Horizontal well casing damage prevention and control method

Abstract

The invention relates to a horizontal well casing damage prevention and control method, which relates to the technical field of shale oil exploitation, and specifically comprises the following steps: obtaining scores corresponding to risk index parameters of a target well in a work area and risk grades of the target well; if the risk level of the target well is a medium risk or a low risk, risk level prediction is carried out on the target well regularly; if the risk level of the target well is high risk or ultrahigh risk, dividing all the risk index parameters into four classes; and if the score of the risk index parameter is greater than or equal to a predetermined score, performing casing damage prevention and control on the target well by using a prevention and control method corresponding to the classification of the risk index parameter. The problems that a previous casing damage prevention and control method needs to depend on accurate recognition of all positions prone to casing deformation in a well, but due to the fact that shale bedding, cracks and faults are widely developed and cannot be completely and accurately recognized actually, casing deformation still happens to unrecognized sections prone to casing deformation are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of shale oil exploitation, and in particular to a method for preventing and controlling casing damage of a horizontal well. Background Art

[0002] my country has huge shale oil resources. The safe, economical and efficient development of shale oil is of great significance to the national energy security. The engineering means of shale oil development are similar to those of shale gas, and large-scale horizontal well hydraulic fracturing technology is used for development. Shale oil has great development potential, but it faces the problem of casing damage. According to statistics, the proportion of casing damage can reach 41.7%. Casing damage will not only cause the bridge plug to fail to be seated in place, reduce the number of subsequent fracturing stages, and affect the fracturing effect, but also increase the construction cost and difficulty, shorten the life cycle of the wellbore, and thus reduce the overall economic benefits of shale oil development.

[0003] The current casing damage prevention and control methods mainly identify the activated faults in the target well area, evaluate the sliding risk of cracks or faults, determine the casing change-prone sections in the well, and avoid the activated faults during construction for the casing change-prone locations; optimize the construction parameters to control the fault activation area; set up a bypass cementing device; and set a glue cavity outside the casing corresponding to the cracks or faults to be filled with high-sealing glue to achieve the purpose of casing damage prevention and control.

[0004] However, in most cases, the shale bedding, cracks and faults in the target well area are widely developed and cannot be accurately identified. Therefore, it is impossible to completely avoid the areas with developed bedding, cracks and faults in the actual drilling process; the quantitative relationship between construction parameters and fault activation is difficult to establish, and the specific operation of optimizing construction parameters is low in feasibility; too many layer-wrap cementing devices are set up, which increases the construction cost; the gap between the formation and the cement sheath does not exist under normal cementing conditions, and it is impossible to set a high-sealing glue to fill the glue cavity; for those easy-to-change sections that have not been accurately identified, casing changes may still occur, and the purpose of casing damage prevention and control cannot be achieved. Other methods, including changing casing parameters, such as increasing casing steel grade, wall thickness, size, etc., changing cement sheath parameters, such as reducing cement sheath Young's modulus, increasing cement sheath thickness, and staged cementing, have not achieved significant results in field practice. Summary of the invention

[0005] The present invention proposes a method for preventing and controlling casing damage in horizontal wells to solve the problem that previous methods for preventing and controlling casing damage rely on accurately identifying all casing-prone locations in the well. However, due to the widespread development of shale bedding, fractures and faults, they cannot be fully and accurately identified in practice, resulting in the problem that casing changes may still occur in unidentified casing-prone sections.

[0006] According to one aspect of the present invention, a method for preventing and controlling casing damage in a horizontal well is provided, comprising:

[0007] Obtain the scores corresponding to each risk indicator parameter of the target well in the work area and the risk level of the target well;

[0008] If the risk level of the target well is medium risk or low risk, the risk level of the target well is predicted regularly;

[0009] If the risk level of the target well is high risk or ultra-high risk, all the risk index parameters are divided into four categories, wherein the first category includes the relative activity coefficient of the fault-crack at the casing risk point and / or the brittleness index of the shale reservoir and / or the angle between the fault-crack surface and the wellbore and / or the shale reservoir fracture pressure, the second category includes the extension length of the fault-crack surface, the third category includes the wellbore temperature difference before and after fracturing, and the fourth category includes the perforation density;

[0010] If the score of the risk indicator parameter is greater than or equal to the predetermined score, the casing damage prevention and control of the target well is carried out using the prevention and control method corresponding to the category of the risk indicator parameter, wherein the prevention and control method corresponding to the first category is to reduce the fracturing pressure to the original first predetermined percentage and reduce the fracturing fluid injection volume to the original second predetermined percentage, the prevention and control method corresponding to the second category is to inject a temporary plugging agent, the prevention and control method corresponding to the third category is to increase the fracturing fluid injection temperature to the original third predetermined percentage and reduce the fracturing fluid injection and return speed to the original fourth predetermined percentage, and the prevention and control method corresponding to the fourth category is to use engineering methods to strengthen the wellbore.

[0011] Preferably, the predetermined score is: 50 or 55 or 65 or 75.

[0012] Preferably, the value range of the first predetermined percentage is: 90-98%;

[0013] The second predetermined percentage has a value range of 80-95%.

[0014] Preferably, the temporary plugging agent is one or more of a cross-linked polymer temporary plugging agent, a fiber temporary plugging agent, an inorganic salt temporary plugging agent or a composite material temporary plugging agent.

[0015] Preferably, the cross-linked polymer temporary plugging agent is one or more of polyacrylamide, polyacrylic acid, and polyethylene wax;

[0016] The fiber temporary plugging agent is one or more of polyester fiber, polylactic acid fiber, and polypropylene fiber;

[0017] The inorganic salt temporary plugging agent is one or more of calcium carbonate, sodium chloride, and benzoic acid flakes;

[0018] The composite material temporary plugging agent is one or more of a composite material of silicon dioxide and a cross-linked polymer, a composite material of fly ash and a cross-linked polymer, and a composite material of fibers and particles.

[0019] Preferably, the third predetermined percentage has a value range of: 120-200%;

[0020] The fourth predetermined percentage has a value range of 80-95%.

[0021] Preferably, the engineering method for strengthening the wellbore comprises:

[0022] One or more of the following methods: cement squeezing, packer installation, casing patching, casing tieback, chemical plugging or casing replacement.

[0023] Preferably, before obtaining the scores corresponding to the risk indicator parameters of the target wells in the work area, the scores corresponding to the risk indicator parameters of the target wells are determined, and the method includes:

[0024] Obtain the risk index parameter values ​​of the target wells in the work area;

[0025] Divide the numerical range of the risk indicator parameter into n sub-limits, divide the score of 0 to 100 into n score segments, and correspond the sub-limits of the risk indicator parameter to the score segments;

[0026] The score corresponding to each risk indicator parameter value of the target well is determined according to the score segments corresponding to the sub-limits of the risk indicator parameter.

[0027] Preferably, before obtaining the risk level of the target well in the work area, the risk level of the target well is determined, and the method includes:

[0028] Determine the risk prediction value of the target well by using a risk assessment formula according to the scores corresponding to the values ​​of the risk indicator parameters of the target well;

[0029] If the risk prediction value is 0-25, the target well is determined to be at low risk of horizontal well casing damage; if the risk prediction value is 25-50, the target well is determined to be at medium risk of horizontal well casing damage; if the risk prediction value is 50-75, the target well is determined to be at high risk of horizontal well casing damage; and if the risk prediction value is 75-100, the target well is determined to be at ultra-high risk of horizontal well casing damage.

[0030] Preferably, the risk assessment formula includes formula (8) or (9);

[0031] F=C1*α1+C2*α2+C3*α3+C4*α4+C5*α5+C6*α6+C7*α7,

[0032] α1+α2+α3+α4+α5+α6+α7=1(8);

[0033] In the formula, F is the risk prediction value, C1 is the score corresponding to the relative activity coefficient of fault-crack, α1 is the weight coefficient of C1, C2 is the score corresponding to the brittleness index of shale reservoir, α2 is the weight coefficient of C2, C3 is the score corresponding to the extension length of fault-crack surface, α3 is the weight coefficient of C3, C4 is the score corresponding to the angle between fault-crack surface and wellbore, α4 is the weight coefficient of C4, C5 is the score corresponding to the fracture pressure of shale reservoir, α5 is the weight coefficient of C5, C6 is the score corresponding to the temperature difference of wellbore before and after fracturing, α6 is the weight coefficient of C6; C7 is the score corresponding to the perforation density, α7 is the weight coefficient of C7;

[0034] F=(C1*C2*C3*C4*C5) 1 / 5 *α1+(C6*C7) 1 / 2 *α2, α1+α2=1 (9);

[0035] Where F is the risk prediction value, C1 is the score corresponding to the fault-crack relative activity coefficient, C2 is the score corresponding to the shale reservoir brittleness index, C3 is the score corresponding to the fault-crack extension length, C4 is the score corresponding to the angle between the fault-crack surface and the wellbore, C5 is the score corresponding to the shale reservoir fracture pressure, C6 is the score corresponding to the wellbore temperature difference before and after fracturing, C7 is the score corresponding to the perforation density, α1 is the weight coefficient of C1*C2*C3*C4*C5, and α2 is the weight coefficient of C6*C7.

[0036] The present invention has at least the following beneficial effects:

[0037] The present invention proposes a method for preventing and controlling casing damage in horizontal wells. According to the risk level of casing change in the target well, for high and ultra-high risk horizontal wells, the risk index parameters are classified according to the most important factors causing casing damage. Each category has its corresponding prevention and control method, and the prevention and control method corresponding to the classification in which the risk index parameter score exceeds the predetermined score is selected to prevent and control casing damage in the horizontal well. The present invention adopts different casing damage prevention and control methods for different high and ultra-high risk indicators, improves the casing damage prevention and control effect of horizontal wells, and avoids the simplification and generalization of casing damage prevention and control. Thereby, effective prevention and control of casing damage is achieved, the normal progress of hydraulic fracturing is guaranteed, and the economic benefits of shale oil development are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings herein are incorporated into and constitute a part of the specification. These drawings illustrate embodiments consistent with the present invention and, together with the specification, are used to explain the technical solutions of the present invention.

[0039] Figure 1 A flow chart of a method for preventing and controlling casing damage in a horizontal well according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] Various exemplary embodiments, features and aspects of the present invention will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0041] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0042] The term "and / or" herein is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the term "at least one" herein represents any combination of at least two of any one or more of a plurality of. For example, including at least one of A, B, and C can represent including any one or more elements selected from the set consisting of A, B, and C.

[0043] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0044] Figure 1 A flow chart of a method for preventing and controlling casing damage in a horizontal well according to an embodiment of the present invention is shown. Figure 1 As shown, a method for preventing and controlling casing damage of a horizontal well includes: step S01: obtaining the scores corresponding to each risk indicator parameter of a target well in a work area and the risk level of the target well;

[0045] Step S02: If the risk level of the target well is medium risk or low risk, the risk level of the target well is predicted regularly;

[0046] Step S03: If the risk level of the target well is high risk or ultra-high risk, all the risk index parameters are divided into four categories, wherein the first category includes the relative activity coefficient of the fault-crack at the casing damage risk point and / or the brittleness index of the shale reservoir and / or the angle between the fault-crack surface and the wellbore and / or the shale reservoir fracture pressure, the second category includes the extension length of the fault-crack surface, the third category includes the wellbore temperature difference before and after fracturing, and the fourth category includes the perforation density;

[0047] Step S04: If the score of the risk indicator parameter is greater than the predetermined score, the casing damage prevention and control of the target well is carried out using the prevention and control method corresponding to the classification of the risk indicator parameter, wherein the prevention and control method corresponding to the first category is to reduce the fracturing pressure to the original first predetermined percentage and reduce the fracturing fluid injection volume to the original second predetermined percentage, the prevention and control method corresponding to the second category is to inject a temporary plugging agent, the prevention and control method corresponding to the third category is to increase the fracturing fluid injection temperature to the original third predetermined percentage and reduce the fracturing fluid injection and return speed to the original fourth predetermined percentage, and the prevention and control method corresponding to the fourth category is to use engineering methods to strengthen the wellbore.

[0048] A method for preventing and controlling casing damage in a horizontal well of the present invention specifically comprises the following steps:

[0049] Step S01: Obtain the scores corresponding to each risk indicator parameter of the target well in the work area and the risk level of the target well.

[0050] The risk indicator parameters include at least: the relative activity coefficient of the fault-crack at the casing damage risk point, the brittleness index of the shale reservoir, the extension length of the fault-crack surface, the angle between the fault-crack surface and the wellbore, the shale reservoir fracture pressure, the temperature difference of the wellbore before and after fracturing, and the perforation density.

[0051] In the present invention, before obtaining the scores corresponding to the risk indicator parameters of the target wells in the work area, the scores corresponding to the risk indicator parameters of the target wells are determined, and the method includes:

[0052] Obtain the risk index parameter values ​​of the target wells in the work area;

[0053] Divide the numerical range of the risk indicator parameter into n sub-limits, divide the score of 0 to 100 into n score segments, and correspond the sub-limits of the risk indicator parameter to the score segments;

[0054] The score corresponding to each risk indicator parameter value of the target well is determined according to the score segment corresponding to the sub-limit of the risk indicator parameter.

[0055] In the embodiment of the present invention, before obtaining the risk indicator parameter values ​​of the target wells in the work area, it is necessary to determine the relative activity coefficient of the fracture and the brittleness index of the shale reservoir in the risk indicator parameters.

[0056] The relative fracture activity coefficient is calculated using formula (1) or (2).

[0057]

[0058] In formula (1): f ais the relative activity coefficient of the fracture (the shear slip trend factor of the interface), σ1, σ2, and σ3 are the three principal stresses of the fracture layer at the casing damage risk point, θ is the angle between the fracture surface (or weak surface) and σ1, α is the angle between the intersection of the fracture surface (or weak surface) and the σ2-σ3 plane and the σ3 axis, and C P is the cohesion of the fracture-fracture surface (or weak surface), μ P is the friction coefficient of the fracture surface (or weak surface), and P is the fluid pressure of the fracture surface (or weak surface).

[0059]

[0060] In formula (2): f a is the relative activity coefficient of the fracture (the shear slip trend factor of the interface), σ1, σ2, and σ3 are the three principal stresses of the fracture layer at the casing damage risk point, β is the angle between the fracture surface (or weak surface) and the σ1 axis, is the inclination angle of the fracture plane (or weak plane), C W is the cohesive force of the fracture surface (or weak surface), μ is the friction coefficient of the fracture surface (or weak surface), and P is the fluid pressure of the fracture surface (or weak surface).

[0061] In equations (1) and (2), the fluid pressure P at the fault surface (or weak surface) is the sum of the formation fluid pressure and the fluid pressure increment caused by hydraulic fracturing, and is calculated as follows:

[0062] P = P0 + ΔP (3);

[0063] Where: ΔP is the fluid pressure increment caused by hydraulic fracturing, and P0 is the formation fluid pressure at the casing change risk point.

[0064] In formula (3), the calculation formula of formation fluid pressure P0 is:

[0065] P0=kρ w gh (4);

[0066] Where: k is the fluid pressure coefficient, ρ w is the density of water, g is the acceleration of gravity, h is the vertical depth of the risk point, and k=1.85.

[0067] According to the formation fluid pressure P0 at the casing change risk point and the modeling data of the ground stress field, the sum of the formation fluid pressure and the fluid pressure increment caused by hydraulic fracturing is calculated by the "Generalized Fracture Theory Application System V1.0" software to obtain the weak surface fluid pressure P.

[0068] In equations (1) and (2), the cohesion and friction coefficient are determined based on experimental data. If there is no experimental data, the cohesion can be taken as 1.0 MPa and the friction coefficient can be taken as 0.6.

[0069] Among them, fault-crack surface refers to fault plane and fracture surface; weak surface refers to fault plane, fracture surface and formation interface; fault-crack surface extension length refers to the length of the fault plane or fracture surface in the longest extension direction; the angle between the fault-crack surface and the wellbore refers to the minimum acute angle formed by the fault plane or fracture plane and the horizontal section of the horizontal wellbore, including the right angle formed by the fault plane or fracture plane and the horizontal section of the horizontal wellbore; the wellbore temperature difference before and after fracturing refers to the temperature difference of the horizontal section of the horizontal wellbore before and after fracturing.

[0070] In the embodiment of the present invention, the shale reservoir brittleness index is calculated using formula (5) or (6) or (7).

[0071] B YB =[(E s -E min ) / (E max -E min )+(ν max -ν s ) / (ν max -ν min )]*100 / 2 (5);

[0072] In formula (5), B YB is the rock mechanical brittleness index of shale, E s is the static Young's modulus of the sample, E min is the lower limit of the static Young's modulus of shale, E max is the upper limit of the static Young's modulus of shale, ν s is the static Poisson's ratio of the sample, ν min is the lower limit of the static Poisson's ratio of shale, ν max is the upper limit of the static Poisson's ratio of shale;

[0073] B M1 =(αX quartz +βX dolomite +γX calcite +ηX feldspar +ζX pyrite +ωX clay +k)*100 (6);

[0074] B M2 =(X quartz +X dolomite +X calcite +X feldspar +X pyrite )*100 (7);

[0075] In formula (6) and (7), B M1 is the shale mineral brittleness index of rock mechanics weight method, B M2 is the brittle mineral method shale mineral brittleness index, X quartz is the mass fraction of quartz in the sample, X dolomite is the mass fraction of dolomite in the sample, X calcite is the mass fraction of calcite in the sample, X feldspar is the mass fraction of feldspar in the sample, X pyrite is the mass fraction of pyrite in the sample, X clay is the mass fraction of clay minerals in the sample; α, β, γ, η, ζ, ω are the weight coefficients of quartz, dolomite, calcite, feldspar, pyrite and clay minerals respectively, and k is the correction constant term.

[0076] Among them, the fault-fracture plane extension length, the angle between the fault-fracture plane and the wellbore, the shale reservoir fracture pressure, the wellbore temperature difference before and after fracturing, and the perforation density parameters are obtained through the shale reservoir parameter data, horizontal well parameter data, and fracturing parameter data of the target horizontal well.

[0077] In an embodiment of the present invention, before dividing the numerical range of the risk indicator parameter into n sub-limits, it also includes: judging whether the risk indicator parameter exceeds the applicable limit, if yes, the horizontal well is not suitable for using the method of the present invention to determine the scores corresponding to each risk indicator parameter. Among them, the applicable limit of the relative activity coefficient of the fault-crack is 0-5, the applicable limit of the brittleness index of the shale reservoir is 0-100, the applicable limit of the extension length of the fault-crack surface is 0-1000m, the applicable limit of the angle between the fault-crack surface and the wellbore is 0-90°, the applicable limit of the shale reservoir fracture pressure is 20-120MPa, the applicable limit of the wellbore temperature difference before and after fracturing is 0-100℃, and the applicable limit of the perforation density is 0-40 / m.

[0078] In the embodiment of the present invention, n is an integer greater than or equal to 1, wherein the mth sublimit corresponds to the mth risk score segment, m is an integer greater than or equal to 1 and less than or equal to n (m=1, 2, 3.......n), and the value of the risk indicator within the mth sublimit is linearly related to the risk score in the mth risk score segment, that is, the risk score is in a linear piecewise function relationship with respect to the value of the risk indicator. With the value of the risk indicator as the independent variable, and within the applicable limit, the value of the risk indicator is divided into n intervals (sublimits), and any interval has a different linear function relationship with the corresponding score segment.

[0079] Among them, when the sub-boundaries correspond to the score segments, the sub-boundaries where the risk indicator parameter values ​​that are relatively most likely to cause casing loss are located correspond to the score segment with the largest score range, that is, the risk indicator parameter values ​​that are more likely to cause casing loss have higher scores, and so on, the sub-boundaries where the risk indicator parameter values ​​that are least likely to cause casing loss are located correspond to the score segment with the smallest score range; that is, the sub-boundaries are sorted from high to low according to the ability to cause casing loss, and the score segments are sorted from large to small according to the score range, and the two are matched one by one after the sorting is completed. The larger the value of n, the more detailed the impact of the risk indicator on the casing loss risk can be.

[0080] Since the impact of risk indicator parameters on horizontal well casing damage may not change at a uniform rate, changes in parameter values ​​within a certain range have a greater impact on casing damage, while the impact is relatively smaller beyond the sensitive section; for example, the fault-fracture surface extension length is mostly concentrated in 200-400, which has a more obvious impact on casing damage, and the impact is greater than 400, but the extension length is less than 400, and occasionally there will be a value close to 1000. When dividing the sub-boundaries, 400-1000 can be divided into one section, 200-399 can be divided into one section, and so on, to complete the sub-boundary division of each risk indicator parameter.

[0081] The numerical ranges of various risk indicator parameters are as follows: fault-fracture relative activity coefficient is 0-5, shale reservoir brittleness index is 0-100, fault-fracture surface extension length is 0-1000m, the angle between the fault-fracture surface and the wellbore is 0-90°, the shale reservoir fracture pressure is 20-120MPa, the wellbore temperature difference before and after fracturing is 0-100°C and the perforation density is 0-40 / m.

[0082] If n=4, the numerical range of the risk index parameter is divided into four sub-limits, and the score of 0-100 is evenly divided into 4 score segments, namely 0-25 points, 25-50 points, 50-75 points, and 75-100 points; each sub-limit corresponds to a different risk index score segment, among which the first sub-limit is very unfavorable for the formation of horizontal well casing damage, and the corresponding score segment is 0-25 points; the second sub-limit is unfavorable for the formation of horizontal well casing damage, and the corresponding score segment is 25-50 points; the third sub-limit is favorable for the formation of horizontal well casing damage, and the corresponding score segment is 50-75 points; the fourth sub-limit is most favorable for the formation of horizontal well casing damage, and the corresponding score segment is 75-100 points.

[0083] The first sub-limit of the relative activity coefficient of fracture-rupture is 0-0.5, corresponding to the casing damage risk score range of 0-25; the second sub-limit is 0.5-1, corresponding to the casing damage risk score range of 25-50; the third sub-limit is 1-1.5, corresponding to the casing damage risk score range of 50-75; the fourth sub-limit is 1.5-5, corresponding to the casing damage risk score range of 75-100.

[0084] The first sub-limit of the shale reservoir brittleness index is 0-30, corresponding to the casing damage risk score range of 0-25; the second sub-limit is 30-55, corresponding to the casing damage risk score range of 25-50; the third sub-limit is 55-65, corresponding to the casing damage risk score range of 50-75; the fourth sub-limit is 65-100, corresponding to the casing damage risk score range of 75-100.

[0085] The first sub-limit of the fault-crack extension length is 0-100, corresponding to the casing damage risk score range of 0-25; the second sub-limit is 100-200, corresponding to the casing damage risk score range of 25-50; the third sub-limit is 200-400, corresponding to the casing damage risk score range of 50-75; the fourth sub-limit is 400-1000, corresponding to the casing damage risk score range of 75-100.

[0086] The first sub-limit of the angle between the fault-fracture surface and the wellbore is 0-10, corresponding to the casing damage risk score range of 0-25; the second sub-limit is 10-20, corresponding to the casing damage risk score range of 25-50; the third sub-limit is 20-50, corresponding to the casing damage risk score range of 50-75; the fourth sub-limit is 50-90, corresponding to the casing damage risk score range of 75-100.

[0087] The first sub-limit of shale reservoir fracture pressure is 20-40, corresponding to the casing damage risk score range of 0-25; the second sub-limit is 40-60, corresponding to the casing damage risk score range of 25-50; the third sub-limit is 60-80, corresponding to the casing damage risk score range of 50-75; the fourth sub-limit is 80-120, corresponding to the casing damage risk score range of 75-100.

[0088] The first sub-limit of the wellbore temperature difference before and after fracturing is 0-25, corresponding to the casing damage risk score range of 0-25; the second sub-limit is 25-60, corresponding to the casing damage risk score range of 25-50; the third sub-limit is 60-80, corresponding to the casing damage risk score range of 50-75; the fourth sub-limit is 80-100, corresponding to the casing damage risk score range of 75-100.

[0089] The first sub-limit of the perforation density is 0-1, corresponding to the casing damage risk score range of 0-25; the second sub-limit of the perforation density is 1-10, corresponding to the casing damage risk score range of 25-50; the third sub-limit of the perforation density is 10-20, corresponding to the casing damage risk score range of 50-75; the fourth sub-limit of the perforation density is 20-40, corresponding to the casing damage risk score range of 75-100.

[0090] If the value of the relative activity coefficient of the risk indicator parameter break-crack is 0.55, it is located in the sub-limit of 0.5 to 1, and the score segment of the risk indicator parameter corresponding to this sub-limit is 25 to 50. According to the linear relationship between the sub-limit and the score segment, it is concluded that for every 0.1 increase in the value of the relative activity coefficient of the break-crack, the score of the risk indicator parameter increases by 5. Therefore, the score of the risk indicator parameter corresponding to the value of the relative activity coefficient of the break-crack of 0.55 is 27.5, that is, the score corresponding to the relative activity coefficient of the risk indicator parameter is 27.5. If the relative activity coefficient of the break-crack is 1.73, it is located in the sub-limit of 1.5 to 5, and the score corresponding to the risk indicator parameter of this sub-limit is 75 to 100. It is concluded that for every 0.1 increase in the value of the relative activity coefficient of the break-crack, the score of the risk indicator parameter increases by 0.71. Therefore, the score corresponding to the relative activity coefficient of the break-crack of 1.73 is 76.6.

[0091] The risk indicator parameter scores corresponding to other risk indicator parameter values ​​are obtained by the above method, that is, first determine the sub-limit where the risk indicator parameter value is located, and the risk indicator parameter score segment corresponding to the sub-limit, then determine the rate of change of the risk indicator parameter score with the increase of the risk indicator parameter value, and then combine the end value of the sub-limit and the score of the risk indicator score segment corresponding to the end value to obtain the score corresponding to the risk indicator parameter, that is, the score corresponding to the risk indicator parameter value.

[0092] In the present invention, before obtaining the risk level of the target well in the work area, the risk level of the target well is determined, and the method includes:

[0093] Determine the risk prediction value of the target well by using a risk assessment formula according to the scores corresponding to the values ​​of the risk indicator parameters of the target well;

[0094] If the risk prediction value is 0-25, the target well is determined to be at low risk of horizontal well casing damage; if the risk prediction value is 25-50, the target well is determined to be at medium risk of horizontal well casing damage; if the risk prediction value is 50-75, the target well is determined to be at high risk of horizontal well casing damage; and if the risk prediction value is 75-100, the target well is determined to be at ultra-high risk of horizontal well casing damage.

[0095] In the present invention, the risk assessment formula includes formula (8) or (9);

[0096] F=C1*α1+C2*α2+C3*α3+C4*α4+C5*α5+C6*α6+C7*α7,

[0097] α1+α2+α3+α4+α5+α6+α7=1 (8);

[0098] In formula (8), F is the risk prediction value, C1 is the score corresponding to the relative activity coefficient of the fault-crack, α1 is the weight coefficient of C1, C2 is the score corresponding to the brittleness index of the shale reservoir, α2 is the weight coefficient of C2, C3 is the score corresponding to the extension length of the fault-crack surface, α3 is the weight coefficient of C3, C4 is the score corresponding to the angle between the fault-crack surface and the wellbore, α4 is the weight coefficient of C4, C5 is the score corresponding to the shale reservoir fracture pressure, α5 is the weight coefficient of C5, C6 is the score corresponding to the wellbore temperature difference before and after fracturing, α6 is the weight coefficient of C6; C7 is the score corresponding to the perforation density, α7 is the weight coefficient of C7;

[0099] F=(C1*C2*C3*C4*C5) 1 / 5 *α1+(C6*C7) 1 / 2 *α2, α1+α2=1 (9);

[0100] In formula (9), F is the risk prediction value, C1 is the score corresponding to the relative activity coefficient of fault-crack, C2 is the score corresponding to the brittleness index of shale reservoir, C3 is the score corresponding to the extension length of fault-crack surface, C4 is the score corresponding to the angle between fault-crack surface and wellbore, C5 is the score corresponding to the fracture pressure of shale reservoir, C6 is the score corresponding to the temperature difference of wellbore before and after fracturing, C7 is the score corresponding to the perforation density, α1 is the weight coefficient of C1*C2*C3*C4*C5, and α2 is the weight coefficient of C6*C7.

[0101] In an embodiment of the present invention, in formula (8), the values ​​of the weight coefficients are: α1=0.2, α2=0.15, α3=0.16, α4=0.1, α5=0.14, α6=0.17, α7=0.08, or the values ​​of the weight coefficients are α1=0.3, α2=0.16, α3=0.14, α4=0.1, α5=0.1, α6=0.15, α7=0.05.

[0102] In formula (9), the values ​​of the weight coefficients are: α1 = 0.6, α2 = 0.4, or the values ​​of the weight coefficients are: α1 = 0.7, α2 = 0.3.

[0103] Step S02: If the risk level of the target well is medium risk or low risk, the risk level of the target well is predicted regularly.

[0104] In the embodiment of the present invention, for low-risk and medium-risk wells, since the risk of casing damage is low, casing damage prevention and control may not be performed temporarily, but various downhole parameters are regularly collected to re-determine the risk level, thereby saving construction costs; when the re-determined risk level becomes high risk or ultra-high risk, casing damage prevention and control is performed on the target well.

[0105] In the embodiment of the present invention, taking the target horizontal wells S1 to S5 as an example, a numerical table of each risk indicator parameter corresponding to each horizontal well is shown in Table 1 below.

[0106] Table 1: Target horizontal well casing damage risk indicator parameter value table

[0107] Horizontal well number-risk point S1-H1 S2-H3 S3-H5 S4-H7 S5-H8 Fracture-fracture relative activity coefficient 1.28 0.55 1.16 1.73 1.57 Shale reservoir brittleness index 30.6 55.0 38.0 46.5 59.8 Fracture-crack extension length (m) 470 350 85 180 880 Angle between fault-fracture surface and wellbore (°) 10.0 56.0 39.0 42.0 77.0 Shale reservoir fracture pressure (MPa) 40 46.8 52.8 60.3 69.6 Wellbore temperature difference before and after fracturing (℃) 20.5 40.0 30.0 63.2 55.3 Perforation density (perforation / m) 16 12 24 8 16

[0108] According to the four sub-limits divided by the above risk indicator parameters, the sub-limit of each risk indicator parameter value in Table 1 is determined. According to the score segment corresponding to the sub-limit and the linear relationship between the two, the score corresponding to each risk indicator parameter value in Table 1 is determined, as shown in Table 2 below.

[0109] Table 2: Target horizontal well casing damage risk indicator parameter score table

[0110] Horizontal well number-risk point S1-H1 S2-H3 S3-H5 S4-H7 S5-H8 Fracture-fracture relative activity coefficient 64.0 27.5 58.0 76.6 75.5 Shale reservoir brittleness index 25.6 50.0 33.0 41.5 62.0 Fracture-crack extension length 77.9 68.8 21.3 45.0 95.0 Angle between fault-fracture surface and wellbore 25.0 78.8 55.8 68.3 91.9 Shale reservoir fracture pressure 25.0 33.5 41.0 50.4 62.0 Wellbore temperature difference before and after fracturing 17.1 33.3 25.0 64.0 46.1 Perforation density 65.0 55.0 80.0 44.4 65.0

[0111] According to the score corresponding to each risk indicator parameter, the risk prediction value corresponding to each target horizontal well is determined using formula (8) or (9). The specific calculation results are shown in Table 3 below.

[0112] Table 3: Calculation table of casing damage risk prediction value of target horizontal well

[0113]

[0114]

[0115] According to the risk prediction value obtained, each horizontal well is divided into risk levels, and the final results are shown in Table 4 below.

[0116] Table 4: Target horizontal well casing damage risk level table

[0117]

[0118] Different prediction values ​​show that the casing damage prediction of the horizontal well S4 risk point H7 is high risk, the casing damage prediction of the horizontal well S5 risk point H8 is high risk, and the rest are medium risk. The data collected through actual on-site construction show that the horizontal well casing damage risk level in Table 4 is consistent with the actual situation.

[0119] Step S03: If the risk level of the target well is high risk or ultra-high risk, all the risk index parameters are divided into four categories, wherein the first category includes the fault-crack relative activity coefficient at the casing damage risk point and / or the shale reservoir brittleness index and / or the angle between the fault-crack surface and the wellbore and / or the shale reservoir fracture pressure, the second category includes the extension length of the fault-crack surface, the third category includes the wellbore temperature difference before and after fracturing, and the fourth category includes the perforation density.

[0120] In the embodiment of the present invention, the first to fourth categories are classified according to the importance of causing casing damage, that is, the relative activity coefficient of the fault-crack at the casing damage risk point, the brittleness index of the shale reservoir, the angle between the fault-crack surface and the wellbore, and the shale reservoir fracture pressure included in the first category are relatively important factors causing casing damage, and the importance of the other three to four categories causing casing damage gradually decreases.

[0121] Step S04: If the score of the risk indicator parameter is greater than or equal to the predetermined score, the casing damage prevention and control of the target well is carried out using the prevention and control method corresponding to the classification of the risk indicator parameter, wherein the prevention and control method corresponding to the first category is to reduce the fracturing pressure to the original first predetermined percentage and reduce the fracturing fluid injection volume to the original second predetermined percentage, the prevention and control method corresponding to the second category is to inject a temporary plugging agent, the prevention and control method corresponding to the third category is to increase the fracturing fluid injection temperature to the original third predetermined percentage and reduce the fracturing fluid injection and return speed to the original fourth predetermined percentage, and the prevention and control method corresponding to the fourth category is to use engineering methods to strengthen the wellbore.

[0122] In the present invention, the predetermined score is: 50 or 55 or 65 or 75.

[0123] In the present invention, the value range of the first predetermined percentage is: 90-98%;

[0124] The second predetermined percentage has a value range of 80-95%.

[0125] In an embodiment of the present invention, if the score corresponding to the relative activity coefficient of the fracture at the casing damage risk point in the first type of risk indicator parameter is greater than or equal to 50, and the score corresponding to the fracture surface extension length of the second type of risk indicator parameter is greater than or equal to 50, then the casing damage prevention method of the target horizontal well is to reduce the fracturing pressure to 90-98% of the original fracturing pressure, reduce the injection amount of the fracturing fluid to 80-95% of the original injection amount of the fracturing fluid, and inject a temporary plugging agent.

[0126] In the present invention, the temporary plugging agent is one or more of a cross-linked polymer temporary plugging agent, a fiber temporary plugging agent, an inorganic salt temporary plugging agent or a composite material temporary plugging agent.

[0127] In the present invention, the cross-linked polymer temporary plugging agent is one or more of polyacrylamide, polyacrylic acid, and polyethylene wax;

[0128] The fiber temporary plugging agent is one or more of polyester fiber, polylactic acid fiber, and polypropylene fiber;

[0129] The inorganic salt temporary plugging agent is one or more of calcium carbonate, sodium chloride, and benzoic acid flakes;

[0130] The composite material temporary plugging agent is one or more of a composite material of silicon dioxide and a cross-linked polymer, a composite material of fly ash and a cross-linked polymer, and a composite material of fibers and particles.

[0131] In the present invention, the third predetermined percentage has a value range of: 120-200%;

[0132] The fourth predetermined percentage has a value range of 80-95%.

[0133] In an embodiment of the present invention, if the scores of the relative activity coefficient of the fracture at the casing damage risk point and the shale reservoir brittleness index in the first type of risk indicator parameters, and the wellbore temperature difference before and after fracturing in the third type of risk indicator parameters are all greater than or equal to 50, then the target horizontal well casing damage prevention method is to reduce the fracturing pressure to 90-98% of the original fracturing pressure, and reduce the fracturing fluid injection amount to 80-95% of the original fracturing fluid injection amount, and increase the fracturing fluid injection temperature to 120-200% of the original fracturing fluid injection temperature, and reduce the fracturing fluid injection and return speed to 80-95% of the original fracturing fluid injection and return speed.

[0134] In the present invention, the engineering method for reinforcing the wellbore includes:

[0135] One or more of the following methods: cement squeezing, packer installation, casing patching, casing tieback, chemical plugging or casing replacement.

[0136] In the embodiment of the present invention, if there are multiple categories in which the risk indicator parameter value is greater than or equal to the predetermined score, multiple prevention and control methods are correspondingly selected to simultaneously perform casing damage prevention and control on the target well.

[0137] If the scores corresponding to the angle between the fault-fracture plane and the wellbore, the shale reservoir fracture pressure in the first category of risk indicator parameters, and the perforation density in the fourth category of risk indicator parameters are all greater than or equal to 50, then the target horizontal well casing damage prevention method is to reduce the fracturing pressure to 90-98% of the original fracturing pressure, and reduce the fracturing fluid injection volume to 80-95% of the original fracturing fluid injection volume, and use one or more of the engineering methods to reinforce the wellbore.

[0138] In the embodiment of the present invention, taking the high-risk target horizontal well S4-H7 as an example, the fracturing pressure at the risk point is 70 MPa and the fracturing fluid injection volume is 1200m 3 , fracturing fluid injection temperature 6℃, fracturing fluid injection speed 10-12m 3 / min, return speed 8-10m 3 / min.

[0139] If the scores of the first type of risk indicator parameters, the relative activity coefficient of the fault-fracture at the casing damage risk point, the angle between the fault-fracture surface and the wellbore, and the shale reservoir fracture pressure, and the third type of risk indicator parameters, the wellbore temperature difference before and after fracturing, are all greater than 50, then the casing damage prevention method adopted for the target horizontal well S4-H7 is: reduce the fracturing pressure to 90% of the original fracturing pressure, and reduce the fracturing fluid injection volume to 80% of the original fracturing fluid injection volume; at the same time, increase the fracturing fluid injection temperature to 200% of the original fracturing fluid temperature, and reduce the fracturing fluid injection and flowback rates to 95% of the original fracturing fluid injection and flowback rates.

[0140] Alternatively, the fracturing pressure is reduced to 98% of the original fracturing pressure, and the fracturing fluid injection volume is reduced to 95% of the original fracturing fluid injection volume; at the same time, the fracturing fluid injection temperature is increased to 120% of the original fracturing fluid temperature, and the fracturing fluid injection and flowback speeds are reduced to 80% of the original fracturing fluid injection and flowback speeds.

[0141] Or, the fracturing pressure is reduced to 95% of the original fracturing pressure, and the fracturing fluid injection volume is reduced to 90% of the original fracturing fluid injection volume; at the same time, the fracturing fluid injection temperature is increased to 180% of the original fracturing fluid temperature, and the fracturing fluid injection and flowback speeds are reduced to 90% of the original fracturing fluid injection and flowback speeds.

[0142] Or, the fracturing pressure is reduced to 97% of the original fracturing pressure, and the fracturing fluid injection volume is reduced to 85% of the original fracturing fluid injection volume; at the same time, the fracturing fluid injection temperature is increased to 150% of the original fracturing fluid temperature, and the fracturing fluid injection and flowback speeds are reduced to 85% of the original fracturing fluid injection and flowback speeds.

[0143] In the embodiment of the present invention, taking the high-risk target horizontal well S5-H8 as an example, the original fracturing pressure at the risk point is 80 MPa, the fracturing fluid injection volume is 1500m 3 , fracturing fluid injection temperature 31°C, fracturing fluid injection speed 11-15m 3 / min, flowback speed 10-13m 3 / min.

[0144] The scores of the first and second risk indicator parameters of the target horizontal well S5-H8, the relative activity coefficient of the fault-crack at the casing damage risk point, the angle between the fault-crack surface and the wellbore, the shale reservoir fracture pressure, the shale reservoir brittleness index, the fault-crack surface extension length of the second risk indicator parameter, and the perforation density of the fourth risk indicator parameter are all greater than 50. The casing damage prevention method adopted for the target horizontal well S5-H8 is: reduce the fracturing pressure to 98% of the original fracturing pressure, and reduce the fracturing fluid injection volume to 95% of the original fracturing fluid injection volume; inject polyester fiber, model LXDGF, produced by Shandong Luxian Building Materials Technology Co., Ltd., with an injection volume of 5% of the fracturing fluid volume and a mass concentration of 6%; and reinforce the wellbore by cementing and lowering the packer engineering method.

[0145] Or, reduce the fracturing pressure to 90% of the original fracturing pressure, and reduce the fracturing fluid injection volume to 80% of the original fracturing fluid injection volume; inject polyacrylamide and calcium carbonate, the polyacrylamide molecular weight is 25 million, produced by Daqing Refining and Chemical, the calcium carbonate model is HL-QS2, produced by Hailong Petroleum Technology Service Co., Ltd., the injection volume is 10% of the fracturing fluid volume, the mass concentration is 5%, and the mass ratio of polyacrylamide to calcium carbonate is 3:1; use the cement squeezing engineering method to reinforce the wellbore.

[0146] Or, reduce the fracturing pressure to 95% of the original fracturing pressure, and reduce the fracturing fluid injection volume to 85% of the original fracturing fluid injection volume; inject polyacrylamide and polypropylene fiber, the molecular weight of polyacrylamide is 25 million, the polypropylene fiber model is LXBGF, produced by Shandong Luxian Building Materials Technology Co., Ltd., the injection volume is 8% of the fracturing fluid volume, the mass concentration is 4%, and the mass ratio of polyacrylamide and polypropylene fiber is 2:1; use the casing patch engineering method to reinforce the wellbore.

[0147] Or, reduce the fracturing pressure to 96% of the original fracturing pressure, and reduce the fracturing fluid injection volume to 95% of the original fracturing fluid injection volume; inject a composite material of silica and cross-linked polymer, the silica model is HL-150, Hubei Huifu Nanomaterials Co., Ltd., the cross-linked polymer model is GWS-1, and the particle size is 1.00mm~3.35mm Shandong Deshunyuan Petroleum Technology Co., Ltd.; the injection volume is 4% of the fracturing fluid volume, the mass concentration is 8%, and the mass ratio of silica to cross-linked polymer is 1:2; use the casing replacement engineering method to reinforce the wellbore.

[0148] It can be understood that the above-mentioned various method embodiments mentioned in the present invention can be combined with each other to form a combined embodiment without violating the principle logic. Due to space limitations, the present invention will not go into details.

[0149] 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.

[0150] The present invention divides the seven risk indicator parameters at the casing damage risk points of the target horizontal well into four categories, and gives four different casing damage prevention and control methods corresponding to the four categories of risk indicator parameters. The casing damage prevention and control method corresponding to the risk indicator parameter classification where the risk indicator parameter corresponding to the score at the casing damage risk point of the horizontal well with high and extra-high risk levels is greater than the predetermined score is selected to perform casing damage prevention and control on the target well, and different casing damage prevention and control methods are used for different high-risk indicators in a personalized manner, thereby improving the casing damage prevention and control effect of the horizontal well and avoiding the simplification and generalization of casing damage prevention and control.

[0151] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for preventing and controlling casing damage in a horizontal well, characterized in that: include: Obtain the scores corresponding to each risk indicator parameter of the target well in the work area and the risk level of the target well; If the risk level of the target well is medium risk or low risk, the risk level of the target well is predicted regularly; If the risk level of the target well is high risk or ultra-high risk, all the risk index parameters are divided into four categories, wherein the first category includes the relative activity coefficient of the fault-crack at the casing risk point and / or the brittleness index of the shale reservoir and / or the angle between the fault-crack surface and the wellbore and / or the shale reservoir fracture pressure, the second category includes the extension length of the fault-crack surface, the third category includes the wellbore temperature difference before and after fracturing, and the fourth category includes the perforation density; If the score of the risk indicator parameter is greater than or equal to the predetermined score, the casing damage prevention and control of the target well is carried out using the prevention and control method corresponding to the category of the risk indicator parameter, wherein the prevention and control method corresponding to the first category is to reduce the fracturing pressure to the original first predetermined percentage and reduce the fracturing fluid injection volume to the original second predetermined percentage, the prevention and control method corresponding to the second category is to inject a temporary plugging agent, the prevention and control method corresponding to the third category is to increase the fracturing fluid injection temperature to the original third predetermined percentage and reduce the fracturing fluid injection and return speed to the original fourth predetermined percentage, and the prevention and control method corresponding to the fourth category is to use engineering methods to strengthen the wellbore.

2. The horizontal well casing damage prevention method according to claim 1, characterized in that: The predetermined score is: 50 or 55 or 65 or 75.

3. The method for preventing and controlling casing damage in a horizontal well according to claim 2, characterized in that: The value range of the first predetermined percentage is: 90-98%; The second predetermined percentage has a value range of 80-95%.

4. The method for preventing and controlling casing damage in a horizontal well according to claim 3, characterized in that: The temporary plugging agent is one or more of a cross-linked polymer temporary plugging agent, a fiber temporary plugging agent, an inorganic salt temporary plugging agent or a composite material temporary plugging agent.

5. The method for preventing and controlling casing damage in a horizontal well according to claim 4, characterized in that: The cross-linked polymer temporary plugging agent is one or more of polyacrylamide, polyacrylic acid, and polyethylene wax; The fiber temporary plugging agent is one or more of polyester fiber, polylactic acid fiber, and polypropylene fiber; The inorganic salt temporary plugging agent is one or more of calcium carbonate, sodium chloride, and benzoic acid flakes; The composite material temporary plugging agent is one or more of a composite material of silicon dioxide and a cross-linked polymer, a composite material of fly ash and a cross-linked polymer, and a composite material of fibers and particles.

6. The method for preventing and controlling casing damage in a horizontal well according to claim 1, characterized in that: The value range of the third predetermined percentage is: 120-200%; The fourth predetermined percentage has a value range of 80-95%.

7. The method for preventing and controlling casing damage in a horizontal well according to claim 1, characterized in that: The engineering method for strengthening the wellbore comprises: One or more of the following methods: cement squeezing, packer installation, casing patching, casing tieback, chemical plugging or casing replacement.

8. The method for preventing and controlling casing damage in a horizontal well according to any one of claims 1 to 7, characterized in that: Before obtaining the scores corresponding to the risk indicator parameters of the target wells in the work area, the scores corresponding to the risk indicator parameters of the target wells are determined, and the method includes: Obtain the risk index parameter values ​​of the target wells in the work area; Divide the numerical range of the risk indicator parameter into n sub-limits, divide the score of 0 to 100 into n score segments, and correspond the sub-limits of the risk indicator parameter to the score segments; The score corresponding to each risk indicator parameter value of the target well is determined according to the score segment corresponding to the sub-limit of the risk indicator parameter.

9. The method for preventing and controlling casing damage in a horizontal well according to claim 8, characterized in that: Before obtaining the risk level of the target well in the work area, the risk level of the target well is determined, and the method includes: Determine the risk prediction value of the target well by using a risk assessment formula according to the scores corresponding to the values ​​of the risk indicator parameters of the target well; If the risk prediction value is 0-25, the target well is determined to be at low risk of horizontal well casing damage; if the risk prediction value is 25-50, the target well is determined to be at medium risk of horizontal well casing damage; if the risk prediction value is 50-75, the target well is determined to be at high risk of horizontal well casing damage; and if the risk prediction value is 75-100, the target well is determined to be at ultra-high risk of horizontal well casing damage.

10. The method for preventing and controlling casing damage in a horizontal well according to claim 9, characterized in that: The risk assessment formula includes formula (8) or (9); F=C1*α1+C2*α2+C3*α3+C4*α4+C5*α5+C6*α6+C7*α7, α1+α2+α3+α4+α5+α6+α7＝1(8)； In the formula, F is the risk prediction value, C1 is the score corresponding to the relative activity coefficient of fault-crack, α1 is the weight coefficient of C1, C2 is the score corresponding to the brittleness index of shale reservoir, α2 is the weight coefficient of C2, C3 is the score corresponding to the extension length of fault-crack surface, α3 is the weight coefficient of C3, C4 is the score corresponding to the angle between fault-crack surface and wellbore, α4 is the weight coefficient of C4, C5 is the score corresponding to the fracture pressure of shale reservoir, α5 is the weight coefficient of C5, C6 is the score corresponding to the temperature difference of wellbore before and after fracturing, α6 is the weight coefficient of C6; C7 is the score corresponding to the perforation density, α7 is the weight coefficient of C7; F=(C1*C2*C3*C4*C5) 1 / 5 *α1+(C6*C7) 1 / 2 *α2,α1+α2=1 (9); Where F is the risk prediction value, C1 is the score corresponding to the fault-crack relative activity coefficient, C2 is the score corresponding to the shale reservoir brittleness index, C3 is the score corresponding to the fault-crack extension length, C4 is the score corresponding to the angle between the fault-crack surface and the wellbore, C5 is the score corresponding to the shale reservoir fracture pressure, C6 is the score corresponding to the wellbore temperature difference before and after fracturing, C7 is the score corresponding to the perforation density, α1 is the weight coefficient of C1*C2*C3*C4*C5, and α2 is the weight coefficient of C6*C7.

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