Analysis method for rotary steering drilling tool combination design

Abstract

The invention discloses an analysis method for rotary steering drilling tool combination design, which comprises the following steps of: performing reasonable basic assumption on an actual rotary steering drilling tool combination, and selecting a corresponding idealized mechanical model; equivalently processing the idealized mechanical model, and establishing a three-dimensional space drilling tool assembly stress analysis model; iteratively solving a three-dimensional space drilling tool combination model according to dense formation drilling boundary conditions; and checking parameters required by the design of the rotary steering drilling tool combination, and giving a design scheme of the rotary steering drilling tool combination. The method has the beneficial effects that the longitudinal and transverse bending beam method for analyzing the mechanical properties of the drilling tool combination has the advantages of simple physical model and high calculation speed, so that the domestic rotary guide mechanical model suitable for dense rock stratum drilling is established by adopting the longitudinal and transverse bending beam theory, and related mechanical parameters are obtained; and a theoretical basis is provided for build-up rate prediction analysis and drilling tool structure optimization design.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling engineering, and particularly relates to an analysis method for the design of a rotary steerable drill string assembly. Background Art

[0002] Since the large-scale commercial application of the rotary steerable drilling system, it has gradually become a common method for directional drilling in complex onshore and offshore formations. In recent years, according to foreign market research reports, the rotary steerable technology is continuously replacing the market share of the conventional directional drilling technology. Through comparison in the oil field operation front line, it shows that under certain single-well drilling cost conditions, the use of the rotary steerable drilling technology helps to increase the speed and efficiency of directional drilling, achieve an increase in the horizontal section length and production, while the drilling cycle is significantly shortened. This exactly shows that the rotary steerable technology plays an important role in reducing the domestic drilling cost and improving the drilling economic benefits.

[0003] Domestic rotary steerable is mainly applied to the development of shale gas and tight gas. During the domestic rotary steerable operation test, the mechanical drilling rate of the rotary steerable tool in the horizontal section has little difference from that of other non-rotary steerable drilling, and it fails to reach the indicators required by the theoretical design.

[0004] The main reasons for the above-mentioned rotary steerable drilling test are as follows: 1. The domestic rotary steerable tool fails to effectively control the wellbore trajectory under high pressure, and can only meet the trajectory requirements by low drilling pressure in combination with the steering tool's directional command, which is the direct reason for the low mechanical drilling rate; 2. Due to formation reasons, the drilling rate difference is obvious under the same parameters, but the parameters cannot be adjusted in time due to the requirements of geological steering; 3. The rotary steerable drill string assemblies of different manufacturers fail to achieve efficient real-time communication, resulting in a measurement blind area between the actual bottom hole and the instrument measurement, and there is a time error between the command sending and the wellbore deviation, leading to a slower drilling time and the failure to adjust the directional drilling parameters in time. Summary of the Invention

[0005] The purpose of the present invention is: The present invention provides an analysis method for the design of a rotary steerable drill string assembly, which solves the problem that the rotary steerable tool cannot reach the design indicators.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] An analysis method for the design of a rotary steerable drilling assembly. Under reasonable basic assumptions and based on the idea of the beam theory of bending and torsion, the drilling assembly is simplified into an idealized mechanical model of a continuous beam-column under the action of bending and torsion loads. According to the continuity conditions at both ends of each span of the continuous beam, a three-moment equation system reflecting the mechanical characteristics of the drilling assembly is obtained. By solving the three-moment equation system, the stress and deformation conditions of the drill string are analyzed. At the same time, the guide fins and flexible subsections are reasonably simplified and equivalent processed to establish a three-dimensional mechanical analysis model of the drilling assembly. According to the boundary conditions, the parameters required for the design of the rotary steerable drilling assembly are iteratively solved and verified, and a design scheme for the rotary steerable drilling assembly is given.

[0008] An analysis method for the design of a rotary steerable drilling assembly includes the following steps:

[0009] S1. Make reasonable basic assumptions for the actual rotary steerable drilling assembly and select the corresponding idealized mechanical model;

[0010] S2. Equivalently process the idealized mechanical model to establish a three-dimensional mechanical analysis model of the drilling assembly;

[0011] S3. Iteratively solve the three-dimensional model of the drilling assembly according to the boundary conditions of drilling in a dense formation;

[0012] S4. Verify the parameters required for the design of the rotary steerable drilling assembly and give a design scheme for the rotary steerable drilling assembly.

[0013] Further, in the above S1, the following basic assumptions are made for the actual rotary steerable drilling assembly:

[0014] (1) The deformation of the drilling assembly belongs to small elastic deformation;

[0015] (2) The bit is centered, that is, the central axis of the bit coincides with the center line of the wellbore;

[0016] (3) The wellbore wall is rigid and the cross-section of the wellbore is circular;

[0017] (4) The drill string above the tangent point is attached to the lower wellbore wall;

[0018] (5) The influence of the rotation and vibration of the drill string during the drilling process is not considered.

[0019] Further, in the above S1, the rotary steerable mechanical model suitable for drilling in dense rock formations is established by using the beam theory of bending and torsion, and the relevant mechanical parameters are obtained, providing a theoretical basis for the prediction and analysis of the build-up rate and the optimization design of the drill string structure;

[0020] Based on the idea of the beam method of combined flexure and torsion, the drill string assembly is simplified into an idealized mechanical model of a continuous beam-column under the action of combined flexure and torsion loads. According to the continuity conditions at both ends of each span of the continuous beam, a three-moment equation system reflecting the mechanical characteristics of the drill string assembly is obtained. By solving the three-moment equation system, the stress and deformation conditions of the drill string are analyzed.

[0021] Furthermore, in S2, for the static push-against rotary steerable system, the basic components include a PDC bit, a hydraulic three-wing rib steering tool, a lower stabilizer, a flexible sub, a measurement and control system, an upper stabilizer, and a non-magnetic pressure bearing. When establishing the mechanical model of the rotary steerable system, it is necessary to reasonably simplify and equivalent process the steering wing ribs and the flexible sub according to the structural principle of the rotary steering drilling tool.

[0022] When the steering tool is working, the three wing ribs push against the wellbore wall, forming a certain pushing force on the bit. At the same time, the pushing forces of each supporting wing rib can be monitored in real time, and the magnitude and direction of the formed steering resultant force are known conditions. Considering its effect, the wing ribs are simplified as concentrated forces for processing; the bit, lower stabilizer, upper stabilizer, and the tangent point on the drill string are simplified as supports; there is a section of flexible sub with a diameter smaller than the body diameter after the lower stabilizer in the rotary steerable system. When considering the variable cross-section problem, the flexible sub is disconnected from the step and forms a two-span beam-column of combined flexure and torsion with the adjacent two stabilizers. Since adding one span results in two more unknowns, namely the internal moment and deflection, two supplementary compatibility equations need to be established using the geometric condition of equal angles of rotation at the section and the mechanical condition of equal shear forces. The equation system is still solvable.

[0023] Furthermore, when using the beam method of combined flexure and torsion to conduct three-dimensional stress analysis on the drill string assembly, the wellbore trajectory where the drill string assembly is located is regarded as an arc on a spatial inclined plane, and the arc is decomposed into the well inclination plane and the variable azimuth plane, and two-dimensional stress analysis is carried out on each plane.

[0024] A and B are two measuring points on the wellbore trajectory. Assume that AB is an arc on the spatial inclined plane R plane. Taking A as the origin, a geodetic coordinate system A-NED is established, where N and E point to the due north and due east directions respectively, and D points vertically downward. The vertical plane P passing through the D axis and points A and B is called the well inclination plane, and the Q plane passing through the straight line AB and perpendicular to the plane P is called the variable azimuth plane. The straight lines AC and BC are the tangents of the wellbore axis at the trajectory endpoints A and B respectively, and the angles between the vectors and the D axis are the well inclination angles α A 、α B at points A and B respectively. The projection of point C on the horizontal plane NAE plane is point C’. The angles between the vectors and the N axis are the azimuth angles φ A 、φ B at points A and B respectively;

[0025] According to the theory of beam under combined flexure and axial load, for the support i connecting the i-th span and the (i + 1)-th span of the beam, the left rotation angle and the right rotation angle can be expressed respectively as:

[0026]

[0027]

[0028] In the formula, F i is the transverse concentrated load on the i-th span of the beam, kN; P i is the axial load on the i-th span of the beam, kN; q i is the transverse uniformly distributed load on the i-th span of the beam, kN; EI i is the flexural rigidity of the i-th span of the beam, kN·m 2 ; M i is the internal bending moment at the i-th support, kN·m; L i is the length of the i-th span of the beam, m; L Fi is the distance from the concentrated load F i on the i-th span of the beam to the left end of the i-th span of the beam, m; y i is the y coordinate at the i-th support, m; k i , u i , X(u i ), Y(u i ), Z(u i ) are the stability coefficient and amplification factor of the i-th span of the beam-column;

[0029] The expression for the flexural rigidity of the beam is:

[0030]

[0031] In the formula, E is the elastic modulus of the beam-column material, kPa; D is the outer diameter of the beam, m; d is the inner diameter of the beam, m;

[0032] The stability coefficient and amplification factor can be expressed respectively as:

[0033]

[0034]

[0035]

[0036]

[0037] From the continuity condition of deformation

[0038]

[0039] The three-moment equation at the \(i\)-th support can be sorted out as follows:

[0040]

[0041] For the mechanical analysis model of the rotary steerable bottomhole assembly's vertical and lateral bending beam in the well inclination \(P\) plane, applying Equation (9), the three-moment equations at the lower stabilizer, the variable cross-section at the right end of the flexible sub, and the upper stabilizer can be obtained, and a three-dimensional space drill string assembly force analysis model is established. The sorted three-equivalent three-dimensional force analysis model is as follows:

[0042]

[0043] Furthermore, in step S3, for the solution of the three-moment equation in the well inclination \(P\) plane, when solving the three-moment equation at the 3rd support, \(M_4\) is the bending moment at the upper tangent point, which is expressed as:

[0044] \(M_4 = E\cdot I_4\cdot K\) P (11);

[0045] The solution process involves five unknown variables, namely the bending moments \(M_1\), \(M_2\), \(M_3\) at the lower stabilizer, the variable cross-section, and the upper stabilizer, the \(Y\)-coordinate \(y_2\) at the variable cross-section, and the length \(L_4\) from the upper stabilizer to the upper tangent point. Since \(L_4\) is unknown, the system of equations becomes a non-linear system of equations. When solving, an initial value of \(L_4\) can be assumed first, and by controlling the difference in the bending moment of the upper stabilizer between two solutions, the bisection method is used for iteration to find \(L_4\), and then the solutions of the system of equations: \(M_1\), \(M_2\), \(M_3\), \(y_2\), \(L_4\) can be obtained.

[0046] Furthermore, in step S4, after the solution is completed, it is further determined whether the stabilizer touches the upper wellbore or the lower wellbore. If the assumed conditions for the stabilizer touching the wellbore are met, the obtained solution is the final solution; if not, the assumed conditions for the stabilizer touching the wellbore should be corrected, and \(L_4\) should be re-assigned and the above solution steps should be repeated until the assumed conditions for the stabilizer touching the wellbore are met to obtain the final solution.

[0047] Furthermore, in step S4, after the above solution of the three-moment equation system for the mechanical properties of the drill string in the well inclination \(P\) plane is completed, for the three-moment equation system in the variable azimuth \(Q\) plane, its specific solution process is the same as that of the three-moment equation system in the well inclination \(P\) plane; after the solution of the three-moment equation systems in the well inclination \(P\) plane and the variable azimuth \(Q\) plane is completed, the force state of the rotary steerable in the spatial inclined plane can be obtained, and the drill string mechanical characteristics such as the lateral force of the bit and the bit rotation angle for quantitatively solving the drilling trend angle can be further obtained.

[0048] Further, in S4, when performing a force analysis on the three-dimensional rotary steerable system, the three-dimensional problem must first be divided into two two-dimensional problems, and three-moment equations are established and solved for the two two-dimensional planes respectively. The input data includes: the well inclination angle and azimuth angle of the upper and lower measurement points, the length of the measured section, the distance from the wing rib to the bit, the tool face angle, the Young's modulus, the weight on bit, the well diameter, the linear weight of each span of the drill string, the length of each span of the drill string, the inner and outer diameters of each span of the drill string, and the outer diameter of each centralizer. The output data includes: the distance from the upper tangent point to the second centralizer, the internal bending moment at each support, the lateral force of the bit, and the bit rotation angle.

[0049] First, the basic parameters are input, and the wellbore curvatures of the P plane and the Q plane are obtained from the wellbore shape parameters. Then, the variable well inclination force and variable azimuth force of the bit are obtained by using the two-dimensional analysis program respectively.

[0050] Further, in S4, the following need to be supplemented: (1) The weight of the drill string in the Q plane is 0, and the magnitude of the axial load of each section of the drill string is equal to the weight on bit; (2) Since the solution is carried out in the P plane and the Q plane respectively, the position L of the upper tangent point obtained in the Q plane 5Q and the position L of the upper tangent point obtained in the P plane 5P are different;

[0051] To reduce the resulting error, when the calculation in the P plane is completed, the position L of the upper tangent point is output 5P , and L 5P is taken as L 5Q and substituted into the three-moment equation to solve for the lateral force of the bit. Finally, the average value of the two results is taken as the final result of the variable azimuth force Q.

[0052] Principle of the present invention: The present invention aims to provide an analysis method for the design of a rotary steerable drilling assembly. Considering the actual drilling performance of the rotary steerable drilling assembly in the well, the following basic assumptions are made: (1) The deformation of the drill string assembly belongs to small elastic deformation; (2) The bit is centered, that is, the central axis of the bit coincides with the center line of the wellbore; (3) The wellbore wall is rigid and the cross-section of the wellbore is circular; (4) The drill string above the upper tangent point is attached to the lower wellbore wall; (5) The influence of the rotation and vibration of the drill string during the drilling process is not considered. The longitudinal and transverse bending beam theory is used to establish a domestic rotary steerable mechanical model suitable for drilling in dense rock formations, and the relevant mechanical parameters are obtained. At the same time, the drill string assembly is simplified into an idealized mechanical model of a continuous beam-column under the action of longitudinal and transverse bending loads, and the idealized mechanical model is equivalently processed to establish a three-dimensional space drill string assembly force analysis model; according to the boundary conditions, the parameters required for the design of the rotary steerable drilling assembly are iteratively solved and verified, and a design scheme for the rotary steerable drilling assembly is given.

[0053] Advantages of the present invention: When considering the flexible sub, although two unknowns, namely the internal bending moment and deflection, are added for each additional span, only after equivalent treatment, two supplementary compatibility equations can be established by using the geometric condition of equal rotation angles and the mechanical condition of equal shear forces at the section, and the relevant system of equations still has a definite solution. In addition, the method of analyzing the mechanical characteristics of the drill string combination by the theory of beam with combined bending and axial loads has the advantages of simple physical model and fast calculation speed. Therefore, the theory of beam with combined bending and axial loads is adopted to establish a domestic rotary steerable mechanical model applicable to drilling in tight formations, and the relevant mechanical parameters are obtained, providing a theoretical basis for the prediction and analysis of the build rate and the optimal design of the drill string structure.

[0054] The main solution of the present invention and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and claimed by the present invention; and in the present invention, (each non-conflicting alternative) alternatives can be freely combined with each other and with other alternatives. Those skilled in the art can understand that there are various combinations according to the prior art and common general knowledge after understanding the solution of the present invention, all of which are technical solutions to be protected by the present invention, and will not be enumerated herein. Brief Description of the Drawings

[0055] Figure 1 It is a schematic diagram of a static push-type rotary steering structure device.

[0056] Figure 2 It is a schematic diagram for the analysis of the equivalent treatment of the flexible sub.

[0057] Figure 3 It is a schematic diagram for the decomposition of the three-dimensional circular wellbore trajectory.

[0058] Figure 4 It is a flow chart for solving the three-dimensional drill string combination model. Detailed Embodiments

[0059] The following non-limiting embodiments are used to illustrate the present invention.

[0060] Embodiment 1

[0061] The technical solution provided by the present invention is that, under reasonable basic assumptions, based on the idea of the theory of beam with combined bending and axial loads, the drill string combination is simplified into an idealized mechanical model of a continuous beam-column under the action of combined bending and axial loads. According to the continuity conditions at both ends of each span of the continuous beam, a three-moment system of equations reflecting the force characteristics of the drill string combination is obtained. By solving the three-moment system of equations, the force and deformation conditions of the drill string are analyzed. At the same time, the guide wing ribs and the flexible sub are reasonably simplified and equivalently treated to establish a three-dimensional drill string combination force analysis model; according to the boundary conditions, the parameters required for the design of the rotary steerable drill string combination are iteratively solved and verified, and a design scheme for the rotary steerable drill string combination is given.

[0062] Specifically, it includes the following operation steps.

[0063] S1. Make reasonable basic assumptions about the actual rotary steerable drill string assembly and select the corresponding idealized mechanical model.

[0064] Rotary steering technology integrates mechanics, electricity, and hydraulics, involving multiple disciplines such as drilling, computer, process control, automation, and engineering mechanics, representing the mainstream trend of drilling technology development. Compared with early steering technologies, rotary steering drilling technology has significant advantages.

[0065] In the early sliding steering drilling technology, the drill string does not rotate during the steering operation, and the drill string adheres to the wellbore wall, increasing the friction of the drill string during the drilling process. In contrast, in rotary steering drilling technology, the drill string is always in a rotating state during the steering process, thus having little impact on the drilling speed of the drill string and effectively reducing the incidence of stuck pipe accidents during drilling. When the sliding steering drilling tool is working, the use of a downhole drilling motor will cause the bit to vibrate, resulting in wellbore enlargement, irregularity, or a spiral wellbore, affecting the further extension of the wellbore trajectory and increasing the difficulty of later exploitation. Rotary steering drilling tools adjust the magnitude and direction of the steering force according to the deviation vector between the actual drilled trajectory and the target wellbore trajectory, and real-time feedback to the downhole and surface control systems through downhole trajectory measurement devices and signal transmission devices to achieve precise closed-loop control of the wellbore trajectory and drill a smoother and more regular wellbore.

[0066] Therefore, considering the above situation, the following basic assumptions are made for the actual rotary steerable drill string assembly:

[0067] (1) The deformation of the drill string assembly belongs to small elastic deformation;

[0068] (2) The bit is centered, that is, the central axis of the bit coincides with the center line of the wellbore;

[0069] (3) The wellbore wall is rigid, and the cross-section of the wellbore is circular;

[0070] (4) The drill string above the upper tangent point adheres to the lower wellbore wall;

[0071] (5) The influence of the rotation and vibration of the drill string during the drilling process is not considered.

[0072] The analysis of the mechanical characteristics of the drill string assembly by the method of the beam with combined bending in vertical and horizontal directions has the advantages of a simple physical model and fast calculation speed. Therefore, the theory of the beam with combined bending in vertical and horizontal directions is used to establish a domestic rotary steerable mechanical model applicable to drilling in tight formations, and the relevant mechanical parameters are obtained, providing a theoretical basis for the prediction and analysis of the build-up rate and the optimization design of the drill string structure.

[0073] Based on the idea of the method of the beam with combined bending in vertical and horizontal directions, the drill string assembly is simplified into an idealized mechanical model of a continuous beam-column under the action of combined bending loads in vertical and horizontal directions. According to the continuity conditions at both ends of each span of the continuous beam, a three-moment equation system reflecting the force characteristics of the drill string assembly is obtained. By solving the three-moment equation system, the force and deformation conditions of the drill string are analyzed.

[0074] S2. Equivalently process the idealized mechanical model and establish a three-dimensional force analysis model for the drill string assembly.

[0075] Taking the domestic static push-against rotary steerable system as an example, as Figure 1 shown, its basic components include a PDC bit 1, a hydraulic three-wing rib guiding tool 2, a lower stabilizer 3, a flexible sub 4, a measurement and control system 5, an upper stabilizer 6, a non-magnetic pressure bearing 7, etc. When establishing the mechanical model of the domestic rotary steerable system, it is necessary to reasonably simplify and equivalently process the guiding wing ribs and the flexible sub according to the structural principle of the rotary steerable drilling tool.

[0076] When the guiding tool is working, the three wing ribs push against the wellbore wall to form a certain pushing force on the bit. At the same time, the pushing forces of each supporting wing rib can be monitored in real time, and the magnitude and direction of the formed guiding resultant force are known conditions. Considering its action effect, the wing ribs are simplified as concentrated forces for processing. The bit, lower stabilizer, upper stabilizer, and the tangent point on the drill string can be simplified as supports. There is usually a flexible sub with a diameter much smaller than the body diameter after the lower stabilizer in the domestic rotary steerable system.

[0077] A further technical solution is that when considering the variable cross-section problem, the flexible sub is disconnected from the step and forms a two-span crosswise and longitudinal bending beam column with the adjacent two stabilizers, as Figure 2 shown. Such processing can make the cross-section of each span of the beam column the same. Since adding one span results in two more unknowns, namely the internal bending moment and deflection, it is necessary to establish two additional compatibility equations by using the geometric condition of equal angles of rotation at the cross-section and the mechanical condition of equal shear forces. The system of equations is still uniquely solvable.

[0078] Due to the influence of various factors, the wellbore trajectory is often a curve in space.

[0079] A further technical solution is that when performing three-dimensional force analysis on the drill string assembly using the crosswise and longitudinal bending beam method, the wellbore trajectory where the drill string assembly is located is usually regarded as an arc on a spatial inclined plane, and the arc is decomposed into the well deviation plane and the variable azimuth plane, and two-dimensional force analysis is performed on each plane.

[0080] As Figure 3 shown, A and B are two measuring points on the wellbore trajectory. Assume that AB is an arc on the spatial inclined plane R plane. Taking A as the origin, a geodetic coordinate system A-NED is established, where N and E point to the due north and due east directions respectively, and D points vertically downward. The vertical plane P passing through the D axis and points A and B is called the well deviation plane, and the Q plane passing through the straight line AB and perpendicular to the plane P is called the variable azimuth plane. The straight lines AC and BC are the tangents of the wellbore axis at the trajectory endpoints A and B respectively. The angles between the vectors and the D axis are the well deviation angles α A 、αB The projection of point C on the horizontal plane NAE is point C'. The included angles between the vector and the N axis are the azimuth angles φ A and φ B at points A and B respectively. According to the theory of beam with combined bending and axial loading, for the support i connecting the i-th and (i + 1)-th beams as shown in Figure 2 , the left rotation angle and the right rotation angle can be expressed respectively as:

[0081]

[0082]

[0083] where F i is the transverse concentrated load on the i-th beam, kN; P i is the axial load on the i-th beam, kN; q i is the transverse uniformly distributed load on the i-th beam, kN; EI i is the flexural rigidity of the i-th beam, kN·m 2 ; M i is the internal bending moment at the i-th support, kN·m; L i is the length of the i-th beam, m; L Fi is the distance from the concentrated load F i of the i-th beam to the left end of the i-th beam, m; y i is the y-coordinate at the i-th support, m; k i , u i , X(u i ), Y(u i ), Z(u i ) are the stability coefficient and amplification factor of the i-th beam-column.

[0084] The expression for the flexural rigidity of the beam is:

[0085]

[0086] where E is the elastic modulus of the beam-column material, kPa; D is the outer diameter of the beam, m; d is the inner diameter of the beam, m.

[0087] The stability coefficient and amplification factor can be expressed respectively as:

[0088]

[0089]

[0090]

[0091]

[0092] From the continuity condition of deformation

[0093]

[0094] The three-moment equation at the \(i\)-th support can be derived as follows:

[0095]

[0096] For the mechanical analysis model of the rotary steerable bottomhole assembly with combined longitudinal and transverse bending beams in the well deviation \(P\) plane, by applying Equation (9), the three-moment equations at the lower stabilizer, the variable cross-section at the right end of the flexible sub, and the upper stabilizer can be obtained, and a three-dimensional force analysis model of the drill string assembly can be established. The sorted three-equivalent three-dimensional force analysis model is as follows:

[0097]

[0098] S3. Iteratively solve the three-dimensional drill string assembly model according to the drilling boundary conditions of the tight formation.

[0099] Taking the solution of the three-moment equation in the well deviation \(P\) plane as an example, solving the three-moment equation at the 3rd support, the bending moment at the upper tangent point can be expressed as:

[0100] M4 = E·I4·K P (11);

[0101] The solution process involves five unknown variables, namely the bending moments at the lower stabilizer, the variable cross-section, and the upper stabilizer, the \(Y\) coordinate at the variable cross-section, and the length from the upper stabilizer to the upper tangent point. Since \(L4\) is unknown, the system of equations becomes a non-linear system of equations. When solving, an initial value of \(L4\) can be assumed first, and by controlling the difference in the bending moment of the upper stabilizer between two solutions, the bisection method can be used for iteration to find \(L4\), and then the solutions of the system of equations: M1, M2, M3, y2, L4 can be obtained.

[0102] S4. Check the parameters required for the design of the rotary steerable drill string assembly and give the design scheme of the rotary steerable drill string assembly.

[0103] After the solution is obtained, further judge whether the stabilizer touches the upper wellbore or the lower wellbore. If the assumed conditions for the stabilizer to touch the wellbore are met, the obtained solution is the final solution; if not, the assumed conditions for the stabilizer to touch the wellbore should be corrected, and a new value should be assigned to \(L4\) and the above solution steps should be repeated until the assumed conditions for the stabilizer to touch the wellbore are met to obtain the final solution.

[0104] After the above solution of the three-moment equations for the mechanical properties of the drill string in the well inclination P plane, for the three-moment equations in the variable azimuth Q plane, the specific solution process is the same as that of the three-moment equations in the well inclination P plane. After solving the three-moment equations in the well inclination P plane and the variable azimuth Q plane, the stress state of the domestic rotary steerable system in the spatial inclined plane can be obtained, and the mechanical characteristics of the drill string such as the lateral force of the bit and the bit rotation angle for quantitatively solving the drilling trend angle can be further obtained.

[0105] The specific solution process for the mechanical properties of the above rotary steerable bottom hole assembly can be represented by the domestic rotary steerable mechanical property solution flow chart as shown in Figure 4 Figure. Through the above derivation, when analyzing the stress of the three-dimensional domestic rotary steerable system, the three-dimensional problem must first be divided into two two-dimensional problems, and three-moment equations are established and solved for the two two-dimensional planes respectively. The input data includes: the well inclination angle and azimuth angle of the upper and lower measuring points, the length of the measuring section, the distance from the wing rib to the bit, the tool face angle, the Young's modulus, the weight on bit, the well diameter, the linear weight of each span of the drill string, the length of each span of the drill string, the inner and outer diameters of each span of the drill string, and the outer diameter of each centralizer. The output data includes: the distance from the upper tangent point to the second centralizer, the internal bending moment at each support, the lateral force of the bit, and the bit rotation angle.

[0106] First, input the basic parameters, obtain the wellbore curvatures of the P plane and the Q plane from the wellbore shape parameters, and then use the two-dimensional analysis program to obtain the variable well inclination force and variable azimuth force of the bit respectively. The following supplementary explanations are needed:

[0107] (1) The weight of the drill string in the Q plane is 0, and the magnitude of the axial load of each section of the drill string is equal to the weight on bit.

[0108] (2) Since the solutions are obtained in the P plane and the Q plane respectively, the position L of the upper tangent point obtained in the Q plane finally 5Q and the position L of the upper tangent point obtained in the P plane 5P are different. To reduce the resulting error, when the calculation in the P plane is completed, output the position L of the upper tangent point 5P , and take L 5P as L 5Q and substitute it into the three-moment equation to solve for the lateral force of the bit. Finally, take the average of the two results as the final result of the variable azimuth force Q.

[0109] According to the above analysis results, a rotary steerable BHA design solution applicable to tight formations is given. The content of an example solution is as follows: Taking the 9600 series BHA of the GEO directional rotary steerable system with a flexible sub as an example, its composition is: Φ215.9mm PDC bit + GEO rotary steerable tool + Φ172mm drill collar × 2m + Φ213mm stabilizer + Φ172mm drill collar + Φ127mm flexible sub × 1.5m + Φ172mm drill collar + Φ213mm stabilizer + Φ172mm drill collar × 50m.

[0110] The basic examples of the present invention and their respective further alternative examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed by the present invention. In the solution of the present invention, any alternative example can be arbitrarily combined with any basic example and alternative example.

[0111] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An analysis method for the design of a rotary steerable drilling tool assembly, characterized in that: It includes the following steps: S1. Make reasonable basic assumptions for the actual rotary steerable drill string assembly and select the corresponding idealized mechanical model; S2. Equivalently process the idealized mechanical model and establish a three-dimensional stress analysis model for the drill string assembly; S3. Iteratively solve the three-dimensional drill string assembly model according to the drilling boundary conditions of the tight formation; S4. Check the parameters required for the design of the rotary steerable drill string assembly and give the design scheme of the rotary steerable drill string assembly.

2. The analysis method for the design of a rotary steerable drilling tool assembly according to claim 1, characterized in that: In S1 described above, the basic assumptions for the actual rotary steerable drill string assembly are as follows: (1) The deformation of the drill string assembly belongs to small elastic deformation; (2) The bit is centered, that is, the central axis of the bit coincides with the center line of the wellbore; (3) The wellbore wall is rigid and the cross-section of the wellbore is circular; (4) The drill string above the upper tangent point of the drill string adheres to the lower wellbore wall; (5) The influence of the rotation and vibration of the drill string during the drilling process is not considered.

3. The analysis method for the design of a rotary steerable drilling tool assembly according to claim 2, characterized in that: In S1 described above, the rotary steerable mechanics model applicable to drilling in tight rock formations is established by using the theory of beam with combined bending and torsion, and the relevant mechanical parameters are obtained, providing a theoretical basis for the prediction and analysis of build-up rate and the optimization design of drill string structure; based on the idea of the beam with combined bending and torsion method, the drill string assembly is simplified into an idealized mechanical model of a continuous beam-column under the action of combined bending and torsion loads. According to the continuity conditions at both ends of each span of the continuous beam, the three-moment equations reflecting the stress characteristics of the drill string assembly are obtained. By solving the three-moment equations, the stress and deformation conditions of the drill string are analyzed.

4. The analysis method for the design of a rotary steerable drilling tool assembly according to any one of claims 1 to 3, characterized in that: In S2 described above, for the static push-against type rotary steerable, the basic components include a PDC bit, a hydraulic three-wing rib steering tool, a lower stabilizer, a flexible sub, a measurement and control system, an upper stabilizer, and a non-magnetic pressure bearing; when establishing the rotary steerable mechanics model, it is necessary to reasonably simplify and equivalently process the steering wing ribs and the flexible sub according to the structural principle of the rotary steerable drilling tool; When the steering tool works, the three wing ribs push against the wellbore wall to form a certain pushing force on the bit. At the same time, the pushing forces of each supporting wing rib can be monitored in real time, and the magnitude and direction of the formed steering resultant force are known conditions. Considering its action effect, the wing ribs are simplified as concentrated forces for processing; the bit, the lower stabilizer, the upper stabilizer, and the upper tangent point of the drill string are simplified as supports for processing; there is a section of flexible sub with a diameter smaller than the body diameter after the lower stabilizer in the rotary steerable; when considering the variable cross-section problem, the flexible sub is disconnected from the step and forms a two-span beam with combined bending and torsion with the adjacent two stabilizers. Since adding one span results in two more unknowns, namely the internal moment and deflection, two supplementary coordination equations need to be established by using the geometric condition of equal rotation angle at the section and the mechanical condition of equal shear force. The system of equations is still solvable.

5. The analysis method for the design of a rotary steerable drilling tool assembly according to claim 4, characterized in that: When performing three-dimensional stress analysis on the drill string assembly by using the beam with combined bending and torsion method, the wellbore trajectory where the drill string assembly is located is regarded as an arc on a spatial inclined plane, and the arc is decomposed into the well deviation plane and the variable azimuth plane, and two-dimensional stress analysis is carried out on each plane; A and B are two measuring points on the wellbore trajectory. Assume that AB is an arc on the inclined plane R in space. Taking A as the origin, a geodetic coordinate system A-NED is established, where N and E point to the due north and due east directions respectively, and D points vertically downward. The vertical plane P passing through the D axis and points A and B is called the well inclination plane, and the Q plane passing through the line AB and perpendicular to the plane P is called the variable azimuth plane. The straight lines AC and BC are the tangents of the wellbore axis at the trajectory endpoints A and B respectively. The angles between the vectors and the D axis are the well inclination angles α A and α B at points A and B respectively. The projection of point C on the horizontal plane NAE is point C'. The angles between the vectors and the N axis are the azimuth angles φ A and φ B at points A and B respectively; According to the theory of beam under combined flexure and axial load, for the support i connecting the i-th span and the (i + 1)-th span of the beam, the left rotation angle and the right rotation angle can be respectively expressed as: Where, F i is the transverse concentrated load on the i-th span beam, kN; P i is the axial load on the i-th span beam, kN; q i is the transverse uniformly distributed load on the i-th span beam, kN; EI i is the flexural rigidity of the i-th span beam, kN·m 2 ; M i is the internal bending moment at the i-th support, kN·m; L i is the length of the i-th span beam, m; L Fi is the concentrated load F of the i-th span beam i distance to the left end of the i-th span beam, m; y i is the y coordinate at the i-th support, m; k i , u i , X(u i ), Y(u i ), Z(u i ) are the stability coefficient and amplification factor of the i-th span beam-column The expression of the flexural rigidity of the beam is: In the formula, E is the elastic modulus of the beam-column material, kPa; D is the outer diameter of the beam, m; d is the inner diameter of the beam, m; the stability coefficient and the amplification factor can be expressed as: From the continuity condition of deformation The three-moment equation at the i-th support can be sorted out as: For the mechanical analysis model of the rotary steerable bottomhole assembly with longitudinal and transverse bending beams in the well deviation P plane, by applying Equation (9), the three-moment equations at the lower stabilizer, the variable cross-section at the right end of the flexible sub, and the upper stabilizer can be obtained, and a mechanical analysis model for the force on the three-dimensional downhole assembly is established. The sorted three-equivalent three-dimensional force analysis model is as follows:

6. The analysis method for the design of a rotary steerable drilling assembly according to claim 5, wherein: In S3 described above, for the solution of the three-moment equation in the well deviation P plane, the three-moment equation at the third support is solved. M4 is the bending moment at the upper tangent point, which is expressed as: M4 = E·I4·K P (11); The solution process involves five unknown variables, namely the bending moments M1, M2, and M3 at the lower stabilizer, the variable cross-section, and the upper stabilizer, the Y coordinate y2 at the variable cross-section, and the length L4 from the upper stabilizer to the upper tangent point. Since L4 is unknown, the system of equations becomes a non-linear system of equations. When solving, an L4 can be assumed as an initial value first, and by controlling the difference in the bending moments of the upper stabilizer in two solutions, the dichotomy method can be used for iteration to find L4, and then the solutions of the system of equations can be obtained: M1, M2, M3, y2, and L4.

7. The analysis method for the design of a rotary steerable drilling assembly according to claim 1, wherein: In S4 described above, after the solution is completed, it is further determined whether the stabilizer is attached to the upper wellbore wall or the lower wellbore wall. If the assumed conditions for the stabilizer to be attached to the wellbore wall are met, the obtained solution is the final solution; if not, the assumed conditions for the stabilizer to be attached to the wellbore wall should be corrected, and L4 should be reassigned and the above solution steps should be repeated until the assumed conditions for the stabilizer to be attached to the wellbore wall are met, and the final solution is obtained.

8. The analysis method for the design of a rotary steerable drilling assembly according to claim 7, wherein: In S4 described above, after the above solution of the three-moment equations for the mechanical properties of the drill string in the well deviation P plane is completed, for the three-moment equations in the variable azimuth Q plane, the specific solution process is the same as that of the three-moment equations in the well deviation P plane; after the solution of the three-moment equations in the two planes of the well deviation P plane and the variable azimuth Q plane is completed, the force state of the rotary steerable in the spatial inclined plane can be obtained, and the mechanical characteristics of the drill string such as the lateral force of the bit and the bit rotation angle for quantitatively solving the drilling trend angle can be further obtained.

9. The analysis method for the design of a rotary steerable drilling assembly according to claim 7, wherein: In S4 described above, when performing a force analysis on the three-dimensional rotary steerable, the three-dimensional problem must first be divided into two two-dimensional problems, and three-moment equations are established and solved for the two two-dimensional planes respectively; the input data includes: the well deviation angles and azimuth angles of the upper and lower measuring points, the length of the measuring section, the distance from the wing rib to the bit, the tool face angle, the Young's modulus, the weight on bit, the well diameter, the linear weight of each span of the drill string, the length of each span of the drill string, the inner and outer diameters of each span of the drill string, and the outer diameter of each centralizer; the output data includes: the distance from the upper tangent point to the second centralizer, the internal bending moment at each support, the lateral force of the bit, and the bit rotation angle; First, the basic parameters are input, and the wellbore curvatures of the P plane and the Q plane are obtained from the wellbore shape parameters, and then the variable well deviation force and variable azimuth force of the bit are obtained by using the two-dimensional analysis program respectively.

10. The analysis method for the design of a rotary steerable drilling assembly according to claim 9, wherein: In S4 mentioned above, the following need to be supplemented: (1) In the Q plane, the weight of the drill string is 0, and the axial load of each section of the drill string is equal to the weight on bit; (2) Since the solutions are obtained in the P plane and the Q plane respectively, the upper tangent point position L 5Q obtained in the Q plane and the upper tangent point position L 5P obtained in the P plane are different; To reduce the resulting error, when the calculation of the P plane is completed, the position L of the upper tangent point is output 5P , and take L 5P as L 5Q Substitute it into the three-moment equation to solve for the lateral force of the drill bit, and finally take the average of the two results as the final result of the variable azimuth force Q.

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