A method for modeling petrophysical elastic parameters of a rock containing intersecting inclined fractures

Abstract

The present application relates to a kind of rock physical elastic parameter modeling method containing intersecting inclined fracture, comprising: obtaining the dry rock elastic coefficient matrix of shale oil reservoir;Obtain the dry rock elastic coefficient matrix of shale oil reservoir containing multiple groups of intersecting inclined fracture;Obtain the saturated rock elastic coefficient matrix of shale oil reservoir containing multiple groups of intersecting inclined fracture;According to the dry rock elastic coefficient matrix of shale oil reservoir, the dry rock elastic coefficient matrix of shale oil reservoir containing multiple groups of intersecting inclined fracture and the saturated rock elastic coefficient matrix of shale oil reservoir containing multiple groups of intersecting inclined fracture, the relationship between the longitudinal wave velocity of shale oil reservoir, the relationship between the shear wave velocity and shale porosity, fracture density, fracture dip, water saturation is established.This method provides a basic tool for the calculation of seismic elastic response of low mature shale oil reservoir containing intersecting inclined fracture, and provides a meaningful theoretical basis for subsequent shale oil seismic exploration and development.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration rock physics, specifically to a method for modeling elastic parameters of low-maturity shale oil reservoirs containing intersecting diagonal fractures. Background Technology

[0002] Shale is generally a sedimentary rock with a layered structure, composed of clay minerals, clastic minerals, and organic matter. Clay minerals, including kaolinite and montmorillonite, are the main components of shale; clastic minerals include quartz and feldspar; and organic matter includes immature organic matter and hydrocarbons. Shale has relatively low porosity and permeability, with porosity typically ranging from 2-15% and permeability generally less than 1 mD, making it an unconventional reservoir. However, due to the presence of high-angle fractures intersecting bedding planes, faults, fractures parallel to bedding planes, early compaction fractures, and fractures associated with nodules, shale reservoirs often produce more hydrocarbons than expected. These fractures serve as both effective storage spaces for hydrocarbons and important pathways for migration, significantly improving production efficiency. Modeling the elastic parameters of shale reservoirs containing these natural fractures can provide a theoretical basis and interpretative context for seismic detection of shale fractures.

[0003] Current elastic modeling of shale oil reservoirs mainly employs equivalent medium models such as SCA and DEM to model the elastic parameters of the rock skeleton formed by different minerals, clays, and pores. Then, Gassmann fluid substitution theory is used for fluid effect modeling. However, the maturity of shale organic matter and the cementation relationship of mineral particles are insufficiently considered. Shale is a special source rock where oil and gas generation and storage originate from the same source; therefore, the maturity of organic matter has a significant impact on the physical properties of shale. At low maturity, shale pores mainly contain kerogen, bitumen, and a small amount of gas. When kerogen and bitumen further decompose to form oil and gas, shale reaches full maturity. Finally, due to continued organic matter decomposition, shale contains only gas and very little residual solids, reaching an over-mature stage. Therefore, it is necessary to fully consider the arrangement and cementation relationship between shale components according to different maturity levels. Furthermore, the influence of fractures in shale reservoirs on elastic parameters often only considers vertical or horizontal fractures, using anisotropic DEM models or Hudson models. These assumptions are too ideal and simplistic; therefore, the influence of multiple sets of fractures with different dip angles needs to be considered. Summary of the Invention

[0004] To address the aforementioned issues, this invention is primarily used for the direct calculation of the elastic parameters of fractured, low-maturity shale oil reservoirs, determining the influence of parameters such as organic matter content, porosity, fluid type, fracture dip angle, and fracture density on the elastic parameters.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for modeling the physical elastic parameters of rocks containing intersecting inclined cracks, comprising:

[0007] Obtain the dry rock elastic coefficient matrix of shale oil reservoirs;

[0008] Based on the logging data and fracture dip angle information of the actual work area, the elastic coefficient matrix of shale reservoirs containing a single set of inclined fracture media is calculated by inputting the single set of inclined fracture media rock physics theoretical models. Furthermore, based on the logging data and fracture dip angle information of the actual work area, the elastic coefficient matrix of shale reservoirs containing multiple sets of inclined fracture media is calculated by inputting the two or more sets of intersecting inclined fracture media rock physics theoretical models. This yields the dry rock elastic coefficient matrix of shale oil reservoirs containing multiple sets of intersecting inclined fractures.

[0009] Fluid substitution was performed using the anisotropic Gassmann formula to obtain the saturated rock elastic coefficient matrix containing multiple sets of intersecting inclined fractured shale oil reservoirs.

[0010] Based on the dry rock elastic coefficient matrix of shale oil reservoirs, the dry rock elastic coefficient matrix of shale oil reservoirs containing multiple sets of intersecting inclined fractures, and the saturated rock elastic coefficient matrix of shale oil reservoirs containing multiple sets of intersecting inclined fractures, the relationship between P-wave velocity, S-wave velocity and shale porosity, fracture density, fracture dip angle, and water saturation of shale oil reservoirs is established.

[0011] The dry rock elastic coefficient matrix of shale oil reservoirs includes:

[0012] The volume fraction, porosity, fluid type, and saturation of the constituent minerals in shale are obtained through laboratory analysis or well logging interpretation.

[0013] The equivalent elastic modulus of the brittle mineral mixture in the shale matrix was calculated using the Hill average modulus model.

[0014] By using an anisotropic differential equivalent medium model, clay pores are added to the matrix minerals to obtain a clay-containing rock skeleton. A physical model of the rock skeleton is established, and the equivalent elastic stiffness tensor of the rock skeleton is calculated.

[0015] By incorporating organic pores into a clay-containing rock skeleton using an anisotropic differential equivalent medium model, a dry shale skeleton with a certain amount of porosity is obtained. A rock physics model of the dry shale skeleton is then established, and the equivalent elastic stiffness tensor of the dry shale skeleton is calculated.

[0016] The Hill average model is expressed as follows:

[0017]

[0018] in:

[0019] V iIt is the volume component of the i-th component;

[0020] M i It is the modulus of the i-th component;

[0021] M VRH This is the average modulus of Hill.

[0022] The expression for the anisotropic differential equivalent medium model is as follows:

[0023]

[0024] in:

[0025] C DEM (v) is the medium stiffness tensor calculated using the DEM model;

[0026] v represents the volume content of the inclusions added to the matrix;

[0027] C i It is the stiffness tensor of inclusions added to the matrix;

[0028] I represents the unit stiffness tensor;

[0029] It is a stiffness tensor related to the shape of the contents.

[0030] The calculation of the elastic coefficient matrix of shale reservoirs containing a single set of inclined fractures includes:

[0031] C eff =(M backgr ound +Z) -1 (3)

[0032]

[0033] in:

[0034] Z N —The normal flexibility of the crack;

[0035] Z T —Tangential compliance of the crack;

[0036] Z—Crack compliance matrix;

[0037] M background It is the compliance matrix of the background medium;

[0038] θ is the angle between the crack surface and the horizontal plane.

[0039] The background medium is a shale dry skeleton.

[0040] The expressions for the normal and tangential compliance of the crack are:

[0041]

[0042] in:

[0043] λ and μ are the Lamé coefficients of the background medium;

[0044] e is the crack density.

[0045] The calculation of the elastic coefficient matrix of shale reservoirs with multiple sets of inclined fractures includes:

[0046] C eff =(M backg round +Z1+Z2+L+Z i +L+Z N ) -1 (6)

[0047]

[0048] in:

[0049] i represents the i-th group of oriented cracks with the same inclination angle;

[0050] θ i It is the angle between the crack surface and the horizontal plane.

[0051] Z N —The normal flexibility of the crack;

[0052] Z T —Tangential compliance of the crack;

[0053] Z—Crack compliance matrix;

[0054] M background It is the flexibility matrix of the background medium.

[0055] The expressions for the normal and tangential compliance of the crack are:

[0056]

[0057] in:

[0058] λ and μ are the Lamé coefficients of the background medium;

[0059] e is the crack density.

[0060] The saturated rock elastic coefficient matrix of shale oil reservoirs containing multiple sets of intersecting inclined fractures was obtained, including:

[0061]

[0062] in:

[0063]

[0064]

[0065]

[0066]

[0067] It is expressed as the pore space modulus of anisotropic media;

[0068] K * Represents the generalized bulk modulus of dry rock;

[0069] K0 represents the bulk modulus of the rock matrix;

[0070] K f The bulk modulus of a pore fluid;

[0071] φ represents the porosity of the background skeleton;

[0072] β m and β n is a weighting coefficient, representing the relationship between the bedrock modulus and the dry rock stiffness tensor.

[0073] The present invention has the following advantages due to the adoption of the above technical solutions:

[0074] Based on the fractured shale oil reservoir model and its quantitative calculations, the relationships between P-wave velocity, S-wave velocity, and shale porosity, fracture density, fracture dip angle, and water saturation in shale oil reservoirs were established. The results show that the influence of shale porosity on P-wave and S-wave velocities is systematic; increased porosity leads to a decrease in velocity, but it does not fundamentally change the trend of velocity variation with fracture density, fracture dip angle, and water saturation. Fracture dip angle has a significant impact on P-wave and S-wave velocities; the smaller the fracture dip angle (closer to the horizontal direction), the faster the P-wave and S-wave velocities decrease with fracture density. Compared to SH waves, the velocity decrease trend of SV waves is less affected by fracture dip angle. Water saturation has the least impact on P-wave and S-wave velocities; due to the small difference in oil and water bulk moduli, the resulting velocity difference is relatively small. Shale porosity, fracture dip angle, and fracture density are the main controlling factors for P-wave and S-wave velocities in shale oil reservoirs, but distinguishing between oil and water based on velocity or elastic parameters is difficult and is influenced by fracture density. This method provides a fundamental tool for calculating the seismic elastic response of low-maturity shale oil reservoirs with intersecting diagonal fractures, and provides a meaningful theoretical basis for subsequent seismic exploration and development of shale oil. Attached Figure Description

[0075] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0076] Figure 1 yes Figure 1 The flowchart for petrographic modeling of low-maturity shale containing intersecting diagonal fractures is shown.

[0077] Figure 2 A schematic diagram of a medium containing a set of inclined cracks is shown;

[0078] Figures 3A-3F The graph shows the trend of shale velocity with fracture density under different porosity conditions. The results show that the effect of shale porosity on P-wave and S-wave velocities is systematic. Increased porosity reduces velocity, but does not change the trend of velocity with fracture density.

[0079] Figures 4A-4C The graph shows the trend of shale velocity with fracture density under different fracture dip angles. The results show that the fracture dip angle has a significant impact on the P-wave and S-wave velocities. The smaller the fracture dip angle, the faster the P-wave and S-wave velocities decrease with fracture density. Compared with SH waves, the SV wave velocity decrease trend is less affected by the fracture dip angle.

[0080] Figures 5A-5C The graph shows the trend of shale velocity variation with fracture density under different water saturation conditions. The results indicate that the velocity difference is small due to the small difference in oil and water bulk modulus. Detailed Implementation

[0081] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0082] This invention belongs to the field of geophysical exploration petrology. Specifically, it applies the equivalent medium theory and the anisotropic Gassmann fluid substitution theory to establish an elastic parameter expression model for shale oil reservoirs with oblique fractures, in order to solve the problem of sweet spot prediction and evaluation in practical engineering. This invention can be used to solve the problem of sweet spot parameter characterization in shale formations with different fracture angles and densities, different organic matter contents, and different hydrocarbon saturations using petrological modeling methods.

[0083] This patent was invented to improve the accuracy of shale prediction and fracture prediction, to make the rock physics model of shale oil reservoirs more consistent with the actual reservoir conditions, and to improve the quality and efficiency of forward and inverse seismic data modeling.

[0084] This invention is primarily used for the direct calculation of elastic parameters in fractured, low-maturity shale oil reservoirs, determining the influence of parameters such as organic matter content, porosity, fluid type, fracture dip angle, and fracture density on these elastic parameters. Through subsequent seismic forward modeling, a physical correlation can be established between shale reservoir parameters (organic matter content, porosity, fracture parameters, and fluid type) and seismic response, providing a theoretical basis for seismic exploration of shale oil reservoirs. This promotes the quantification of seismic interpretation and provides strong scientific evidence for reducing the risks of shale oil exploration and development, thus possessing significant application value.

[0085] This invention designs a method for modeling the physical elastic parameters of rocks containing intersecting inclined cracks, the main steps of which include:

[0086] 1. Calculation of the dry rock elastic coefficient matrix of shale oil reservoirs

[0087] 1-1. The volume fraction, porosity, fluid type, and saturation of shale constituent minerals are obtained through laboratory analysis or well logging interpretation.

[0088] 1-2. Calculate the equivalent elastic modulus of the brittle mineral mixture in the shale matrix using the Hill model.

[0089] 1-3. Using an anisotropic differential equivalent medium model, clay pores are added to the matrix minerals to obtain a clay-containing rock skeleton. A physical model of the rock skeleton is established, and the equivalent elastic stiffness tensor of the rock skeleton is calculated.

[0090] 1-4. Using an anisotropic differential equivalent medium model, organic pores are added to the clay-containing rock skeleton to obtain a dry shale skeleton with a certain amount of porosity. A rock physics model of the dry shale skeleton is established, and the equivalent elastic stiffness tensor of the dry shale skeleton is calculated.

[0091] In detail, for steps 1-2: the Hill average modulus is used to calculate the modulus of the matrix mineral mixture. The Hill average modulus formula is as follows:

[0092]

[0093] Where V i M is the volume component of the i-th component. i M is the modulus of the i-th component. VRH This is the average modulus of Hill.

[0094] In detail, for steps 1-3 and 1-4, the anisotropic differential equivalent medium model is used. The expression of the anisotropic differential equivalent medium model is as follows:

[0095]

[0096] Where C DEM (v) is the medium stiffness tensor calculated using the DEM model, where v is the volume fraction of inclusions added to the matrix, and C i It is the stiffness tensor of the inclusions added to the matrix, where I is the unit stiffness tensor. It is a stiffness tensor related to the shape of the contents.

[0097] 2. Calculation of the elastic coefficient matrix of dry rock in shale oil reservoirs with multiple sets of intersecting inclined fractures

[0098] Based on the logging data and fracture dip angle information of the actual work area, the elastic coefficient matrix of the shale reservoir containing a single set of inclined fractures is calculated by inputting the established rock physics theoretical model of the single-set inclined fracture medium. The calculation formula is as follows:

[0099] C eff =(M background +Z) -1 (3)

[0100]

[0101] Where: Z N —The normal compliance of the crack, Z T — Tangential compliance of the crack, Z — Crack compliance matrix, M background It is the compliance matrix of the background medium (shale skeleton). θ is the angle (i.e., dip angle) between the fracture surface and the horizontal plane.

[0102] The expressions for the normal and tangential compliance of the crack are:

[0103]

[0104] Where: λ and μ are the Lamé coefficients of the background medium (shale skeleton), and e is the fracture density.

[0105] Based on the logging data and fracture dip angle information of the actual work area, the elastic coefficient matrix of the shale reservoir containing multiple sets of inclined fractures is calculated by inputting the established rock physics theoretical models of two or more sets of intersecting inclined fracture media.

[0106] The calculation formula is as follows:

[0107] C eff =(M ba ckgrou nd+Z1+Z2+L+Z i +L+Z N ) -1 (6)

[0108]

[0109] Where: i represents the i-th group of oriented cracks with the same inclination angle. θ i This is the angle (i.e., dip angle) between the crack surface and the horizontal plane. The expressions for the normal and tangential compliance of a crack are:

[0110]

[0111] 3. Calculation of the elastic coefficient matrix of saturated rock in shale oil reservoirs with multiple sets of intersecting inclined fractures

[0112] The following anisotropic Gassmann formula was used for fluid substitution to calculate the saturated rock elastic coefficient matrix of shale oil reservoirs containing multiple sets of intersecting inclined fractures:

[0113]

[0114] in:

[0115]

[0116]

[0117]

[0118]

[0119] K represents the pore space modulus of anisotropic media. * K represents the generalized bulk modulus of dry rock; K0 represents the bulk modulus of the rock matrix; K f The bulk modulus of the porous fluid is represented by φ; the porosity of the background skeleton is represented by β. m and β n is a weighting coefficient, representing the relationship between the bedrock modulus and the dry rock stiffness tensor.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for modeling the physical elastic parameters of rocks containing intersecting inclined cracks, characterized in that, include: Obtain the dry rock elastic coefficient matrix of shale oil reservoirs; Based on the logging data and fracture dip angle information of the actual work area, the elastic coefficient matrix of shale reservoirs containing a single set of inclined fracture media is calculated by inputting the single set of inclined fracture media rock physics theoretical models. Furthermore, based on the logging data and fracture dip angle information of the actual work area, the elastic coefficient matrix of shale reservoirs containing multiple sets of inclined fracture media is calculated by inputting the two or more sets of intersecting inclined fracture media rock physics theoretical models. This yields the dry rock elastic coefficient matrix of shale oil reservoirs containing multiple sets of intersecting inclined fractures. Fluid substitution was performed using the anisotropic Gassmann formula to obtain the saturated rock elastic coefficient matrix containing multiple sets of intersecting inclined fractured shale oil reservoirs. Based on the dry rock elastic coefficient matrix of the shale oil reservoir, the dry rock elastic coefficient matrix of the shale oil reservoir containing multiple sets of intersecting inclined fractures, and the saturated rock elastic coefficient matrix of the shale oil reservoir containing multiple sets of intersecting inclined fractures, the relationship between the P-wave velocity and S-wave velocity of the shale oil reservoir and the shale porosity, fracture density, fracture dip angle, and water saturation is established.

2. The method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 1, characterized in that, The dry rock elastic coefficient matrix of the shale oil reservoir obtained includes: The volume fraction, porosity, fluid type, and saturation of the constituent minerals in shale are obtained through laboratory analysis or well logging interpretation. The equivalent elastic modulus of the brittle mineral mixture in the shale matrix was calculated using the Hill average modulus model. By using an anisotropic differential equivalent medium model, clay pores are added to the matrix minerals to obtain a clay-containing rock skeleton. A physical model of the rock skeleton is established, and the equivalent elastic stiffness tensor of the rock skeleton is calculated. By incorporating organic pores into a clay-containing rock skeleton using an anisotropic differential equivalent medium model, a dry shale skeleton with a certain amount of porosity is obtained. A rock physics model of the dry shale skeleton is then established, and the equivalent elastic stiffness tensor of the dry shale skeleton is calculated.

3. The method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 2, characterized in that, The expression for the Hill average modulus model is as follows: in: V i It is the volume component of the i-th component; M i It is the modulus of the i-th component; M VRH This is the average modulus of Hill.

4. The method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 2, characterized in that, The expression for the anisotropic differential equivalent medium model is as follows: in: C DEM (v) represents the medium stiffness tensor calculated using the DEM model; v represents the volume content of the inclusions added to the matrix; C i For the stiffness tensor of the inclusions added to the matrix; I represents the unit stiffness tensor; This is the stiffness tensor related to the shape of the containing object.

5. The method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 1, characterized in that, The calculation of the elastic coefficient matrix of a shale reservoir containing a single set of inclined fractures includes: C eff =(M background +Z) -1 (3) in: Z N The normal compliance of the crack; Z T The tangential compliance of the crack; Z is the crack compliance matrix; M background The compliance matrix of the background medium; θ is the angle between the crack surface and the horizontal plane.

6. The method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 5, characterized in that, The background medium is a shale skeleton.

7. A method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 6, characterized in that, The expressions for the normal and tangential compliance of the crack are: in: λ and μ are the Lamé coefficients of the background medium; e is the crack density.

8. The method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 1, characterized in that, The calculation of the elastic coefficient matrix of shale reservoirs containing multiple sets of inclined fractures includes: C eff = (M background + Z1 + Z2 + L + Z i + L + Z N ) -1 (6) in: i represents the i-th group of oriented cracks with the same inclination angle; θ i The angle between the crack surface and the horizontal plane; Z Ni The normal compliance of the crack; Z Ti The tangential compliance of the crack; Z i This represents the crack compliance matrix; M background represents the flexibility matrix of the background medium.

9. A method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 8, characterized in that, The expressions for the normal and tangential compliance of the crack are: in: λ and μ are the Lamé coefficients of the background medium; e is the crack density.

10. A method for modeling the physical elastic parameters of rock containing intersecting inclined cracks according to claim 1, characterized in that, The obtained saturated rock elastic coefficient matrix contains multiple sets of intersecting inclined fracture shale oil reservoirs. include: in: The pore space modulus of anisotropic media; K * For generalized dry rock bulk modulus; K0 is the bulk modulus of the rock matrix; K f The bulk modulus of the pore fluid; φ represents the porosity of the background skeleton; β m and β n is a weighting coefficient, representing the relationship between the bedrock modulus and the dry rock stiffness tensor.

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