A method and system for static force analysis of a riserless drilling fluid recovery string

Abstract

This invention provides a method and system for static stress analysis of riserless drilling fluid recovery tubing, belonging to the field of deepwater oil drilling. The method analyzes the influence of ocean currents and axial effective stress on the drilling fluid recovery tubing, using real-time acquired data to obtain the longitudinal and lateral loads on the tubing, and uses these loads to determine the safety of the tubing. This invention considers the effects of tensioner tension, tubing weight, tubing buoyancy, tubing friction resistance, upper and lower pump weights, and various wave currents on the drilling fluid recovery tubing. It can accurately analyze the static stress of the drilling fluid recovery tubing in a riserless drilling system, calculate the longitudinal and lateral loads in real time, and ensure the safe operation of the drilling fluid recovery tubing. This provides technical support for the promotion of riserless drilling technology and contributes to its widespread application.

Description

Technical Field

[0001] This invention belongs to the field of deepwater oil drilling, specifically relating to a static stress analysis method and system for a riserless drilling fluid recovery string, used to analyze the stress situation of the riserless drilling fluid recovery string during deepwater drilling. Background Technology

[0002] In recent years, to address the challenges of limited safety margins for formation pore pressure and fracture pressure, and a narrow safety density window for drilling fluids during deepwater oil drilling, deepwater riserless drilling fluid recovery technology has been proposed. For example... Figure 6 As shown, this technology eliminates the need for conventional risers during drilling, allowing the drill pipe to be directly exposed to seawater. A suction module installed at the subsea wellhead ensures a seal between the wellbore and the seawater. Cuttings and drilling fluid are returned to the drilling platform via a small-diameter drilling fluid recovery string (also known as a reverse runoff line). Specifically, in this system, drilling fluid is pumped into the drill pipe from the surface, reaches the bottom of the well, impacts and breaks up the rock, carrying cuttings back up through the annulus. At the top of the annulus, it enters the subsea lift pump via the subsea suction module. Under the action of the subsea lift pump, the cuttings and drilling fluid return to the drilling platform through the drilling fluid recovery string. After treatment by the surface drilling fluid treatment system, the drilling fluid re-enters the drilling fluid circulation system. However, due to the complex and variable sea conditions during deepwater drilling, the drilling fluid recovery string is affected by complex loads such as deep-sea waves and currents. The drilling fluid recovery string will move irregularly under the action of waves and currents, and the stress analysis is not yet clear, which poses a great risk to the drilling process and has become the main bottleneck restricting the development of deepwater tubular drilling fluid recovery technology.

[0003] Currently, the analysis of the stress on drilling fluid recovery tubing usually considers the influence of ocean currents on the drilling fluid recovery tubing, and mainly analyzes the influence of lateral loads on the stress on the drilling fluid recovery tubing. There is basically no research on the stress analysis of drilling fluid recovery tubing that considers the coupling effect of longitudinal and lateral loads.

[0004] Chinese patent publication CN102607787A discloses an experimental method for testing the influence of internal flow on the dynamic characteristics of marine risers. Specifically, it relates to an experimental method and apparatus that can effectively apply internal flow and top tension when simulating the vortex-induced vibration of marine risers, and test the influence of internal flow on the dynamic characteristics of the marine risers. In conducting experimental research on the vortex-induced vibration of marine risers, this patent's experimental apparatus for applying internal flow and top tension, and the experimental method using this apparatus, continuously apply a known amount of top tension, change the magnitude of internal flow and external flow respectively, and use strain gauges and optical fiber gratings to measure the influence of internal flow on the dynamic characteristics of the marine riser. This allows for testing the influence of internal flow on the dynamic characteristics of marine risers when simulating the vortex-induced vibration of marine risers, thereby improving the accuracy of marine riser vortex-induced vibration model tests and obtaining more accurate experimental conclusions.

[0005] The Chinese open-source paper, "Dynamic Characteristics of Top-Stretched Riser under the Combined Action of Internal Solitary Waves and Non-Uniform Ocean Currents" (Series A, July 2012, Vol. 27, No. 4), mainly studies the nonlinear dynamic response of deep-sea top-stretched risers under the combined action of internal solitary waves and non-uniform ocean currents in two fluid layers. The results show that under the multimodal vortex-induced force caused by ocean current non-uniformity, deep-sea top-stretched risers will experience large-amplitude multimodal transverse combined vortex-induced resonance. During the process of multimodal combined resonance in deep-sea risers, the presence of internal solitary waves not only significantly increases the amplitude of the transverse combined resonance but also causes a sudden large deformation response in the downstream direction.

[0006] However, the two published documents mentioned above only consider the influence of one or two wave flows on the tubing string. In contrast, the drilling fluid recovery tubing string without a riser is not only affected by multiple wave flows, but also by multiple forces along its axis. Currently, there is no technology available for analyzing the static stress of the drilling fluid recovery tubing string. Summary of the Invention

[0007] The purpose of this invention is to solve the problems existing in the prior art and provide a static stress analysis method and system for a riserless drilling fluid recovery string. The analysis is based on the coupling of longitudinal and transverse loads to ensure the safety of the riserless drilling fluid recovery string, prevent string damage, and thus ensure safe drilling in deep water.

[0008] This invention is achieved through the following technical solution:

[0009] The first aspect of the present invention provides a static stress analysis method for a drilling fluid recovery string without a riser. The method analyzes the influence of ocean current force and axial effective stress on the drilling fluid recovery string, uses real-time acquired data to obtain the longitudinal and lateral loads on the drilling fluid recovery string in real time, and uses the longitudinal and lateral loads to determine whether the drilling fluid recovery string is safe.

[0010] A further improvement of the present invention is that:

[0011] The longitudinal load is the effective axial stress, which includes: tensioner tension, tubing weight, tubing buoyancy, tubing frictional resistance, and the force generated by the gravity of the upper and lower pumps.

[0012] The lateral load is ocean current force, which includes the forces generated by tidal currents, wind-driven currents, wave currents, and internal solitary waves.

[0013] A further improvement of the present invention is that:

[0014] The method includes:

[0015] The first step is to collect data;

[0016] The second step is to calculate the lateral load on the drilling fluid recovery string in real time.

[0017] The third step is to calculate the longitudinal load on the drilling fluid recovery string in real time.

[0018] The fourth step is to obtain the bending normal stress of the drilling fluid recovery string based on the lateral and longitudinal loads it is subjected to.

[0019] The fifth step is to use bending normal stress to determine whether the drilling fluid recovery string is safe.

[0020] A further improvement of the present invention is that:

[0021] The first step includes the following operations:

[0022] (11) Use an acoustic Doppler current profiler to perform real-time measurements to obtain ocean current parameters;

[0023] (12) The density ρ of seawater was measured using a balance beaker. f and the fluid density ρ inside the drilling fluid recovery string m The density ρ1 of the upper layer and the density ρ2 of the lower layer of seawater in the internal solitary wave were determined using a magnetoacoustic sensor.

[0024] (13) The outer diameter D of the drilling fluid recovery string was measured using a vernier caliper. o , inner diameter d o Then, the outer cross-sectional area A of the drilling fluid recovery string is calculated. roInternal cross-sectional area A ri ;

[0025] (14) Input the weight per unit length W of the drilling fluid recovery string. e (z,t), the gravity W of the upper and lower pumps bumpup and W bumpdown The elastic modulus E of the drilling fluid recovery string;

[0026] (15) Obtain the tension force T from the tensioner. top (t);

[0027] (16) Calculate the buoyancy F per unit length of the tubular column. buo (z,t), frictional resistance F per unit length of tubular column mf (z,t);

[0028] (17) Use an underwater positioning sensor fixed on the drilling fluid recovery string to determine the angle θ between the drilling fluid recovery string and the vertical line of gravity at different depths.

[0029] A further improvement of the present invention is that:

[0030] The second step includes:

[0031] The current force P acting on the drilling fluid recovery string was calculated using the Morison formula. f That is, lateral load.

[0032] A further improvement of the present invention is that:

[0033] The third step includes the following operations:

[0034] The axial effective stress T is calculated using the following formula. e (z,t), i.e., longitudinal load:

[0035]

[0036] Where z represents depth, t represents time, and g is gravitational acceleration.

[0037] A further improvement of the present invention is that:

[0038] The fourth step includes the following operations:

[0039] (41) The lateral offset of the drilling fluid recovery string is obtained using the lateral offset control equation:

[0040] The lateral offset control equation is as follows:

[0041]

[0042] in,

[0043] In the formula, y is the lateral offset of the drilling fluid recovery string; I is the moment of inertia of the section;

[0044] (42) Obtain the bending normal stress σ of the drilling fluid recovery string by utilizing the lateral offset of the string:

[0045]

[0046] in,

[0047] In the formula, A represents the area, and M is the bending moment of the drilling fluid recovery string.

[0048] A further improvement of the present invention is that:

[0049] The fifth step includes the following operations:

[0050] Determine whether the bending normal stress σ of the tubing is less than the maximum bending normal stress σ of the tubing. s If yes, the tubing is considered safe; otherwise, the tubing is considered unsafe.

[0051] A second aspect of the present invention provides a static stress analysis system for a riserless drilling fluid recovery string, the system comprising:

[0052] Data acquisition unit: collects data;

[0053] Lateral load acquisition unit: connected to the data acquisition unit, it calculates the lateral load on the drilling fluid recovery string in real time;

[0054] Longitudinal load acquisition unit: connected to the data acquisition unit, it calculates the longitudinal load on the drilling fluid recovery string in real time;

[0055] Bending normal stress acquisition unit: It is connected to the lateral load acquisition unit and the longitudinal load acquisition unit respectively, and obtains the bending normal stress of the drilling fluid recovery string based on the lateral and longitudinal loads subjected to the drilling fluid recovery string;

[0056] Judgment Unit: Connected to the bending normal stress acquisition unit, it uses bending normal stress to determine whether the drilling fluid recovery string is safe.

[0057] A third aspect of the present invention provides a computer-readable storage medium storing at least one computer-executable program, which, when executed by the computer, causes the computer to perform the steps in the above-described static stress analysis method for drilling fluid recovery string without riser.

[0058] Compared with the prior art, the beneficial effects of the present invention are:

[0059] This invention considers the effects of tensioner tension, tubing weight, tubing buoyancy, tubing frictional resistance, upper and lower pump weights, and various wave flows on the drilling fluid recovery tubing. It can accurately analyze the static stress of the drilling fluid recovery tubing in a riserless drilling system, calculate the longitudinal and lateral loads it experiences in real time, and ensure the safe operation of the drilling fluid recovery tubing. This provides technical support for the promotion of riserless drilling technology and facilitates its widespread application. Attached Figure Description

[0060] Figure 1-1 Displacement of drilling fluid recovery string under the influence of different ocean current velocities;

[0061] Figure 1-2 Bending moment of drilling fluid recovery string under the influence of different ocean current velocities;

[0062] Figure 1-3 Bending normal stress of drilling fluid recovery string under the influence of different ocean current velocities;

[0063] Figure 2-1 Displacement of the drilling fluid recovery string under different top pump positions;

[0064] Figure 2-2 Bending moment of drilling fluid recovery string under different top pump positions;

[0065] Figure 2-3 Bending normal stress of drilling fluid recovery string under the influence of different top pump positions;

[0066] Figure 3-1 Displacement of the drilling fluid recovery string under different bottom pump positions;

[0067] Figure 3-2 Bending moment of drilling fluid recovery string under different bottom pump positions;

[0068] Figure 3-3 Bending normal stress of drilling fluid recovery string under the influence of different bottom pump positions;

[0069] Figure 4-1 Displacement of drilling fluid recovery string under the influence of different tensioner forces;

[0070] Figure 4-2 Bending moment of drilling fluid recovery string under the influence of different tensioner forces;

[0071] Figure 4-3 Bending normal stress of drilling fluid recovery string under the influence of different tensioner forces;

[0072] Figure 5 A flowchart illustrating the steps of the method of this invention;

[0073] Figure 6 A schematic diagram of the forces acting on the drilling fluid recovery string. Detailed Implementation

[0074] The present invention will now be described in further detail with reference to the accompanying drawings:

[0075] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0076] Deepwater riserless drilling fluid recovery drilling system, such as Figure 6 As shown, a drilling fluid recovery string 8 is installed below the offshore drilling platform, an upper pump 7 is installed above the drilling fluid recovery string 8, a lower pump 9 is installed below the drilling fluid recovery string 8, and a seabed anchoring point 10 is installed below the lower pump 9. The drill pipe 4 extends from the offshore drilling platform to below the mudline 6 on the seabed. The seabed wellhead 5 is located at the mudline 6 and is connected to the lower pump 9 through a return hose. The drilling fluid recovery string 8 is subjected to an axial effective stress 3 along its length direction, i.e., a longitudinal load, generated by the tension of the tensioner of the seabed anchoring point 10 and the drilling platform, as well as its own weight, buoyancy, frictional resistance, and the weight of the upper pump 7 and the lower pump 9. At the same time, it is subjected to a lateral load generated by the tidal current + wind-generated current + wave current 1 and the internal isolated wave 2 in the seawater.

[0077] This invention primarily analyzes the static stress of the drilling fluid recovery string in a deepwater riserless drilling system. Conventional static stress analyses of drilling fluid recovery strings mainly consider the effects of lateral loads such as ocean currents, but do not simultaneously consider the effects of ocean currents and axial effective stress on the static stress of the drilling fluid recovery string. The method of this invention considers the influence of both longitudinal and lateral loads, such as ocean currents and axial effective stress, on the drilling fluid recovery string and performs a static stress analysis on it.

[0078] This invention utilizes the characteristics of riserless drilling technology and addresses the stress factors of the drilling fluid recovery string in deep water. By analyzing the influence of factors such as ocean currents (tidal currents, wind-driven currents, wave currents, and internal isolated waves) and axial effective stress (tensioner tension, string weight, string buoyancy, string frictional resistance, upper pump, and lower pump weight), a static stress model of the drilling fluid recovery string under longitudinal and transverse load coupling (i.e., the coupled effect of ocean currents and axial effective stress) is established. This model accurately analyzes the stress situation of the drilling fluid recovery string in the riserless drilling system, ensuring that the stress on the drilling fluid recovery string is within a reasonable range and does not cause damage. This guarantees the stress safety of the drilling fluid recovery string, improves deep-water operation efficiency, provides technical support for preventing drilling fluid recovery string damage and ensuring safe drilling, and also provides technical support for the promotion and application of deep-water riserless drilling technology.

[0079] The method of this invention analyzes the influence of factors such as ocean currents and axial effective stress, and uses real-time acquired data to obtain the longitudinal and lateral loads of the drilling fluid recovery string in real time, and uses the longitudinal and lateral loads to determine whether the drilling fluid recovery string is safe.

[0080] The specific analysis steps are as follows:

[0081] (1) Analyze the load on the drilling fluid recovery string

[0082] Based on the actual operating conditions of the drilling fluid recovery string, the main loads borne by the recovery string are analyzed as lateral and longitudinal loads. The lateral load is mainly ocean current force, which includes the forces generated by tidal currents, wind-driven currents, wave currents, and internal solitary waves; the longitudinal load is mainly axial effective stress.

[0083] (2) Conduct stress sensitivity analysis of the recovery tubing

[0084] For the various influencing factors analyzed above, the influence of ocean current wave velocity on the stress of the tubing is analyzed for ocean current force; for axial effective stress, the influence of its magnitude on the stress of the tubing is mainly analyzed.

[0085] (3) Stress analysis of tubular columns under longitudinal and transverse load coupling

[0086] Based on the analyzed sensitivity factors, the stress conditions of the recovery tubing under the coupled longitudinal and lateral loads are calculated to ensure that the recovery tubing will not be damaged, thus providing a safety guarantee for riserless drilling technology.

[0087] Figure 5 This diagram illustrates the influencing factors of the static stress analysis method for riserless drilling fluid recovery string based on longitudinal and transverse load coupling. Sensitivity analysis was performed on each influencing factor, and detailed results are shown below. Figures 1-1 to 4-3 As shown, the details are as follows:

[0088] (1) Influence of ocean current velocity

[0089] Calculate the displacement, bending moment, and bending normal stress of the drilling fluid recovery string under the influence of different ocean current velocities, such as... Figures 1-1 to 1-3 As shown. From Figures 1-1 to 1-3 As can be seen, the displacement and bending moment of the drilling fluid recovery string increase with the increase of surface wave velocity. The reason and pattern are the same as those for the drill pipe, but the displacement change of the drilling fluid recovery string is very small, indicating that the influence of ocean current force on the drilling fluid recovery string is relatively small.

[0090] (2) The influence of the position of the upper pump

[0091] The displacement, bending moment, and bending normal stress of the drilling fluid recovery string under different top pump positions were calculated. The calculation results are as follows: Figures 2-1 to 2-2 As shown. From Figures 2-1 to 2-2 As can be seen, the displacement of the drilling fluid recovery string tends to increase slightly as the top pump position moves upward. The inflection point of the bending moment changes with the position of the top pump, while the bending moment changes very little at other positions.

[0092] (3) The influence of the position of the lower pump

[0093] Calculate the displacement, bending moment, and bending normal stress of the drilling fluid recovery string at different lower pump positions. The calculation results are as follows: Figures 3-1 to 3-3 As shown. From Figures 3-1 to 3-3 As can be seen, as the bottom pump position moves upward, the displacement of the drilling fluid recovery string tends to decrease slightly, which is the opposite of the movement pattern of the top pump position. Similarly, the inflection point of the bending moment changes with the position of the bottom pump, while the bending moment changes very little at other positions.

[0094] (4) The effect of tensioner tension

[0095] The displacement, bending moment, and bending normal stress of the drilling fluid recovery string were calculated under the influence of different tensioner forces. The calculation results are as follows: Figures 4-1 to 4-3 As shown. From Figures 4-1 to 4-3 As can be seen, with the increase of the tensioner tension, the displacement and bending moment of the drilling fluid recovery string both decrease slightly. Although the adjustable range of the tensioner tension is greater than that of the drilling string, the displacement change range of the drilling fluid recovery string is still very small, making it difficult to observe on the graph. Combined with the analysis of the influence of the tensioner tension on the drill pipe, it can be seen that adjusting the tensioner tension of both the drill pipe and the drilling fluid recovery string does not significantly improve the clearance between them.

[0096] The embodiments of the method of the present invention are as follows:

[0097] Example 1

[0098] The method includes:

[0099] The first step is to collect data: the size and physical properties of the drilling fluid recovery string, the gravity and position parameters of the upper and lower pumps, as well as real-time measured ocean current parameters and the angle between the drilling fluid recovery string and the vertical line of gravity.

[0100] The second step is to calculate the lateral load on the drilling fluid recovery string in real time.

[0101] The third step is to calculate the longitudinal load on the drilling fluid recovery string in real time.

[0102] The fourth step is to obtain the bending normal stress of the drilling fluid recovery string based on the lateral and longitudinal loads it is subjected to.

[0103] The fifth step is to use bending normal stress to determine whether the drilling fluid recovery string is safe.

[0104]

Example 2

[0105] The first step includes the following operations:

[0106] ① The various parameters of the ocean current, namely the ocean current parameters, are measured in real time using an acoustic Doppler current profiler, as shown in Table 1. The parameters of the relevant ocean current waves measured by the acoustic Doppler current profiler are changing in real time.

[0107]

[0108]

[0109] Table 1

[0110] ② The density ρ of seawater was measured using a balance beaker. f and the fluid density ρ inside the drilling fluid recovery string m The density ρ1 of the upper layer and the density ρ2 of the lower layer of seawater in the internal solitary wave were determined using a magnetoacoustic sensor.

[0111] ③ Measure the outer diameter D of the drilling fluid recovery string using vernier calipers. o , inner diameter d o Then, based on the outer and inner diameters, the outer cross-sectional area A of the drilling fluid recovery string is calculated using existing formulas. ro Internal cross-sectional area A ri ;

[0112] ④ Enter the weight per unit length (W) of the drilling fluid recovery tubing provided by the manufacturer. e (z,t), the gravity W of the upper and lower pumps bumpup and W bumpdown The elastic modulus E of the drilling fluid recovery string;

[0113] ⑤ The tension at the connection between the recovery string and the platform, determined using the tensioner on the existing drilling platform, i.e., the tensioner tension, T top (t);

[0114] ⑥ Calculate the buoyancy force per unit length of the tubular column at depth z at time t using existing buoyancy formulas, F. buo (z,t); The frictional resistance per unit length of the tubing at depth z at time t, calculated using existing frictional resistance formulas, F. mf (z,t);

[0115] ⑦ Multiple underwater positioning sensors fixed to the drilling fluid recovery string are used to determine the angle θ between the drilling fluid recovery string and the vertical line of gravity at different depths. This angle value changes in real time.

[0116]

Example 3

[0117] The second step includes:

[0118] The following Morison formula can be used to calculate the current force, i.e., the lateral load, on the drilling fluid recovery string:

[0119]

[0120] In the formula: P f For ocean current force, N / m; C D C is the drag coefficient, dimensionless; M ρ is the inertial force coefficient, dimensionless; f The density of seawater is kg / m³. 3 ;v f a is the velocity of the fluid particle, in m / s; f Let be the acceleration of the fluid particle, in m / s². 2 ;D o Let be the outer diameter of the drilling fluid recovery string, in meters (m).

[0121] The formula for calculating the velocity of a fluid particle is as follows:

[0122] v f =v tidel (z)+v wind (z)+v wave (z)+v in (z) (2)

[0123] In the formula: v f v is the velocity of the fluid particle, in m / s; tidel (z) represents the velocity of the tidal current, in m / s; v wind (z) represents the velocity of the wind current; v wave (z) represents the velocity of the wave current, in m / s; v in (z) represents the velocity of the internal solitary wave current, in m / s.

[0124] The formula for calculating the acceleration of a fluid particle is as follows:

[0125] a f =a wave +a in (3)

[0126] In the formula: a wave Let be the acceleration of a fluid particle under wave action, in m / s². 2 ;a in Let be the acceleration of a fluid particle under the action of an internal solitary wave, in m / s². 2 .

[0127] ①The formula for calculating the velocity of tidal currents is as follows:

[0128]

[0129] In the formula: v tidel (z) represents the velocity of the tidal current, in m / s; v tidel (0) is the velocity of the tidal current at the sea surface, m / s; h is the depth of the sea (the distance from the sea level to the mudline of the seabed), m; z is the depth of the particle (this depth is an assumed depth, and the seawater velocity at each depth is different), m.

[0130] ②The formula for calculating the velocity of wind-generated current is as follows:

[0131]

[0132] In the formula: v wind (z) represents the velocity of the wind-generated current, in m / s; v wind (0) represents the speed of the wind-driven current over the sea surface, in m / s.

[0133] ③ The formulas for calculating the velocity and acceleration of wave flow are as follows:

[0134]

[0135]

[0136] In the formula: v wave H represents the velocity of the wave flow, in m / s. wave Wave height, m; T wave ω is the wave period, s; ​​ω is the circumferential frequency of the wave flow, rad / s; k is the wave number; x represents the distance the wave travels, m; kx-wt represents the wave phase angle of the wave flow.

[0137] ④ The formula for calculating the velocity of an internal solitary wave is as follows:

[0138] The internal solitary wave is described by the KdV equation. Assume the seawater consists of two layers of different densities: the upper layer has a thickness and density of h1 and ρ1, respectively, and the lower layer has a thickness and density of h2 and ρ2, respectively. The amplitude of the internal solitary wave is A0 (obtained using specialized instruments such as Acoustic Doppler Current Profiler (ADCP) and Synthetic Aperture Radar (SAR)). When h1 < h2, A0 < 0; when h1 > h2, A0 > 0.

[0139] The amplitude of an internal solitary wave is calculated using the following formula:

[0140] A(y,t)=A0 sech 2 φ (8)

[0141] The particle velocity caused by the internal solitary wave is calculated using the following formula:

[0142]

[0143] The particle acceleration caused by the internal solitary wave is calculated using the following formula:

[0144]

[0145] In the formula: The phase angle of the internal solitary wave; λ is the wavelength of the internal solitary wave;

[0146] Δρ=ρ2-ρ1;

[0147] In formulas (9) and (10), "upper" refers to the upper layer of seawater and "lower" refers to the lower layer of seawater.

[0148]

Example 4

[0149] The third step includes the following operations:

[0150] Calculate the effective axial stress, i.e., the longitudinal load:

[0151] Assuming the drilling fluid recovery string is filled with flowing fluid, the effective axial stress is calculated by the following formula:

[0152] In the formula: T e (z,t) represents the effective axial stress, N, T. top (t) represents the tension force of the tensioner at time t, in N; W e (z,t) represents the weight per unit length of the drilling fluid recovery string at depth z and time t, in N / m (this weight is provided by the manufacturer and does not change with depth or time); F buo (z,t) represents the buoyancy force per unit length of the drilling fluid recovery string at time t at depth z, in N / m; θ is the angle between the drilling fluid recovery string and the vertical line of gravity, in °; A ro A ri These are the outer and inner cross-sectional areas of the drilling fluid recovery string, respectively, in meters. 2 ,∫0 z ρ represents the definite integral over the depth range 0-z; f and ρ m These are the densities of the fluids inside the seawater and drilling fluid recovery strings, respectively; F mf (z,t) represents the frictional resistance exerted on the drilling fluid recovery string per unit length by the fluid at time t at depth z (calculated using the general formula for straight pipe resistance), in N / m, where g is the acceleration due to gravity. Wb umpup and W bumpdown The weights of the upper and lower pumps, respectively, are in N.

[0153] Two booster pumps, namely the upper pump 7 and the lower pump 9, are added at different positions on the drilling fluid recovery string in the system. The gravity of the two booster pumps also affects the stress analysis of the drilling fluid recovery string. This invention considers the influence of the gravity of the booster pumps on the stress condition of the drilling fluid recovery string. The upper pump 7 and the lower pump 9 are assumed to be two gravity points applied to the drilling fluid recovery string.

[0154] Example 5

[0155] The fourth step includes the following operations:

[0156] (41) The lateral offset of the drilling fluid recovery string is obtained using the lateral offset control equation:

[0157] Under the combined action of ocean current force and axial effective stress, the lateral displacement control equation of the drilling fluid recovery string is as follows:

[0158]

[0159] in,

[0160] In the formula, y is the lateral offset of the drilling fluid recovery string, in meters; E is the elastic modulus of the drilling fluid recovery string, in Pa; and I is the moment of inertia of the cross section, in meters. -4 ;T e (z,t) represents the effective axial stress of the drilling fluid recovery string, W e (z,t) represents the unit wet weight of the drilling fluid recovery string, in N; P f Let N be the force of the ocean current. The lateral offset of the drilling fluid recovery string can be obtained by solving formula (12) using various existing methods (such as numerical simulation methods).

[0161] (42) Obtaining the bending normal stress of the tubular column using lateral offset:

[0162]

[0163] in,

[0164] In the formula: A represents the area; M is the bending moment of the drilling fluid recovery string, N·m; I is the moment of inertia of the recovery string, m. -4 σ represents the bending normal stress of the tubular column, in N;

[0165] Example 6

[0166] The fifth step includes the following operations:

[0167] The maximum bending normal stress criterion is used to determine whether the drilling fluid recovery string has been damaged, that is, to determine whether the bending normal stress σ of the string is less than the maximum bending normal stress σ of the string. sIf yes, the tubing is considered safe; otherwise, the tubing is considered unsafe.

[0168] The specific formula is as follows:

[0169] σ<σ s (16)

[0170] Where: σ s This is the maximum bending normal stress of the tubular column. This maximum bending stress value is a fixed value, which is an inherent property of the material and can be provided by the manufacturer.

[0171] In the above model, wave force is a lateral load, and axial effective stress is a longitudinal load. This invention considers both lateral and longitudinal loads. The simultaneous consideration of these factors constitutes the coupling effect of lateral and longitudinal loads. Therefore, the factors considered in this invention are more comprehensive, resulting in a more accurate analysis of the stress situation of the drilling fluid recovery string.

[0172] The present invention also provides a static stress analysis system for drilling fluid recovery string without riser, and an embodiment of the system is as follows:

[0173]

Example 7

[0174] The system includes:

[0175] Data acquisition unit: Collects the dimensional and physical property parameters of the drilling fluid recovery string, the gravity and position parameters of the upper and lower pumps, as well as the real-time measured ocean current parameters and the angle between the drilling fluid recovery string and the vertical line of gravity.

[0176] Lateral load acquisition unit: connected to the data acquisition unit, it calculates the lateral load on the drilling fluid recovery string in real time;

[0177] Longitudinal load acquisition unit: connected to the data acquisition unit, it calculates the longitudinal load on the drilling fluid recovery string in real time;

[0178] Bending normal stress acquisition unit: It is connected to the lateral load acquisition unit and the longitudinal load acquisition unit respectively, and obtains the bending normal stress of the drilling fluid recovery string based on the lateral and longitudinal loads subjected to the drilling fluid recovery string;

[0179] Judgment Unit: Connected to the bending normal stress acquisition unit, it uses bending normal stress to determine whether the drilling fluid recovery string is safe.

[0180] The present invention also provides a computer-readable storage medium, embodiments of which are as follows:

[0181] Example 8

[0182] The computer-readable storage medium stores at least one computer-executable program, which, when executed by the computer, causes the computer to perform the steps in the above-described static stress analysis method for drilling fluid recovery string without riser.

[0183] This invention can provide a more accurate description of the static stress of the riserless drilling fluid recovery string, and perform real-time calculations of its stress state, ensuring the safe operation of the drilling fluid recovery string and contributing to the promotion and application of riserless drilling technology.

[0184] This invention clarifies the stress state of the drilling fluid recovery string in a deepwater riserless drilling system under the coupled effects of longitudinal and lateral loads, providing technical support for accurately calculating the static stress of the drilling fluid recovery string. This ensures that the stress on the drilling fluid recovery string is within a reasonable range, avoiding failure of the recovery string. It provides theoretical and technical reserves for the application and promotion of deepwater riserless drilling technology and has broad application prospects.

[0185] Finally, it should be noted that the above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and have no limiting significance.

Claims

1. A method for analyzing static force of a riserless drilling fluid recovery string, characterized in that: The method analyzes the influence of ocean current force and axial effective stress on the drilling fluid recovery string, uses real-time acquired data to obtain the longitudinal and lateral loads on the drilling fluid recovery string, and uses the longitudinal and lateral loads to determine whether the drilling fluid recovery string is safe. The longitudinal load is the effective axial stress, which includes: tensioner tension, tubing weight, tubing buoyancy, tubing frictional resistance, and the force generated by the gravity of the upper and lower pumps. The lateral load is ocean current force, which includes the forces generated by tidal currents, wind-driven currents, wave currents, and internal solitary waves. The method includes: The first step is to collect data; The second step is to calculate the lateral load on the drilling fluid recovery string in real time. The third step is to calculate the longitudinal load on the drilling fluid recovery string in real time. The fourth step is to obtain the bending normal stress of the drilling fluid recovery string based on the lateral and longitudinal loads it is subjected to. The fifth step is to use bending normal stress to determine whether the drilling fluid recovery string is safe. The first step includes the following operations: (11) Use an acoustic Doppler current profiler to perform real-time measurements to obtain ocean current parameters; (12) The density of seawater was measured using a balance beaker. and fluid density within the drilling fluid recovery string ρ m Determining the density of upper seawater in the internal solitary wave using a magnetoacoustic sensor. and the density of the lower layer of seawater ; (13) The outer diameter of the drilling fluid recovery string was measured using a vernier caliper. D o , inner diameter d o Then, the outer cross-sectional area of ​​the drilling fluid recovery string is calculated. Internal cross-sectional area ; (14) Input the weight per unit length of the drilling fluid recovery string. The gravity of the upper pump and the lower pump and Elastic modulus of drilling fluid recovery string E ; (15) Obtain the tension force from the tensioner. ; (16) Calculate the buoyancy per unit length of the tubular column. Frictional resistance per unit length of tubular string ; (17) Use underwater positioning sensors fixed on the drilling fluid recovery string to determine the angle between the drilling fluid recovery string and the vertical line of gravity at different depths. ; The second step includes: The current force on the drilling fluid recovery string was calculated using the Morison formula. That is, lateral load; The third step includes the following operations: The axial effective stress is calculated using the following formula. That is, longitudinal load: Where z represents depth, t represents time, and g is gravitational acceleration; The fourth step includes the following operations: (41) Obtain the lateral offset of the drilling fluid recovery string using the lateral offset control equation: The lateral offset control equation is as follows: （12） in, (13) In the formula, y is the lateral offset of the drilling fluid recovery string; I The moment of inertia of the cross section; (42) Obtain the bending normal stress of the drilling fluid recovery string by utilizing the lateral displacement of the drilling fluid recovery string. : （14） in, (15) In the formula, A represents the area. M The bending moment of the drilling fluid recovery tubing.

2. The static stress analysis method for drilling fluid recovery string without riser according to claim 1, characterized in that: The fifth step includes the following operations: Determining the bending normal stress of the tubular column Is it less than the maximum bending normal stress of the tubular column? If yes, the tubing is considered safe; otherwise, the tubing is considered unsafe.

3. A static stress analysis system for a drilling fluid recovery string without a riser, based on the method described in any one of claims 1-2, characterized in that: The system includes: Data acquisition unit: collects data; Lateral load acquisition unit: connected to the data acquisition unit, it calculates the lateral load on the drilling fluid recovery string in real time; Longitudinal load acquisition unit: connected to the data acquisition unit, it calculates the longitudinal load on the drilling fluid recovery string in real time; Bending normal stress acquisition unit: It is connected to the lateral load acquisition unit and the longitudinal load acquisition unit respectively, and obtains the bending normal stress of the drilling fluid recovery string based on the lateral and longitudinal loads subjected to the drilling fluid recovery string; Judgment Unit: Connected to the bending normal stress acquisition unit, it uses bending normal stress to determine whether the drilling fluid recovery string is safe.

4. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores at least one computer-executable program, which, when executed by the computer, causes the computer to perform the steps in the static stress analysis method for the drilling fluid recovery string without a riser as described in any one of claims 1-2.

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