Patent Application
20200096671
When an oil/gas reservoir is exploited, the original in-situ pressure in the reservoir may be altered. Production, for example, can lead to a decrease in the in-situ pressure, which can in turn lead to the deformation of the rock inside depleted areas within the reservoir and beyond. As the rock deforms, the state of stress can change across the reservoir and, in response, the natural fractures present in the rock can potentially close. For a reservoir where the hydrocarbon flow is mainly through the natural fractures, this could result in a decrease of permeability and secondary porosity, which may affect production.
In reservoir simulation, the permeability, porosity, and other properties of rock in a reservoir can be used to determine production levels. Thus, effectively and efficiently accounting for changes in permeability, porosity, etc. due to simulated production in a reservoir models can improve, for example, simulation accuracy and efficiency.
Embodiments of the disclosure may provide a method modeling a subterranean volume, the method including obtaining data representing one or more physical characteristics of the subterranean volume, and generating a reservoir model of the subterranean volume using the data. The geomechanical model represents one or more geomechanical characteristics of the subterranean volume. The method also includes calculating strains, stresses, or both resulting from pressure changes in the subterranean volume using the geomechanical model, determining one or more local correlations between pressure changes and changes in permeability, porosity, or both in the subterranean volume using the calculated strains and stresses, generating one or more compaction tables for the subterranean volume using the local correlations, calculating pressure changes in the subterranean volume by simulating fluid flow in the subterranean volume using a reservoir model, and modifying the reservoir model using the one or more compaction tables and the calculated pressure changes.
In some embodiments, the compaction tables relate pressure to porosity and/or permeability in individual cells or groups of cells in the reservoir model of the subterranean volume.
In some embodiments, the one or more local correlations are specified for individual cells of the subterranean volume in the geomechanical model, the reservoir model, or both.
In some embodiments, the method also includes again simulating fluid flow in the subterranean volume using the modified reservoir model.
In some embodiments, the data is collected using one or more physical devices positioned in a well or on a surface proximal to the subterranean volume.
In some embodiments, the one or more local correlations represent a relationship between pressure depletion, normal strain (ϵn), and shear strain (ϵs) in the subterranean volume.
In some embodiments, determining the one or more local correlations includes calculating the derivatives of strain verses pressure using the formula: ϵndot=ϵn/Dp and ϵsdot=ϵs/Dp, where Dp is pressure change, and wherein ϵndot and ϵsdot are the slopes of the normal strain and shear strain, respectively, over pressure.
In some embodiments, determining the one or more local correlations further comprises calculating normal strain and the shear strain of fractures using the formula: ϵn=ϵndot(P-Po) and ϵs=ϵsdot(P-Po), where P is pressure and Po is an initial pressure for which the apertures of the fractures are known.
In some embodiments, determining the one or more local correlations further comprises predicting changes in pressure using the formula: Δa(P)=f(ϵndot)(P-Po)+g(ϵsdot)(P-Po), where f and g are functions relating changes in the normal strain and the shear strain to the changes in aperture.
In some embodiments, predicting the changes in aperture comprises predicting changes in pressure depletion using the formula: Δa(Dp)=sDp (ϵndot*ϵn+theta(phi)*ϵsdot*ϵs), where s is a characteristic spacing of discontinuities, phi is the dilation angle, and theta(phi) is a function that depends on cumulated strain and describes an effective dilation of one or more fractures.
In some embodiments, computing the permeability changes comprises employing a cubic law for permeability-aperture in planar fractures.
Embodiments of the disclosure may further provide a non-transitory computer-readable medium storing instructions that, when executed by at least one processor of a computing system, cause the computing system to perform operations. The operations include obtaining data representing one or more physical characteristics of a subterranean volume, and generating a geomechanical model of the subterranean volume using the data. The geomechanical model represents one or more geomechanical characteristics of the subterranean volume and one or more fluid flow characteristics of the subterranean volume. The operations also include calculating strains, stresses, or both resulting from pressure changes in the subterranean volume using the reservoir model, determining one or more local correlations between pressure changes and changes in permeability, porosity, or both in the subterranean volume using the calculated strains and stresses, generating one or more compaction tables for the subterranean volume using the local correlations, calculating pressure changes in the subterranean volume by simulating fluid flow in the subterranean volume using a reservoir model, and modifying the reservoir model using the one or more compaction tables and the calculated pressure changes.
Embodiments of the disclosure may further provide a computing system including one or more processors, and a memory system comprising one or more non-transitory computer-readable media storing instructions that, when executed by at least one of the one or more processors, cause the computing system to perform operations. The operations include obtaining data representing one or more physical characteristics of a subterranean volume, generating a geomechanical model of the subterranean volume using the data. The geomechanical model represents one or more geomechanical characteristics of the subterranean volume. The operations also include calculating strains, stresses, or both resulting from pressure changes in the subterranean volume using the reservoir model, determining one or more local correlations between pressure changes and changes in permeability, porosity, or both in the subterranean volume using the calculated strains and stresses, generating one or more compaction tables for the subterranean volume using the local correlations, calculating pressure changes in the subterranean volume by simulating fluid flow in the subterranean volume using a reservoir model, and modifying the reservoir model using the one or more compaction tables and the calculated pressure changes.
The foregoing summary is provided merely to introduce some of the aspects of the present disclosure and should not be considered limiting or exhaustive.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and together with the description, serve to explain the principles of the present teachings.
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawing and figure. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.
The terminology used in the description of the invention herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof Further, as used herein, the term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in response to detecting,” depending on the context.
In the example of
In an example embodiment, the simulation component 120 may rely on entities 122. Entities 122 may include earth entities or geological objects such as wells, surfaces, bodies, reservoirs, etc. In the system 100, the entities 122 can include virtual representations of actual physical entities that are reconstructed for purposes of simulation. The entities 122 may include entities based on data acquired via sensing, observation, etc. (e.g., the seismic data 112 and other information 114). An entity may be characterized by one or more properties (e.g., a geometrical pillar grid entity of an earth model may be characterized by a porosity property). Such properties may represent one or more measurements (e.g., acquired data), calculations, etc.
In an example embodiment, the simulation component 120 may operate in conjunction with a software framework such as an object-based framework. In such a framework, entities may include entities based on pre-defined classes to facilitate modeling and simulation. A commercially available example of an object-based framework is the MICROSOFT®.NET® framework (Redmond, Wash.), which provides a set of extensible object classes. In the .NET® framework, an object class encapsulates a module of reusable code and associated data structures. Object classes can be used to instantiate object instances for use in by a program, script, etc. For example, borehole classes may define objects for representing boreholes based on well data.
In the example of
As an example, the simulation component 120 may include one or more features of a simulator such as the ECLIPSE™ reservoir simulator (Schlumberger Limited, Houston Tex.), the INTERSECT™ reservoir simulator Schlumberger Limited, Houston Tex.), etc. As an example, a simulation component, a simulator, etc. may include features to implement one or more meshless techniques (e.g., to solve one or more equations, etc.). As an example, a reservoir or reservoirs may be simulated with respect to one or more enhanced recovery techniques (e.g., consider a thermal process such as SAGD, etc.).
In an example embodiment, the management components 110 may include features of a commercially available framework such as the PETREL® seismic to simulation software framework (Schlumberger Limited, Houston, Tex.). The PETREL® framework provides components that allow for optimization of exploration and development operations. The PETREL® framework includes seismic to simulation software components that can output information for use in increasing reservoir performance, for example, by improving asset team productivity. Through use of such a framework, various professionals (e.g., geophysicists, geologists, and reservoir engineers) can develop collaborative workflows and integrate operations to streamline processes. Such a framework may be considered an application and may be considered a data-driven application (e.g., where data is input for purposes of modeling, simulating, etc.).
In an example embodiment, various aspects of the management components 110 may include add-ons or plug-ins that operate according to specifications of a framework environment. For example, a commercially available framework environment marketed as the OCEAN® framework environment (Schlumberger Limited, Houston, Tex.) allows for integration of add-ons (or plug-ins) into a PETREL® framework workflow, The OCEAN® framework environment leverages .NET® tools (Microsoft Corporation, Redmond, Wash.) and offers stable, user-friendly interfaces for efficient development, In an example embodiment, various components may be implemented as add-ons (or plug-ins) that conform to and operate according to specifications of a framework environment (e.g., according to application programming interface (API) specifications, etc.
As an example, a framework may include features for implementing one or more mesh generation techniques. For example, a framework may include an input component for receipt of information from interpretation of seismic data, one or more attributes based at least in part on seismic data, log data, image data, etc. Such a framework may include a mesh generation component that processes input information, optionally in conjunction with other information, to generate a mesh.
In the example of
As an example, the domain objects 182 can include entity objects, property objects and optionally other objects. Entity objects may be used to geometrically represent wells, surfaces, bodies, reservoirs, etc., while property objects may be used to provide property values as well as data versions and display parameters. For example, an entity object may represent a well where a property object provides log information as well as version information and display information (e.g., to display the well as part of a model).
In the example of
In the example of
As mentioned, the system 100 may be used to perform one or more workflows. A workflow may be a process that includes a number of worksteps. A workstep may operate on data, for example, to create new data, to update existing data, etc. As an example, a may operate on one or more inputs and create one or more results, for example, based on one or more algorithms. As an example, a system may include a workflow editor for creation, editing, executing, etc. of a workflow. In such an example, the workflow editor may provide for selection of one or more pre-defined worksteps, one or more customized worksteps, etc. As an example, a workflow may be a workflow implementable in the PETREL® software, for example, that operates on seismic data, seismic attribute(s), etc. As an example, a workflow may be a process implementable in the OCEAN® framework. As an example, a workflow may include one or more worksteps that access a module such as a plug-in (e.g., external executable code, etc.).
In numerical modeling of flow and hydrocarbon recovery there are several options for accounting or not accounting for potential changes in permeability rock porosity, and other properties during production. For example, in a simple approximation, flow and production in the reservoir can be modeled without accounting for potential changes in the permeability of the fractured rock during production. Namely, hydrocarbon production and pressure changes in the reservoir are estimated on the basis of the initial hydraulic properties of the reservoir rock (e.g., porosity, saturations, and permeability) and operational parameters, such as bottom-hole pressure controls. Within this approach, fractures opening/closure during production may be disregarded. This approach can be efficient in terms of time and computational requirements but neglects the potential effects of pressure drawdown on future production.
As another example, a fully two-way coupled process can be modeled. Here, changes in pressure due to production can be first estimated by a reservoir model. These changes can then be fed to a geomechanics calculation in which the changes in stress and the rock deformation are estimated. Such information can then be used to estimate the opening/closure of the natural fractures and its impact on the local pore volume and permeability. The information derived from the geomechanics calculation can then be fed back to the reservoir model to compute a new state of pressures and produced volumes while accounting for the permeability/porosity changes in a previous step. Such an approach may be more accurate than the simple approximation, but it may also be more computationally expensive than the simple approximation because the geomechanics calculations are added on top of the reservoir flow ones. The skill set to execute the workflow is also higher since it involves the coupling of a numerical model of the reservoir flow and its geomechanical characteristics, which are typically two different domains of knowledge.
Here, the solutions depart from an in-situ condition of stress, pressure, permeability, saturations, and porosities. The reservoir model updates the hydraulic variables on the basis of the input values and the geomechanics calculation updates the rest of the parameters including the stress state, the deformation of the rock, and the conductivity of the natural fractures. The new state of parameters, which include an updated porosity and permeability, can then be consumed by the reservoir calculation, thus advancing the solutions in time.
In between the two options mentioned above, there is also the possibility of a pseudo-coupling. Here, the potential opening/closure of the natural fractures and its impact on the reservoir permeability can be fed to the reservoir model at each stage, just as in the two-way coupled approach. However, in this case, there may not be a geomechanics calculation involved and, instead, empirical correlations relating pressure changes and permeability, named “Compaction Tables,” can be used. This method may be economical in terms of computational resources used but may rely on an appropriate choice of the correlations relating pressure changes to permeability changes. A drawback of this approach is that the adequate compaction tables to use are not known a priori and empirical correlations, intuition criteria, and operator criteria prevail in the construction and testing of the pressure-permeability correlations used in the modeling.
Embodiments described herein extend the pseudo-coupling approach described above by allowing a physics-based selection of the compaction tables. Embodiments can be utilized without further expertise and with relatively little extra computational power and time.
The methodology proposed herein can start with a numerical representation of the subsurface in terms of its mechanical properties and distribution of fractures, e.g., a geomechanical model. The mechanical properties may include the Young's modulus and Poisson's ratio or any combination of the elastic properties of materials that can completely define its elastic response to applied loads. These properties can be derived from log data, seismic inversion or lab tests. The mechanical properties might also include strength properties such as the compressional and shear strength of the rock, friction angle, etc. These properties may be derived from measurements taken, or directly measured, using downhole tools, surface measurement devices (e.g., geophones), and/or the like.
The method can also use an initial numerical representation of the natural fractures in the rock. This may be derived from statistical Discrete Fracture Network Models (DFN), well log imagery, or forward modeling, among other techniques. A model for the stiffness of the fractures or the stiffness of the fractured rock can also be used together with the strength properties of the discontinuities, such as their friction angle, and frictional strength coefficient.
The response to pressure changes of a model rock, described by the aforementioned parameters, is then evaluated. For this purpose, the method can involve computing in three dimensions (3D) the strains and stresses resulting from pressure changes in the model rock. In an embodiment, the pressure may be assumed to decrease (depletion) evenly across the reservoir from an initial step with a uniform pressure distribution. The 3D solutions for the stress and strains are obtained for the prescribed change in pressure.
Having the solutions for the full strain tensor in 3D due to the prescribed uniform change in pressure ΔP, a local correlation can be obtained across the model between pressure depletion and induced changes in permeability and porosity. Such results can be gathered in the form of a correlation among the three quantities.
The proposed method may directly capture the heterogeneities in the distribution of properties or fracture density in the geomechanics calculation, which may produce compaction tables for different regions across the reservoir. The obtained correlations can then be used in the schema shown in
In particular, as shown in
At stage 402, the fluid flow in the subterranean volume may be simulated for a first time step, resulting in the computation of volumes of fluid (e.g., hydrocarbons) produced from the reservoir, pressure changes in the reservoir, and/or saturation changes in the subterranean volume.
At stage 403, the compaction tables may be generated via geomechanical calculations using a geomechanical model, as will be described in greater detail below. In general, however, reservoir conditions may be employed along with pressure history in order to calculate a correlation between pressure, porosity, and permeability, which may be organized as a compaction table. The compaction table may represent the degree to which fractures can be expected to close (changing the porosity and/or permeability) in response to changing pressure.
At stage 404, the compaction tables may be fed to the reservoir model, and used to change the reservoir model. The changing porosity and/or permeability (geomechanical properties) may affect the rate at which fluid flows in the subterranean volume. Accordingly, at stage 406, another simulation of fluid flow may be conducted, e.g., for a second time step, which may take into consideration the changed geomechanical properties by using the reservoir model that is modified according to the compaction tables. This process may repeat, with the fluid flow model being modified each time using the same (or potentially updated) compaction tables, thereby accounting for the geomechanical changes that occur during production potentially without having to run a geomechanical calculation for the subterranean volume for each time step.
In some embodiments, slopes of the relationships for normal and shear strain may be generally valid for any change in pressure in the reservoir (linear response). Hence, in 510, the normal and shear strains of the fractures can be computed for any pressure P as ϵn=ϵndot(P-Po) and ϵs=ϵsdot(P-Po), where Po is an initial pressure for which the apertures of the fractures are known.
Continuing in 510, a local correlation can be obtained and the derivatives of the strain verses pressure can be computed. Having the solutions for the full strain tensor in 3D due to the prescribed change in pressure ΔP, the local correlation can be obtained across the model between pressure depletion, normal strain (ϵn), and shear strain (ϵs) of the discontinuities ϵn, ϵs across the model. This information can then be used to compute the derivatives of the strain versus pressure as: ϵndot=ϵn/Dp and ϵsdot=ϵs/Dp for the given pressure drop, where Dp is pressure change.
In 520, the ϵndot and ϵsdot slopes can be computed. The aforementioned slopes ϵndot and ϵsdot may be local. For example, they may vary across the reservoir depending on the local characteristics of the rock, the density and orientation of the fractures and their relative compliances. In geocellular models, these slopes can be computed for each cell of the model. These slopes can also capture grid dependencies when the solutions were obtained by numerical methods in geo-cellular models.
In 530, the changes in aperture Δa can be predicted. Changes of the fractures across the model for any change in pressure, Δa(P)=f(ϵndot)(P-Po)+g(ϵsdot)(P-Po) can be computed, where f and g are functions relating the changes in normal and shear strains to the changes in aperture. As an example, a possible combination of such functions is: Δa(Dp)=sDp (ϵndot*ϵn+theta(phi)*ϵsdot*ϵs), where s is the characteristic spacing of the discontinuities, phi is the dilation angle, and theta(phi) is a function that can depend on the cumulated strain ϵs and describes the effective dilation of the fractures. In such a way, the second term might tend to zero if the fractures are opening (pressure increases) and might take finite values when shearing occurs when enough normal strain has been cumulated to bring the fracture surfaces closer than a prescribed threshold. Thus, the presence of asperities can be accounted for.
In 540, permeability changes can be computed from the changes in aperture for any pressure change Dp, while assuming any suitable model linking aperture-permeability. An example of such model can be the cubic law for permeability-aperture in planar fractures K=(â2)/12, yet the ultimate form of the model of permeability-aperture can vary in different embodiments.
In 550, the compaction tables can be generated. The permeability changes computed in 540 can be used as compaction tables, as derived from numerical modeling, accounting for the particular characteristics of the rock and the in-situ fractures. The compaction tables can be used in reservoir simulation to efficiently and dynamically determine permeability and porosity of rock in the reservoir during production and, thus, production levels can be determined with greater accuracy.
In some embodiments, the compaction tables can be used in simulating “tight” reservoirs, where pressure depletion is common and permeabilities can be due to natural and induced fractures.
The method may include calculating strains and stresses resulting from the pressure changes in the subterranean volume using the model, as at 565, as described above. The method may then proceed to determining local correlations between pressure depletion and induced changes in permeability and porosity using the computed strains and stresses, as at 570, as described above. The method may also include generating compaction table using the model and the correlations, as at 575.
As graphically depicted in
The method may also include modifying the reservoir model using the compaction tables and the calculated pressure changes, as at 585. This process of calculating pressure changes (e.g., using the fluid flow simulation) and then modifying the reservoir model based on the pressure changes correlated to the permeability/porosity in the compaction tables may then be repeated, e.g., using the same compaction tables. Thus, the method may provide for a hybrid technique of simulating fluid flow in a reservoir, which may efficiently link the geomechanical and reservoir fluid flow models. In particular, the fluid flow simulation may be made quicker by avoiding recalculating the geomechanical changes induced by pressure changes, while accuracy is enhanced by considering geomechanical changes resulting from changes in reservoir pressure as provided in the calculated compaction tables. Moreover, accuracy is enhanced by, in some cases, avoiding referring to extrinsic source of information, despite the geomechanical changes being a priori unknown.
In some embodiments, the methods of the present disclosure may be executed by a computing system.
A processor may include a microprocessor, microcontroller, processor module or subsystem, programmable integrated circuit, programmable gate array, or another control or computing device.
The storage media 806 may be implemented as one or more computer-readable or machine-readable storage media. Note that while in the example embodiment of
In some embodiments, computing system 800 contains one or more reservoir simulation module(s) 808. In the example of computing system 800, computer system 801A includes the reservoir simulation module 808. In some embodiments, a single reservoir simulation module may be used to perform some aspects of one or more embodiments of the methods disclosed herein. In other embodiments, a plurality of reservoir simulation modules may be used to perform some aspects of methods herein.
It should be appreciated that computing system 800 is one example of a computing system, and that computing system 800 may have more or fewer components than shown, may combine additional components not depicted in the example embodiment of
Further, the steps in the processing methods described herein may be implemented by running one or more functional modules in information processing apparatus such as general purpose processors or application specific chips, such as ASICs, FPGAs, PLDs, or other appropriate devices. These modules, combinations of these modules, and/or their combination with general hardware are included in various embodiments.
The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. Moreover, the order in which the elements of the methods are described herein is illustrative and the order may be re-arranged, and/or two or more elements may occur simultaneously. The embodiments were chosen and described in order to explain the principals of the invention and its practical applications, to thereby enable others skilled in the art to utilize the described embodiments with various modifications as are suited to the particular use contemplated.
This application claims priority to U.S. Provisional Patent Application having Ser. No. 62/428,927, which was filed on Dec. 1, 2016, and is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/064291 | 12/1/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62428927 | Dec 2016 | US |
