Lacustrine facies shale oil reservoir fracturing property evaluation method based on brittleness and fracture toughness

Abstract

The invention discloses a method for evaluating the fracturing property of a lacustrine facies shale oil reservoir based on brittleness and fracture toughness, and mainly solves the problem that the fracturing effect is not ideal enough when the fracturing property of the shale oil reservoir is evaluated by purely depending on a brittleness index. The method comprises the following steps: calculating dynamic rock mechanical parameters Poisson's ratio and Young modulus; calculating a static Poisson's ratio and a Young's modulus according to the established dynamic and static conversion model; brittleness indexes calculated by dynamic and static rock elastic mechanical parameters are compared with indoor three-stress experimental data for analysis, and the consistency of the static brittleness index and the experimental data is better; calculating the fracture toughness and the reservoir fracturing index under the confining pressure; and evaluating the fracturing property of the shale oil reservoir through the fracturing property index of the reservoir. According to the shale oil reservoir fracturing evaluation method, the brittleness index and the fracture toughness are comprehensively considered, shale oil reservoir fracturing evaluation is carried out by adopting the fracturing evaluation index, the fracturing effect is improved, and technical support is provided for optimizing the fracturing layer position and effectively formulating a development scheme.

Description

Technical Field

[0001] The invention relates to a method for evaluating the fracturability of a lacustrine shale oil reservoir based on brittleness and fracture toughness, and belongs to the technical field of unconventional oil and gas development. Background Art

[0002] Shale oil reservoirs generally require fracturing to obtain industrial oil flow, so the accuracy of reservoir fracturability evaluation becomes the key to whether shale oil can achieve good development results. At present, the fracturing sections actually selected for domestic shale oil reservoirs are based on the brittleness index as the only reference basis, and this method has a certain reference value. For typical self-generated and self-storage type in-situ residual accumulation shale oil reservoirs, due to their overall saline lake sedimentary environment, the reservoir physical properties are poor, heterogeneity is strong, and the lithology is complex. Simply relying on the brittleness index to evaluate the fracturability of shale oil reservoirs is likely to cause the problem of unsatisfactory fracturing results. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the problem in the background technology that the existing shale oil reservoir fracturing ability is evaluated solely by relying on the brittleness index, resulting in unsatisfactory fracturing effect, and to provide a lacustrine shale oil reservoir fracturing ability evaluation method based on brittleness and fracture toughness. The lacustrine shale oil reservoir fracturing ability evaluation method based on brittleness and fracture toughness comprehensively considers the characteristics of both brittleness index and fracture toughness, adopts the fracturing ability evaluation index to evaluate the fracturing ability of shale oil reservoirs, improves the fracturing effect, and provides technical support for optimizing fracturing layers and effectively formulating development plans.

[0004] The present invention solves the problem through the following technical solution: The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness comprises the following steps:

[0005] Step S101: Based on array acoustic logging data and conventional density logging data, dynamic rock elastic parameters Poisson's ratio, Young's modulus and bulk density are obtained respectively;

[0006] Step S102: establishing a rock elastic mechanics parameter dynamic and static Poisson's ratio and Young's modulus conversion model according to an indoor triaxial stress test, and obtaining the static Poisson's ratio and Young's modulus;

[0007] Step S103: Calculate the brittleness index based on the obtained dynamic and static rock elastic mechanics parameters; compare and analyze the brittleness index calculated from the dynamic and static rock elastic mechanics parameters with the indoor three-stress experimental data, and determine the brittleness index with better consistency with the experimental data as the preferred brittleness index;

[0008] Step S104: using the logging data to obtain the overburden pressure and tensile strength, and calculating the fracture toughness under confining pressure;

[0009] Step S105: Based on the obtained brittleness index and fracture toughness; comprehensively considering the two characteristics of the brittleness index and fracture toughness, obtaining a reservoir fracturing evaluation index through normalized brittleness index and fracture toughness; using the fracturing evaluation index to evaluate the fracturing of shale oil reservoirs.

[0010] Furthermore, the method for obtaining the dynamic rock elasticity parameter Poisson's ratio in step S101 includes:

[0011] Extract P-wave time difference and S-wave time difference through array acoustic logging data;

[0012] The dynamic Poisson's ratio is determined by the relationship between the dynamic rock elastic mechanics parameter Poisson's ratio and the longitudinal wave time difference and the transverse wave time difference;

[0013] And / or, the method for determining the dynamic rock elasticity parameter Young's modulus comprises:

[0014] Extract P-wave time difference and S-wave time difference through array acoustic logging data;

[0015] The bulk density is obtained through conventional density logging data;

[0016] The dynamic Young's modulus is determined by the relationship between the dynamic Young's modulus and the longitudinal wave time difference, the transverse wave time difference and the volume density.

[0017] Furthermore, the relationship between the dynamic Poisson's ratio and the longitudinal wave time difference and the transverse wave time difference is:

[0018]

[0019] Where: V P is the longitudinal wave time difference, μs / ft; V S is the shear wave time difference, μs / ft; υ is the dynamic Poisson's ratio;

[0020] and / or,

[0021] The relationship between dynamic Young's modulus and longitudinal wave time difference, transverse wave time difference and volume density is:

[0022]

[0023] Where: ρ is the volume density, g / cm 3 ; E is the dynamic Young's modulus.

[0024] Furthermore, the method of establishing a rock elasticity parameter dynamic and static Poisson's ratio and Young's modulus conversion model according to an indoor triaxial stress experiment in step S102 includes the following steps:

[0025] By applying different stress and strain conditions to rock samples, the stress state of rock in geological environment is simulated to obtain the static Poisson's ratio and Young's modulus of rock mechanics.

[0026] By measuring the propagation speed of ultrasonic shear and longitudinal waves in rock samples, the dynamic Poisson's ratio and Young's modulus can be obtained through mathematical conversion of shear and longitudinal waves and rock mechanical parameters.

[0027] By fitting the static Poisson's ratio and Young's modulus and the dynamic Poisson's ratio and Young's modulus, the correlation between the static Poisson's ratio and Young's modulus and the dynamic Poisson's ratio and Young's modulus is found; the relationship with the highest correlation coefficient is selected as the conversion model of the static Poisson's ratio and Young's modulus and the dynamic Poisson's ratio and Young's modulus.

[0028] Furthermore, the established rock elastic parameters dynamic and static conversion model is a dynamic and static Poisson's ratio and Young's modulus conversion model:

[0029] υ 静 =a*υ 动 +b;

[0030] E 静 =c*E 动 –d;

[0031] Where: a, b, c, d are the correlation coefficients of dynamic and static conversion respectively.

[0032] Furthermore, in step S103, the brittleness index BI calculated by the dynamic and static rock elastic mechanical parameters is compared and analyzed with the indoor three-stress experimental data to determine that the brittleness index calculated by the static rock elastic mechanical parameters is more consistent with the experimental data, and the brittleness index calculated by the static rock elastic mechanical parameters is preferably used.

[0033] Furthermore, the preferred static rock elastic mechanical parameters are used to calculate the brittleness index, and its expression is:

[0034] B I =(ΔE+Δυ) / 2;

[0035] Where:

[0036] ΔE=(E max -E) / (E max -E min ); Δυ=(υ max -υ) / (υ max -υ min );

[0037] ΔE and Δυ are the normalized Young's modulus and Poisson's ratio, respectively; E max 、E minare the maximum and minimum values ​​of Young's modulus of the reservoir in the research area obtained through statistical analysis; υ max ,υ min are the maximum and minimum values ​​of the reservoir Poisson's ratio in the study area obtained through statistical analysis; E and υ are Young's modulus and Poisson's ratio at a certain depth, respectively.

[0038] Furthermore, the step S104 uses the logging data to calculate the fracture toughness K under confining pressure. IC的 The expression is:

[0039] K IC =0.2176P S +0.0059σ T 3 +0.0923σ T 2 +0.517σ T -0.3322

[0040] Where: P S is the overburden pressure: calculated in discrete integral form, MPa;

[0041] σ T For tensile strength: calculated using empirical formula, MPa;

[0042] and / or,

[0043] The overburden pressure P S The calculation formula is:

[0044]

[0045] Where: g is the acceleration due to gravity, m / s 2 ; h is the burial depth of the formation; ρ(h) is the bulk density of the formation at the burial depth h, g / cm 3 ;

[0046] The tensile strength σ T The calculation formula is:

[0047]

[0048] Where: C0 is the compressive strength;

[0049] The calculation formula of the compressive strength C0 is:

[0050] C0=[0.0026(1-V cl )+0.008V cl ]E

[0051] Where: V cl is the mud content, obtained through conventional gamma logging data.

[0052] Furthermore, the method for obtaining the fracturability evaluation index FI in step S105 includes:

[0053] The normalized brittleness index is obtained by obtaining the brittleness index at a certain depth of the reservoir and the maximum and minimum values ​​of the regional brittleness index; the normalized fracture toughness is obtained by obtaining the fracture toughness at a certain depth of the reservoir and the maximum and minimum values ​​of the regional fracture toughness; the fracturing evaluation index is determined according to the relationship between the normalized brittleness index, the normalized fracture toughness and the fracturing evaluation index.

[0054] Further, the fracturability evaluation index expression is:

[0055] F I =(B In +K IC_n ) / 2;

[0056] Where: B In =(B rit -B rit_min ) / (B rit_max -B rit_min );

[0057] K IC_n =(K IC_max -K IC ) / (K IC_max -K IC_min );

[0058] B rit_max , B rit_min are the maximum and minimum values ​​of the regional brittleness index, respectively;

[0059] K IC_max , K IC_min are the maximum and minimum values ​​of regional fracture toughness, respectively;

[0060] F I K is the fracturing evaluation index; IC is the fracture toughness at a certain depth of the reservoir; K IC_n is the normalized fracture toughness; B rit is the brittleness index at a certain depth of the reservoir, B In is the normalized brittleness index;

[0061] The conclusion of the shale oil reservoir fracturing evaluation using the fracturing evaluation index is: the shale oil reservoir fracturing evaluation is performed by comprehensively considering the two characteristics of brittleness index and fracture toughness; the larger the reservoir fracturing index, the better the fracturing property.

[0062] Compared with the above background technology, the present invention has the following beneficial effects:

[0063] The purpose of the present invention is to provide an accurate and reliable method for evaluating the fracturability of saline lake phase shale oil reservoirs. It solves the problem that the prior art relies solely on the brittleness index to evaluate the fracturability of shale oil reservoirs, resulting in unsatisfactory fracturing effects. Fracture toughness is the main parameter that characterizes the difficulty of reservoir fracturing, and the static elastic parameters can better represent the loading conditions of rocks in petroleum engineering. Combining brittleness and fracture toughness can more accurately and effectively evaluate the fracturability of shale oil reservoirs. Based on the brittleness index calculated by the dynamic and static elastic parameter conversion model and the fracture toughness under confining pressure, the present invention establishes a new method for evaluating the fracturability of saline lake phase shale oil reservoirs, which provides new ideas for the evaluation of the fracturability of shale oil reservoirs, provides a reference basis for the selection of subsequent fracturing layers, and provides technical support for the effective formulation of shale oil reservoir development plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0065] Figure 1 This is a dynamic and static conversion relationship diagram of Poisson's ratio according to an embodiment of the present invention;

[0066] Figure 2 This is a diagram showing the dynamic and static conversion relationship of Young's modulus according to an embodiment of the present invention;

[0067] Figure 3 A comparison chart of the brittleness index calculated by dynamic and static rock mechanical parameters and experimental data in an embodiment of the present invention;

[0068] Figure 4 This is a schematic diagram of the reservoir fracturability evaluation of Well XX2-2 in Example 2 of the present invention. Specific implementation method:

[0069] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0070] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure.

[0071] In addition, those skilled in the art should understand that the drawings are only provided to illustrate the purpose, features and advantages of the present disclosure, and the drawings are not actually drawn to scale.

[0072] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0073] The inventive concept of the disclosed method is: extract the longitudinal and transverse wave time differences through array acoustic logging data, and combine with the density curve to calculate the dynamic rock mechanical parameters Poisson's ratio and Young's modulus respectively. According to the indoor triaxial stress experiment, a dynamic and static conversion model is established to obtain the static Poisson's ratio and Young's modulus. The brittleness index calculated by the dynamic and static rock elastic mechanical parameters is compared and analyzed with the indoor three-stress experimental data. The brittleness index calculated by the static rock elastic mechanical parameters is more consistent with the experimental data. The fracture toughness under confining pressure is calculated by the overburden pressure and tensile strength. The reservoir fracturing index is calculated by the normalized brittleness index and fracture toughness. The reservoir fracturing index is used to evaluate the fracturing of shale oil reservoirs. It can be seen from the example that the reservoir fracturing is also related to the fracture toughness. The larger the reservoir fracturing index, the better the fracturing.

[0074] To realize the inventive concept, the embodiments of the present disclosure adopt the following technical solutions. The principles and steps of the method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness are as follows:

[0075] Step S101: extracting the longitudinal and transverse wave time differences through array acoustic logging data, and combining with the density curve to calculate the dynamic rock elastic parameters Poisson's ratio, Young's modulus and bulk density respectively;

[0076] The expression of Poisson's ratio υ is:

[0077]

[0078] The expression of Young's modulus E is:

[0079]

[0080] Where V P is the longitudinal wave time difference, μs / ft; V S is the shear wave time difference, μs / ft; ρ is the volume density, g / cm 3 ; Obtained using array acoustic and density logging data respectively.

[0081] Step S102: According to the indoor triaxial stress test, a rock elastic mechanics parameter dynamic and static Poisson's ratio and Young's modulus conversion model is established to obtain the static Poisson's ratio and Young's modulus.

[0082] The expressions are:

[0083] υ 静 =a*υ动 +b;

[0084] E 静 =c*E 动 –d;

[0085] Where: a, b, c, d are the correlation coefficients of dynamic and static conversion experiments respectively.

[0086] Step S103: Calculate the brittleness index B of the dynamic and static rock elastic parameters I By comparing and analyzing the indoor three-stress experimental data, the static rock elastic mechanical parameters are optimized to calculate the brittleness index, and its expression is:

[0087] B I =(ΔE+Δυ) / 2

[0088] Where: △E, △υ are the normalized Young's modulus and Poisson's ratio, respectively, and are dimensionless.

[0089] Step S104: Calculate the fracture toughness K under confining pressure using logging data IC , whose expression is:

[0090] K IC =0.2176P S +0.0059σ T 3 +0.0923σ T 2 +0.517σ T -0.3322

[0091] Where: P S is the overburden pressure: calculated in discrete integral form, MPa; σ T Tensile strength: calculated using empirical formula, MPa.

[0092] Step S105: Comprehensively consider the characteristics of brittleness index and fracture toughness, and use the fracturability evaluation index F I The fracturability evaluation of shale oil reservoir is carried out, and the expression is:

[0093] F I =(B In +K IC_n ) / 2,

[0094] Where: B In =(B rit -B rit_min ) / (B rit_max -B rit_min ), K IC_n =(K IC_max -K IC ) / (KIC_max -K IC_min ), B rit_max , B rit_min are the maximum and minimum values ​​of the regional brittleness index respectively; K IC_max , K IC_min are the maximum and minimum values ​​of regional fracture toughness, respectively.

[0095] Example 1

[0096] The following specifically takes the XX2-2 well in a block of the Jimusar Depression as an example to specifically illustrate the fracturability evaluation method of the lacustrine shale oil reservoir based on brittleness and fracture toughness of the present invention, including the following steps:

[0097] Step S101: Extract the longitudinal and transverse wave time differences through the array acoustic logging data of the XX2-2 well, and calculate the dynamic rock elastic parameters Poisson's ratio and Young's modulus respectively by combining with the density curve.

[0098] The expression of Poisson's ratio υ is:

[0099]

[0100] The expression of Young's modulus E is:

[0101]

[0102] Where V P is the longitudinal wave time difference, μs / ft; V S is the shear wave time difference, μs / ft; ρ is the volume density, g / cm 3 .

[0103] Step S102: Figure 1 , Figure 2 In order to fit the dynamic and static Poisson's ratio and Young's modulus according to the rock elastic parameters established by the indoor triaxial stress experiment, a dynamic and static conversion model was established; the dynamic and static conversion relationship of rock elastic parameters was clarified, and the values ​​of a, b, c, and d were determined; the expressions of static Poisson's ratio and Young's modulus were obtained as follows:

[0104] υ 静 =1.086*υ+0.035;

[0105] E 静 =0.789*E-0.5753.

[0106] And use this expression to calculate the static Poisson's ratio and Young's modulus.

[0107] Step S103: Dynamic and static brittleness index B I Comparative analysis was performed with the indoor three-stress experimental data. Figure 3It can be seen that the static brittleness index is more consistent with the experimental data. The static rock elastic mechanical parameters are preferred to calculate the brittleness index, and its expression is:

[0108] B I =(ΔE+Δυ) / 2

[0109] Where: △E, △υ are the normalized Young's modulus and Poisson's ratio, dimensionless. The maximum values ​​of the dynamic and static Young's modulus in this layer are 44.1 and 35.5 respectively; the minimum values ​​are 10.2 and 9.0 respectively; the maximum values ​​of the dynamic and static Poisson's ratio are 0.69 and 0.34 respectively; the minimum values ​​are 0.21 and 0.19 respectively.

[0110] Step S104: Calculate the fracture toughness K under confining pressure using logging data IC , whose expression is:

[0111] K IC =0.2176P S +0.0059σ T 3 +0.0923σ T 2 +0.517σ T -0.3322

[0112] Where: P S is the overburden pressure: calculated in discrete integral form, MPa; σ T Tensile strength: calculated using empirical formula, MPa.

[0113] Step S105: Comprehensively consider the characteristics of brittleness index and fracture toughness, and use the fracturability evaluation index F I The fracturability evaluation of shale oil reservoir is carried out, and the expression is:

[0114] F I =(B In +K IC_n ) / 2,

[0115] Where: B In =(B rit -B rit_min ) / (B rit_max -B rit_min ), K IC_n =(K IC_max -K IC ) / (K IC_max -K IC_min ), B rit_max , B rit_min are the maximum and minimum values ​​of the regional brittleness index respectively; K IC_max , K IC_minare the maximum and minimum values ​​of regional fracture toughness, respectively. BIn is the normalized brittleness index. The maximum brittleness index (B rit_max ) and minimum brittleness index (B rit_min ) are: 0.55, 0.18; K IC_n is the normalized fracture toughness, the maximum fracture toughness (K IC_max ) and minimum fracture toughness (K IC_min ) are: 110 and 43MPa respectively.

[0116] Figure 4 The figure is the result of reservoir fracturing evaluation of Well XX2-2. The corresponding parameters calculated by the above formula are as follows: Figure 4 As shown in the figure, it can be seen that the fracturing index of the production layer of Well XX2-2 is relatively larger than that of other layers, and the fracturing effect is better, with daily liquid production / daily oil production of 12.34 tons / 8.7 tons. When evaluating the fracturing performance of shale oil reservoirs, it is not the case that the larger the brittleness index of the reservoir, the better the fracturing performance. Fracturing performance is also related to fracture toughness. The larger the reservoir fracturing index, the better the fracturing performance.

[0117] The method of the present invention provides a new idea for the evaluation of the fracturability of saline lake shale oil reservoirs, ensuring the accuracy of the fracturability evaluation. The method provides a reference basis for the selection of subsequent fracturing layers and provides a practical technical method for the development of shale oil reservoirs.

[0118] Those skilled in the art will appreciate that, in the above method of specific implementation, the order in which the steps are written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of the steps should be determined by their functions and possible internal logic.

[0119] The above-described embodiments are only embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present disclosure. It should be noted that, for a person of ordinary skill in the art, without departing from the concept of the present disclosure, several variations, equivalent substitutions, improvements, etc. may be made, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the attached claims.

Claims

1. A method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness, characterized in that: The following steps are involved: Step S101: Based on array acoustic logging data and conventional density logging data, dynamic rock elastic parameters Poisson's ratio, Young's modulus and bulk density are obtained respectively; Step S102: establishing a rock elastic mechanics parameter dynamic and static Poisson's ratio and Young's modulus conversion model according to an indoor triaxial stress test, and obtaining the static Poisson's ratio and Young's modulus; Step S103: Calculate the brittleness index based on the obtained dynamic and static rock elastic mechanics parameters; compare and analyze the brittleness index calculated from the dynamic and static rock elastic mechanics parameters with the indoor three-stress experimental data, and determine the brittleness index with better consistency with the experimental data as the preferred brittleness index; Step S104: using the logging data to obtain the overburden pressure and tensile strength, and calculating the fracture toughness under confining pressure; Step S105: Based on the obtained brittleness index and fracture toughness; comprehensively considering the two characteristics of the brittleness index and fracture toughness, obtaining a reservoir fracturing evaluation index through normalized brittleness index and fracture toughness; using the fracturing evaluation index to evaluate the fracturing of shale oil reservoirs.

2. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 1, characterized in that: The method for obtaining the Poisson's ratio of the dynamic rock elasticity parameter in step S101 includes: Extract P-wave time difference and S-wave time difference through array acoustic logging data; The dynamic Poisson's ratio is determined by the relationship between the dynamic rock elastic mechanics parameter Poisson's ratio and the longitudinal wave time difference and the transverse wave time difference; and / or, The method for determining the dynamic rock elasticity parameter Young's modulus comprises: Extract P-wave time difference and S-wave time difference through array acoustic logging data; The bulk density is obtained through conventional density logging data; The dynamic Young's modulus is determined by the relationship between the dynamic Young's modulus and the longitudinal wave time difference, the transverse wave time difference and the volume density.

3. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 2, characterized in that: The relationship between the dynamic Poisson's ratio and the longitudinal wave time difference and the transverse wave time difference is: Where: V P is the longitudinal wave time difference, μs / ft; V S is the shear wave time difference, μs / ft; υ is the dynamic Poisson's ratio; and / or, The relationship between dynamic Young's modulus and longitudinal wave time difference, transverse wave time difference and volume density is: Where: ρ is the volume density, g / cm 3 ; E is the dynamic Young's modulus.

4. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 1, characterized in that: The method of step S102 establishing a rock elasticity parameter dynamic and static Poisson's ratio and Young's modulus conversion model according to an indoor triaxial stress experiment comprises the following steps: By applying different stress and strain conditions to rock samples, the stress state of rock in geological environment is simulated to obtain the static Poisson's ratio and Young's modulus of rock mechanics. By measuring the propagation speed of ultrasonic shear and longitudinal waves in rock samples, the dynamic Poisson's ratio and Young's modulus can be obtained through mathematical conversion of shear and longitudinal waves and rock mechanical parameters. By fitting the static Poisson's ratio and Young's modulus and the dynamic Poisson's ratio and Young's modulus, the correlation between the static Poisson's ratio and Young's modulus and the dynamic Poisson's ratio and Young's modulus is found; the relationship with the highest correlation coefficient is selected as the conversion model of the static Poisson's ratio and Young's modulus and the dynamic Poisson's ratio and Young's modulus.

5. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 1, characterized in that: The established rock elastic parameters dynamic and static conversion model is a dynamic and static Poisson's ratio and Young's modulus conversion model: u 静 =a*υ 动 +b; E 静 =c*E 动 –d; Where: a, b, c, d are the correlation coefficients of dynamic and static conversion respectively.

6. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 1, characterized in that: In step S103, the brittleness index BI calculated by dynamic and static rock elastic mechanical parameters is compared and analyzed with the indoor three-stress experimental data to determine that the brittleness index calculated by static rock elastic mechanical parameters is more consistent with the experimental data, and the brittleness index calculated by static rock elastic mechanical parameters is preferred.

7. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 6, characterized in that: The preferred static rock elastic mechanical parameters are used to calculate the brittleness index, and its expression is: B I =(ΔE+Δυ) / 2; Where: ΔE=(E max -E) / (E max -E min );Dy=(y max -υ) / (υ max -u min ); ΔE and Δυ are the normalized Young's modulus and Poisson's ratio, respectively; E max 、E min They are the maximum and minimum values ​​of Young's modulus of the reservoir in the research area obtained through statistical analysis; υ max ,υ min are the maximum and minimum values ​​of the reservoir Poisson's ratio in the research area obtained through statistical analysis; E and υ are Young's modulus and Poisson's ratio at a certain depth, respectively.

8. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 1, characterized in that: The step S104 uses the logging data to calculate the fracture toughness K under confining pressure IC的 The expression is: K IC =0.2176P S +0.0059σ T 3 +0.0923σ T 2 +0.517σ T -0.3322 Where: P S is the overburden pressure: calculated in discrete integral form, MPa; σ T For tensile strength: calculated using empirical formula, MPa; and / or, The overburden pressure P S The calculation formula is: Where: g is the acceleration due to gravity, m / s 2 ; h is the burial depth of the formation; ρ(h) is the bulk density of the formation at the burial depth h, g / cm 3 ; The tensile strength σ T The calculation formula is: Where: C0 is the compressive strength; The calculation formula of the compressive strength C0 is: C0=[0.0026(1-V cl )+0.008V cl ]E Where: V cl is the mud content, obtained through conventional gamma logging data.

9. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 1, characterized in that: The method of obtaining the fracturability evaluation index FI in step S105 comprises: The normalized brittleness index is obtained by obtaining the brittleness index at a certain depth of the reservoir and the maximum and minimum values ​​of the regional brittleness index; The normalized fracture toughness is obtained by obtaining the maximum and minimum values ​​of the fracture toughness at a certain depth of the reservoir and the regional fracture toughness; The fracturing evaluation index is determined according to the relationship between the normalized brittleness index, the normalized fracture toughness and the fracturing evaluation index.

10. The method for evaluating the fracturability of lacustrine shale oil reservoirs based on brittleness and fracture toughness according to claim 9, characterized in that: The fracturability evaluation index expression is: F I =(B In +K IC_n ) / 2; Where: B In =(B rit -B rit_min ) / (B rit_max -B rit_min ); K IC_n =(K IC _ max -K IC ) / (K IC_max -K IC_min ); B rit_max , B rit_min are the maximum and minimum values ​​of the regional brittleness index, respectively; K IC_max , K IC_min are the maximum and minimum values ​​of regional fracture toughness, respectively; F I K is the fracturing evaluation index; IC is the fracture toughness at a certain depth of the reservoir; K IC_n is the normalized fracture toughness; B rit is the brittleness index at a certain depth of the reservoir, B In is the normalized brittleness index; The conclusion of the shale oil reservoir fracturing evaluation using the fracturing evaluation index is: the shale oil reservoir fracturing evaluation is performed by comprehensively considering the two characteristics of brittleness index and fracture toughness; the larger the reservoir fracturing index, the better the fracturing property.

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