Shale-sandstone interlayer type shale oil reservoir well wall stability detection method and system

Abstract

The invention relates to the technical field of petroleum drilling engineering, and discloses a shale-sandstone interlayer type shale oil reservoir well wall stability detection method and system, and the method comprises the steps: obtaining the reservoir characteristics of a shale-sandstone interlayer type shale oil reservoir; on the basis of reservoir characteristics, a rock mechanical test is carried out, and a borehole wall instability micromechanism is determined; based on a borehole wall instability micromechanism, determining a strength failure criterion of shale and sandstone; analyzing horizontal well wall surrounding rock stress distribution, calculating collapse pressure and fracture pressure of different rock stratums, and determining a safe density window of well wall stability; establishing a shale-sandstone horizontal well wall finite element model; and based on measured data of the to-be-analyzed well, determining a well wall stability value of the to-be-analyzed well by utilizing the finite element model, and determining a well wall stability state by combining the safety density window of well wall stability. According to the method, multiple influence parameters are combined, accurate prediction of the borehole wall stability is achieved, and reliable technical support is provided for shale-sandstone interlayer type shale oil reservoir development.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum drilling engineering, and in particular to a method and system for detecting the wellbore stability of a shale oil reservoir with a shale-sandstone interlayer. Background Art

[0002] In oil drilling projects, optimizing drilling technology can reduce drilling costs and construction accidents, while wellbore stability is the basis for safe drilling. Wellbore instability in oil drilling projects is a global technical problem and one of the core issues for achieving safe and efficient drilling. Shale oil reservoirs are a special type of oil and gas reservoirs, and their storage space and seepage characteristics are significantly different from those of traditional sandstone, carbonate rock and other reservoirs. Shale oil reservoirs are mainly composed of fine-grained sedimentary rocks such as shale and mudstone. These rocks usually have the characteristics of low porosity and low permeability, making the development of shale oil more difficult. China National Petroleum Corporation Changqing Oilfield Company has discovered a large shale oil field with a proven geological reserve of more than 10×108t in the Chang 7 section of the Ordos Basin. Therefore, shale oil has become a key area for unconventional oil and gas exploration and development. When exploiting the formation, how to maintain wellbore stability has become a key issue in the field of petroleum engineering.

[0003] When exploiting shale oil, we often face the situation that shale and sandstone are intricate and overlapped in the vertical direction of the reservoir, and the weak structural planes between the layers are also very developed. This leads to the occurrence of complex downhole situations such as drilling resistance and drill sticking in shale-sandstone interlayer shale oil reservoirs, high well diameter expansion rate, and serious well wall collapse, which leads to a series of problems such as long drilling cycle and high drilling cost. Strengthening the well wall stability detection of shale-sandstone interlayer shale oil reservoirs has become the key to ensure the smooth exploitation of shale-sandstone interlayer shale oil reservoirs, which deserves in-depth study by technical personnel in this field. Summary of the invention

[0004] The purpose of the present invention is to provide a shale-sandstone interlayer shale oil reservoir wellbore stability detection method and system, which combines multiple influencing parameters to achieve accurate prediction of wellbore stability and provide reliable technical support for the development of shale-sandstone interlayer shale oil reservoirs.

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

[0006] A method for detecting the wellbore stability of a shale oil reservoir with shale-sandstone interlayers, the method comprising the following steps:

[0007] S1, obtain the reservoir characteristics of shale oil reservoirs with shale-sandstone interlayers;

[0008] S2, based on the reservoir characteristics, rock mechanics tests are conducted to determine the microscopic mechanism of wellbore instability in shale oil reservoirs with shale-sandstone interlayers;

[0009] S3, based on the microscopic mechanism of wellbore instability, determine the strength failure criteria of shale and sandstone;

[0010] S4, analyze the stress distribution of the surrounding rock of the horizontal wellbore in the shale-sandstone interlayer shale oil reservoir, calculate the collapse pressure and fracture pressure of different rock formations, and determine the safe density window for wellbore stability;

[0011] S5, establishing a finite element model of the shale-sandstone horizontal wellbore wall based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion;

[0012] S6, based on the measured data of the well to be analyzed in the shale-sandstone interlayer shale oil reservoir, using the finite element model of the wellbore of the shale-sandstone horizontal well, determining the wellbore stability value of the well to be analyzed;

[0013] S7, determining the wellbore stability state based on the wellbore stability safety density window and the wellbore stability value of the well to be analyzed.

[0014] Furthermore, in S1, the reservoir characteristics of the shale-sandstone interlayer shale oil reservoir are obtained, specifically including:

[0015] The shale-sandstone interlayer shale oil reservoir in the area to be detected is taken as the object, and the reservoir characteristics are obtained by using seismic exploration technology. The reservoir characteristics include geological structure, lithology combination, sand-to-ground ratio, and single sand body thickness.

[0016] Further, the S2, based on the reservoir characteristics, conducts rock mechanics tests to determine the microscopic mechanism of wellbore instability of shale-sandstone interlayer shale oil reservoirs, specifically including:

[0017] Based on the reservoir characteristics, the GCTS-3000 rock mechanics test system was used to obtain the compressive strength, elastic modulus, Poisson's ratio of shale and sandstone and their respective failure forms as test results. Based on the test results, the microscopic mechanism of wellbore instability in shale oil reservoirs with shale-sandstone interlayers was determined.

[0018] Furthermore, the S3, based on the microscopic mechanism of wellbore instability, determines the strength failure criteria of shale and sandstone, specifically including:

[0019] Based on the compressive strength, elastic modulus, Poisson's ratio and respective failure modes of shale and sandstone, the strength failure criteria of shale and sandstone are determined; among them, the strength failure criterion of shale is the multiple weak plane strength criterion, and the strength failure criterion of sandstone is the Mohr-Coulomb strength criterion.

[0020] Further, in S4, analyzing the stress distribution of the surrounding rock of the horizontal well wall in the shale-sandstone interlayer shale oil reservoir specifically includes:

[0021] The maximum horizontal geostress, minimum horizontal geostress, overburden stress, wellbore radius, Poisson's ratio, effective stress coefficient and pore pressure parameters are obtained, and the wellbore surrounding rock stress expression is used to analyze the wellbore surrounding rock stress distribution of horizontal wells in shale-sandstone interlayer shale oil reservoirs.

[0022] Furthermore, in S4, the collapse pressure and fracture pressure of different rock formations are calculated to determine the safe density window for wellbore stability, which specifically includes:

[0023] Calculate the collapse pressure of shale and sandstone:

[0024]

[0025] Calculate the fracture pressure of shale and sandstone:

[0026] P f-页 =3σ H-页 -σ h-页 -αP p +σ t-页

[0027] P f-砂 =3σ H-砂 -σ h-砂 -αP p +σ t-砂

[0028] Where P c-页 is the shale collapse pressure, MPa; P c-砂 is the collapse pressure of sandstone, MPa; σ H-页 is the maximum in-situ stress of shale, MPa; σ h-页 is the minimum in-situ stress of shale, MPa; σ H-砂 is the maximum in-situ stress of sandstone, MPa; σ h-砂 is the minimum ground stress of sandstone, MPa; C 页 is the cohesion of shale, MPa; C 砂 is the cohesion of sandstone, MPa; α is the effective stress coefficient; P p is the pore pressure, MPa; P f-页 is the shale fracture pressure, MPa; P f-砂 is the fracture pressure of sandstone, MPa; σ t-页 is the tensile strength of shale, MPa; σ t-砂 is the tensile strength of sandstone, MPa; is the internal friction angle of shale, (°); is the internal friction angle of sandstone, (°);

[0029] The lower limit of the shale safety density window is determined based on the calculated shale collapse pressure value, and the upper limit of the shale safety density window is determined based on the calculated shale fracture pressure value;

[0030] The lower limit of the sandstone safety density window is determined based on the calculated sandstone collapse pressure value, and the upper limit of the sandstone safety density window is determined based on the calculated sandstone fracture pressure value.

[0031] Further, in said S5, based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion, a finite element model of the shale-sandstone horizontal wellbore is established, specifically including:

[0032] Based on the basic parameters of shale-sandstone interlayer shale oil reservoirs, the Mohr-Coulomb strength criterion and multi-weak plane strength criterion algorithm were used to establish a finite element model of the shale-sandstone horizontal wellbore wall.

[0033] Among them, the basic parameters include the well depth position of the shale-sandstone interlayer shale oil reservoir, the maximum horizontal ground stress, the minimum horizontal ground stress, the overburden rock pressure, the well pressure, the shale density, the shale cohesion, the shale internal friction angle, the sandstone density, the sandstone cohesion, and the sandstone internal friction angle.

[0034] Furthermore, the S5 also includes analyzing the influence of different elastic moduli, Poisson's ratios and ground stresses on the wellbore stability based on the finite element model of the shale-sandstone horizontal wellbore, specifically including:

[0035] When the elastic modulus of shale is constant and the elastic modulus of sandstone increases, the difference between the circumferential stress and the radial stress increases, which means that the wellbore is prone to instability.

[0036] When the Poisson's ratio of sandstone is constant and the Poisson's ratio of shale increases, the difference between the circumferential stress and the radial stress changes slightly. Therefore, it can be seen that the change of the Poisson's ratio of shale has little effect on the stability of the wellbore.

[0037] When the Poisson's ratio of shale is constant and the Poisson's ratio of sandstone increases, the difference between the circumferential stress and the radial stress increases, and the risk of wellbore instability increases;

[0038] When the stratum is in the reverse fault stress mechanism, it satisfies σ H >σ h >σ v , where σ H represents the maximum horizontal principal stress, σ h represents the minimum horizontal principal stress, σ v It indicates that the difference between vertical stress, circumferential stress and radial stress is large, which makes wellbore collapse and instability prone to occur.

[0039] Further, the step S7, determining the wellbore stability based on the wellbore stability safety density window and the wellbore stability value of the well to be analyzed, specifically includes:

[0040] The obtained wellbore stability value of the well to be analyzed is compared with the safety density window of wellbore stability, and after exceeding the safety density window, a wellbore stability warning is issued.

[0041] The present invention also provides a shale-sandstone interlayer shale oil reservoir wellbore stability detection system, which is used to execute the above-mentioned shale-sandstone interlayer shale oil reservoir wellbore stability detection method, comprising:

[0042] A reservoir characteristic acquisition module is used to obtain reservoir characteristics of shale-sandstone interlayer shale oil reservoirs;

[0043] A wellbore instability micro-mechanism determination module, used to perform rock mechanics tests based on the reservoir characteristics to determine the wellbore instability micro-mechanism of the shale-sandstone interlayer shale oil reservoir;

[0044] A strength failure criterion determination module is used to determine the strength failure criterion of shale and sandstone based on the microscopic mechanism of wellbore instability;

[0045] The safety density window determination module is used to analyze the stress distribution of the surrounding rock of horizontal wells in shale-sandstone interlayer shale oil reservoirs, calculate the collapse pressure and fracture pressure of different rock formations, and determine the safety density window for wellbore stability;

[0046] A finite element model building module is used to establish a finite element model of the shale-sandstone horizontal wellbore wall based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion;

[0047] A stability calculation module, for determining the wellbore stability value of the wellbore to be analyzed based on the measured data of the wellbore to be analyzed in the shale-sandstone interlayer shale oil reservoir and using the wellbore finite element model of the shale-sandstone horizontal wellbore;

[0048] The stability comparison module is used to determine the wellbore stability state based on the wellbore stability safety density window and the wellbore stability value of the well to be analyzed.

[0049] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the shale-sandstone interlayer shale oil reservoir wellbore stability detection method and system provided by the present invention takes the shale-sandstone interlayer shale oil reservoir as the object, analyzes its reservoir characteristics; and performs reservoir characteristic analysis and rock mechanics tests to determine the microscopic mechanism of wellbore instability; combines the actual situation of studying the formation sandstone-shale, selects different criteria, and reveals the rock destruction mechanism; analyzes the stress distribution of the surrounding rock of the horizontal wellbore wall and calculates the collapse pressure and the fracture pressure respectively; in addition, establishes a finite element model of the wellbore wall of the shale-sandstone horizontal well, and analyzes the influence of different elastic moduli, Poisson's ratio and ground stress on the wellbore stability, and calculates the wellbore stability value of the well to be analyzed based on the measured data and the finite element model. The present invention combines multiple influencing parameters, determines the safe density window based on the collapse pressure and fracture pressure calculation formula, and detects the wellbore stability state. It is applicable to shale-sandstone interlayer shale oil reservoirs in Chang 7 area. It takes comprehensive factors into consideration and predicts wellbore stability more accurately, providing scientific basis and technical support for the research on shale-sandstone interlayer shale oil reservoir exploitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] 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.

[0051] Figure 1 Flow chart of a method for detecting wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to an embodiment of the present invention;

[0052] Figure 2 Schematic diagram of rock failure forms under triaxial stress in an embodiment of the present invention, wherein (a) is the failure form of a shale sample under 0 MPa, 15 MPa, and 30 MPa stresses, and (b) is the failure form of a sandstone sample under 0 MPa, 15 MPa, and 30 MPa stresses;

[0053] Figure 3 Schematic diagram of collapse pressure and fracture pressure corresponding to different well depths in an embodiment of the present invention;

[0054] Figure 4 It is a schematic diagram of the geometric structure of the shale-sandstone interlayer wellbore model in an embodiment of the present invention, wherein point A is the midpoint of the upper shale, point B is the upper shale-sandstone interface, point C is the midpoint of the sandstone, point D is the sandstone-lower shale interface, and point E is the midpoint of the lower shale. DETAILED DESCRIPTION

[0055] 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.

[0056] The purpose of the present invention is to provide a method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers. The method combines multiple influencing parameters, determines the safe drilling fluid density window based on the collapse pressure and fracture pressure calculation formula, and obtains the wellbore stability value. The method is suitable for shale oil reservoirs with shale-sandstone interlayers in Chang 7 area, takes comprehensive factors into consideration, and predicts the wellbore stability more accurately.

[0057] 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.

[0058] like Figure 1 As shown, the method for detecting the wellbore stability of a shale oil reservoir with a shale-sandstone interlayer provided by the present invention comprises the following steps:

[0059] S1, obtain the reservoir characteristics of shale oil reservoirs with shale-sandstone interlayers;

[0060] For example, the embodiment of the present invention takes the shale-sandstone interlayer shale oil reservoir in Chang 7 area as the object, and uses seismic exploration technology to obtain reservoir characteristics, which include geological structure, lithology combination, sand-to-ground ratio, and single sand body thickness.

[0061] S2, based on the reservoir characteristics, rock mechanics tests are conducted to determine the microscopic mechanism of wellbore instability in shale-sandstone interlayer shale oil reservoirs, specifically including:

[0062] Based on the reservoir characteristics, the GCTS-3000 rock mechanics test system was used to obtain the compressive strength, elastic modulus, Poisson's ratio of shale and sandstone and their respective failure forms (such as Figure 2 The experimental results are shown in Figure 3 and the microscopic mechanism of wellbore instability in shale oil reservoirs with shale-sandstone interlayers is determined based on the experimental results.

[0063] The purpose of reservoir characteristic analysis and rock mechanics tests is to analyze the microscopic mechanism of wellbore instability. Through the microscopic mechanism of wellbore instability, we can deeply understand the causes and conditions of wellbore instability and reveal the mechanical mechanism of wellbore instability, including the influence of shale-sandstone interlayer shale oil reservoir on the wellbore, which provides a basis for the selection of shale and sandstone strength criteria and the establishment of finite element model of shale-sandstone horizontal wellbore.

[0064] S3, based on the microscopic mechanism of wellbore instability, determine the strength failure criteria of shale and sandstone; specifically including:

[0065] Based on the compressive strength, elastic modulus, Poisson's ratio and respective failure modes of shale and sandstone, the strength failure criteria of shale and sandstone are determined; among them, the strength failure criterion of shale is the multiple weak plane strength criterion, and the strength failure criterion of sandstone is the Mohr-Coulomb strength criterion.

[0066] According to the actual conditions of the formation rock, different strength failure criteria are selected to ensure the objectivity and accuracy of the strength failure criteria. According to the analysis of sandstone failure forms, sandstone is mainly controlled by shear failure. When analyzing the stability of sandstone wellbore, the Mohr-Coulomb strength failure criterion is mainly used for research. The traditional prediction model that only considers homogeneous formations or a single weak plane cannot accurately calculate the appropriate safe drilling fluid density window, so shale selects the multi-weak plane strength criterion. The selection of rock failure criteria is mainly based on rock properties, failure properties and rock failure process. In addition to the Mohr-Coulomb strength criterion used for the above-mentioned sandstone, the Drucker-Prager criterion was also used for experiments, but after investigating relevant literature, it was concluded that the Mohr-Coulomb strength failure criterion for sandstone is more accurate.

[0067] S4, analyzes the stress distribution of the surrounding rock of horizontal wells in shale-sandstone interlayer shale oil reservoirs, calculates the collapse pressure and fracture pressure of different rock formations, and determines the safe density window for wellbore stability, including:

[0068] The maximum horizontal geostress, minimum horizontal geostress, overburden stress, wellbore radius, Poisson's ratio, effective stress coefficient and pore pressure parameters can be obtained through stress experiments or logging data, and the stress distribution of the surrounding rock of horizontal wells in shale-sandstone interlayer shale oil reservoirs can be analyzed using the wellbore surrounding rock stress expression;

[0069] According to the maximum geostress of shale, the minimum geostress of shale, the maximum geostress of sandstone, the minimum geostress of sandstone, the cohesion of shale, the cohesion of sandstone, the effective stress coefficient, the pore pressure, the tensile strength of shale, and the tensile strength of sandstone, the collapse pressure and the fracture pressure formula are substituted to obtain the collapse pressure and the fracture pressure value, such as Figure 3 As shown:

[0070] Calculate the collapse pressure of shale and sandstone:

[0071]

[0072] Calculate the fracture pressure of shale and sandstone:

[0073] P f-页 =3σ H-页 -σh-页 -αP p +σ t-页

[0074] P f-砂 =3σ H-砂 -σ h-砂 -αP p +σ t-砂

[0075] Where P c-页 is the shale collapse pressure, MPa; P c-砂 is the collapse pressure of sandstone, MPa; σ H-页 is the maximum in-situ stress of shale, MPa; σ h-页 is the minimum in-situ stress of shale, MPa; σ H-砂 is the maximum in-situ stress of sandstone, MPa; σ h-砂 is the minimum ground stress of sandstone, MPa; C 页 is the cohesion of shale, MPa; C 砂 is the cohesion of sandstone, MPa; α is the effective stress coefficient; P p is the pore pressure, MPa; P f-页 is the shale fracture pressure, MPa; P f-砂 is the fracture pressure of sandstone, MPa; σ t-页 is the tensile strength of shale, MPa; σ t-砂 is the tensile strength of sandstone, MPa; is the internal friction angle of shale, (°); is the internal friction angle of sandstone, (°).

[0076] Among them, the safe density window for wellbore stability is determined, including the shale safe density window and the sandstone safe density window, which specifically include:

[0077] Determine the shale safety density window: By substituting the shale related parameters into the collapse pressure calculation formula and the fracture pressure calculation formula, the collapse pressure value is the lower limit of the shale safety density window, and the fracture pressure value is the upper limit of the shale safety density window; To determine the upper limit range of the shale safety density window, the relevant parameters in the shale fracture pressure formula are required: σ H-页 , σ h-页 , P p , α, σ t-页 To determine the lower limit of the shale safety density window, we need the relevant parameters in the shale collapse pressure formula: H-页 , σ h-页 , P p , C 页 , K 页 , α.

[0078] Determine the safe density window of sandstone. Similarly, substitute the sandstone related parameters into the collapse pressure calculation formula and the fracture pressure calculation formula. The collapse pressure value obtained is the lower limit of the sandstone safe density window, and the fracture pressure value is the upper limit of the sandstone safe density. Determine the upper limit range of the sandstone safe density, that is, the relevant parameters in the sandstone fracture pressure formula are needed: σ H-砂 , σ h-砂 ,α,P p , σ t-砂 To determine the lower limit of the sandstone safety density window, we need the relevant parameters in the sandstone collapse pressure formula: H-砂 , σ h-砂 , C 砂 , K 砂 , α、P p .

[0079] S5, based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion, a finite element model of the shale-sandstone horizontal wellbore is established, specifically including:

[0080] Based on the location of the reservoir (well depth), maximum horizontal geostress, minimum horizontal geostress, overburden pressure, wellbore pressure, shale density, shale cohesion, shale internal friction angle, sandstone density, sandstone cohesion, sandstone internal friction angle and other related basic parameters, the Mohr-Coulomb and multi-weak plane strength criterion algorithms were used to establish the finite element model of the shale-sandstone horizontal wellbore wall.

[0081] The S5 further includes analyzing the influence of different elastic moduli, Poisson's ratios and ground stresses on the wellbore stability based on the finite element model of the shale-sandstone horizontal wellbore, specifically including:

[0082] The final values ​​of elastic modulus, Poisson's ratio and geostress are determined through indoor experiments, field data and reference to relevant literature. The radial stress distribution of shale with different elastic moduli, the circumferential stress distribution cloud diagram of sandstone with different Poisson's ratios and three typical geostress mechanisms are obtained, namely normal fault (σ v >σ H >σ h ), strike-slip fault (σ H >σ v >σ h ), reverse fault (σ H >σ h >σ v ) Three types of ground stress and stress distribution around the wellbore.

[0083] The effects of different elastic moduli, Poisson's ratios and ground stresses on wellbore stability are not random but follow certain rules.

[0084] When the elastic modulus of shale is constant and the elastic modulus of sandstone increases, the difference between the circumferential stress and the radial stress increases, that is, the wellbore is prone to instability.

[0085] When the Poisson's ratio of sandstone is constant, as the Poisson's ratio of shale increases, the difference between circumferential stress and radial stress changes little. It can be seen that the change of shale Poisson's ratio has almost no effect on wellbore stability. However, when the Poisson's ratio of shale is constant and the Poisson's ratio of sandstone increases, the difference between circumferential stress and radial stress increases, and the risk of wellbore instability increases.

[0086] When the stratum is in the reverse fault stress mechanism, it satisfies σ H >σ h >σ v , where σ H represents the maximum horizontal principal stress, σ h represents the minimum horizontal principal stress, σ v It indicates that the difference between vertical stress, circumferential stress and radial stress is large, which makes wellbore collapse and instability prone to occur.

[0087] S6, based on the measured data of the well to be analyzed in the shale-sandstone interlayer shale oil reservoir, using the finite element model of the wellbore of the shale-sandstone horizontal well, determining the wellbore stability value of the well to be analyzed;

[0088] Specifically, the measured data include shale in-situ stress, shale in-situ stress, sandstone in-situ stress, sandstone minimum in-situ stress, shale cohesion, sandstone cohesion, effective stress coefficient, pore pressure, shale tensile strength, and sandstone tensile strength. Substitute the relevant parameters of shale and sandstone into the collapse pressure and fracture pressure calculation formulas. If the obtained value is within the safe density window range (i.e., the lower limit is the collapse pressure value and the upper limit is the fracture pressure value), it can be determined that the wellbore wall of the well to be analyzed is stable, otherwise, the wellbore wall is unstable.

[0089] S7, based on the safety density window of wellbore stability and the wellbore stability value of the well to be analyzed, determining the wellbore stability state, specifically including:

[0090] The safety density window of wellbore stability is a set threshold value, and the wellbore stability value of the well to be analyzed is compared with the safety density window of wellbore stability. After exceeding the safety density window, a wellbore stability warning is issued.

[0091] The present invention also provides a shale-sandstone interlayer shale oil reservoir wellbore stability detection system, which is used to execute the above-mentioned shale-sandstone interlayer shale oil reservoir wellbore stability detection method, comprising:

[0092] A reservoir characteristic acquisition module is used to obtain reservoir characteristics of shale-sandstone interlayer shale oil reservoirs;

[0093] A wellbore instability micro-mechanism determination module, used to perform rock mechanics tests based on the reservoir characteristics to determine the wellbore instability micro-mechanism of the shale-sandstone interlayer shale oil reservoir;

[0094] A strength failure criterion determination module is used to determine the strength failure criterion of shale and sandstone based on the microscopic mechanism of wellbore instability;

[0095] The safety density window determination module is used to analyze the stress distribution of the surrounding rock of horizontal wells in shale-sandstone interlayer shale oil reservoirs, calculate the collapse pressure and fracture pressure of different rock formations, and determine the safety density window for wellbore stability;

[0096] A finite element model building module is used to establish a finite element model of the shale-sandstone horizontal wellbore wall based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion;

[0097] A stability calculation module, for determining the wellbore stability value of the wellbore to be analyzed based on the measured data of the wellbore to be analyzed in the shale-sandstone interlayer shale oil reservoir and using the wellbore finite element model of the shale-sandstone horizontal wellbore;

[0098] The stability comparison module is used to determine the wellbore stability state based on the wellbore stability safety density window and the wellbore stability value of the well to be analyzed.

[0099] In summary, the present invention takes the shale-sandstone interlayer shale oil reservoir in Chang 7 area as the object, analyzes its reservoir characteristics; carries out shale-sandstone reservoir characteristics analysis and mechanical experiments, and analyzes the microscopic mechanism of wellbore instability; combines the actual situation of sandstone-shale in the formation, selects different criteria, and reveals the rock failure mechanism; analyzes the stress distribution of the surrounding rock of the horizontal wellbore wall and calculates the collapse pressure and fracture pressure; establishes a finite element model of the wellbore wall of shale-sandstone horizontal well, and analyzes the influence of different elastic moduli, Poisson's ratio and ground stress on the stability of the wellbore wall. The present invention combines a variety of influencing parameters, determines the safe density window based on the calculation formula of collapse pressure and fracture pressure, and detects the stability state of the wellbore wall. It is suitable for shale-sandstone interlayer shale oil reservoirs in Chang 7 area, takes comprehensive factors into consideration, and predicts the stability of the wellbore wall more accurately, providing scientific basis and technical support for the research on the exploitation of shale-sandstone interlayer shale oil reservoirs.

[0100] 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.

[0101] 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 detecting the wellbore stability of a shale oil reservoir with shale-sandstone interlayers, characterized in that: The following steps are involved: S1, obtain the reservoir characteristics of shale oil reservoirs with shale-sandstone interlayers; S2, based on the reservoir characteristics, rock mechanics tests are conducted to determine the microscopic mechanism of wellbore instability in shale oil reservoirs with shale-sandstone interlayers; S3, based on the microscopic mechanism of wellbore instability, determine the strength failure criteria of shale and sandstone; S4, analyze the stress distribution of the surrounding rock of the horizontal wellbore in the shale-sandstone interlayer shale oil reservoir, calculate the collapse pressure and fracture pressure of different rock formations, and determine the safe density window for wellbore stability; S5, establishing a finite element model of the shale-sandstone horizontal wellbore wall based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion; S6, based on the measured data of the well to be analyzed in the shale-sandstone interlayer shale oil reservoir, using the finite element model of the wellbore of the shale-sandstone horizontal well, determining the wellbore stability value of the well to be analyzed; S7, determining the wellbore stability state based on the wellbore stability safety density window and the wellbore stability value of the well to be analyzed.

2. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 1 is characterized in that: In S1, the reservoir characteristics of the shale-sandstone interlayer shale oil reservoir are obtained, specifically including: The shale-sandstone interlayer shale oil reservoir in the area to be detected is taken as the object, and the reservoir characteristics are obtained by using seismic exploration technology. The reservoir characteristics include geological structure, lithology combination, sand-to-ground ratio, and single sand body thickness.

3. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 1, characterized in that: S2, based on the reservoir characteristics, conducts rock mechanics tests to determine the microscopic mechanism of wellbore instability in shale-sandstone interlayer shale oil reservoirs, specifically including: Based on the reservoir characteristics, the GCTS-3000 rock mechanics test system was used to obtain the compressive strength, elastic modulus, Poisson's ratio of shale and sandstone and their respective failure forms as test results. Based on the test results, the microscopic mechanism of wellbore instability in shale oil reservoirs with shale-sandstone interlayers was determined.

4. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 3 is characterized in that: The S3, based on the microscopic mechanism of wellbore instability, determines the strength failure criteria of shale and sandstone, specifically including: Based on the compressive strength, elastic modulus, Poisson's ratio and respective failure modes of shale and sandstone, the strength failure criteria of shale and sandstone are determined; among them, the strength failure criterion of shale is the multiple weak plane strength criterion, and the strength failure criterion of sandstone is the Mohr-Coulomb strength criterion.

5. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 1, characterized in that: In S4, the stress distribution of the surrounding rock of the horizontal well wall in the shale-sandstone interlayer shale oil reservoir is analyzed, which specifically includes: The maximum horizontal geostress, minimum horizontal geostress, overburden stress, wellbore radius, Poisson's ratio, effective stress coefficient and pore pressure parameters are obtained, and the wellbore surrounding rock stress expression is used to analyze the wellbore surrounding rock stress distribution of horizontal wells in shale-sandstone interlayer shale oil reservoirs.

6. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 5, characterized in that: In S4, the collapse pressure and fracture pressure of different rock formations are calculated to determine the safe density window for wellbore stability, which specifically includes: Calculate the collapse pressure of shale and sandstone: Calculate the fracture pressure of shale and sandstone: P f-页 =3σ H-页 -s h-页 -αP p +s t-页 P f-砂 =3σ H-砂 -s h-砂 -αP p +s t-砂 Where P c-页 is the shale collapse pressure, MPa; P c-砂 is the collapse pressure of sandstone, MPa; σ H-页 is the maximum in-situ stress of shale, MPa; σ h-页 is the minimum in-situ stress of shale, MPa; σ H-砂 is the maximum in-situ stress of sandstone, MPa; σ h-砂 is the minimum ground stress of sandstone, MPa; C 页 is the cohesion of shale, MPa; C 砂 is the cohesion of sandstone, MPa; α is the effective stress coefficient; P p is the pore pressure, MPa; P f-页 is the shale fracture pressure, MPa; P f-砂 is the fracture pressure of sandstone, MPa; σ t-页 is the tensile strength of shale, MPa; σ t-砂 is the tensile strength of sandstone, MPa; is the internal friction angle of shale; is the internal friction angle of sandstone; The lower limit of the shale safety density window is determined based on the calculated shale collapse pressure value, and the upper limit of the shale safety density window is determined based on the calculated shale fracture pressure value; The lower limit of the sandstone safety density window is determined based on the calculated sandstone collapse pressure value, and the upper limit of the sandstone safety density window is determined based on the calculated sandstone fracture pressure value.

7. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 1, characterized in that: In S5, based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion, a finite element model of the shale-sandstone horizontal wellbore is established, which specifically includes: Based on the basic parameters of shale-sandstone interlayer shale oil reservoirs, the Mohr-Coulomb strength criterion and multi-weak plane strength criterion algorithm were used to establish a finite element model of the shale-sandstone horizontal wellbore wall. Among them, the basic parameters include the well depth position of the shale-sandstone interlayer shale oil reservoir, the maximum horizontal ground stress, the minimum horizontal ground stress, the overburden rock pressure, the well pressure, the shale density, the shale cohesion, the shale internal friction angle, the sandstone density, the sandstone cohesion, and the sandstone internal friction angle.

8. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 7, characterized in that: The S5 further includes analyzing the influence of different elastic moduli, Poisson's ratios and ground stresses on the wellbore stability based on the finite element model of the shale-sandstone horizontal wellbore, specifically including: When the elastic modulus of shale is constant and the elastic modulus of sandstone increases, the difference between the circumferential stress and the radial stress increases, which means that the wellbore is prone to instability. When the Poisson's ratio of sandstone is constant and the Poisson's ratio of shale increases, the difference between the circumferential stress and the radial stress changes slightly. Therefore, it can be seen that the change of the Poisson's ratio of shale has little effect on the stability of the wellbore. When the Poisson's ratio of shale is constant and the Poisson's ratio of sandstone increases, the difference between the circumferential stress and the radial stress increases, and the risk of wellbore instability increases; When the stratum is in the reverse fault stress mechanism, it satisfies σ H >σ h >σ v , where σ H represents the maximum horizontal principal stress, σ h represents the minimum horizontal principal stress, σ v It indicates that the difference between vertical stress, circumferential stress and radial stress is large, which makes wellbore collapse and instability prone to occur.

9. The method for detecting the wellbore stability of shale oil reservoirs with shale-sandstone interlayers according to claim 1, characterized in that: The step S7, determining the wellbore stability based on the wellbore stability safety density window and the wellbore stability value of the well to be analyzed, specifically includes: The obtained wellbore stability value of the well to be analyzed is compared with the safety density window of wellbore stability, and after exceeding the safety density window, a wellbore stability warning is issued.

10. A shale-sandstone interlayer type shale oil reservoir wellbore stability detection system, used to execute the shale-sandstone interlayer type shale oil reservoir wellbore stability detection method according to any one of claims 1 to 9, characterized in that: include: A reservoir characteristic acquisition module is used to obtain reservoir characteristics of shale-sandstone interlayer shale oil reservoirs; A wellbore instability micro-mechanism determination module, used to perform rock mechanics tests based on the reservoir characteristics to determine the wellbore instability micro-mechanism of the shale-sandstone interlayer shale oil reservoir; A strength failure criterion determination module is used to determine the strength failure criterion of shale and sandstone based on the microscopic mechanism of wellbore instability; The safety density window determination module is used to analyze the stress distribution of the surrounding rock of horizontal wells in shale-sandstone interlayer shale oil reservoirs, calculate the collapse pressure and fracture pressure of different rock formations, and determine the safety density window for wellbore stability; A finite element model building module is used to establish a finite element model of the shale-sandstone horizontal wellbore wall based on the basic parameters of the shale-sandstone interlayer shale oil reservoir and the strength failure criterion; A stability calculation module, for determining the wellbore stability value of the wellbore to be analyzed based on the measured data of the wellbore to be analyzed in the shale-sandstone interlayer shale oil reservoir and using the wellbore finite element model of the shale-sandstone horizontal wellbore; The stability comparison module is used to determine the wellbore stability state based on the wellbore stability safety density window and the wellbore stability value of the well to be analyzed.

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