Wellbore stability evaluation method, wellbore collapse pressure calculation method and system

Abstract

The present disclosure provides a method for evaluating wellbore stability, a method for calculating wellbore collapse pressure, and a system. The wellbore stability evaluation method includes the following steps: using seismic, drilling, logging, well logging, completion, and testing data to determine geomechanical parameters and rock mechanics parameters; according to the geomechanical parameters and rock mechanics parameters, and given the well inclination angle, well inclination azimuth, and allowable diameter expansion rate, a mathematical calculation model is established to obtain the collapse pressure; according to the collapse pressure, the collapse pressure equivalent density is calculated, and a relationship diagram of the collapse pressure equivalent density, well inclination angle, and well inclination azimuth is drawn, and the change trend on the relationship diagram is used to realize the judgment of wellbore stability. The wellbore stability evaluation method disclosed in the present disclosure directly establishes the relationship between completion electrical logging caliper data and allowable diameter expansion rate and collapse pressure, which is convenient for comparative analysis and application of actual drilling site data.

Description

Technical Field

[0001] The present disclosure relates to the field of drilling technology, and in particular to a method for calculating the wellbore collapse pressure of a directional well that allows wellbore expansion, and a method and system for evaluating wellbore stability. Background Art

[0002] In recent years, due to breakthroughs in directional well, horizontal well and branch well technology, unconventional oil and gas resources such as tight oil and gas, shale oil and gas, coalbed methane, and offshore oil and gas have become hot areas for oil and gas exploration and development. However, the use of complex well structures such as directional wells, horizontal wells, and branch wells has to face a series of engineering and technical difficulties and challenges during the drilling process, among which the wellbore collapse problem is one of the most difficult problems. In order to solve the wellbore collapse problem, domestic and foreign scholars have carried out a lot of in-depth research from multiple aspects such as wellbore collapse pressure prediction, anti-collapse drilling fluid, and anti-collapse process technology, and have made great progress. The wellbore collapse problem has been significantly reduced, but it still cannot be completely solved.

[0003] From a mechanical point of view, wellbore collapse is caused by the breaking of the original stress balance relationship after drilling through the formation to form a wellbore, resulting in the redistribution of stress in the formation around the wellbore. When the redistributed stress exceeds the formation strength, a wellbore collapse accident will occur. Therefore, an important aspect of solving the wellbore collapse problem is to accurately predict the wellbore collapse pressure and adopt a reasonable drilling fluid system and density to prevent the occurrence of wellbore collapse accidents. In order to accurately calculate the wellbore collapse pressure, domestic and foreign scholars have proposed and established a large number of theoretical models and calculation methods. The general idea of ​​these methods is to calculate the wellbore stress distribution by comprehensively considering factors such as ground stress, wellbore trajectory, and wellbore pressure, and then bring the calculated stress into the rock strength criterion for calculation, so as to obtain the minimum wellbore pressure required to maintain the stability of the wellbore, which is the wellbore collapse pressure.

[0004] A Chinese patent application with publication number CN109377101A disclosed on February 22, 2019 a quantitative evaluation method for wellbore stability based on a risk control model. It proposed a risk control model, introduced an allowable collapse width, and obtained the wellbore collapse pressure by calculating the critical wellbore pressure of the critical point of destruction corresponding to the allowable collapse width, thus overcoming the shortcomings of traditional theoretical models and calculation methods.

[0005] However, since the rock strength criterion usually has a certain deviation, it is difficult to establish an equivalent relationship between the allowable collapse width and the completion electrical logging diameter data. In actual drilling projects, a certain degree of wellbore expansion (i.e., wellbore diameter expansion) is usually allowed, which leads to the calculated wellbore collapse pressure often being conservative. The existing theoretical models and calculation methods cannot overcome these problems. Summary of the invention

[0006] The purpose of the present disclosure is to solve at least one of the above-mentioned deficiencies in the prior art. For example, the present disclosure provides a method for calculating the wellbore collapse pressure of a directional well that allows wellbore expansion, directly establishes the relationship between completion electrical logging wellbore data and the allowable expansion rate and collapse pressure, and can more accurately calculate the wellbore collapse pressure of a directional well, facilitate the comparison and analysis of actual drilling site data and application, and can provide a theoretical basis for the optimization design of drilling fluid density, wellbore trajectory optimization design, and safe and efficient drilling of complex structure wells such as directional wells, horizontal wells, and branch wells.

[0007] One aspect of the present disclosure provides a method for evaluating wellbore stability allowing wellbore expansion, comprising the following steps: S1, determining geomechanical parameters and rock mechanics parameters of a target formation, wherein the geomechanical parameters include vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p , rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot's coefficient α p S2. Based on the geomechanical parameters and rock mechanics parameters, and given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, a mathematical calculation model for the wellbore collapse pressure of the directional well that allows wellbore expansion is established, and the collapse pressure p is obtained by solving the equation. c ; S3, according to the collapse pressure p c Calculate the collapse pressure equivalent density ρ c , and plot the collapse pressure equivalent density ρ c The relationship diagram of the three angles of inclination Φ and inclination azimuth Ω is shown in the figure. The collapse pressure equivalent density ρ c The stability of the wellbore is judged by comparing the changing trends of the well inclination angle Φ and the well inclination azimuth Ω.

[0008] In an exemplary embodiment of the present disclosure, step S2 may include the following steps: S21, by vertical geostress σ v , maximum horizontal ground stress σ H and the minimum horizontal ground stress σ h , and given the well inclination angle Φ and well inclination azimuth Ω, calculate the far-field stress component in the wellbore rectangular coordinates; S22, given the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of S23, through the formation pore pressure p p , Poisson's ratio v, Biot coefficient αp , allowable expansion rate HER and far-field stress component, calculate the wellbore pressure p m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w S24, calculate the wellbore pressure p through the wellbore stress components m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w When the respective principal stresses σ, the principal stresses σ include the maximum principal stress σ1 and the minimum principal stress σ3; S25, determine the maximum value σ of the maximum principal stress σ1 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max ; S26, through the rock cohesion and internal friction angle, as well as the maximum principal stress σ1 and minimum principal stress σ3 corresponding to the maximum wellbore angle θmax, the wellbore pressure p is calculated m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w S27, using the dichotomy method to judge the value of the destruction criterion function to determine the zero point of the destruction criterion function or the value range of the zero point of the destruction criterion function; S28, on the basis of determining the value range of the zero point of the destruction criterion function, determine the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The absolute value of the difference between the two meets the requirement of accuracy ε to determine the zero point approximation of the failure criterion function; S29, the zero point of the failure criterion function or the zero point approximation of the failure criterion function is used as the collapse pressure p c .

[0009] In an exemplary embodiment of the present disclosure, step S27 may include: if f(pw)=0, then the average wellbore pressure p w is the zero point of the failure criterion function, the collapse pressure p c Equal to the average wellbore pressure p w ; if f(p w1 )·f(p w )<0, then let p w2 =p w , at this time, the zero point of the destruction criterion function∈(p w1 ,p w ); if f(p w )·f(p w2 )<0, then let p w1 =p w, at this time, the zero point of the destruction criterion function∈(p w ,p w2 ).

[0010] In an exemplary embodiment of the present disclosure, step S28 includes: in f(p w1 )·f(p w )<0 or f(p w )·f(p w2 )<0, further determine whether the accuracy requirement ε is met. Specifically: if the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is less than the accuracy ε, the minimum wellbore pressure p w1 or maximum wellbore pressure p w2 As the collapse pressure p c ; If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is not less than the accuracy ε, the well inclination angle Φ, the well inclination azimuth Ω and the allowable expansion rate HER are re-given, and steps S22 to S28 are repeated until the accuracy ε requirement is met.

[0011] In an exemplary embodiment of the present disclosure, the step of determining the wellbore stability may be: S31, according to the collapse pressure equivalent density ρ c The angle of the minimum and maximum well inclination angle Φ determines the relative stability between vertical wells, inclined wells or horizontal wells. If the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a trend of gradually increasing. When the well inclination angle Φ is small (the minimum is 0°), the collapse pressure equivalent density ρ c The minimum, that is, the stability of vertical wells is better than that of inclined wells and horizontal wells. When the well inclination angle Φ is 90°, the collapse pressure equivalent density ρ c maximum, that is, the stability of horizontal well drilling is the worst; if the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a decreasing trend. When the well inclination angle Φ is large (maximum 90°), the collapse pressure equivalent density ρ c The minimum, that is, the stability of drilling horizontal wells is better than that of vertical wells and inclined wells. When the well inclination angle Φ is 0°, the collapse pressure equivalent density ρ c maximum, that is, the stability of vertical wells is the worst; if the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a trend of first increasing and then decreasing. The collapse pressure equivalent density ρ is determined as c The minimum well inclination angle Φ can be used to determine whether a vertical well or a horizontal well has better stability. When the well inclination angle Φ is certain, the collapse pressure equivalent density ρ c The maximum, that is, the stability of the inclined well is the worst; if the collapse pressure equivalent density ρc With the increase of well inclination angle Φ, it shows a trend of first decreasing and then increasing. When the well inclination angle Φ is certain, the collapse pressure equivalent density ρ c The minimum, that is, the stability of drilling inclined wells is better than that of drilling horizontal wells and vertical wells. S32, by judging the collapse pressure equivalent density ρ c When the well inclination azimuth angle Ω is the minimum, the vertical well, inclined well or horizontal well drilled in the direction of the well inclination azimuth angle Ω has the best stability.

[0012] The present disclosure also provides a wellbore stability evaluation system that allows wellbore expansion. The evaluation system includes: a parameter determination module configured to determine geomechanical parameters and rock mechanics parameters of a target formation. The geomechanical parameters include vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p , rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot's coefficient α p The collapse pressure calculation module is configured to establish a mathematical calculation model for the wellbore collapse pressure of a directional well that allows wellbore expansion based on geomechanical parameters and rock mechanics parameters, given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, and solve for the collapse pressure p c , the relationship graph module is configured according to the collapse pressure p c Calculate the collapse pressure equivalent density ρ c , and plot the collapse pressure equivalent density ρ c A relationship diagram relative to the change of the well inclination angle Φ and the well inclination azimuth Ω; and a judgment module, configured to determine the collapse pressure equivalent density ρ on the relationship diagram c The stability of the wellbore is judged by comparing the changing trends of the well inclination angle Φ and the well inclination azimuth Ω.

[0013] In an exemplary embodiment of the present disclosure, the mathematical calculation model of the wellbore collapse pressure of a directional well that allows the wellbore to expand can be configured as follows: v , maximum horizontal ground stress σ H and the minimum horizontal ground stress σ h , and given the well inclination angle Φ and well inclination azimuth Ω, calculate the far-field stress component in the wellbore rectangular coordinates; given the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of the formation pore pressure pp , Poisson's ratio v, Biot coefficient α p , allowable expansion rate HER and far-field stress component, calculate the wellbore pressure p m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective wellbore stress components at the time of the wellbore pressure p are calculated by using the wellbore stress components. m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The principal stress σ includes the maximum principal stress σ1 and the minimum principal stress σ3; Determine the maximum value σ of the maximum principal stress σ1 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max ; The wellbore pressure p is calculated by the rock cohesion and internal friction angle, as well as the maximum principal stress σ1 and minimum principal stress σ3 corresponding to the maximum wellbore angle θmax m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective destruction criterion function values ​​are used; the destruction criterion function value is judged by using the dichotomy method to determine the zero point of the destruction criterion function or the value range of the zero point of the destruction criterion function; on the basis of determining the value range of the zero point of the destruction criterion function, the minimum wellbore pressure p is judged. w1 and the maximum wellbore pressure p w2 The absolute value of the difference between the two meets the accuracy requirement ε to determine the zero point approximation of the failure criterion function; and the zero point of the failure criterion function or the zero point approximation of the failure criterion function is used as the collapse pressure p c .

[0014] In an exemplary embodiment of the present disclosure, the judgment module may be configured to: c The angle of the minimum and maximum well inclination angle Φ determines the relative stability between vertical wells, inclined wells or horizontal wells. If the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a trend of gradually increasing. When the well inclination angle Φ is small (the minimum is 0°), the collapse pressure equivalent density ρ c The minimum, that is, the stability of vertical wells is better than that of inclined wells and horizontal wells. When the well inclination angle Φ is 90°, the collapse pressure equivalent density ρ c maximum, that is, the stability of horizontal well drilling is the worst; if the collapse pressure equivalent density ρ cAs the well inclination angle Φ increases, it shows a decreasing trend. When the well inclination angle Φ is large (maximum 90°), the collapse pressure equivalent density ρ c The minimum, that is, the stability of drilling horizontal wells is better than that of vertical wells and inclined wells. When the well inclination angle Φ is 0°, the collapse pressure equivalent density ρ c maximum, that is, the stability of vertical wells is the worst; if the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a trend of first increasing and then decreasing. The collapse pressure equivalent density ρ is determined as c The minimum well inclination angle Φ can be used to determine whether a vertical well or a horizontal well has better stability. When the well inclination angle Φ is certain, the collapse pressure equivalent density ρ c The maximum, that is, the stability of the inclined well is the worst; if the collapse pressure equivalent density ρ c With the increase of well inclination angle Φ, it shows a trend of first decreasing and then increasing. When the well inclination angle Φ is certain, the collapse pressure equivalent density ρ c The minimum, that is, the stability of drilling inclined wells is better than that of drilling horizontal wells and vertical wells. c When the well inclination azimuth angle Ω is the minimum, the vertical well, inclined well or horizontal well drilled in the direction of the well inclination azimuth angle Ω has the best stability.

[0015] In yet another aspect, the present disclosure provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements any exemplary embodiment of the above-mentioned wellbore stability evaluation method.

[0016] In another aspect, the present disclosure provides a method for calculating the wellbore collapse pressure of a directional well that allows the wellbore to expand. The method comprises: S1, determining the geomechanical parameters and rock mechanics parameters of the target formation, wherein the geomechanical parameters include the vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p , rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot coefficient α p S2. According to the geomechanical parameters and rock mechanics parameters, and given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, a mathematical calculation model for the wellbore collapse pressure of the directional well that allows wellbore expansion is established, and the collapse pressure p is obtained by solving the problem. c Wherein, step S2 includes: S21, through the vertical ground stress σ v , maximum horizontal ground stress σ H and the minimum horizontal ground stress σ h , and given the well inclination angle Φ and well inclination azimuth Ω, calculate the far-field stress component in the wellbore rectangular coordinates; S22, given the minimum wellbore pressure pw1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of S23, through the formation pore pressure p p , Poisson's ratio v, Biot coefficient α p , allowable expansion rate HER and far-field stress component, calculate the wellbore pressure p m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w S24, calculate the wellbore pressure p through the wellbore stress components m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w When the respective principal stresses σ, the principal stresses σ include the maximum principal stress σ1 and the minimum principal stress σ3; S25, determine the maximum value σ of the maximum principal stress σ1 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max ; S26, through the rock cohesion and internal friction angle, as well as the maximum principal stress σ1 and minimum principal stress σ3 corresponding to the maximum wellbore angle θmax, the wellbore pressure p is calculated m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w S27, using the dichotomy method to judge the value of the destruction criterion function to determine the zero point of the destruction criterion function or the value range of the zero point of the destruction criterion function; S28, on the basis of determining the value range of the zero point of the destruction criterion function, determine the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The absolute value of the difference between the two meets the requirement of accuracy ε to determine the zero point approximation of the failure criterion function; S29, the zero point of the failure criterion function or the zero point approximation of the failure criterion function is used as the collapse pressure p c .

[0017] Compared with the prior art, the beneficial effects of the present disclosure may include:

[0018] It overcomes the shortcomings of existing theoretical models and calculation methods, and directly establishes the relationship between completion electrical logging data and allowable expansion rate and collapse pressure, thus realizing a wellbore stability evaluation method that allows wellbore expansion.

[0019] More accurate calculation of directional wellbore collapse pressure, facilitating comparative analysis and application of actual drilling site data;

[0020] It can provide a theoretical basis for the optimization design of drilling fluid density, wellbore trajectory, and safe and efficient drilling of complex structure wells such as directional wells, horizontal wells, and branch wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart showing a wellbore stability evaluation method allowing wellbore expansion according to the present disclosure is shown;

[0022] Figure 2 A schematic diagram showing the cohesive force required to maintain the well wall stability disclosed in the present invention is shown;

[0023] Figure 3 The figure shows the relationship between the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the traditional wellbore stability evaluation method for normal faults;

[0024] Figure 4 The figure shows the relationship between the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the wellbore stability evaluation method based on the risk control model for a normal fault;

[0025] Figure 5 A relationship diagram among the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the calculation method of the wellbore collapse pressure of a directional well that allows wellbore expansion disclosed in the present invention for a normal fault is shown;

[0026] Figure 6 The figure shows the relationship between the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the traditional wellbore stability evaluation method for the strike-slip fault;

[0027] Figure 7 The figure shows the relationship between the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the wellbore stability evaluation method based on the risk control model for the strike-slip fault;

[0028] Figure 8 A relationship diagram among the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the calculation method of the wellbore collapse pressure of a directional well that allows wellbore expansion disclosed in the present invention for a strike-slip fault is shown;

[0029] Fig. 9 The figure shows the relationship between the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the traditional wellbore stability evaluation method for reverse faults;

[0030] Fig.10The figure shows the relationship between the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the wellbore stability evaluation method based on the risk control model for reverse faults;

[0031] Fig.11 The figure shows the relationship between the collapse pressure equivalent density, the well inclination angle Φ and the well inclination azimuth angle Ω obtained by using the calculation method of the wellbore collapse pressure of the directional well that allows the wellbore expansion disclosed in the present invention for the reverse fault.

[0032] Description of reference numerals:

[0033] 1. Wellbore, 2. Area where collapse is allowed. DETAILED DESCRIPTION

[0034] Hereinafter, the method for calculating the wellbore collapse pressure of a directional well that allows wellbore expansion according to the present disclosure will be described in detail in conjunction with specific embodiments.

[0035] The method for calculating the wellbore collapse pressure of a directional well that allows wellbore expansion disclosed in the present invention comprises the following steps:

[0036] S1. Determine the geomechanical parameters and rock mechanics parameters of the target stratum. The geomechanical parameters include vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p , rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot's coefficient α p The method of determining the geomechanical parameters and rock mechanical parameters of the target formation can utilize seismic, drilling, well logging, well logging, completion and testing data.

[0037] S2. Based on geological parameters and rock mechanics parameters, and given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, a mathematical calculation model for the wellbore collapse pressure of a directional well that allows wellbore expansion is established to solve the collapse pressure p c ;

[0038] Wherein, the step S2 of establishing a mathematical calculation model of the wellbore collapse pressure of a directional well that allows the wellbore to expand may include the following steps:

[0039] S21, through the vertical ground stress σ v , maximum horizontal ground stress σ H and the minimum horizontal ground stress σ h , and the given well inclination angle Φ and well inclination azimuth Ω, calculate the far-field stress component in the wellbore rectangular coordinates.

[0040] The far-field stress components in the wellbore rectangular coordinate system can be calculated based on the coordinate transformation principle in spatial analytic geometry using the following formula:

[0041]

[0042] In formula (2): xx , σ yy , σ zz , τ xy , τ yz , τ xz is the far-field stress component in the wellbore rectangular coordinate system; Φ is the well inclination angle Φ; Ω is the well inclination azimuth Ω; σ v is the vertical ground stress; H is the maximum horizontal ground stress; h is the minimum horizontal ground stress.

[0043] S22, given minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of .

[0044] The minimum wellbore pressure p of the present disclosure w1 , maximum wellbore pressure p w2 and precision ε are given artificially. For example, the minimum wellbore pressure p of the present disclosure is w1 Can be 0. For example, the minimum wellbore pressure p of the present disclosure is w1 Can be negative.

[0045] S23, through the formation pore pressure p p , Poisson's ratio v, Biot coefficient α p , the allowable expansion ratio HER and the far-field stress component calculated in step S21, and given the allowable expansion ratio HER, the wellbore pressure p is calculated m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective wellbore stress components at .

[0046] like Figure 2 The schematic diagram of the cohesive force required to maintain the stability of the wellbore wall is shown in FIG. The present disclosure assumes an allowable expansion rate of the wellbore, and the collapse point occurs at point B in the figure. Point B in the figure is the maximum radius r of the wellbore after the allowable expansion rate is given. b Position. To calculate the borehole wall stress component in the formation along the 360° direction around the well, the following formula can be used:

[0047]

[0048] In formula (3):

[0049] r b =(1+HER)r w (4)

[0050]

[0051] In equations (3), (4) and (5): rr , σ θθ , σ zz , τ θz , τ rθ , τ rz is the borehole wall stress component under the condition of given expansion rate in the borehole cylindrical coordinate system; r w is the radius of the drill bit used for drilling; r b is the maximum radius of the wellbore after the allowable expansion rate; HER is the allowable expansion rate; θ is the wellbore angle; v is the Poisson's ratio; α p is the Biot coefficient; p p is the pore pressure; p m is the wellbore pressure.

[0052] S24, the wellbore stress components calculated by S23 are calculated along the 360° direction around the wellbore, and the wellbore pressures are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective principal stresses σ are as follows:

[0053]

[0054] In formula (6):

[0055]

[0056] I1=σ rr +σ θθ +σ zz (8)

[0057]

[0058]

[0059]

[0060]

[0061] In equations (6), (7), (8), (9), (10), (11) and (12): σ1 is the maximum principal stress; σ3 is the minimum principal stress; I1 is the first invariant of the stress tensor; I2 is the second invariant of the stress tensor; I3 is the third invariant of the stress tensor; J2 is the second invariant of the stress deviator; J3 is the third invariant of the stress deviator; θ is the wellbore angle; p m is the wellbore pressure.

[0062] In step S23 and step S24, the well angle θ is not a fixed value but a variable. Usually, the well angle θ is determined by the maximum horizontal ground stress σ H Starting from the direction of the wellbore, the wellbore angle θ varies in the range of 0° to 360°. In the formula of step S23, the wellbore angle θ is used to determine all the wellbore stress components when a wellbore angle θ is given, and then in step S24, the wellbore pressure is determined to be the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w That is to say, it is necessary to calculate the wellbore stress components under the wellbore angle θ in all cases in step S23, and then determine the wellbore pressure as the minimum wellbore pressure p in step S24. w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective maximum principal stress σ1 and minimum principal stress σ3.

[0063] S25, when the wellbore pressure calculated according to S24 is the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w When the respective maximum principal stress σ1 and minimum principal stress σ3 are determined, the maximum value σ of the maximum principal stress σ1 is determined. 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max , using the following formula:

[0064] In formula (13): 1max is the maximum value of the maximum principal stress; θ max is the wellbore angle corresponding to the maximum value of the maximum principal stress; θ is the wellbore angle; p m is the wellbore pressure.

[0065] The maximum value σ of the maximum principal stress σ1 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max There are three, corresponding to the wellbore pressure as the minimum wellbore pressure pw1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The value of .

[0066] S26, through rock cohesion and internal friction angle, and the maximum wellbore angle θ max The corresponding maximum principal stress σ1 and minimum principal stress σ3 are used to calculate the wellbore pressure p m is the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The Mohr-Coulomb failure criterion function can be used to calculate the three wellbore pressures p m The respective function values ​​are given by the following formula:

[0067] In formula (14): c is the rock cohesion, is the internal friction angle.

[0068] It should be noted that in the binary method used in the present disclosure, the interval range [p w1 ,p w2 ], in this step, the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The failure criterion function value f(p w1 )·f(p w2 )<0.

[0069] S27. Determine the value of the failure criterion function and determine the collapse pressure p c The dichotomy method can be used to determine S26. The three function values ​​obtained using the Mohr-Coulomb failure criterion function can be used to determine the zero point of the failure criterion function, thereby determining the collapse pressure p. c . Use the dichotomy method to judge, the judgment method is as follows:

[0070] If f(p w )=0, then the average wellbore pressure p w is the zero point of the failure criterion function, the collapse pressure p c Equal to the average wellbore pressure p w ;

[0071] If f(p w1 )·f(p w )<0, then let p w2 =p w , at this time, the zero point of the destruction criterion function∈(p w1 ,p w ), that is, the collapse pressure p c ∈(pw1 ,p w );

[0072] If f(p w )·f(p w2 )<0, then let p w1 =p w , at this time, the zero point of the destruction criterion function∈(p w ,p w2 ), that is, the collapse pressure p c ∈(p w ,p w2 ).

[0073] S28, based on the value range of the zero point of the failure criterion function determined in step S27, determine the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The absolute value of the difference between the two meets the accuracy requirement ε to determine the zero approximation of the destruction criterion function. w1 )·f(p w )<0 or f(p w )·f(p w2 )<0, further determine whether the accuracy requirement ε is met, using the binary method, the determination method is as follows:

[0074] If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is less than the accuracy ε, the minimum wellbore pressure p w1 or maximum wellbore pressure p w2 As the collapse pressure p c ;

[0075] If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is not less than the accuracy ε, the well inclination angle Φ, the well inclination azimuth Ω and the allowable expansion rate HER are re-given, and steps S22 to S28 are repeated until the accuracy ε requirement is met.

[0076] That is, if the collapse pressure p c If the accuracy requirement ε is not met, steps S22 to S28 need to be repeated until the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 And the collapse pressure p calculated by given well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER c It also needs to be clarified that the minimum wellbore pressure p used for comparing the difference in step S28 is w1 and the maximum wellbore pressure p w2The latest p obtained in step 27 is used. w1 With p w2 , rather than the artificially determined p in step S22 w1 With p w2 .

[0077] Step S22, step S26, step S27 and step S28 are all steps of binary search, which is a commonly used method in the art and will not be described in detail in this disclosure.

[0078] S29, output the collapse pressure p when the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER are given and the accuracy requirement ε is met c .

[0079] In the present disclosure, the mathematical calculation model of the wellbore collapse pressure of a directional well that allows wellbore expansion in step S2 can be submitted through a post-programming program system, and ultimately a relationship diagram among the final wellbore collapse pressure equivalent density, well inclination angle Φ, and well inclination azimuth angle Ω is formed. Therefore, the calculation results of each step in the mathematical calculation model may not be reflected.

[0080] Figure 1 The flowchart of a method for evaluating wellbore stability allowing wellbore expansion provided by the present disclosure is shown, including steps S1 and S2 (step S2 includes S21 to S29) in the above-mentioned method for calculating wellbore collapse pressure of a directional well allowing wellbore expansion, and also includes step S3:

[0081] S3, according to the collapse pressure p c Calculate the collapse pressure equivalent density ρ c , and plot the collapse pressure equivalent density ρ c The relationship diagram of the three angles of inclination Φ and inclination azimuth Ω is shown in the figure. The collapse pressure equivalent density ρ c The stability of the wellbore is judged by comparing the changing trends of the well inclination angle Φ and the well inclination azimuth Ω.

[0082] Collapse pressure equivalent density ρ c The calculation formula is:

[0083] ρ c =p c / gH (1)

[0084] In formula (1): c is the collapse pressure equivalent density, p c is the collapse pressure, g is the gravity acceleration, and H is the depth of the directional well. The gravity acceleration g is determined according to the situation.

[0085] Through the variables of well inclination angle Φ and well inclination azimuth angle Ω, when the allowable expansion rate HER and height H are determined, the change of the collapse pressure equivalent density with the well inclination angle Φ and the well inclination azimuth angle Ω can be concretely reflected.

[0086] In step S3, the steps of determining the wellbore stability are:

[0087] S31, according to the collapse pressure equivalent density ρ c With the change of well inclination angle Φ, the relative stability between vertical wells, inclined wells or horizontal wells can be judged. Specifically, if the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a trend of gradually increasing. When the well inclination angle Φ is small (the minimum is 0°), the collapse pressure equivalent density ρ c The minimum, that is, the stability of vertical wells is better than that of inclined wells and horizontal wells. When the well inclination angle Φ is 90°, the collapse pressure equivalent density ρ c maximum, that is, the stability of horizontal well drilling is the worst; if the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a decreasing trend. When the well inclination angle Φ is large (maximum 90°), the collapse pressure equivalent density ρ c The minimum, that is, the stability of drilling horizontal wells is better than that of vertical wells and inclined wells. When the well inclination angle Φ is 0°, the collapse pressure equivalent density ρ c maximum, that is, the stability of vertical wells is the worst; if the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows a trend of first increasing and then decreasing. The collapse pressure equivalent density ρ is determined as c The minimum well inclination angle Φ can be used to determine whether a vertical well or a horizontal well has better stability. When the well inclination angle Φ is certain, the collapse pressure equivalent density ρ c The maximum, that is, the stability of the inclined well is the worst; if the collapse pressure equivalent density ρ c With the increase of well inclination angle Φ, it shows a trend of first decreasing and then increasing. When the well inclination angle Φ is certain, the collapse pressure equivalent density ρ c Minimum, that is, the stability of drilling inclined wells is better than that of drilling horizontal wells and vertical wells.

[0088] S32, by judging the collapse pressure equivalent density ρ c The direction of the well inclination azimuth Ω when it is the minimum value, then the vertical well, inclined well or horizontal well drilled in the direction of this well inclination azimuth Ω has the best stability.

[0089] To facilitate understanding, some special cases are given. For example, when the collapse pressure equivalent density ρ c The minimum value is obtained when the well inclination angle Φ is 0°, which means that drilling a vertical well (the well inclination angle Φ of a vertical well is 0°) is the most stable; when the collapse pressure equivalent density ρ cThe minimum value is obtained when the well inclination angle Φ is 90°, which means that drilling a horizontal well (the well inclination angle Φ of a horizontal well is 0°) is the most stable; when the collapse pressure equivalent density ρ c The minimum value is obtained when the well inclination angle Φ is 45°, which means that the inclined well (the well inclination angle Φ of the inclined well has a certain degree) is the most stable. Determine the collapse pressure equivalent density ρ when the well inclination angle Φ changes c After determining the relative stability between vertical wells, inclined wells or horizontal wells, the collapse pressure equivalent density ρ is determined when the well inclination angle Φ remains unchanged. c The minimum well inclination azimuth Ω can be used to obtain the relative stability between vertical wells, inclined wells or horizontal wells and the specific angle from which the well is drilled has good stability, thereby realizing the evaluation of wellbore stability.

[0090] In addition, if the collapse pressure equivalent density ρ c As the well inclination angle Φ increases, it shows irregular changes. The well inclination angle Φ and the well inclination azimuth Ω can be judged comprehensively, or they can be evaluated at different angles or regions (for example, when the well inclination azimuth Ω is 90°, the change law of the well inclination angle Φ can be judged, and when the well inclination angle Φ is 60°, the change law of the well inclination azimuth Ω can be judged). In short, the principle of judgment is the collapse pressure equivalent density ρ c The direction of the well inclination angle Φ and the well inclination azimuth Ω when they are minimum, and then the most suitable well in this direction is selected according to the judgment method in the above steps S31 and S32, that is, the well drilled is the most stable.

[0091] The present disclosure also provides a wellbore stability evaluation system that allows wellbore expansion, including a parameter determination module, a collapse pressure calculation module, a relationship graphics module and a judgment module.

[0092] The parameter determination module is configured to determine the geomechanical parameters and rock mechanical parameters of the target formation, wherein the geomechanical parameters include the vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p , rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot's coefficient α p .

[0093] The collapse pressure calculation module is configured to establish a mathematical calculation model for the wellbore collapse pressure of a directional well that allows wellbore expansion based on geomechanical parameters and rock mechanics parameters, and given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, and solve to obtain the collapse pressure p c The mathematical calculation model is steps S21 to S29 in the above-mentioned wellbore stability evaluation method allowing wellbore expansion, which will not be described in detail here.

[0094] The relationship graph module is configured to be based on the collapse pressure p c Calculate the collapse pressure equivalent density ρ c , and plot the collapse pressure equivalent density ρ c Relationship diagram of the change of well inclination angle Φ and well inclination azimuth Ω.

[0095] The judgment module is configured to calculate the collapse pressure equivalent density ρ on the relationship diagram c The wellbore stability is judged relative to the changing trend of the wellbore inclination angle Φ and the wellbore inclination azimuth angle Ω. The judging configuration of the judging module is the step of judging the wellbore stability in step S3 of the wellbore stability evaluation method allowing wellbore expansion, which will not be repeated here.

[0096] The present disclosure further provides a computer-readable storage medium storing a computer program, which, when executed by a processor, can implement the above-mentioned method for evaluating the wellbore collapse pressure and wellbore stability of a directional well that allows wellbore expansion.

[0097] Taking the formation at 3000m in a well in Sichuan Basin as a specific embodiment, the wellbore stability evaluation method allowing wellbore expansion disclosed in the present invention comprises the following steps:

[0098] S1. Use seismic, drilling, logging, well logging, completion and testing data to determine the geomechanical parameters and rock mechanics parameters of the target formation. Geomechanical parameters include vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p Rock mechanical parameters include rock cohesion, internal friction angle, Poisson's ratio v and Biot coefficient α p ;

[0099] In this specific embodiment, the formation pore pressure is 31.5 MPa, the rock cohesion is 15 MPa, the internal friction angle is 30°, the Poisson's ratio v is 0.25, and the Biot coefficient α p is 0.85. Vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h Take three stress states, namely normal fault stress state, strike-slip fault stress state and reverse fault stress state, as shown in the following table:

[0100]

[0101] S2. Based on geological parameters and rock mechanics parameters, and given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, a mathematical calculation model for the wellbore collapse pressure of a directional well that allows wellbore expansion is established to solve the collapse pressure pc ;

[0102] Wherein, the step S2 of establishing a mathematical calculation model of the wellbore collapse pressure of a directional well that allows the wellbore to expand may include the following steps:

[0103] S21, through the vertical ground stress σ v , maximum horizontal ground stress σ H and the minimum horizontal ground stress σ h , and given the well inclination angle Φ and well inclination azimuth Ω, the far-field stress component in the wellbore rectangular coordinates can be calculated using formula (2).

[0104] S22, given minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of .

[0105] In this specific embodiment, the inventors of the present disclosure set the minimum wellbore pressure p w1 =2p p , that is, negative twice the formation pore pressure, the maximum wellbore pressure p w1 +10p p , which is ten times the formation pore pressure, the average wellbore pressure p w +4p p , which is four times the formation pore pressure, and the accuracy ε is set to 0.01.

[0106] S23, through the formation pore pressure p p , Poisson's ratio v, Biot coefficient α p , the allowable expansion ratio HER and the far-field stress component calculated in step S21, and given the allowable expansion ratio HER, the wellbore pressure p is calculated m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The wellbore stress components can be calculated using formula (3).

[0107] S24, the wellbore stress components calculated by S23 are calculated along the 360° direction around the wellbore, and the wellbore pressures are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p wThe respective principal stresses σ are calculated, where the principal stresses σ include the maximum principal stress σ1 and the minimum principal stress σ3, and the following formulas (6), (7), (8), (9), (10), (11) and (12) are used.

[0108] S25, when the wellbore pressure calculated according to S24 is the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w When the respective maximum principal stress σ1 and minimum principal stress σ3 are determined, the maximum value σ of the maximum principal stress σ1 is determined. 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max , using formula (13).

[0109] S26, through rock cohesion and internal friction angle, and the maximum wellbore angle θ max The corresponding maximum principal stress σ1 and minimum principal stress σ3 are used to calculate the wellbore pressure p m is the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective failure criterion function values ​​are as follows. Formula (14) can be used.

[0110] S27. Determine the value of the failure criterion function and determine the collapse pressure p c The dichotomy method can be used to determine S26. The three function values ​​obtained using the Mohr-Coulomb failure criterion function can be used to determine the zero point of the failure criterion function, thereby determining the collapse pressure p. c . Use the dichotomy method to judge, the judgment method is as follows:

[0111] If f(p w )=0, then the average wellbore pressure p w is the zero point of the failure criterion function, the collapse pressure p c Equal to the average wellbore pressure p w ;

[0112] If f(p w1 )·f(p w )<0, then let p w2 =p w , at this time, the zero point of the destruction criterion function∈(p w1 ,p w ), that is, the collapse pressure p c ∈(p w1 ,p w );

[0113] If f(p w )·f(p w2)<0, then let p w1 =p w , at this time, the zero point of the destruction criterion function∈(p w ,p w2 ), that is, the collapse pressure p c ∈(p w ,p w2 ).

[0114] S28, based on the value range of the zero point of the failure criterion function determined in step S27, determine the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The absolute value of the difference between the two meets the accuracy requirement ε to determine the zero approximation of the destruction criterion function. w1 )·f(p w )<0 or f(p w )·f(p w2 )<0, further determine whether the accuracy requirement ε is met, using the binary method, the determination method is as follows:

[0115] If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is less than the accuracy ε, the minimum wellbore pressure p w1 or maximum wellbore pressure p w2 As the collapse pressure p c ;

[0116] If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is not less than the accuracy ε, the well inclination angle Φ, the well inclination azimuth Ω and the allowable expansion rate HER are re-given, and steps S22 to S28 are repeated until the accuracy ε requirement is met.

[0117] S29, output the collapse pressure p when the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER are given and the accuracy requirement ε is met c .

[0118] S3, the collapse pressure p obtained according to step S2 c Calculate the collapse pressure equivalent density ρ c , changing the well inclination angle Φ and well inclination azimuth Ω, plotting the collapse pressure equivalent density ρ c The relationship between the well inclination angle Φ and the well inclination azimuth Ω is used to calculate the wellbore collapse pressure of the directional well when the allowable expansion rate HER is given. Among them, the collapse pressure equivalent density ρ c The calculation formula can be adopted as formula (1).

[0119] like Figures 4 to 11The figure shows the relationship between the wellbore collapse pressure equivalent density, wellbore inclination angle Φ, and wellbore inclination azimuth angle Ω in step S3 calculated under the three stress states in step S1. For comparison, the results calculated by the traditional wellbore stability evaluation method and a wellbore stability quantitative evaluation method based on a risk control model disclosed in publication number CN109377101A are also given. Figures 4 to 11 In the figure, the increase in grayscale indicates the equivalent density of the wellbore collapse pressure ρ c The increase of the inclination angle Φ from the center of the circle along the radius increases from 0° to 90°, and the circumference of the circle is expressed as the inclination azimuth Ω increases from 0° to 360°. The inclination azimuth Ω at 0° (360°) and 180° is the maximum horizontal stress direction, and the inclination azimuth Ω at 90° and 270° is the minimum horizontal stress σ h Direction (limited to the specific embodiment, for more general situations, the well inclination azimuth Ω at 0° (360°) and 180° may not be consistent with the maximum horizontal ground stress direction). The analysis and evaluation process and results of the three stress states are as follows:

[0120] (1) For normal faults, as shown in the table above, σ v >σ H >σ h (i.e. σ v =100MPa,σ H =90MPa,σ h =70MPa)

[0121] Using the traditional wellbore stability evaluation method (hereinafter referred to as the traditional method), such as Figure 3 The collapse pressure equivalent density ρ is shown as c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, with the increase of well inclination angle Φ (0°~90°), it shows a gradually increasing trend, that is, the stability of vertical wells and inclined wells is obviously better than that of horizontal wells; and with the increase of well inclination azimuth angle Ω (0°~180°), the collapse pressure equivalent density ρ c It shows a trend of decreasing first and then increasing, with the minimum value in the direction of the minimum horizontal stress and the maximum value in the direction of the maximum horizontal stress. Figure 3 It can be seen that the stability of the horizontal well drilled at about 30° along the direction of the minimum horizontal stress is the best, the stability of the horizontal well drilled along the direction of the maximum horizontal stress is the worst, and the stability of the horizontal well drilled along the direction of the minimum horizontal stress is relatively good.

[0122] A wellbore stability evaluation method based on a risk control model disclosed in publication number CN109377101A (hereinafter referred to as the comparative method) is used. Figure 4 The collapse pressure equivalent density ρ is shown as c, the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, with the increase of well inclination angle Φ (0°~90°), it shows a gradually increasing trend, that is, the stability of vertical wells and inclined wells is obviously better than that of horizontal wells; with the increase of well inclination azimuth angle Ω (0°~180°), the collapse pressure equivalent density ρ c It shows a trend of decreasing first and then increasing, with the minimum value in the direction of the minimum horizontal stress and the maximum value in the direction of the maximum horizontal stress. Figure 4 It can be seen that the stability of vertical wells is the best, the stability of horizontal wells drilled along the direction of maximum horizontal stress is the worst, and the stability of horizontal wells drilled along the direction of minimum horizontal stress is relatively good. However, compared with the traditional method, the collapse pressure equivalent density ρ c Significantly lower, the collapse pressure equivalent density ρ of the traditional method c 1.68~1.97g / cm 3 , Collapse pressure equivalent density ρ of the comparison method c 1.34~1.86g / cm 3 , the equivalent density of collapse pressure in the direction of maximum and minimum horizontal stress ρ c The difference is significantly reduced, that is, the influence of the well inclination azimuth Ω on the wellbore stability is not as great as predicted by the traditional model.

[0123] The method for calculating the wellbore collapse pressure of a directional well that allows wellbore expansion disclosed in the present invention (hereinafter referred to as the method disclosed in the present invention) is as follows: Figure 5 The collapse pressure equivalent density ρ is shown as c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, with the increase of well inclination angle Φ (0°~90°), it shows a gradually increasing trend, that is, the stability of vertical wells and inclined wells is obviously better than that of horizontal wells; with the increase of well inclination azimuth angle Ω (0°~180°), the collapse pressure equivalent density ρ c Overall, the changes are relatively minor. Figure 5 It can be seen that the stability of drilling vertical wells is the best, the stability of drilling horizontal wells is the worst, and the stability of horizontal wells drilled along the direction of minimum horizontal stress and the direction of maximum horizontal stress is basically the same. Compared with the traditional method and the comparative method, the collapse pressure equivalent density ρ calculated by the method disclosed in this paper is c The lowest, the collapse pressure equivalent density ρ calculated by traditional methods c 1.68~1.97g / cm 3 , the collapse pressure equivalent density ρ calculated by the comparison method c 1.34~1.86g / cm 3 , the collapse pressure equivalent density ρ calculated by the disclosed method c1.34~1.69g / cm 3 , and the collapse pressure equivalent density ρ in the direction of maximum and minimum horizontal stress c The difference is further reduced, that is, the influence of the well inclination azimuth Ω on the wellbore stability is not as great as predicted by the traditional model.

[0124] (2) For strike-slip faults, as shown in the table above, σ H >σ v >σ h (i.e. σ v =80MPa,σ H =90MPa,σ h =70MPa)

[0125] Using traditional methods, such as Figure 6 The collapse pressure equivalent density ρ is shown as c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, with the increase of well inclination angle Φ (0°~90°), it shows a gradually decreasing trend, that is, the stability of drilling horizontal wells is obviously better than that of vertical wells and inclined wells; and with the increase of well inclination azimuth angle Ω (0°~180°), the collapse pressure equivalent density ρ c It shows a trend of increasing first and then decreasing, with the minimum value being obtained in the direction about 30° away from the direction of the maximum horizontal stress and the maximum value being obtained in the direction of the minimum horizontal stress. Figure 6 It can be seen that horizontal wells drilled at a deviation of about 30° from the maximum horizontal geostress have the best stability, while vertical wells have the worst stability. Horizontal wells drilled along the direction of maximum horizontal geostress are more stable than those drilled in the direction of minimum horizontal geostress.

[0126] Use contrast methods, such as Figure 7 The collapse pressure equivalent density ρ is shown as c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, with the increase of well inclination angle Φ (0°~90°), it shows a trend of first increasing and then decreasing, that is, the stability of vertical wells and horizontal wells is better than that of inclined wells; with the increase of well inclination azimuth angle Ω (0°~180°), the collapse pressure equivalent density ρ c It shows a trend of increasing first and then decreasing, reaching a minimum value in the direction about 40° away from the direction of the maximum horizontal stress, and a maximum value in the direction of the minimum horizontal stress. Figure 7It can be seen that vertical wells and horizontal wells drilled in a direction about 40° away from the maximum horizontal geostress direction have the best stability, while high-angle wells and horizontal wells drilled in the direction of minimum horizontal geostress have the worst stability. Horizontal wells drilled in the direction of maximum horizontal geostress are more stable than those drilled in the direction of minimum horizontal geostress. The collapse pressure equivalent density ρ calculated by traditional methods c 1.50~1.71g / cm 3 , the collapse pressure equivalent density ρ calculated by the comparison method c 1.34~1.58g / cm 3 , the equivalent density of collapse pressure in the direction of maximum and minimum horizontal stress ρ c The difference is slightly reduced, while the difference in collapse pressure equivalent density between vertical well and small well inclination angle Φ is particularly large.

[0127] Using the disclosed method, such as Figure 8 The collapse pressure equivalent density ρ is shown as c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, with the increase of well inclination angle Φ (0°~90°), it shows a gradually increasing trend, that is, the stability of vertical wells is significantly better than that of inclined wells and horizontal wells, among which the stability of vertical wells is the best, while the stability of horizontal wells is the worst; with the increase of well inclination azimuth Ω (0°~180°), the collapse pressure equivalent density ρ c On the whole, it shows a trend of first slightly increasing and then slightly decreasing, with the minimum value being obtained in the direction about 15° away from the direction of the maximum horizontal stress and the maximum value being obtained in the direction of the minimum horizontal stress. Figure 8 It can be seen that the stability of horizontal wells drilled in a direction about 15° away from the maximum horizontal geostress direction is relatively good, and the horizontal wells drilled along the maximum horizontal geostress direction are more stable than the horizontal wells drilled in the minimum horizontal geostress direction. Compared with the traditional method and the comparative method, the collapse pressure equivalent density ρ calculated by the method disclosed in this paper is c The lowest, the collapse pressure equivalent density ρ calculated by traditional methods c 1.50~1.71g / cm 3 , the collapse pressure equivalent density ρ calculated by the comparison method c 1.34~1.58g / cm 3 , the collapse pressure equivalent density ρ calculated by the disclosed method c 1.14~1.47g / cm 3 , and the collapse pressure equivalent density ρ in the direction of maximum and minimum horizontal stress c The difference is further reduced, that is, the influence of the well inclination azimuth Ω on the wellbore stability is not as great as predicted by the traditional model.

[0128] (3) For reverse faults, as shown in the table above, σ H >σ h >σ v (i.e. σ v =60MPa,σ H =90MPa,σ h =70MPa)

[0129] Using traditional methods, such as Fig. 9 The collapse pressure equivalent density ρ is shown as c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, the collapse pressure equivalent density ρ increases with the increase of the well inclination angle Φ (0°~90°); and with the increase of the well inclination azimuth angle Ω (0°~180°), the collapse pressure equivalent density ρ increases with the increase of the well inclination angle Φ (0°~90°). c It shows a trend of increasing first and then decreasing, reaching the minimum value in the direction of the maximum horizontal stress and the maximum value in the direction of the minimum horizontal stress, gradually decreasing along the direction of the maximum horizontal stress and gradually increasing along the direction of the minimum horizontal stress. Fig. 9 It can be seen that the stability of horizontal wells drilled along the direction of maximum horizontal geostress is significantly better than that of vertical wells and inclined wells. The stability of horizontal wells drilled along the direction of maximum horizontal geostress is the best, and the stability of horizontal wells drilled along the direction of minimum horizontal geostress is the worst.

[0130] Use contrast methods, such as Fig.10 The collapse pressure equivalent density ρ is shown as c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, with the increase of well inclination angle Φ (0°~90°), it shows irregular changes, first increasing and then decreasing along the direction of maximum horizontal stress, and gradually increasing along the direction of minimum horizontal stress; with the increase of well inclination azimuth Ω (0°~180°), the collapse pressure equivalent density ρ c It shows a trend of increasing first and then decreasing, with the minimum value in the direction of maximum horizontal stress and the maximum value in the direction of minimum horizontal stress. Fig.10 It can be seen that the stability of horizontal wells drilled along the direction of maximum horizontal geostress is significantly better than that of vertical wells and inclined wells, and the stability of horizontal wells drilled along the direction of minimum horizontal geostress is the worst. However, compared with the traditional wellbore stability evaluation method, the collapse pressure equivalent density ρ c Obviously lower than the collapse pressure equivalent density ρ calculated by traditional methods c 1.42~1.79g / cm 3 , the collapse pressure equivalent density ρ calculated by the comparison method c 1.21~1.69g / cm 3, the equivalent density of collapse pressure in the direction of maximum and minimum horizontal stress ρ c The difference is slightly reduced, while the collapse pressure equivalent density ρ in the case of vertical well and small well angle Φ c The difference is relatively large.

[0131] Using the disclosed method, such as Fig.11 The collapse pressure equivalent density ρ is obtained c , the relationship between the well inclination angle Φ and the well inclination azimuth Ω, the collapse pressure equivalent density ρ c In general, it shows a gradual increasing trend with the increase of well inclination angle Φ (0°~90°); with the increase of well inclination azimuth angle Ω (0°~180°), the collapse pressure equivalent density ρ c On the whole, it shows a trend of increasing first and then decreasing, with the minimum value in the direction of maximum horizontal ground stress and the maximum value in the direction of minimum horizontal ground stress. Fig.11 It can be seen that the stability of vertical wells is significantly better than that of inclined wells and horizontal wells. The stability of vertical wells is the best, while the stability of horizontal wells is the worst. Horizontal wells drilled along the direction of maximum horizontal geostress are more stable than those drilled along the direction of minimum horizontal geostress. Compared with the traditional method and the comparative method, the collapse pressure equivalent density ρ calculated by the method disclosed in this paper is c The lowest, the collapse pressure equivalent density ρ calculated by traditional methods c 1.42~1.79g / cm 3 , the collapse pressure equivalent density ρ calculated by the comparison method c 1.21~1.69g / cm 3 , the collapse pressure equivalent density ρ calculated by the disclosed method c 1.14~1.60g / cm 3 , and the collapse pressure equivalent density ρ in the direction of maximum and minimum horizontal stress c The difference is significantly reduced, that is, the influence of the well inclination azimuth Ω on the wellbore stability is not as great as predicted by the traditional model.

[0132] Comparative analysis of the collapse pressure equivalent density ρ calculated by the traditional method, the comparative method and the disclosed method under three stress states: normal fault, strike-slip fault and reverse fault c As a result, the following conclusions can be drawn: The collapse pressure equivalent density ρ calculated by the disclosed method is c The lowest, the collapse pressure equivalent density ρ calculated by traditional methods c The highest, while the collapse pressure equivalent density ρ calculated by the comparison method c The collapse pressure equivalent density ρ calculated by the disclosed method and the comparative method is c It is relatively close, that is, the collapse pressure equivalent density ρ calculated by the method disclosed in this paperc Therefore, allowing the wellbore to expand can effectively reduce the critical wellbore pressure equivalent density ρ required to maintain wellbore stability c Or drilling fluid density, that is to say, allowing a certain degree of wellbore expansion rate to significantly reduce the collapse pressure and still prevent wellbore collapse and instability.

[0133] In summary, the present invention overcomes the shortcomings of existing theoretical models and calculation methods, directly establishes the relationship between completion electrical logging wellbore data and the allowable expansion rate and collapse pressure, can more accurately calculate the wellbore collapse pressure of directional wells, facilitates the comparison and analysis and application of actual drilling site data, and can provide a theoretical basis for the optimization design of drilling fluid density, wellbore trajectory optimization design, and safe and efficient drilling of complex structure wells such as directional wells, horizontal wells, and branch wells.

[0134] Although the present disclosure has been described above in conjunction with exemplary embodiments and the accompanying drawings, it should be apparent to those skilled in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A method for evaluating wellbore stability allowing wellbore expansion, characterized in that: The wellbore stability evaluation method comprises the following steps: S1. Determine the geomechanical parameters and rock mechanics parameters of the target stratum, wherein the geomechanical parameters include vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p The rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot's coefficient α p ; S2. Based on the geomechanical parameters and the rock mechanics parameters, and given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, a mathematical calculation model for the wellbore collapse pressure of a directional well that allows wellbore expansion is established to solve for the collapse pressure p c ; S3, according to the collapse pressure p c Calculate the collapse pressure equivalent density ρ c , and plot the collapse pressure equivalent density ρ c , the well inclination angle Φ and the well inclination azimuth Ω, and the collapse pressure equivalent density ρ on the relationship diagram c The stability of the wellbore is judged relative to the changing trend of the well inclination angle Φ and the well inclination azimuth angle Ω; The step S2 comprises the following steps: S21, through the vertical geostress σ v , the maximum horizontal ground stress σ H and the minimum horizontal in-situ stress σ h , and the given well inclination angle Φ and the well inclination azimuth Ω, calculate the far-field stress component in the wellbore rectangular coordinates; S22, given the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , the average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of S23, through the formation pore pressure p p , the Poisson's ratio v, the Biot coefficient α p , the allowable expansion rate HER and the far-field stress component, and calculate the wellbore pressure p m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w S24, calculate the wellbore pressure p through the wellbore stress components m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective principal stresses σ are as follows, wherein the principal stresses σ include a maximum principal stress σ1 and a minimum principal stress σ3; S25, determining a maximum value σ of the maximum principal stress σ1 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max ; S26, through the rock cohesion and the internal friction angle, as well as the maximum principal stress σ1 and the minimum principal stress σ3 corresponding to the maximum wellbore angle θmax, the wellbore pressure p is calculated m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w S27, using the dichotomy method to judge the value of the destruction criterion function to determine the zero point of the destruction criterion function or the value range of the zero point of the destruction criterion function; S28, based on the determination of the value range of the zero point of the destruction criterion function, determine the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The absolute value of the difference between the two meets the requirement of accuracy ε to determine the zero point approximation of the failure criterion function; S29, using the zero point of the failure criterion function or the zero point approximation of the failure criterion function as the collapse pressure p c ； The step S27 comprises: if f(p w )=0, then the average wellbore pressure p w is the zero point of the failure criterion function, the collapse pressure p c Equal to the average wellbore pressure p w ; if f(p w1 )·f(p w )<0, then let p w2 =p w , at this time, the zero point of the destruction criterion function∈(p w1 ,p w ); if f(p w )·f(p w2 )<0, then let p w1 =p w , at this time, the zero point of the destruction criterion function∈(p w ,p w2 ); The step S28 comprises: w1 )·f(p w )<0 or f(p w )·f(p w2 )<0, further determine whether the accuracy requirement ε is met. Specifically: if the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is less than the accuracy ε, the minimum wellbore pressure p w1 or maximum wellbore pressure p w2 As the collapse pressure p c ; If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is not less than the accuracy ε, the well inclination angle Φ, the well inclination azimuth Ω and the allowable diameter expansion rate HER are re-given, and steps S22 to S28 are repeated until the accuracy ε requirement is met; The step of judging the wellbore stability is as follows: S31, according to the collapse pressure equivalent density ρ c The angles of the well inclination angle Φ at the minimum and maximum are used to judge the relative stability between the vertical well, the inclined well or the horizontal well; S32, by judging the collapse pressure equivalent density ρ c When the well inclination angle Ω is the minimum, the vertical well, inclined well or horizontal well drilled in the direction has the best stability.

2. A wellbore stability evaluation system that allows wellbore expansion, characterized in that: The evaluation system includes: The parameter determination module is configured to determine the geomechanical parameters and rock mechanical parameters of the target formation, wherein the geomechanical parameters include the vertical stress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p The rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot's coefficient α p ; The collapse pressure calculation module is configured to establish a mathematical calculation model of the wellbore collapse pressure of the directional well that allows wellbore expansion based on the geomechanical parameters and the rock mechanics parameters, and given the well inclination angle Φ, the well inclination azimuth Ω and the allowable expansion rate HER, and solve to obtain the collapse pressure p c ; A relationship graphical module is configured to calculate the relationship according to the collapse pressure p c Calculate the collapse pressure equivalent density ρ c , and plot the collapse pressure equivalent density ρ c A relationship diagram relative to changes in the well inclination angle Φ and the well inclination azimuth angle Ω; and The judgment module is configured to determine the collapse pressure equivalent density ρ on the relationship diagram. c The stability of the wellbore is judged relative to the changing trend of the well inclination angle Φ and the well inclination azimuth angle Ω; The mathematical calculation model of the wellbore collapse pressure of the directional well that allows the wellbore to expand is configured as follows: The vertical geostress σ v , the maximum horizontal ground stress σ H and the minimum horizontal in-situ stress σ h , and given the well inclination angle Φ and the well inclination azimuth Ω, calculate the far-field stress component in the wellbore rectangular coordinates; Given the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , the average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of The formation pore pressure p p , the Poisson's ratio v, the Biot coefficient α p , the allowable expansion rate HER and the far-field stress component, and calculate the wellbore pressure p m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective wellbore stress components at ; The wellbore pressure p is calculated by using the wellbore stress components. m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective principal stresses σ are as follows, wherein the principal stresses σ include the maximum principal stress σ1 and the minimum principal stress σ3; Determine the maximum value σ of the maximum principal stress σ1 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max ; The wellbore pressure p is calculated by the rock cohesion and the internal friction angle, as well as the maximum principal stress σ1 and the minimum principal stress σ3 corresponding to the maximum wellbore angle θmax. m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w When , the respective failure criterion function values ​​are; The value of the destruction criterion function is judged by using a dichotomy method to determine the zero point of the destruction criterion function or the value range of the zero point of the destruction criterion function; On the basis of determining the value range of the zero point of the failure criterion function, the minimum wellbore pressure p is determined. w1 and the maximum wellbore pressure p w2 Whether the absolute value of the difference between meets the accuracy requirement ε to determine the zero approximation of the failure criterion function; and The zero point of the failure criterion function or the approximate value of the zero point of the failure criterion function is taken as the collapse pressure p c ; The judgment module is configured to: according to the collapse pressure equivalent density ρ c The angles of the well inclination Φ at the minimum and maximum are used to determine the relative stability between vertical wells, inclined wells or horizontal wells; by determining the collapse pressure equivalent density ρ c When the well inclination angle Ω is the minimum, the vertical well, inclined well or horizontal well drilled in the direction has the best stability.

3. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the wellbore stability evaluation method as claimed in claim 1 is implemented.

4. A method for calculating the wellbore collapse pressure of a directional well that allows wellbore expansion, characterized in that: The calculation method includes: S1. Determine the geomechanical parameters and rock mechanics parameters of the target stratum, wherein the geomechanical parameters include vertical geostress σ v , maximum horizontal ground stress σ H , minimum horizontal ground stress σ h and formation pore pressure p p The rock mechanical parameters include rock cohesion c, internal friction angle Poisson's ratio v and Biot's coefficient α p ;and S2. Based on the geomechanical parameters and the rock mechanics parameters, and given the well inclination angle Φ, well inclination azimuth Ω and allowable expansion rate HER, a mathematical calculation model for the wellbore collapse pressure of a directional well that allows wellbore expansion is established to solve for the collapse pressure p c ; Wherein, the step S2 comprises: S21, through the vertical geostress σ v , the maximum horizontal ground stress σ H and the minimum horizontal in-situ stress σ h , and given the well inclination angle Φ and the well inclination azimuth Ω, calculate the far-field stress component in the wellbore rectangular coordinates; S22, given minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 , and calculate the average wellbore pressure p w , the average wellbore pressure p w is the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 The average value of S23, through the formation pore pressure p p , the Poisson's ratio v, the Biot coefficient α p , the allowable expansion rate HER and the far-field stress component, and calculate the wellbore pressure p m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective wellbore stress components at ; S24, calculate the wellbore pressure p through the wellbore stress component m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w The respective principal stresses σ are as follows, wherein the principal stresses σ include the maximum principal stress σ1 and the minimum principal stress σ3; S25, determining the maximum value σ of the maximum principal stress σ1 1max and the maximum value σ 1max The corresponding maximum wellbore angle θ max ; S26, calculate the wellbore pressure p by using the rock cohesion and the internal friction angle, as well as the maximum principal stress σ1 and the minimum principal stress σ3 corresponding to the maximum wellbore angle θmax m are the minimum wellbore pressure p w1 , maximum wellbore pressure p w2 and the average wellbore pressure p w When , the respective failure criterion function values ​​are; S27, using a dichotomy method to judge the value of the destruction criterion function to determine the zero point of the destruction criterion function or the value range of the zero point of the destruction criterion function; S28. Based on the determination of the value range of the zero point of the failure criterion function, the minimum wellbore pressure p is determined. w1 and the maximum wellbore pressure p w2 Whether the absolute value of the difference meets the accuracy requirement ε, so as to determine the zero approximation of the failure criterion function; S29, taking the zero point of the failure criterion function or the approximate value of the zero point of the failure criterion function as the collapse pressure p c ; Wherein, the step S27 comprises: If f(p w )=0, then the average wellbore pressure p w is the zero point of the failure criterion function, the collapse pressure p c Equal to the average wellbore pressure p w ; If f(p w1 )·f(p w )<0, then let p w2 =p w , at this time, the zero point of the destruction criterion function∈(p w1 ,p w ); If f(p w )·f(p w2 )<0, then let p w1 =p w , at this time, the zero point of the destruction criterion function∈(p w ,p w2 ); Wherein, the step S28 comprises: in f(p w1 )·f(p w )<0 or f(p w )·f(p w2 )<0, further determine whether the accuracy requirement ε is met, specifically: If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is less than the accuracy ε, the minimum wellbore pressure p w1 or maximum wellbore pressure p w2 As the collapse pressure p c ; If the minimum wellbore pressure p w1 and the maximum wellbore pressure p w2 If the absolute value of the difference is not less than the accuracy ε, the well inclination angle Φ, the well inclination azimuth Ω and the allowable expansion rate HER are re-given, and steps S22 to S28 are repeated until the accuracy ε requirement is met.

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