Method and system for maintaining shale oil well wall stability under hydration effect

Abstract

The invention relates to the technical field of petroleum drilling engineering, and discloses a method and system for maintaining shale oil borehole wall stability under hydration, and the method comprises the following steps: measuring mineral components, pore distribution and permeability anisotropy of shale in a shale oil experimental area to obtain shale related parameters; based on shale related parameters, performing a mechanical experiment on the shale sample, testing mechanical properties of a dry shale core under different confining pressures, and determining an upper and lower limit included angle of shale bedding surface damage; under the soaking of different drilling fluid systems, the strength data of the shale sample is corrected, and the shale strength criterion is perfected; determining a drilling fluid safety density window of the target layer based on actual measurement data of shale in the shale oil experimental area; based on the drilling fluid safety density window, well wall stability control under the engineering condition is carried out. According to the method, the well wall stability control technology is determined by determining the drilling fluid safety density window of the target layer, and technical support is provided for effectively maintaining the well wall stability in gulongshale oil drilling.

Description

Technical Field

[0001] The present invention relates to the technical field of oil drilling engineering, and in particular to a method and a system for maintaining the stability of a shale oil well wall under hydration. Background Art

[0002] Shale oil refers to oil stored in organic-rich, nanoscale pore-sized rock formations. It has abundant reserves and is widely distributed. It is one of the hot areas for unconventional resource exploration after shale gas. As an important oil and gas production base in my country, the Songliao Basin is rich in resources and has a variety of reservoir types. In the past 50 years, the cumulative oil production has reached 25×10 8 t, ranking first in China. The efficient development of shale oil plays a vital role in ensuring national energy security.

[0003] The development of terrestrial shale oil in China is still in its infancy, especially the horizontal well exploration of Gulong shale oil, which lacks mature theories, technologies and experiences that can be used as reference. Due to the development of nano-micron-scale pores and fractures in shale, the drilling fluid will induce expansion stress after entering the formation, changing the distribution of circumferential stress. At the same time, shale hydration will reduce the strength of the formation rock. Therefore, the drilling fluid needs to have a strong ability to inhibit hydration to slow down the hydration effect of shale and drilling fluid. The changes in shale strength caused by the surface hydration of illite and the intrusion of drilling fluid into pores are the main causes of the instability of the wellbore wall in the Gulong shale formation. The existing technical solutions cannot effectively maintain the wellbore stability problem in the drilling of Gulong shale oil. How to maintain the stability of the Gulong shale oil wellbore wall under the action of hydration has become a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0004] The purpose of the present invention is to provide a method and system for maintaining the stability of shale oil wellbore under hydration, clarify the drilling fluid safety density window of the target layer based on field data, determine the wellbore stability control technology, and provide technical support for effectively maintaining the wellbore stability in Gulong shale oil drilling.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for maintaining the stability of a shale oil well wall under hydration, the method comprising the following steps:

[0007] S1, determine the mineral composition, pore distribution and permeability anisotropy of shale in the shale oil experimental block to obtain shale related parameters;

[0008] S2, based on shale related parameters, mechanical experiments are carried out on shale samples to test the mechanical properties of dry shale cores under different confining pressures and to clarify the upper and lower limit angles of shale bedding plane failure;

[0009] S3, improve the shale strength criterion by correcting the strength data of shale samples immersed in different drilling fluid systems;

[0010] S4, based on the measured data of shale in the shale oil experimental block, determine the drilling fluid safety density window of the target layer;

[0011] S5, based on the drilling fluid safety density window, performs wellbore stability control under engineering conditions.

[0012] Furthermore, in S1, the mineral composition, pore distribution and permeability anisotropy of the shale in the shale oil experimental block are determined, specifically including:

[0013] The shale in the shale oil experimental block was measured using XRD diffractometer, SEM scanning electron microscope and three-dimensional Darcy's law to obtain the mineral composition, pore distribution and permeability anisotropy parameters of the shale.

[0014] Furthermore, S2, based on shale related parameters, conducts mechanical experiments on shale samples, tests the mechanical properties of dry shale cores under different confining pressures, and clarifies the upper and lower limit angles of shale bedding plane failure, specifically including:

[0015] Based on shale related parameters, uniaxial or triaxial mechanical tests are carried out on shale samples to test the mechanical properties of dry shale cores under different confining pressures;

[0016] Based on mechanical properties, the rock multi-weak plane strength criterion is adopted to clarify the conditions for shale bedding plane failure:

[0017] β1(i)<β(i)<β2(i)

[0018]

[0019] Wherein, σ1 is the maximum principal stress, MPa; σ3 is the minimum principal stress, MPa; β(i) is the angle between the normal of structural surface i and the direction of the maximum principal stress, (°); β1(i) and β2(i) are the upper and lower limit angles of shale failure along the bedding plane, (°); c wi is the cohesion, MPa; is the internal friction angle, (°).

[0020] Furthermore, the S3 also includes analyzing the change of triaxial compressive strength of shale after displacement with different drilling fluids, specifically including:

[0021] In the horizontal direction, the triaxial compressive strength variation formula is:

[0022]

[0023] In the vertical direction, the triaxial compressive strength variation formula is:

[0024]

[0025] Among them, σ 3水-油基 represents the change of triaxial compressive strength in the horizontal direction during oil-based displacement, σ 3水-醇基 represents the change of triaxial compressive strength in the horizontal direction during alcohol displacement, σ 3水-水基 represents the change of triaxial compressive strength in the horizontal direction during water-based displacement; σ 3垂-油基 represents the change of triaxial compressive strength in the vertical direction when oil-based drilling fluid is displaced, σ 3垂-醇基 represents the change of triaxial compressive strength in the vertical direction when the alcohol-based drilling fluid is displaced, σ 3垂-水基 represents the change of triaxial compressive strength in the vertical direction when water-based drilling fluid is displaced; x 油基驱替 Indicates the change after oil-based drilling fluid displacement, x 醇基驱替 represents the change after displacement of alcohol-based drilling fluid, x 水基驱替 Indicates the changes after water-based drilling fluid displacement.

[0026] Furthermore, the S3 improves the shale strength criterion by correcting the strength data of the shale samples when immersed in different drilling fluid systems, specifically including:

[0027] The strength data of rock samples were corrected by using the rock multi-weak plane strength algorithm when immersed in different drilling fluid systems including water-based drilling fluid, alcohol-based drilling fluid and oil-based drilling fluid.

[0028] Based on the corrected strength data, the Jager single weak plane failure criterion and the Mohr-Columb criterion are combined to improve the shale strength criterion.

[0029] Furthermore, in S4, based on the measured data of shale in the shale oil experimental block, the drilling fluid safety density window of the target layer is determined, which specifically includes:

[0030] Obtain measured data of shale in the shale oil experimental block, including: mineral composition of shale, pore distribution and permeability anisotropy, collapse pressure, fracture pressure and depth of the formation;

[0031] Based on the collapse pressure, fracture pressure and the depth of the corresponding formation, the safe density window of the drilling fluid in the target layer is determined.

[0032] Furthermore, the S5, based on the drilling fluid safety density window, performs wellbore stability control under engineering conditions, specifically including:

[0033] Under engineering conditions, the drilling fluid safety density window is used as the threshold to ensure that the drilling fluid density used when drilling into the target layer does not exceed the corresponding drilling fluid safety density window to maintain wellbore stability.

[0034] Furthermore, the specific measures for ensuring that the density of the drilling fluid used when drilling into the target layer does not exceed the corresponding drilling fluid safety density window include:

[0035] By adjusting the formula of drilling fluid, the viscosity and density of drilling fluid can be increased to enhance its supporting effect on the well wall;

[0036] Ensure the smooth flow of drilling fluid circulation and filtration systems to ensure the stability of hydraulic pressure and fluid flow;

[0037] Control the drilling speed to avoid the instability of the well wall caused by excessive drilling speed and ensure the stability of the drilling process;

[0038] According to the characteristics of the shale oil layer, the formula of the cement slurry is adjusted to enhance the supporting effect of the cement slurry on the well wall.

[0039] The present invention also provides a system for maintaining the stability of a shale oil well wall under hydration, which is used to execute the above-mentioned method for maintaining the stability of a shale oil well wall under hydration, comprising:

[0040] The shale parameter acquisition module is used to determine the mineral composition, pore distribution and permeability anisotropy of shale in the shale oil experimental block and obtain shale related parameters;

[0041] Mechanical property analysis module, which is used to conduct mechanical experiments on shale samples based on shale-related parameters, test the mechanical properties of dry shale cores under different confining pressures, and clarify the upper and lower limit angles of shale bedding plane failure;

[0042] Strength criterion improvement module, used to improve the shale strength criterion by correcting the strength data of shale samples under different drilling fluid systems;

[0043] The safety density window determination module is used to determine the drilling fluid safety density window of the target layer based on the measured data of shale in the shale oil experimental block;

[0044] The stability control module is used to control the wellbore stability under engineering conditions based on the drilling fluid safety density window.

[0045] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the method and system provided by the present invention for maintaining the stability of the shale oil well wall under hydration, determining the mineral composition, pore distribution and permeability anisotropy of the shale in the shale oil experimental block, testing the mechanical properties of dry shale cores under different confining pressures, clarifying the upper and lower limit angles of shale bedding plane destruction, and on this basis exploring the principle of well wall instability in the shale oil area. Under immersion in different drilling fluid systems, the shale failure criterion is further improved by correcting the strength data of shale; the present invention clarifies the drilling fluid safety density window of the target layer based on field data, and studies how to solve the problem of well wall instability, by establishing a well wall stability control technology under engineering conditions, and providing corresponding implementation measures. The present invention can solve the problem that the existing technical solutions cannot effectively maintain the well wall stability in Gulong shale oil drilling, and provide a scientific basis and technical support for shale oil reservoir exploitation research. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] Figure 1 is a flow chart of a method for maintaining shale oil well wall stability under hydration in an embodiment of the present invention;

[0048] Figure 2 This is a schematic diagram of the wellbore collapse induced by defects such as micro-cracks and hydration in the Gulong shale oil reservoir according to an embodiment of the present invention;

[0049] Figure 3 is the mineral component content of the Gulong shale oil reservoir in the embodiment of the present invention, wherein (a) is the whole rock mineral component, and (b) is the clay mineral component;

[0050] Figure 4 1 is a digital core image of an embodiment of the present invention, wherein (a) is a horizontal sample and (b) is a vertical sample;

[0051] Figure 5 Schematic diagram of the relationship between the main permeability direction and the bedding according to the embodiment of the present invention, an x, y coordinate system is established, wherein the dotted line represents the bedding, k 11 That is, 1 refers to the direction parallel to the bedding, k 33 That is, 3 refers to the direction perpendicular to the bedding;

[0052] Figure 6 is a prediction curve of shale strength distribution with weak surface inclination angle under different confining pressures in an embodiment of the present invention;

[0053] Figure 7 It is a schematic diagram of the change in rock strength after displacement with different drilling fluids according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] The purpose of the present invention is to provide a method for maintaining the stability of shale oil wellbore under hydration, clarify the drilling fluid safety density window of the target layer based on field data, determine the wellbore stability control technology, and provide technical support for effectively maintaining the wellbore stability in Gulong shale oil drilling.

[0056] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] like Figure 1 As shown, the present invention takes Gulong shale oil as an example, and provides a method for maintaining the stability of the shale oil well wall under hydration, comprising the following steps:

[0058] S1, such as Figure 2 As shown in the figure, it is used to reflect the wellbore collapse induced by micro cracks, hydration and other defects in Gulong shale oil. Figure 3 , 4 As shown in Figures 5 and 5, the mineral composition, pore distribution and permeability anisotropy of the shale in the Gulong shale oil experimental block were determined to obtain shale related parameters;

[0059] Specifically, Figure 3 As shown in the figure, XRD diffractometer was used to analyze the mineral components of the shale oil experimental block. These mineral composition analysis results provide detailed mineral composition data for a deeper understanding of the shale characteristics of the Qingshankou Formation at different angles in the Gulong shale oil area, and lay the foundation for studying the effects of its hydration characteristics and brittle mineral content on reservoir properties. Figure 4 As shown in the figure, the original shale samples were photographed in the horizontal and vertical directions using a SEM scanning electron microscope and then two-dimensional grayscale images were obtained. The laminae in the sample images were rendered, and the three-dimensional state of the laminae on the sample was displayed in the digital image through calculation. The digital core model of the ancient Longye was initially constructed, and its pore structure was quantitatively characterized. Figure 5 As shown in Figure 1, the permeability of shale depends on the size and distribution of pores. Under a certain pressure difference, fluid can flow in the pores. The three-dimensional Darcy's law can be used to calculate the permeability anisotropy related parameters.

[0060] S2, such as Figure 6 As shown in the figure, based on shale related parameters, mechanical experiments were carried out on shale samples to test the mechanical properties of dry shale cores under different confining pressures, and to clarify the upper and lower limit angles of shale bedding plane failure, including:

[0061] Based on shale related parameters, uniaxial or triaxial mechanical tests are carried out on shale samples to test the mechanical properties of dry shale cores under different confining pressures;

[0062] Based on mechanical properties, the rock multi-weak plane strength criterion is adopted to clarify the conditions for shale bedding plane failure:

[0063] β1(i)<β(i)<β2(i)

[0064]

[0065] Wherein, σ1 is the maximum principal stress, MPa; σ3 is the minimum principal stress, MPa; β(i) is the angle between the normal of structural surface i and the direction of the maximum principal stress, (°); β1(i) and β2(i) are the upper and lower limit angles of shale failure along the bedding plane, (°); c wi is the cohesion, MPa; is the internal friction angle, (°).

[0066] The purpose of this step is mainly to select a suitable strength failure criterion, based on the Mohr-Columb criterion, and judge whether the rock is destroyed along the body or the weak plane according to β(i). The rock failure condition along the weak plane is: β1(i)<β(i)<β2(i). At this time, the rock multiple weak plane strength failure criterion is adopted; if β(i) is not in the upper and lower limit angle range, the rock is destroyed along the body, and the conventional Mohr-Coulomb criterion can be used for calculation.

[0067] S3, by correcting the strength data of shale samples immersed in different drilling fluid systems, improve the shale strength criteria, including:

[0068] Different drilling fluid systems mainly include water-based drilling fluid, alcohol-based drilling fluid and oil-based drilling fluid;

[0069] The strength data of shale is corrected by using the rock multi-weak plane strength algorithm;

[0070] Based on the strength data, the Jager single weak plane failure criterion and the Mohr-Columb criterion are mainly used to improve the shale strength criterion.

[0071] After being immersed in different drilling fluids, the triaxial compressive strength in the horizontal and vertical directions will change. By substituting its data into the shale strength criterion, the application scope of the shale strength criterion can be broadened.

[0072] The S3 also includes analyzing the changes in the triaxial compressive strength of shale after displacement with different drilling fluids, specifically including:

[0073] In the horizontal direction, the triaxial compressive strength variation formula is:

[0074]

[0075] In the vertical direction, the triaxial compressive strength variation formula is:

[0076]

[0077] Among them, σ 3水-油基 represents the change of triaxial compressive strength in the horizontal direction during oil-based displacement, σ 3水-醇基 represents the change of triaxial compressive strength in the horizontal direction during alcohol displacement, σ 3水-水基 represents the change of triaxial compressive strength in the horizontal direction during water-based displacement; σ 3垂-油基 represents the change of triaxial compressive strength in the vertical direction when oil-based drilling fluid is displaced, σ 3垂-醇基 represents the change of triaxial compressive strength in the vertical direction when the alcohol-based drilling fluid is displaced, σ 3垂-水基 represents the change of triaxial compressive strength in the vertical direction when water-based drilling fluid is displaced; x 油基驱替 Indicates the change after oil-based drilling fluid displacement, x 醇基驱替 represents the change after displacement of alcohol-based drilling fluid, x 水基驱替 Indicates the changes after water-based drilling fluid displacement.

[0078] like Figure 7 As shown in the figure, based on the above triaxial compressive strength change formula, the change of triaxial compressive strength of rock after displacement with different drilling fluids is studied: when loading along the vertical direction of the bedding, the oil-based drilling fluid has the least effect on the triaxial compressive strength of rock; when loading along the horizontal direction, the drilling fluid displacement has a greater impact on the triaxial compressive strength of rock. Whether it is water-based drilling fluid, alcohol-based drilling fluid or oil-based drilling fluid, the decrease in triaxial compressive strength in the horizontal direction is about twice that of the triaxial compressive strength in the vertical direction.

[0079] S4, based on the measured data of shale in the shale oil experimental block, determine the safe density window of drilling fluid in the target layer, including:

[0080] The determination of the drilling fluid safety density window suitable for most areas needs to be based on field data parameters, mainly including: first, the analysis of the corresponding formation (mineral composition, pore distribution, permeability), etc., secondly, relevant parameters such as collapse pressure, fracture pressure and formation depth, and then substitute them into the formula for calculation (collapse pressure / formation depth, fracture pressure / formation depth), and finally obtain the drilling fluid safety density window of the target layer.

[0081] Based on the collapse pressure, fracture pressure and corresponding layer depth, the safe density window of drilling fluid is determined.

[0082] On the one hand, when the drilling fluid density is too low, it may not be able to effectively support the wellbore wall, increasing the risk of blowout or formation fluid invasion; on the other hand, when the drilling fluid density is too high, it may cause the drilling speed to slow down, easily causing differential pressure to stick the drill, and sometimes cause formation leakage, increase the friction resistance of the upper or lower drill tools, and increase the pump pressure due to poor fluidity. Therefore, when the drilling fluid safety density window is determined, the instability of the wellbore wall can be effectively reduced.

[0083] S5, based on the drilling fluid safety density window, performs wellbore stability control under engineering conditions.

[0084] Under engineering conditions, the drilling fluid safety density window is used as the threshold to ensure that the drilling fluid density used when drilling into the target layer does not exceed the corresponding drilling fluid safety density window to maintain wellbore stability.

[0085] By establishing the wellbore stability control technology under engineering conditions and providing corresponding implementation measures; according to the drilling fluid safety density window, the wellbore stability of the well to be analyzed is maintained.

[0086] The specific measures to ensure that the density of the drilling fluid used when drilling into the target layer does not exceed the corresponding drilling fluid safety density window include:

[0087] By adjusting the formula of drilling fluid, the viscosity and density of drilling fluid can be increased to enhance its supporting effect on the well wall;

[0088] Ensure the smooth flow of drilling fluid circulation and filtration systems to ensure the stability of hydraulic pressure and fluid flow;

[0089] Control the drilling speed to avoid the instability of the well wall caused by excessive drilling speed and ensure the stability of the drilling process;

[0090] According to the characteristics of the shale oil layer, the formula of the cement slurry is adjusted to enhance the supporting effect of the cement slurry on the well wall.

[0091] For example, the Qingshankou Formation is the main stratum of the Gulong shale oil, among which the middle and upper parts of the Qing 2nd and Qing 3rd sections have strong slurrying properties, while the lower parts of the Qing 2nd and 3rd sections and the Qing 1st section are prone to peeling off. This well section is mainly characterized by strong inhibition and plugging properties, mainly supplementing coating agent inhibitors and strengthening plugging.

[0092] Specifically, the density is 1.63 g / cm 3 , Gel: 3 / 6, plastic adhesion 46Pa·s, dynamic shear force 6.5Pa, dynamic plastic ratio 0.14, oil-water ratio 77:23, demulsification voltage 308V. Three openings and standby time 60m 3 Old pulp, using 60m 3 Old pulp and 60m 3 Mix the new pulp in a 1:1 ratio and increase the weight to 1.70g / cm 3 After maintenance, the drilling fluid performance and dosage are determined. The drilling fluid performance meets the construction requirements of this well. Through practical experience, the drilling fluid density is controlled at 1.71g / cm 3 -1.73g / cm 3 In between, appropriate mechanical support can be provided to the well wall, which can effectively prevent stratum spalling.

[0093] On the other hand, the wellbore stability control technology under engineering conditions is established, and corresponding implementation measures are provided. Specifically, the HTHP (110℃) water loss is controlled to be less than 2mL, and the filtrate entering the formation is reduced as much as possible; the use time of the high-speed centrifuge is increased, and timely adjustments are made according to the density change trend on site; heavy slurry (density 2.0g / cm 3 ) To maintain the density of drilling fluid, the heavy slurry requires good rheological properties. Before preparing the heavy slurry each time, it should be prepared in a ratio of 4:1 with the glue liquid; the glue liquid should be continuously replenished for dilution; the newly prepared glue liquid is mainly used to increase the demulsification voltage and oil-water ratio. The concentration of the main emulsifier and auxiliary emulsifier is 4% main emulsion + 2% auxiliary emulsion.

[0094] The present invention also provides a system for maintaining the stability of a shale oil well wall under hydration, which is used to execute the above-mentioned method for maintaining the stability of a shale oil well wall under hydration, comprising:

[0095] The shale parameter acquisition module is used to determine the mineral composition, pore distribution and permeability anisotropy of shale in the shale oil experimental block and obtain shale related parameters;

[0096] Mechanical property analysis module, which is used to conduct mechanical experiments on shale samples based on shale-related parameters, test the mechanical properties of dry shale cores under different confining pressures, and clarify the upper and lower limit angles of shale bedding plane failure;

[0097] Strength criterion improvement module, used to improve the shale strength criterion by correcting the strength data of shale samples under different drilling fluid systems;

[0098] The safety density window determination module is used to determine the drilling fluid safety density window of the target layer based on the measured data of shale in the shale oil experimental block;

[0099] The stability control module is used to control the wellbore stability under engineering conditions based on the drilling fluid safety density window.

[0100] In summary, the present invention takes Gulong shale oil as the research object, determines the mineral composition, pore distribution and permeability anisotropy of the shale in the Gulong shale oil experimental block, tests the mechanical properties of dry shale cores under different confining pressures, clarifies the upper and lower limit angles of shale bedding plane destruction, and attempts to explore the principle of wellbore instability in the Gulong shale oil area based on this. Under immersion in different drilling fluid systems, the shale failure criterion is further improved by correcting the strength data of the shale; the present invention clarifies the drilling fluid safety density window of the target layer based on field data, and studies how to solve the problem of wellbore instability, by establishing a wellbore stability control technology under engineering conditions, and provides corresponding implementation measures. The present invention can solve the problem that the existing technical solutions cannot effectively maintain the wellbore stability in Gulong shale oil drilling.

[0101] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

[0102] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined by the attached claims.

Claims

1. A method for maintaining the stability of shale oil wellbore under hydration, characterized in that: The following steps are involved: S1, determine the mineral composition, pore distribution and permeability anisotropy of shale in the shale oil experimental block to obtain shale related parameters; S2, based on shale related parameters, mechanical experiments are carried out on shale samples to test the mechanical properties of dry shale cores under different confining pressures and to clarify the upper and lower limit angles of shale bedding plane failure; S3, improve the shale strength criterion by correcting the strength data of shale samples immersed in different drilling fluid systems; S4, based on the measured data of shale in the shale oil experimental block, determine the drilling fluid safety density window of the target layer; S5, based on the drilling fluid safety density window, performs wellbore stability control under engineering conditions.

2. The method for maintaining the stability of shale oil wellbore under hydration according to claim 1, characterized in that: In S1, the mineral composition, pore distribution and permeability anisotropy of shale in the shale oil experimental block are determined, specifically including: The shale in the shale oil experimental block was measured using XRD diffractometer, SEM scanning electron microscope and three-dimensional Darcy's law to obtain the mineral composition, pore distribution and permeability anisotropy parameters of the shale.

3. The method for maintaining the stability of shale oil wellbore under hydration according to claim 1, characterized in that: S2, based on shale related parameters, conducts mechanical experiments on shale samples, tests the mechanical properties of dry shale cores under different confining pressures, and clarifies the upper and lower limit angles of shale bedding plane failure, specifically including: Based on shale related parameters, uniaxial or triaxial mechanical tests are carried out on shale samples to test the mechanical properties of dry shale cores under different confining pressures; Based on mechanical properties, the rock multi-weak plane strength criterion is adopted to clarify the conditions for shale bedding plane failure: β1(i)<β(i)<β2(i) Wherein, σ1 is the maximum principal stress, MPa; σ3 is the minimum principal stress, MPa; β(i) is the angle between the normal of structural plane i and the direction of the maximum principal stress, (°); β1(i) and β2(i) are the upper and lower limit angles of shale failure along the bedding plane, (°); c wi is the cohesion, MPa; is the internal friction angle, (°).

4. The method for maintaining the stability of shale oil wellbore under hydration according to claim 3, characterized in that: The S3 also includes analyzing the changes in the triaxial compressive strength of shale after displacement with different drilling fluids, specifically including: In the horizontal direction, the triaxial compressive strength variation formula is: In the vertical direction, the triaxial compressive strength variation formula is: Among them, σ 3水-油基 represents the change of triaxial compressive strength in the horizontal direction during oil-based displacement, σ 3水-醇基 represents the change of triaxial compressive strength in the horizontal direction during alcohol displacement, σ 3水-水基 represents the change of triaxial compressive strength in the horizontal direction during water-based displacement; σ 3垂-油基 represents the change of triaxial compressive strength in the vertical direction when oil-based drilling fluid is displaced, σ 3垂-醇基 represents the change of triaxial compressive strength in the vertical direction when the alcohol-based drilling fluid is displaced, σ 3垂-水基 represents the change of triaxial compressive strength in the vertical direction when water-based drilling fluid is displaced; x 油基驱替 Indicates the change after oil-based drilling fluid displacement, x 醇基驱替 represents the change after displacement of alcohol-based drilling fluid, x 水基驱替 Indicates the changes after water-based drilling fluid displacement.

5. The method for maintaining the stability of shale oil wellbore under hydration according to claim 1, characterized in that: S3, when immersed in different drilling fluid systems, improves the shale strength criteria by correcting the strength data of shale samples, specifically including: The strength data of rock samples were corrected by using the rock multi-weak plane strength algorithm when immersed in different drilling fluid systems including water-based drilling fluid, alcohol-based drilling fluid and oil-based drilling fluid. Based on the corrected strength data, the Jager single weak plane failure criterion and the Mohr-Columb criterion are combined to improve the shale strength criterion.

6. The method for maintaining the stability of shale oil wellbore under hydration according to claim 1, characterized in that: In S4, based on the measured data of shale in the shale oil experimental block, the drilling fluid safety density window of the target layer is determined, which specifically includes: Obtain measured data of shale in the shale oil experimental block, including: mineral composition of shale, pore distribution and permeability anisotropy, collapse pressure, fracture pressure and depth of the formation; Based on the collapse pressure, fracture pressure and the depth of the corresponding formation, the safe density window of the drilling fluid in the target layer is determined.

7. The method for maintaining the stability of shale oil wellbore under hydration according to claim 1, characterized in that: S5, based on the drilling fluid safety density window, performs wellbore stability control under engineering conditions, specifically including: Under engineering conditions, the drilling fluid safety density window is used as the threshold to ensure that the drilling fluid density used when drilling into the target layer does not exceed the corresponding drilling fluid safety density window to maintain wellbore stability.

8. The method for maintaining the stability of shale oil wellbore under hydration according to claim 7, characterized in that: The specific measures to ensure that the density of the drilling fluid used when drilling into the target layer does not exceed the corresponding drilling fluid safety density window include: By adjusting the formula of drilling fluid, the viscosity and density of drilling fluid can be increased to enhance its supporting effect on the well wall; Ensure the smooth flow of drilling fluid circulation and filtration systems to ensure the stability of hydraulic pressure and fluid flow; Control the drilling speed to avoid the instability of the well wall caused by excessive drilling speed and ensure the stability of the drilling process; According to the characteristics of the shale oil layer, the formula of the cement slurry is adjusted to enhance the supporting effect of the cement slurry on the well wall.

9. A system for maintaining the stability of a shale oil well wall under hydration, used for executing the method for maintaining the stability of a shale oil well wall under hydration as claimed in any one of claims 1 to 8, characterized in that: include: The shale parameter acquisition module is used to determine the mineral composition, pore distribution and permeability anisotropy of shale in the shale oil experimental block and obtain shale related parameters; Mechanical property analysis module, which is used to conduct mechanical experiments on shale samples based on shale-related parameters, test the mechanical properties of dry shale cores under different confining pressures, and clarify the upper and lower limit angles of shale bedding plane failure; Strength criterion improvement module, used to improve the shale strength criterion by correcting the strength data of shale samples under different drilling fluid systems; The safety density window determination module is used to determine the drilling fluid safety density window of the target layer based on the measured data of shale in the shale oil experimental block; The stability control module is used to control the wellbore stability under engineering conditions based on the drilling fluid safety density window.

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