A method and device for evaluating dynamic shear capacity of a ram blowout preventer

Abstract

The present invention provides a method for evaluating the dynamic shear capacity of a ram blowout preventer, which relates to the technical field of petroleum exploration and development. The dynamic shear stress calculation step adopts a three-parameter generalized strength criterion under the coupling of tension, compression, and shear according to the stress state of the ram blowout preventer during the shearing process, and analyzes and derives the stress distribution of the drill pipe under the dynamic working condition to obtain a theoretical formula for stress calculation of the drill pipe; the shear force estimation step uses the equivalent relationship between the ram shear and compressive stresses and the material yield criterion theory to obtain the shear resultant force F; the external force on the shear ram in its movement direction is comprehensively considered to calculate the ram comprehensive shear force F. max The evaluation method of the present invention introduces a three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear, and proposes a method for constructing a theoretical model for calculating dynamic drill pipe shear stress, which has high applicability. The present invention also relates to a dynamic shear capacity evaluation device for a gate blowout preventer, which can be tested and inspected.

Description

Technical Field

[0001] The present invention relates to the technical field of oil exploration and development, and further relates to a method for evaluating the dynamic shear capacity of a ram blowout preventer. In addition, the present invention also relates to a device for evaluating the dynamic shear capacity of a ram blowout preventer. Background Art

[0002] As oil exploration and development gradually expand into complex oil and gas fields such as deepwater, ultra-deep wells, and unconventional wells, the requirements for on-site well control safety are becoming increasingly stringent. Ram BOPs, the "throat" of the drilling well control system, require rapid activation of ram BOPs to shut down the well in the event of emergencies such as overflows, kicks, and blowouts during drilling, workover, and well testing, preventing uncontrolled blowouts and other serious accidents.

[0003] Due to the complex structure of the ram blowout preventer, the harsh well environment and many influencing factors, the probability of shear failure of the ram blowout preventer is as high as 50% during actual operation. Therefore, the research on the ram blowout preventer is very important.

[0004] Current research on the shear capacity of ram blowout preventers (BOPs) primarily focuses on theoretical calculations and simulation analysis of shear force and shear stress during static drill pipe shearing. However, existing theoretical analysis methods are relatively conservative and ignore factors such as the elastic-plastic deformation of the drill pipe cross section during shearing, as well as the complex wellbore conditions. Furthermore, most existing simulation analysis methods assume that the ram can normally shear the static drill pipe, which is inconsistent with the drill pipe shearing behavior under actual blowout conditions. Therefore, existing methods cannot accurately assess the shear capacity of shear rams under dynamic conditions.

[0005] For those skilled in the art, how to more accurately evaluate the blowout prevention performance of a ram blowout preventer is a technical problem that needs to be solved. Summary of the Invention

[0006] The present invention provides a method for evaluating the dynamic shear capacity of a ram blowout preventer. By introducing a three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear, the method can more accurately evaluate the blowout prevention performance of the ram blowout preventer. The specific scheme is as follows:

[0007] A method for evaluating the dynamic shear capacity of a ram blowout preventer, comprising:

[0008] Dynamic shear stress calculation: Based on the stress state of the ram BOP during the shear process, the three-parameter generalized strength criterion under the coupled action of tension, compression, and shear is adopted. Combined with the stress distribution of the drill pipe under dynamic working conditions, the theoretical formula for drill pipe stress calculation is obtained.

[0009] Shear force estimation, starting from the equivalent relationship of shear and compressive stress of the gate, combined with the material yield criterion theory, obtains the shear force F of the shear gate in its movement direction; comprehensively considers the external force of the shear gate in its movement direction, and calculates the gate comprehensive shear force F max .

[0010] Optionally, the stress distribution of the drill pipe under dynamic working conditions is analyzed and deduced to obtain a theoretical formula for calculating the stress of the drill pipe, including:

[0011] The theoretical formula for calculating the stress of the moving drill rod under the working condition of the moving drill rod is obtained:

[0012]

[0013] in:

[0014] σ m is the equivalent stress;

[0015] X t is the tensile strength of the material; X c is the compressive strength of the material;

[0016] n represents the drill pipe shear strength S and the material tensile strength X t The relationship between

[0017] m is the tensile and compressive strength ratio coefficient of the drill pipe material, m=X t / X c ;

[0018] σ zz ≠0, τ yx ≠0,σ yy =σ xx =τ zy =τ xz =0.

[0019] Optionally, the stress distribution of the drill pipe under dynamic working conditions is analyzed and deduced to obtain a theoretical formula for calculating the stress of the drill pipe, including:

[0020] The theoretical formula for calculating the torsional drill pipe stress under the drill pipe torsional working condition is obtained:

[0021]

[0022] in:

[0023] σ m is the equivalent stress;

[0024] n represents the drill pipe shear strength S and the material tensile strength X t The relationship between

[0025] τ yx ≠0,σ yy =σ xx =σ zz =τ zy =τ xz =0.

[0026] Optionally, the comprehensive consideration of the external force on the shear ram in its movement direction includes:

[0027] Comprehensively consider the shear force F of the shear ram in its movement direction, the hydrostatic pressure F in the well i , fluid impact force F l and friction resistance F f , calculate the gate comprehensive shear force F max :

[0028] F max =F+F i +F l +F f .

[0029] Optionally, the friction resistance F f The least square method was used for mean fitting, and the friction resistance F f Calculated according to the following formula:

[0030]

[0031] in:

[0032] n is a positive integer.

[0033] Optionally, it also includes:

[0034] Dynamic shear simulation of the ram blowout preventer: a simulation model is constructed. Based on the actual external influences on the drill pipe, boundary constraints are added to replace the external force influences during the shear process, and only the degrees of freedom in the horizontal direction are retained;

[0035] The shear force curve obtained by simulation results verifies the gate comprehensive shear force F max .

[0036] Alternatively, the Johnson-Cook model is used to simulate metal materials with high strain rate deformation. The failure strain function of the drill pipe model is:

[0037]

[0038] in:

[0039] ε f is the failure (plastic) strain; D1~D5 are failure model parameters; is the ratio of hydrostatic pressure to equivalent stress; is the dimensionless equivalent strain rate; T * =(TT r ) / (T m -T) is the dimensionless temperature, where T r is the reference temperature, °C, T m is the melting point of the material, °C;

[0040] Introduce the Shock EOS Linear state equation in the analysis module:

[0041] u s =C1+S1u p

[0042] in:

[0043] u s is the impact velocity; u p is the particle velocity; C1 is u s -u p The intercept of the curve is the volume speed of sound; S1 is the slope coefficient of the curve.

[0044] Optionally, constructing the simulation model includes:

[0045] The shear ram is defined as a rigid body and the drill pipe is defined as a flexible body;

[0046] The shear ram is divided by tetrahedral mesh elements, and the mesh of the ram blade contact surface area is refined; the drill pipe is divided by hexahedral mesh elements.

[0047] Optionally, it also includes:

[0048] A mesh independence analysis was performed to determine the number of mesh sizes for the shear gate finite element model.

[0049] The present invention also provides a ram blowout preventer dynamic shear capacity assessment device, which is applied to any of the above-mentioned ram blowout preventer dynamic shear capacity assessment methods;

[0050] It includes a sealed test chamber, a ram blowout preventer and a hydraulic control device, wherein the test chamber is used to accommodate a drill pipe, and the ram blowout preventer is installed in the test chamber;

[0051] The hydraulic control device includes an electric pump, a switch valve, a regulating valve and an accumulator, and the hydraulic control device provides hydraulic power for the ram blowout preventer;

[0052] A pressure gauge is provided on the console, and the pressure gauge is used to display the pressure of the accumulator and the drill pipe during the working process.

[0053] The present invention provides a method for evaluating the dynamic shear capacity of a ram blowout preventer, comprising two steps: dynamic shear stress calculation and shear force estimation. The dynamic shear stress calculation step adopts a three-parameter generalized strength criterion under the coupling of tension, compression, and shear according to the stress state of the ram blowout preventer during the shearing process, and analyzes and derives the stress distribution of the drill pipe under the dynamic working condition to obtain a theoretical formula for stress calculation of the drill pipe. The shear force estimation step utilizes the equivalent relationship between the ram shear and compressive stresses and the material yield criterion theory to obtain the shear resultant force F of the shear ram in its moving direction. The external force of the shear ram in its moving direction is comprehensively considered to calculate the ram comprehensive shear force F. max The evaluation method of the present invention addresses the problems of complex working conditions in wells and difficulty in analyzing the shear influence law. It introduces a three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear, and proposes a method for constructing a theoretical model for calculating dynamic drill pipe shear stress, which has high applicability. The present invention also relates to a dynamic shear capacity evaluation device for a gate blowout preventer, and tests are conducted using the device to verify the dynamic shear capacity evaluation method for a gate blowout preventer. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 Schematic diagram of the force analysis of the drill pipe due to shearing movement of the gate;

[0056] Figure 2 Schematic diagram of the force analysis of the ram shear and torsion drill pipe;

[0057] Figure 3 This is a schematic diagram of the gate shear motion and velocity decomposition;

[0058] Figure 4 Schematic diagram of equivalent distribution of gate shear stress;

[0059] Figure 5 This is a schematic diagram of the finite element simulation model of the shear gate;

[0060] Figure 6 Schematic diagram of shear flow field of ram blowout preventer;

[0061] Figure 7 This is a schematic diagram of a device for evaluating the dynamic shear capacity of a ram blowout preventer;

[0062] Figure 8 Schematic diagram of the gate force during the shearing process;

[0063] Figure 9 Schematic diagram of the logic relationship of the dynamic shear capacity evaluation method of the ram blowout preventer of the present invention. DETAILED DESCRIPTION

[0064] The core of the present invention is to provide a dynamic shear capacity evaluation method for a ram blowout preventer, which introduces a three-parameter generalized strength criterion under the coupled action of tension, compression and shear, and can more accurately evaluate the blowout prevention performance of the ram blowout preventer.

[0065] In order to enable those skilled in the art to better understand the technical solution of the present invention, the dynamic shear capacity evaluation method and device of the ram blowout preventer of the present invention will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0066] The present invention provides a method for evaluating the dynamic shear capacity of a ram blowout preventer, which overcomes the defects of the traditional method for evaluating the shear capacity of a ram blowout preventer, and comprises the following steps:

[0067] S1. Dynamic shear stress calculation: Based on the stress state of the ram BOP during the shear process, a three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear is adopted. This is combined with the stress distribution under the dynamic working conditions of the drill pipe to analyze and derive the theoretical formula for drill pipe stress calculation. A dynamic shear stress calculation module for the ram BOP is established. Based on the stress state of the ram BOP during the shear process, a three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear is introduced. This criterion is combined with the stress distribution under the dynamic working conditions of the drill pipe to analyze and derive the stress distribution during the dynamic shear process of the ram.

[0068] This step first analyzes the stress on the drill pipe in a blowout scenario to clarify the stress state of the drill pipe under the conditions of drill pipe movement and torsion. Secondly, based on the three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear, and combined with the stress conditions of the dynamic drill pipe, theoretical models for drill pipe stress calculation suitable for movement and torsion conditions are constructed.

[0069] S2. Shear force estimation: using the equivalent relationship of gate shear compressive stress and material yield criterion theory, the shear force F of the shear gate in its movement direction is obtained; considering the external force of the shear gate in its movement direction, the gate comprehensive shear force F is calculated. max A shear force estimation module for the ram BOP was set up. The effects of the shear ram's structural dimensions, hydrostatic pressure in the well, fluid impact force, and motion friction on the shear process were comprehensively considered. Based on the equivalent relationship between shear compressive stress, a theoretical calculation model for shear force was constructed.

[0070] Steps S1 and S2 are two independent processes. The technical solution of the present invention establishes a mechanistic model for the dynamic shear conditions of a ram BOP. To address the complex wellbore conditions and the difficulty in analyzing the shear effects, a three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear is introduced, and a method for constructing a theoretical model for calculating dynamic drill pipe shear stress is proposed. This method has high applicability and can more accurately evaluate the blowout prevention performance of a ram BOP.

[0071] On the basis of the above scheme, with respect to the above step S1, which states: "analyzing and deducing the stress distribution of the drill rod under dynamic working conditions to obtain a theoretical formula for calculating the stress of the drill rod", the present invention provides a drill rod stress calculation model formula under two working conditions: the drill rod movement condition and the drill rod torsion condition:

[0072] Theoretical formula for calculating the stress of the drill pipe under the condition of drill pipe movement:

[0073]

[0074] Theoretical formula for calculating torsional drill pipe stress under drill pipe torsion conditions:

[0075]

[0076] The specific analysis process is as follows:

[0077] When a blowout occurs during drilling, the formation fluid pressure will far exceed the operating pressure in the well, causing a high-pressure mixture of oil, natural gas, sand, stone particles, etc. in the well to gush out to the wellhead, thereby generating an upward thrust at the lower end of the drill pipe. At the same time, under the action of the wellhead lifting system, the drill pipe will be in an upward state.

[0078] In order to simplify the model, only the thrust generated by the downhole pressure on the drill pipe needs to be considered, and the influence of impurities such as cuttings particles on the shear can be ignored. Therefore, the shear motion plane of the gate is taken as the Oxy plane, and the axial movement direction of the drill pipe is taken as the positive direction of the z axis to establish the corresponding spatial coordinate system. The force state of the drill pipe at this time can be obtained, as shown in the following example: Figure 1 shown.

[0079] During the shearing movement of the gate, the drill rod may also be in a torsion state due to the action of the turntable. The force analysis of the drill rod at this time is as follows: Figure 2 In the Oxy plane, the drill pipe is squeezed and sheared by the vertical shear force of the gate, and at the same time, the drill pipe is also subjected to the torque τ provided by the turntable.

[0080] The three-parameter generalized strength criterion is introduced and defined as follows based on the relationship between the parameters:

[0081] I1=σ zz +σ yy +σxx (1.1)

[0082]

[0083] Among them, I1 reflects the material stress spherical tensor; J2 reflects the material stress deviator tensor.

[0084] First, since the tensile and compressive strengths of the drill pipe material are not equal, it is necessary to construct an equivalent function based on the dual-parameter strength criterion with the influence of tension and compression alone, and define σ m is the equivalent stress, and the corresponding function equation can be obtained:

[0085]

[0086] Where: m—drill pipe material tensile and compressive strength ratio coefficient, m=X t / X c ;X t —Material tensile strength; X c —Material compressive strength.

[0087] Secondly, it is necessary to consider the influence of shear strength on the equivalent function. At this time, the shear strength S of the drill pipe and the tensile strength X t The relationship between them is: By introducing n to modify the existing equivalent function, we can obtain the equivalent stress function based on the coupling of tension, compression and shear phases:

[0088]

[0089] According to the force analysis of the drill pipe caused by the gate shearing movement, the stress parameter values of the drill pipe in each direction are as follows: zz ≠0, τ yx ≠0,σ yy =σ xx =τ zy =τ xz = 0. At this time, the stress deviator and spherical tensor of the drill pipe material can be expressed as: I1=σ zz , substituting it into the coupling equivalent stress function, we can obtain the theoretical model formula suitable for the stress calculation of the moving drill rod:

[0090]

[0091] in:

[0092] σ m is the equivalent stress;

[0093] X t is the tensile strength of the material; X c is the compressive strength of the material;

[0094] n represents the drill pipe shear strength S and the material tensile strength X t The relationship between

[0095] m is the tensile and compressive strength ratio coefficient of the drill pipe material, m=X t / X c ;

[0096] τ is shear stress, σ is stress, σ zz ≠0, τ yx ≠0,σ yy =σ xx =τ zy =τ xz =0.

[0097] The formula (1.5) obtained above is also the theoretical model formula applicable to the stress calculation of the moving drill pipe.

[0098] Similarly, under torsion conditions, the stress parameter values of the drill pipe in each direction are as follows: τ yx ≠0,σ yy =σ xx =σ zz =τ zy =τ xz = 0. At this time, the stress deviator and spherical tensor of the drill pipe material can be expressed as: I1=0, and substituting it into the coupling equivalent stress function, we can obtain the theoretical model formula suitable for torsional drill pipe stress calculation:

[0099]

[0100] in:

[0101] σ m is the equivalent stress;

[0102] n represents the drill pipe shear strength S and the material tensile strength X t The relationship between

[0103] τ yx ≠0,σ yy =σ xx =σ zz =τ zy =τ xz =0.

[0104] The above formula (1.6) is also the theoretical model formula applicable to the calculation of torsional drill pipe stress.

[0105] Furthermore, considering the external force of the shear ram in its movement direction in step S2, a theoretical calculation formula is provided:

[0106] F max =F+F i +F l +F f

[0107] The specific analysis process is as follows:

[0108] The shear force estimation of the ram blowout preventer is mainly based on the equivalence relationship between the ram shear and compressive stress and the material yield criterion theory method, and an initial theoretical calculation model of the shear force suitable for the double V-type ram is constructed.

[0109] First, the shear contact end surface between the upper and lower shear rams and the drill pipe is taken as the Oxy plane, and the shear motion direction of the ram is taken as the positive direction of the x-axis to establish the corresponding coordinate system. Since the double V-shaped shear ram has a symmetrical shape, the shear ram motion on one side is analyzed first, and the movement speed and displacement of the ram are analyzed along the shear edge direction, such as Figure 3 shown.

[0110] Among them, C0 is the point when the shear ram just contacts the drill pipe surface. Under the action of the hydraulic pressure of the cylinder, the ram will continue to move in the positive direction of the x-axis. After that, this point is defined as C t In this process, the movement velocity and displacement of the shear gate are expressed as follows:

[0111]

[0112] Where P0 is the oil pressure in the cylinder; A0 is the effective area of the piston; M is the mass of the shear ram; t is the shearing time of the ram. Assuming the time when the ram just contacts the drill pipe is t0, the shear displacement of the ram at time t is According to the shear velocity decomposition, the gate displacement in the shear edge direction can be obtained as follows:

[0113]

[0114] In the process of calculating the shear force based on the equivalent relationship of the gate shear compressive stress, determining the stress distribution state of the sheared drill pipe and the indentation boundary of the gate shear drill pipe foundation is the key to model construction. According to the analysis of relevant indentation experiments, the compressive stress of the drill pipe is continuously distributed, and the compressive stress in front of the shear gate indentation is approximately rectangular and satisfies the equivalent distribution centered on the shear point. The indentation shape in front of the shear gate and the drill pipe stress distribution on the Oxy and Oyz surfaces all satisfy the rectangular distribution. Thus, the equivalent model of the gate shear stress distribution can be obtained as follows: Figure 4 shown.

[0115] According to the equivalent results, the KN segment is the projected length of the portion where the shear ram cuts into the drill pipe in the y-axis direction. Based on the symmetry effect, its calculation formula is:

[0116]

[0117] The FK segment is the projected length of the gate shear end surface in the y-axis direction, and its calculation formula is:

[0118]

[0119] According to the shape characteristics of the foundation indentation, the calculation formula for the effective action area of the gate shear stress can be obtained as follows:

[0120]

[0121] Then the calculation formula of the gate shear force can be derived from the yield criterion of the material:

[0122]

[0123] Where h is the cutting edge thickness of the shear ram; It is the inclination angle of the gate shear blade, that is, the angle between the cutting edge and the vertical perpendicular line.

[0124] The shear force calculated by the above formula is the force applied by one side of the shear ram. Combined with the structural characteristics of the double V-shaped shear ram, the shear force of the shear ram in its direction of movement can be obtained as follows:

[0125] F=2×F1sinα / 2 (2.7)

[0126] In the actual shearing process, the influence of resistance such as motion friction, hydrostatic pressure and fluid impact force must also be considered. Finally, the hydrostatic pressure F in the well can be obtained by comprehensively considering the i , fluid impact force F l and the friction force F f The estimation method of the gate comprehensive shear force expression is:

[0127] F max =F+F i +F l +F f (2.8)

[0128] The hydrostatic pressure in the well is F i , fluid impact force F l and the friction force F f All are located in the Oxy horizontal plane.

[0129] In order to ensure the accuracy of the results, it is necessary to solve the problem through multiple sets of data. The friction resistance type in the shearing process is dynamic friction, and its value can be defined as a certain value. Therefore, the least squares method is used for mean fitting. The friction resistance calculation formula obtained by this method is:

[0130]

[0131] Wherein: n is a positive integer.

[0132] Based on any of the above technical solutions and their combination, the present invention uses finite element dynamic shear simulation to verify the above calculation results. The dynamic shear simulation of the ram blowout preventer specifically includes:

[0133] Construct a simulation model. According to the actual external influence on the drill pipe, add boundary constraints to replace the external force influence during the shearing process, and only retain the horizontal degree of freedom. Use the shear force curve obtained by simulation results to verify the gate comprehensive shear force F max .

[0134] During the simulation analysis of the ram shear drill pipe, it is first necessary to use 3D modeling software to construct 3D models of the double V-shaped integral shear ram and S135 drill pipe based on 3D data. Finally, the assembled models are imported into the finite element display dynamics module in a standard format.

[0135] Secondly, a correct constitutive model for the drill pipe material can truly reflect the shearing process between the gate and the drill pipe. The Johnson-Cook model can be used in the finite element software analysis step to simulate metal materials with high strain rate deformation, making it easier to describe the material properties of sheared drill pipe. The strength component of the model considers the following effects: 1) material hardening due to deformation, 2) high strain rate hardening, and 3) high temperature softening. During the analysis, the Johnson-Cook model can reflect the relationship between the deviatoric stress tensor and the deviatoric strain tensor during the drill pipe shearing process. The failure strain function of the drill pipe model is:

[0136]

[0137] Where: ε f is the failure (plastic) strain; D1~D5 are failure model parameters; is the ratio of hydrostatic pressure to equivalent stress; is the dimensionless equivalent strain rate; T * =(TT r ) / (T m -T) is the dimensionless temperature, where T r is the reference temperature, °C, T m is the melting point of the material, ℃.

[0138] In addition, in order to better fit the fracture state of the drill pipe, the Shock EOSLinear state equation is also introduced in the analysis module. This equation mainly has the following relationship:

[0139] u s =C1+S1u p(3.2)

[0140] Where: u s is the impact velocity; u p is the particle velocity; C1 is u s -u p The intercept of the curve is the volume speed of sound; S1 is the slope coefficient of the curve.

[0141] In addition, for the above constitutive model formula, the stress-strain curves of the gate and drill pipe material specimens can be collected through the basic model tension and compression fracture test, and then the Johnson-Cook constitutive model parameters can be determined by the least squares fitting method.

[0142] This method mainly takes the drill rod as the research object, and takes the gate plate to be able to shear the drill rod normally as a prerequisite. Therefore, the shear gate plate can be defined as a rigid body and the drill rod can be defined as a flexible body for simulation analysis. In the process of model mesh division, the shear gate plate is divided by tetrahedral mesh units, and the mesh of the gate plate cutting edge contact surface area is refined; the drill rod is divided by hexahedral mesh units. In order to reduce the number of meshes in the overall model and save simulation calculation space, the drill rod model is divided into three sections with reference to the experimental shear deformation. Since the drill rod moves and the shear fracture is offset downward, it is necessary to lengthen the length of the shear area at the lower end of the drill rod and refine the mesh of the middle shear area. In the process of model mesh refinement, the mesh size, mapping surface mesh and contact size commands are mainly used to control the mesh size of the gate plate cutting edge area, the number of mesh layers of the drill rod section and the surface contact area, such as Figure 5 .

[0143] To determine the mesh size and number of the shear gate finite element model, a mesh independence analysis was performed on the central shear region, which was the focus of the study. By modifying the mesh size of the shear region model to control the mesh number, and using the peak shear force of the model as the output reference, the peak shear force variation curves for different mesh sizes were obtained, thereby determining the appropriate mesh and node number for the finite element model.

[0144] Since the shearing process of the ram blowout preventer is an extremely complex dynamic process, the model is appropriately simplified, and the influence of external forces in the shearing process is replaced by adding boundary constraints in the model analysis. For example, under the condition of drill pipe movement, upward thrust is added to the upper and lower surfaces of the drill pipe to simulate the mud thrust and top drive pull on the drill pipe, and torque is applied to the drill pipe to simulate the influence of the turntable. During the movement of the shear ram, the vertical direction is supported by the shell and it does not move, while the horizontal direction is pushed by the hydraulic pressure of the cylinders on both sides to make closing movements. Therefore, it is necessary to constrain the movement in other directions, and only the degrees of freedom in the horizontal direction need to be retained.

[0145] According to the above analysis steps, the finite element simulation model of the ram BOP shear process can be finally obtained. By adding calculation modules such as stress, strain, and shear force in the Solution solver, the corresponding ram shear state parameters can be obtained.

[0146] Finally, to clarify the impact of fluid impact during the ram shear process, it is also necessary to consider the internal fluid effects and perform fluid-solid coupling simulation of the ram BOP shear process. In fluid analysis, basic physical conservation laws must be followed, including the conservation of mass, momentum, and energy, which are expressed as follows:

[0147]

[0148]

[0149]

[0150] The fluid density is ρ a is the fluid density, t is the time, u a is the volume of the fluid, p is the fluid pressure, μ is the effective viscosity of the fluid, F is the mass force acting on the fluid, c p is the thermal conductivity of the fluid, T is the internal energy per unit mass of the fluid, q is the volume heating rate per unit mass,

[0151] Combine Figure 6 In the process of constructing the fluid-solid coupling model, it is necessary to add a wellbore outer wall on the basis of the dynamic shear model of the gate to make it a closed fluid domain, and then import the model into the analysis software for pre-processing. The final fluid-solid coupling analysis model is obtained by dividing the fluid domain, defining boundary conditions, etc., in which the fluid inlet is set to the corresponding velocity inlet, the outlet is the pressure outlet, the fluid medium is mainly water, and a steady-state calculation is performed. According to the simulation calculation results, it can be found that the fluid at the wellhead will experience turbulence at the gate shear point and continuously impact the gate, so that the lateral pressure of the fluid on the gate is extracted, and the impact force of the fluid in the lateral direction is calculated in combination with the cross-sectional area of the gate.

[0152] The present invention also provides a dynamic shear capacity evaluation device for a ram blowout preventer, which is applied to the above-mentioned dynamic shear capacity evaluation method for a ram blowout preventer; the evaluation device comprises a sealed test chamber 1, a ram blowout preventer 2 and a hydraulic control device; Figure 7 The test chamber 1 is used to accommodate the drill pipe 3, and the ram blowout preventer 2 is installed in the test chamber 1; the test chamber 1 is a closed chamber, and the drill pipe 3 is vertically suspended and installed in the inner cavity of the test chamber 1. The ram blowout preventer 2 is arranged in the middle of the test chamber 1, and the ram blowout preventer 2 cuts the drill pipe 3 under the action of oil pressure thrust.

[0153] The hydraulic control device includes an electric pump, a switching valve, a regulating valve and an accumulator. The hydraulic control device provides hydraulic power for the ram blowout preventer 2. A pressure gauge is set on the console to display the pressure of the accumulator and the drill pipe during operation.

[0154] A model test was conducted using a physical test evaluation device to further verify the above-mentioned dynamic shear capacity evaluation method of the ram blowout preventer.

[0155] The design of the ram blowout preventer shear test device mainly includes a hydraulic control device, a shear ram blowout preventer and a drill pipe. The hydraulic control device mainly provides hydraulic power for the blowout preventer. The internal components mainly include an electric pump, a switching valve, a regulating valve and an accumulator. The stainless steel seismic-resistant pressure gauge on the console can respectively display the pressure changes of the accumulator and the manifold during operation.

[0156] Before the shear test, the lower end of the ram blowout preventer needs to be installed on a fixed base, and the upper end needs to be sealed with an end cover. The blowout preventer is connected to the hydraulic control device through a high-pressure manifold. The test drill pipe is then suspended vertically at the upper end and stabilized in the center position. Finally, high-pressure liquid is injected into the blowout preventer cavity through the fixed base at the bottom to stabilize it in a certain hydrostatic pressure environment.

[0157] After completing the preparatory work, the hydraulic control system was activated, raising the internal pressure of the hydraulic control system's accumulator to the standard 21 MPa. The system's bypass valve was then adjusted to the "open" position. The handle of the three-position, four-way valve was operated to allow the high-pressure hydraulic oil from the accumulator group to enter the manifold and reach the BOP cylinder, thereby pushing the ram to complete the shearing operation. Finally, the equipment was shut down, the power was disconnected, the ram was opened, and the BOP shear ram was inspected, with test records kept. The shear force data during the shearing process were obtained based on the changes in the manifold pressure gauge on the hydraulic control system console, thereby validating the proposed shear force calculation model.

[0158] At the same time, through the force analysis of the shearing process, the force of the gate during the shearing process is as follows: Figure 8 As shown, the force conditions and dimensions of the locking shaft 4, the gate shaft 5, and the piston 6 are shown.

[0159] Since the gate moves at a slow speed when shearing against the pipe, it can be equivalent to uniform motion. Therefore, the relationship between the various forces can be expressed as:

[0160] P0×S0=F+F i +F f (4.1)

[0161] Where: P0 is the oil pressure in the blowout preventer cylinder; S0 is the effective area of the hydraulic oil, which can be expressed as follows according to its structure: r0 is the radius of the locking shaft, r1 is the radius of the gate shaft, and r2 is the radius of the piston; F is the gate shear force; F i F is the resistance of the blowout preventer well pressure to the gate shear movement; f It is the friction resistance during the gate shearing movement.

[0162] It can be concluded that when there is pressure in the blowout preventer cavity, it mainly produces resistance to the shear movement of the gate moving toward the center, resulting in a relatively large operating oil pressure during the shear process. Since the resistance surface of the hydrostatic pressure in the well to the gate movement will change with the movement of the gate, in order to simplify the calculation process, the cross section of the gate shaft is mainly used as the resistance surface of the hydrostatic pressure in the well, thus obtaining the resistance F of the hydrostatic pressure in the well to the gate movement. i The calculation formula is:

[0163] F i =P i ×S1 (4.2)

[0164] Where: P i is the wellbore pressure during the BOP shearing process; S1 is the cross-sectional area of the ram shaft, and its calculation formula is: r1 is the radius of the gate axis.

[0165] According to the above analysis, the friction resistance during the gate shearing movement can be expressed as:

[0166] F f =|P0×S0-P i ×S1-F| (4.3)

[0167] In order to ensure the accuracy of the results, it is necessary to solve the problem through multiple sets of data. The friction resistance type in the shearing process is dynamic friction, and its value can be defined as a certain value. Therefore, the least squares method is used for mean fitting. The friction resistance calculation formula obtained by this method is:

[0168]

[0169] Substitute the fluid impact force, friction resistance and hydrostatic pressure obtained above into formula (2.8) to obtain the friction resistance of the gate shear motion under various working conditions.

[0170] Combine Figure 9The present invention discloses a method for evaluating the dynamic shear capacity of a ram-type blowout preventer (BOP) and establishes a mechanism model for the dynamic shear conditions of the ram-type BOP. To address the complex wellbore conditions and the difficulty in analyzing the shear influence, a three-parameter generalized strength criterion under the coupled effects of tension, compression, and shear is introduced, and a method for constructing a theoretical model for calculating dynamic string shear stress is proposed. Based on theoretical methods such as the equivalent relationship between ram shear-compression stress and the material yield criterion, a theoretical calculation model for BOP shear force is constructed that takes into account the influence of factors such as kinetic friction, hydrostatic pressure, and fluid impact force. The model's high applicability is demonstrated through simulation models.

[0171] A parametric analysis-based method for estimating the shear force of a ram-type blowout preventer (BOP) is proposed. By incorporating theories related to shear compressive stress equivalence and the yield criterion, a shear force estimation method suitable for double-V shear rams is proposed. This method is then refined through ram shear testing and simulation techniques, improving the accuracy of the calculation results. This method comprehensively analyzes the influence of factors such as ram structural dimensions, kinematic friction, wellbore hydrostatic pressure, and fluid impact on ram shear force, offering the advantage of balancing structural dimensions with operating parameters.

[0172] A simulation model of the dynamic shear process of the gate blowout preventer was constructed. In order to solve the problems of variable shear stress state of the gate and difficulty in obtaining effective performance data, the explicit dynamic simulation technology was used, combined with the material constitutive model parameters, to simulate the gate shear motion process, analyze the deformation state and stress-strain distribution characteristics of the shear gate and the tubing at each stage, realize the characteristic law analysis of the gate shear parameters, and verify the theoretical calculation process. The dynamic shear simulation is based on the actual working conditions of the blowout preventer shear process, and constructs a gate blowout preventer shear simulation analysis model and a fluid-solid coupling model. It comprehensively considers factors including but not limited to the material constitutive model, material motion state, and hydrostatic pressure. It can accurately and effectively obtain the change law of each shear capacity characterization parameter during the dynamic shear process of the gate, verify the accuracy of the constructed theoretical model, and provide a methodological idea for the analysis and research of the dynamic shear mechanism of the gate.

[0173] The present invention also provides a dynamic shear capacity assessment device for a gate blowout preventer and constructs a gate blowout preventer shear test device. By sealing the end cover of the blowout preventer and providing a suspension device, shear tests of the gate blowout preventer under different hydrostatic pressures can be performed. The pressure changes of the accumulator and the manifold during the shearing process are read in real time by a seismic-resistant pressure gauge, and the shear force data is calculated. The shear force change curve of the gate blowout preventer under different hydrostatic pressures can be obtained by pressurizing the blowout preventer cavity and reading the shear oil pressure data in real time. At the same time, the shear motion friction force can be calculated in combination with the experimental data. The theoretical calculation model is verified by comparing the experimental data with the calculation results of the theoretical model.

[0174] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating the dynamic shear capacity of a ram blowout preventer, characterized in that: include: Dynamic shear stress calculation: Based on the stress state of the ram BOP during the shear process, the three-parameter generalized strength criterion under the coupled action of tension, compression, and shear is adopted. Combined with the stress distribution of the drill pipe under dynamic working conditions, the theoretical formula for drill pipe stress calculation is obtained. Shear force estimation, using the gate shear compressive stress equivalent relationship and material yield criterion theory, the shear force F of the shear gate in its movement direction is obtained: ; in, is the gate shear force: ; is the equivalent stress, is the effective action area of the gate shear stress; is the cutting edge thickness of the shear ram; is the inclination angle of the gate shear blade, is the shear displacement of the gate, is the yield strength of the drill pipe material; It is the V-angle of the gate; Considering the external force of the shear ram in its movement direction, calculate the comprehensive shear force F of the ram max .

2. The method for evaluating the dynamic shear capacity of a ram blowout preventer according to claim 1, wherein: The above analysis and deduction combined with the stress distribution of the drill pipe under dynamic working conditions yields a theoretical formula for calculating the stress of the drill pipe, including: The theoretical formula for calculating the stress of the moving drill rod under the working condition of the moving drill rod is obtained: ； in: is the equivalent stress; is the tensile strength of the material; is the compressive strength of the material; n represents the drill pipe shear strength S and the material tensile strength The relationship between ; is the tensile and compressive strength ratio coefficient of the drill pipe material, ; ， ， ； represents the normal stress acting in the x-direction, represents the normal stress acting in the y direction, represents the normal stress acting in the z direction, represents the shear stress acting along the y direction on the plane in the x direction, represents the shear stress acting along the z direction on the plane in the y direction, It represents the shear stress acting along the x-direction on the plane in the z-direction.

3. The dynamic shear capacity evaluation method of a ram blowout preventer according to claim 1, characterized in that: The above analysis and deduction combined with the stress distribution of the drill pipe under dynamic working conditions yields a theoretical formula for calculating the stress of the drill pipe, including: The theoretical formula for calculating the torsional drill pipe stress under the drill pipe torsional working condition is obtained: ； in: is the equivalent stress; n represents the drill pipe shear strength S and the material tensile strength The relationship between ; ， ; represents the normal stress acting in the x-direction, represents the normal stress acting in the y direction, represents the normal stress acting in the z direction, represents the shear stress acting along the y direction on the plane in the x direction, represents the shear stress acting along the z direction on the plane in the y direction, It represents the shear stress acting along the x-direction on the plane in the z-direction.

4. The method for evaluating the dynamic shear capacity of a ram blowout preventer according to claim 1, wherein: The comprehensive consideration of the external forces on the shear ram in its direction of movement includes: Comprehensively consider the shear force F of the shear ram in its movement direction, the hydrostatic pressure F in the well i , fluid impact force F l and friction resistance F f , calculate the gate comprehensive shear force F max : 。 5. The method for evaluating the dynamic shear capacity of a ram blowout preventer according to claim 4, wherein: Friction resistance F f The least square method was used for mean fitting, and the friction resistance F f Calculated according to the following formula: ； in: n is a positive integer.

6. The method for evaluating the dynamic shear capacity of a ram blowout preventer according to any one of claims 1 to 5, characterized in that: Also includes: Dynamic shear simulation of the ram blowout preventer: a simulation model is constructed. Based on the actual external influences on the drill pipe, boundary constraints are added to replace the external force influences during the shear process, and only the degrees of freedom in the horizontal direction are retained; The shear force curve obtained by simulation results verifies the gate comprehensive shear force F max .

7. The method for evaluating the dynamic shear capacity of a ram blowout preventer according to claim 6, wherein: The Johnson-Cook model is used to simulate metal materials with high strain rate deformation. The failure strain function of the drill pipe model is: ； in: is the plastic strain at failure; is the failure model parameter; is the ratio of hydrostatic pressure to equivalent stress; is the dimensionless equivalent strain rate; is the dimensionless temperature, where is the reference temperature, °C, is the melting point of the material, °C; Introduce the Shock EOS Linear state equation in the analysis module: ； in: is the impact velocity; is the particle velocity; for The intercept of the curve, the volume speed of sound; is the slope coefficient of the curve.

8. The method for evaluating the dynamic shear capacity of a ram blowout preventer according to claim 7, wherein: The construction of the simulation model includes: The shear ram is defined as a rigid body and the drill pipe is defined as a flexible body; The shear ram is divided by tetrahedral mesh elements, and the mesh of the ram blade contact surface area is refined; the drill pipe is divided by hexahedral mesh elements.

9. The method for evaluating the dynamic shear capacity of a ram blowout preventer according to claim 8, wherein: Also includes: A mesh independence analysis was performed to determine the number of mesh sizes for the shear gate finite element model.

10. A dynamic shear capacity evaluation device for a ram blowout preventer, characterized in that: The method for evaluating the dynamic shear capacity of a ram blowout preventer as claimed in any one of claims 1 to 9; It includes a sealed test chamber, a ram blowout preventer and a hydraulic control device, wherein the test chamber is used to accommodate a drill pipe, and the ram blowout preventer is installed in the test chamber; The hydraulic control device includes an electric pump, a switch valve, a regulating valve and an accumulator, and the hydraulic control device provides hydraulic power for the ram blowout preventer; A pressure gauge is provided on the console, and the pressure gauge is used to display the pressure of the accumulator and the drill pipe during the working process.

Images