the input data, or a communication interface for connecting the computer system to a telecommunication network enabling downloading of said input data therefrom. The computer system may also comprise a display 40 for displaying three-dimensional representations of the obtained model of a reservoir, and / or two- dimensional representations, which may be sectional view of the model, and / or any relevant information relative to the obtained model.

[0051] A usual categorization of fractures is based on presence or absence of relative movement between the rocks on either side of the fracture. Accordingly, a first category of fractures are joints, which refer to a fracture in a rock mass where there has been no significant movement or displacement of the rocks on either side of the fracture. Joints grow perpendicular to stratification. A second category of fractures are faults, which refer to fractures in a rock mass due to a relative displacement of rocks on either side of the fracture, where this displacement can be for instance: a horizontal sliding of the rock masses on both sides of the fracture, a vertical sliding, resulting from either a compressional or extensional relative movement of the rock masses on both sides of the fracture.

[0052] The method disclosed below enables modelling a geological reservoir including at least fault zones, where the generation process of fault zones is designed to accurately reflect the geometry and geological behavior of corresponding this type of fracture.

[0053] As used herein, fault zones refer to broad areas where numerous faults are concentrated and interact. Fault zones regularly exhibit complex structures, and may include a core zone, and a damage zone. The core zone corresponds to the location of primary faulting, and may be filled with fault breccia, which is a type of rock formed by the grinding and crushing of rock fragment along a fault zone during the movement of the Earth’s crust, and which consists of fragments of rocks that have been broken during intense frictional faults associated with faulting. The spaces between fragments are often filled with fine-grained material, such as clay or other crushed rock, forming a matrix. Damage zone relates to a zone within or adjacent the core zone, in which faulting occurs as a result of interactions and stress distributions within the core zone.

[0054] Referring to figures 1 a and 1 b, the main steps of a method for modelling a geological reservoir including fault zones will now be disclosed. The method may in particular be used for modelling a real geological reservoir, i.e. a reservoir existing in real life, and for which ground data describing at least some geological and / or geometrical properties is available or can be acquired. The ground data can notably include, or be derived from, campaigns of seismic reflections, in-situ observations of geologists, satellite or aerial images, or wellbore data, including well logs, cores and plugs. The ground data may provide, or may enable deriving, parameters used for modelling the fractures. The method thus enables forming more accurate and complete models of real reservoirs, for analyzing said models and using them for various applications, for instance for performing fluid-flow simulations, predicting reservoir production, determining location of injection and / or production wells, determining production scenarios, evaluating carbon storage capacities, determining fluid circulation or leakage within the reservoir, evaluating risks of pollution of ground water, etc.

[0055] The method comprises a step 100 of obtaining an initial model of the reservoir. The initial model of the reservoir is a numerical representation of the three-dimensional arrangement or rock structures forming the reservoir, which is defined at least by a three-dimensional volume V of determined dimensions.

[0056] In embodiments, the initial model of the reservoir further comprises a plurality of surfaces extending within said volume. The plurality of surfaces may include a plurality of stratigraphic surfaces, separating successive layers of rocks called beds. In embodiments, the initial model of the reservoir may comprise a plurality of distinct mechanical units, where each mechanical unit comprises a plurality of beds, and two successive beds, or two successive mechanical units are separated by a stratigraphic surface.

[0057] In what follows, a mechanical unit is defined as a geological formation comprising a plurality of beds, and whose upper and lower surfaces limit the vertical persistence of a given type of fracture. Rocks within a mechanical unit usually share similar properties, such as strength and deformation characteristics.

[0058] A bed refers to a layer of sedimentary rock, which results from the deposition of sediments over time. Each bed represents a single episode of sedimentation, often characterized by features such as grain size, mineral composition, level of sorting, or other sedimentary features.

[0059] At least one well may also be represented in the initial model of the reservoir, at a location corresponding to its actual location relative to the reservoir to be modelled. The well may in particular be an exploration well from which ground data has been acquired. The method also comprises a step 200 of receiving ground data relative to the reservoir.

[0060] The ground data relative to the reservoir may comprise a chronology of the formation of fractures, enabling defining at least one, or a chronology of successive fracturing sets to be modelled.

[0061] In embodiments, such chronology may be a geological calendar of the formation process of the reservoir to be modelled. With reference to figure 2, is shown an example of an excerpt of a geological calendar of the formation process of a reservoir that may be used within the scope of the present disclosure.

[0062] A geological calendar is a timeline that extends far beyond human history, and is used to represent the major events in Earth’s evolution. A geological calendar typically divides Earth’s history into several eons, which are further subdivided into eras, periods, epochs and ages. The most recent eon, the Phanerozoic, is the one in which complex life forms, including humans, have evolved. It is divided into the Paleozoic, Mesozoic and Cenozoic eras which is turn, are further divided into periods. For instance, the Mesozoic era is divided into the Cretaceous, Jurassic and Triassic periods, which are further divided into epochs and ages. The exemplary excerpt of figure 2 shows the division in ages of some epochs of Paleogene and Cretaceous eras. These various divisions of Earth’s history, namely eons, eras, periods, epochs and ages, are further associated to respective geological times defining the beginning and the end of each division.

[0063] Within the context of the present disclosure, the geological calendar of the formation of the reservoir further comprises a plurality of geological events having occurred during the formation of the reservoir and having contributed to shaping the reservoir according to its present-day state. Each geological event is associated to at least one geological time, at which the event occurred. The geological time is typically expressed in millions of years before present. For events spreading over a long period of time, i.e. typically more than one million years, a geological event may be associated to a geological time of beginning of the event and a determined duration. The geological events occurring during the formation of the reservoir may be correlated to determined ages or epochs of the evolution of Earth, i.e. may start at the beginning of an age and end at the end of said age or another age. The geological events in particular comprise deformation stages, during which fractures can appear within the model. The deformation stages are denoted Frac 1 and 2 in the example of figure 2. The method for modelling the reservoir may thus comprise implementing a plurality of fracturing sets, where each deformation stage of the geological calendar corresponds to at least one fracturing set. Moreover, the geological events of the geological calendar may include other types of geological events that may also be simulated between two fracturing sets. Notably, the geological events may include sedimentation events, referred to as Sed1 and Sed 2 in figure 2, and diagenetic events, referred to as D1 in figure 2.

[0064] Sedimentation events may be modelled using forward stratigraphic modelling, in particular using the methods disclosed in WO2020 / 229863 or WO2020 / 229866 filed by the applicant. Diagenetic events can for instance include eogenesis events, i.e. early diagenetic events occurring soon after sedimentation, or dissolution, and may be modelled respectively using the methods disclosed in PCT / IB2023 / 000437 and PCT / IB2023 / 000218.

[0065] When the method comprises implementing the successive geological events in accordance with the calendar, the same model of the reservoir is used for successively modelling each geological event, with the outputs of an event that are used in the setup of the next event. In particular, when the method comprises modelling in sequence a deformation event and a diagenetic event, the fractures generated within the model during the fracturing sets corresponding to the deformation event are integrated within the model, and used for simulating diagenesis. As fractures generally have increased permeability with respect to the surrounding matrix, the accuracy of the fractures disposition may strongly influence the evolution of the reservoir due to diagenesis.

[0066] Alternatively or in addition, the received ground data may include at least one: a Type of fractures to be modelled, a localization of fractures, a density of fractures, geometric parameters of fractures.

[0067] The received ground data may be obtained from observation, interpretation and measurements acquired on the reservoir, by the means listed above. Back to figure 1a and 1 b, the method then comprises implementing at least one fracturing set 300, where at least one fracturing set comprises generating fault zones in the model.

[0068] The step of implementing the fracturing sets 300 is also performed in accordance with the received ground data. Depending on the type of received ground data, said data may be taken into account for the definition and chronology of the fracturing sets (in particular when the received ground data comprises chronological information regarding the formation of fractures), or for the definition of parameters of the fractures generated during a fracturing set.

[0069] Implementing the fracturing set 300 comprises receiving input parameters 310 regarding the fault zones to be modelled, and generating said fault zones 320 based on the received parameters and ground data. The received input parameters may be provided by a user.

[0070] Generally, all fractures and fractures segments are modelled as bounded surfaces, and which define two opposite walls separated by the fracture, corresponding to a hanging wall and footwall of the fracture.

[0071] The received input parameters for the fractures may include one or more of a localization of the fractures, a density of the fractures, and geometric parameters of the fractures.

[0072] The geometric parameters may include one or more of the following parameters, which are schematically represented in figure 3, showing a single wall siding a fracture plane: strike direction, where strike refers to the line formed by the intersection between a horizontal plane and the fracture plane, dip angle, where the dip is a vector perpendicular to the strike line and extending along the fracture plane, and dip angle is the angle between the horizontal plane and the fracture plane, measured perpendicular to the strike line down to the fracture plane, dip azimuth, which is the angle formed between the dip and the North, length along the main direction of the fracture plane, height, which may be measured either along the fracture plane, orthogonally to length, as shown in figure 3, or vertically, aperture, which is the distance between the two walls siding the fracture plane aspect ratio, which is the ratio of the length of the fracture to its height or the ratio of the length to its aperture.

[0073] As recited above, fault zones generally comprise a primary damage zone filled with fault breccia, and a secondary damage zone in which secondary faulting occur. In order to accurately represent such zones, from the standpoint of petrophysics and rheology, fault zones are modelled using a core zone, which corresponds to the primary damage zone, and a surrounding damage zone. The core zone is represented as a single fracture (which is equivalent to all the primary zone faulting), and is associated with a parameter reflecting impermeability of the zone caused by the fault breccia. Said parameter may be for instance a null permeability. Alternatively, said parameter may be a transmissibility reduction coefficient, comprised between 0 and 1 , where 0 denotes a null transmissibility, and which value is selected by a user.

[0074] Thus, regarding fault zones in particular, the received input parameters or ground data may comprise: a localization of fault zones, a parameter of density of fault segments within the damage zone. The density of fault segments within the damage zone may be constant or may vary, for instance decrease with the distance from the core zone, geometric parameters of the core zone, including size and orientation, geometric parameters of the damage zone. These parameters may include two sets of parameters corresponding respectively to each side of the core zone.

[0075] In embodiments, a plurality of fault zone types are defined, with each fault zone type being associated with at least one of: a range of values of a dip angle of the single fault representing the core zone, as well as relative positions of the hanging wall and footwall, and a relative size of the damage zone on each side of the core zone.

[0076] For instance, the plurality of fault zone types may include: a dip-slip normal type, a dip-slip reverse type, a strike-slip type. A strike slip may for instance be associated to a range of dip angles comprised between 80 and 90°, and identical sizes of the damage zone on both sides of the core zone (i.e. in the footwall and hanging wall).

[0077] The dip-slip types correspond to dip angle values different from 90°, for instance a range comprised between 50 and 70 for the normal type and between 20 and 40° for the reverse type. The dip angle value may for instance be selected among these ranged by the user. Moreover, these types of fault zones may be associated with asymmetrical sizes of the damage zones, depending on whether they belong to the hanging wall or footwall.

[0078] The input parameters may thus also include a fault zone type selected by the user among the plurality of pre-defined fault zone types.

[0079] In embodiments, the input parameters comprise all parameters that are necessary for modelling the fault zones and which have not been already provided by the knowledge provided by the available ground data.

[0080] In embodiments, and as shown in figure 1 b, said step of receiving input parameters 310 may be performed once for all fracturing sets 300 to be modelled. In that case, step 310 corresponds to a step of setup of the sequence of fracturing sets to be modelled, in which all fracturing sets are defined, the associated parameters and ground data used for the generation of fractures of the set.

[0081] With reference to figure 4, the fault zone generation process 320 comprises a step 321 of generating a plurality of core zone seeds based on the received input parameters I ground data. The generation of core zone seeds may be implemented using a stochastic process, in particular a Poisson process, to randomly draw core zone seeds within the model according to the received density.

[0082] The fault generation process then comprises generating 322 a single fault representing the core zone from at least a core zone seed, and a damage zone extending around the core zone, on both sides thereof. The core zone and damage zone are developed according to received geometric parameters (dip azimuth, dip angle, length, height, aperture, aspect ratio, dimensions of the damage zone with respect to those of the core zone, possibly based on the selected type of fault zone). The damage zone is typically a parallelepipedal zone within which the core zone is included.

[0083] The generation of fault zones then comprises generating 323 a plurality of fault segments seeds in the damage zone. The generation of fault segments seeds is performed using a stochastic process, in particular a Poisson process, according to the received density of fault segments within the damage zone. It is underlined that, within the present disclosure, the terms “fault segment” designate an elementary component of a fracture or network of fractures. Therefore, despite using the word “segment”, a fault segment relates to a surfacic i.e. two-dimensionnal element.

[0084] The generation process then comprises iteratively generating fault segments 324 from the fault segment seeds.

[0085] The generation 324 of fault segments from segment seeds may comprise steps of generating a fault segment 324a from a seed, and optionally managing intersection 324b between the generated fault segment and a previously generated fault segment.

[0086] The intersection rules are as follows: two fault segments within the damage zone cross each other, a fault segment intersecting the core zone abuts against the latter.

[0087] The geometrical parameters of the fault segments may be set by a user, except for the dip angle which is equal to the core zone dip angle, within a tolerance range that may be for instance or + / - 10°. In case of intersection of a fault segment with a fracture of a previous fracturing set, pre-defined intersection rules are applied.

[0088] Back to figures 1 a and 1 b, the model obtained once the one or more fracturing sets 300 have been implemented is enriched, as compared to the initial model, with a plurality of fractures, which possibly intersect with one another, and optionally with observable faults described in the received ground data.

[0089] The method may then comprise assigning 400 a geological attribute value to each fault. The geological attribute value may be a petrophysical parameter, for instance a permeability, transmissibility value or a transmissibility reduction coefficient for the core zones of fault zones. For instance, the permeability value may be a function of the aperture, and the considered fluid that would flow within the fractures. For instance, a permeability value may be assigned to a fault according to the following equation:

[0090] Where b is the aperture of the fracture, p is the dynamic viscosity, p is the density of the fluid, g is the acceleration due to gravity, and v is the kinematic viscosity of the considered fluid.

[0091] Moreover, the method may also comprise processing 500 the network of fractures in order to convert it into a suitable format for later applications.

[0092] In embodiments, when the method has included modelling fault zones or fracture corridors, step 500 may include computing a pseudo-equivalent fracture 510 from a plurality of fault segments, to render the network of fractures less computationally intensive. Regarding fault zones, as schematically represented in figures 6a and 6b, a pseudo-equivalent fracture may be computed for all fault segments of a damage zone, that are located on a same side of the core zone. Hence, two pseudo-equivalent fractures may be computed on both sides of the core zone, for a less computationally intensive representation of the damage zone.

[0093] With reference to figure 1a, computing a pseudo-equivalent fracture from a set of fault segments comprises a substep 511 of computing an equivalent permeability Keq corresponding to the fault segments. This step may e.g. be performed by application of the teaching of [Oda, 1985]. The pseudo-equivalent fracture may be associated with a permeability value equal to said equivalent permeability Keq.

[0094] Computing a pseudo-equivalent fracture then comprises a substep 512 of designing the pseudo-equivalent fracture, i.e. attributing geometrical parameters to the fracture.

[0095] Regarding fault zones, a pseudo-equivalent fracture may be centered on the gravity center of each side of the damage zone. The pseudo-equivalent fracture length, height, dip azimuth and dip angle may be set as those of the core zone, respectively.

[0096] Last, the pseudo-equivalent fracture is also assigned an aperture, which may be derived from the permeability and surface of the fracture by the following equation: b3.S

[0097] K~ 127

[0098] Where b is the aperture of the pseudo-equivalent fracture, K its permeability, S its surface, and V the total volume represented by the fracture i.e. the fracture corridor or the part of the damage zone located on one side of the core zone, depending on the fault segments that are replaced by the pseudo-equivalent fracture.

[0099] In embodiments, step 500 may also comprise triangulating the surfaces of at least some of the generated fractures. Step 500 may also computing 520 a mesh within the obtained model, the mesh being formed of a plurality of three-dimensional cells, and conforming to the surfaces representing the fractures. The three-dimensional cells may for instance be hexahedrons or tetrahedrons.

[0100] Alternatively, the processing 500 may comprise generating a graph 530 representing the network of fractures, the graph comprising a plurality of nodes and connections between the nodes. The nodes may then be formed by the seeds of the fractures, and be associated with all the parameters of the corresponding fractures. The connections between the nodes may be formed between two fractures which intersect each other.

[0101] Even though figure 1 a shown steps 520 and 530 as alternatives with respect to step 510, the method may encompass a step 510 followed by either of steps 520 and 530.

[0102] The obtained representation of the network of fractures may be displayed for an interpreter to visualize and analyze the reservoir therefrom. Alternatively, further processing may also be performed on the model integrating the network of fractures. As mentioned above, the method may then comprise modelling diagenetic events in the obtained model. In particular when the network of fractures are represented as a graph, the teachings of PCTIB2023 / 000217 for modelling dissolution within said network are applicable.

[0103] Optionally, the method may also comprise a step 600 of upscaling the obtained network of fractures. Upscaling is a computation step that aims at deriving information and properties from a smaller or more detailed scale towards a larger, coarser scale. It enables in particular to increase the computational efficiency of the model.

[0104] Various upscaling methods known to the skilled person may be performed on the obtained network of fractures. The upscaling may be implemented to output a single equivalent medium, where this medium may either represent only the network of fractures, or may represent a medium that is equivalent to the rock matrix and the network of fractures that are within said matrix. Alternatively, the upscaling may be implemented to output a dual media including an upscaled equivalent rock matrix and an upscaled equivalent network of fractures. Some upscaling softwares known to the skilled person are available for instance in the Gocad-Skua suite, or Petrel marketed by SLB,etc.

[0105] Once upscaled, the obtained model of the geological reservoir may be used as known by the skilled perform for performing computations and simulations based on fluid flows within the reservoir.

[0106] REFERENCES

[0107] [Peacock, 2016] Peacock et al. “Glossary of fault and other fracture networks”, in Journal of Structural Geology, Volume 92, 2016, Pages 12-29, ISSN 0191-8141

[0108] [Libby, 2019]: Libby, S., et al, “Grown Discrete Fracture Networks: a new method for generating fractures according to their deformation history”; June 2019, ARMA 53rdUS Rock Mechanics / Geomechanics Symposium.

[0109] [Oda, 1985]: Oda, M. et al. « Permeability tensor for discontinuous rock masses”, Geotechnique, Vol. 35, Issue 4, pp483-495, 1985.

Claims

CLAIMS1. A computer-implemented method for modelling a reservoir comprising fault zones, comprising:Obtaining an initial model of the reservoir (100) and ground data (200), Implementing (300) at least one set of fault zones generation in the initial model, comprising receiving input parameters (310), and, based on the received ground data and input parameters: o generating at least one core zone of a fault zone, and a damage zone extending around the core zone, and o Generating a plurality of fault segments within the damage zone.

2. The computer-implemented method according to claim 1 , wherein the ground data comprises at least one of:- a localization of the fault zone,- geometric parameters of the fault zone,- a density of fault segments within the damage zone, and- a chronology of the formation of fractures.

3. The computer-implemented method according to claim 1 or 2, wherein the core zone is a single fault.

4. The computer-implemented method according to any of the preceding claims, wherein generating the at least one core zone comprises generating (321 ) a plurality of core zone seeds, by implementing a probabilistic process based on a determined distribution.

5. The computer-implemented method according to any of the preceding claims, wherein generating a plurality of fault segments within the damage zone comprises generating a plurality of fault segments seeds (323) within the damage zone, and generating fault segments (324) from at least part of the segments seeds.

6. The computer-implemented method according to any of the preceding claims, wherein the generation (324) of a fault segment comprises managing intersection with a previously generated fault, wherein:When the current fault segment intersects a previously generated fault segment, the two fault segments cross, andWhen the current fault segment intersects the core zone, the current fault segment abuts against the core zone.

7. The computer-implemented method according to any of the preceding claims, wherein each set of fault zones generation (300) further comprises selecting (310) a fault zone type among a plurality of pre-determined fault zone types, and each fault zone type is associated with at least one of:A range of values of a dip angle of the core zone, andA relative size of damage zone on each side of the core zone.

8. The computer-implemented method according to any of the preceding claims, further comprising assigning a null permeability to the core zone.

9. The computer-implemented method according to any of the preceding claims, further comprising a step (510) of computing two equivalent fractures on each side of the core zone, where each equivalent fracture is computed from all the generated fault segments on the part of the damage zone located on the respective side of the core zone.

10. The computer-implemented method according to claim 9, wherein computing an equivalent fracture from a plurality of fault segments comprises computing an equivalent permeability (511 ) Keq of the fault segments, and generating an equivalent fracture (512) having geometrical parameters inferred from geometrical parameters of the core zone, and having an assigned permeability inferred from the equivalent permeability.

11. 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 (1 ).

12. A non-transitory computer-readable storage having stored thereon code instructions which, when executed by a computer (1 ), cause said computer to implement the method according to any of the preceding claims.

13. A computer (1 ), configured for implementing the method according to any claims 1 - 10.

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