Method for evaluating lubricating property of thread compound

Abstract

The invention discloses a method for evaluating the lubricating property of thread compound, which comprises the following steps of: quantitatively evaluating the friction coefficient of the thread compound to obtain the relative lubricating coefficient Fs of the thread compound, and applying the relative lubricating coefficient Fs to the setting of the screwing-on torque Tf of an oil casing screwed joint to obtain the lubricating property of the thread compound. And the thread compound with different relative lubrication coefficients Fs sets the corresponding screwing-on torque Tf so as to control pipe screwing of the screwed joint of the oil casing pipe. Precise control over pipe screwing of the oil casing pipe screwed joint is achieved, and the problems that pipe screwing is not in place or over-screwing is caused by improper torque selection are reduced.

Description

Technical Field

[0001] The invention relates to lubricating grease used for threaded connection in petroleum pipe engineering, and more particularly to a method for evaluating lubricating properties of thread grease. Background Art

[0002] Thread compound is a lubricant applied to the thread of the joint before make-up. It acts as a lubricant during make-up and can assist in sealing against high external pressure during operation. If thread compound is not applied to the thread contact surface or the thread compound does not act as an effective protective layer, sticking may occur. In addition to preventing sticking and sealing, thread compound also provides consistent and repeatable friction performance at threaded connections. When the rotating shoulder connection is lifted, the friction force acting on the connection shoulder and the side of the thread will produce resistance to tightening. Under the same make-up torque, the joint with low friction resistance will be tightened more than the joint with high friction resistance. The API RP 5A3 standard also mentions that for a given connection screwing amount, the required torque should vary in direct proportion to the apparent friction coefficient of the thread compound / connection system, and the friction performance of the thread compound / connection system affects the torque required to tighten the connection, the torque required to further tighten the connection, and the torque required to unfasten the connection.

[0003] In 1992, API published API RP7A1 "Recommended Practice for Testing Rotary Shoulder Joint Thread Grease", which provides the test methods for make-up and make-out torque and friction coefficient, the composition of reference thread grease and its friction coefficient of 0.08. The release of this standard provides a correction factor for the tightening torque of shoulder joints in terms of threads for drilling operations, and proposes a small-size friction performance test method for thread grease, which uses a bolt-type specimen with threads and shoulders and records the torque-angle value to determine. However, the small-size test method is based on the comparison of the friction performance of lead-based reference thread grease, which has limited effect on the determination of the friction coefficient of non-metallic thread grease at present. In addition, the small-size test uses a round thread with a fixed shoulder, which does not retain thread grease, so the film thickness formed is very thin. The surface contact pressure is relatively high, between 200MPa and 425MPa, compared with the surface contact pressure of API casing, tubing and line pipe connections of only 35MPa to 140MPa. Therefore, the small-size test has no direct correlation with the full-size test, so it is not representative of oilfield service.

[0004] Carper et al. studied the effects of load, sliding speed, material, surface roughness and surface geometry on the friction coefficient of OCTG joints by using a friction and wear tester and API modified thread grease. The study found that in addition to load, sliding speed, material and surface roughness and surface geometry have a significant effect on the friction coefficient. In addition, it is proposed that the friction coefficient is a statistical quantity, and multiple repeated tests are required to obtain a reasonably accurate average value. Subsequently, Carper et al. showed in another study that the wear tester and test method previously developed can distinguish the differences in the average wear failure stress and friction coefficient of different thread greases.

[0005] In 2006, Ji Lingkang of the China Petroleum Pipe Research Institute conducted a simulation test of threading and unthreading under different conditions to investigate the factors that may affect the sticking of oil and casing during the casing operation in the oil field. The results showed that the friction resistance of the threaded connection can be significantly improved under the protection of thread grease, and the quality of thread grease has a great influence on the tendency of sticking. Good quality thread grease has a small friction coefficient and can reduce the threading torque and sticking tendency. In addition, the mixed use of thread grease and anti-rust oil or the use of anti-rust oil alone will cause sticking. The anti-rust oil must be cleaned before use, and the lubricating grease used for repeated threading must also be carefully cleaned to prevent the embedded solid hard particles from scratching the thread surface during the subsequent downhole operation.

[0006] A thread grease quantitative oil supply device is disclosed in Chinese Patent 202120364193.4, which solves the problem that the oil supply amount of the same parts of existing products cannot be accurately quantified when applying thread grease, or the supply amount between different parts cannot be changed at any time; the thread grease quantitative oil supply device of the present invention has a simple structure, low cost, convenient and direct operation, and has good market promotion prospects.

[0007] Chinese Patent No. 202010220349.1 discloses the composition and preparation method of a high-lubricity thread grease, which does not contain heavy metal fillers, has good anti-wear and extreme pressure properties under heavy load conditions, and exhibits good lubrication properties.

[0008] A thread grease parameter detection device is disclosed in Chinese Patent 201721677646.9. It has a simple structure, is convenient for applying thread grease to pipes with different inner diameters, is easy to use, and effectively improves the efficiency of thread grease parameter testing.

[0009] Chinese Patent No. 201110131701.5 discloses a method for evaluating the anti-galling performance of drill thread. The method can quantitatively evaluate the physical performance of drill thread, obtain the anti-galling performance of drill thread products, provide technical support and basis for analyzing the causes of galling of drill thread in actual use, solve technical confusion and difficulties in actual production, and has important practical guiding value and significance.

[0010] These patented technologies mainly introduce thread grease composition design schemes and thread grease parameter detection and evaluation methods, but there is no design method for quantitative evaluation of thread grease friction characteristics.

[0011] The make-up torque has a significant impact on the performance of special threaded joints. However, different thread greases have a significant impact on the make-up torque due to their different friction characteristics. In actual use, the make-up torque fluctuates many times due to the use of different thread greases, which eventually leads to abnormal make-up of threaded joints. Therefore, it is very necessary to develop an evaluation method for the lubrication characteristics of thread grease based on the characteristics of thread grease. Summary of the invention

[0012] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for evaluating the lubrication properties of thread grease, so as to achieve precise control of the tightening of oil casing threaded joints and reduce the occurrence of problems such as under-tightening or over-tightening of the pipe caused by improper torque selection.

[0013] To achieve the above object, the present invention adopts the following technical solution:

[0014] A method for evaluating the lubrication properties of thread grease:

[0015] By quantitatively evaluating the friction coefficient of the thread grease, the relative lubrication coefficient Fs of the thread grease is obtained, and the relative lubrication coefficient Fs is applied to the setting of the make-up torque Tf of the oil casing threaded joint. The thread greases with different relative lubrication coefficients Fs are used to set the corresponding make-up torque Tf to achieve the control of the threading of the oil casing threaded joint.

[0016] Preferably, the lubrication property evaluation method specifically comprises the following steps:

[0017] S1. Repeat the make-up and break-out operations on the threaded joint in sequence for multiple times according to the make-up torque Tf using the basic thread compound to obtain a make-up torque-turn number curve and a break-out torque-turn number curve;

[0018] S2, reading the make-up inflection point torques Ts11, Ts12, Ts13, ... from the make-up torque-turn number curve respectively;

[0019] S3, respectively calculating the cumulative values ​​of the friction factors of the shackle F11, F12, F13, ... from the shackle torque-turn number curve;

[0020] S4, repeating steps S1 to S3 using the thread compound to be tested, and obtaining the make-up inflection point torques Ts21, Ts22, Ts23, ... in the make-up torque-turns curve, and the cumulative values ​​of the break-out friction factors F21, F22, F23, ... in the break-out torque-turns curve;

[0021] S5, calculating the relative lubrication coefficient Fs according to the cumulative value factor weight α of the shackle friction factor and the make-up inflection point torque factor weight β, where the sum of α and β is 1;

[0022] S6. Calculate and adjust the torque Tn, and finally obtain the make-up torque Tf.

[0023] Preferably, in step S3, the cumulative value F of the friction factor of the shackle is calculated as follows:

[0024] F=∫TΔr

[0025] Where T is the torque value of the ordinate in the shackle torque-turns curve, and r is the circle value of the abscissa in the shackle torque-turns curve.

[0026] Preferably, in step S5, the relative lubrication coefficient Fs is calculated as follows:

[0027]

[0028] Preferably, the cumulative value factor weight α of the shackle friction factor is 0.7, and the make-up inflection point torque factor weight β is 0.3.

[0029] Preferably, in step S6, the adjustment torque Tn is calculated as follows:

[0030] Tn=Tf*Fs.

[0031] The present invention provides a method for evaluating the lubrication characteristics of thread grease, and based on the evaluation results, the applicable torque of the thread grease is converted to guide the pipe tightening operation of the oil casing threaded joint. The relative lubrication coefficient of the thread grease is obtained by quantitatively evaluating the friction characteristics of the thread grease, and the coefficient is applied to the setting of the make-up torque of the oil casing threaded joint. Different make-up torques are set for thread greases with different lubrication coefficients, thereby achieving precise control of the pipe tightening of the oil casing threaded joint and reducing the occurrence of problems such as under-tightening or over-tightening caused by improper torque selection. This method can quantitatively evaluate the friction characteristics of different thread greases, and the evaluation results are accurate and reliable, and can be directly used to guide the pipe tightening operation of the oil casing threaded joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic flow chart of the lubrication characteristic evaluation method of the present invention;

[0033] Figure 2 1 is a schematic diagram of the make-up and make-out test curves of the basic thread grease A in the embodiment of the lubrication property evaluation method of the present invention, (a) is the make-up torque-turn number curve, (b) is the make-up torque-turn number curve;

[0034] Figure 3 1 is a schematic diagram of the make-up and make-out test curves of the thread grease B to be tested in the embodiment of the lubrication property evaluation method of the present invention, (a) is the make-up torque-turn number curve, and (b) is the make-up torque-turn number curve. DETAILED DESCRIPTION

[0035] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0036] Combination Figure 1 As shown, a method for evaluating the lubrication properties of a thread grease provided by the present invention is as follows:

[0037] By quantitatively evaluating the friction coefficient of thread grease, the relative lubrication coefficient Fs of thread grease is obtained, and the relative lubrication coefficient Fs is applied to the setting of the make-up torque Tf of the oil casing threaded joint. The thread grease with different relative lubrication coefficients Fs sets the corresponding make-up torque Tf to achieve accurate control of the pipe tightening of the oil casing threaded joint, and reduce the occurrence of problems such as under-tightening or over-tightening caused by improper torque selection. Specifically, the following steps are included:

[0038] S1. Use basic thread compound to repeatedly make-up and make-off operations on the threaded joint in sequence according to the make-up torque Tf to obtain a make-up torque-turn number curve and a make-off torque-turn number curve;

[0039] S2, reading the make-up inflection point torques Ts11, Ts12, Ts13, etc. from the make-up torque-turn number curve respectively;

[0040] S3, respectively calculating the cumulative values ​​of the friction factors of the shackle F11, F12, F13, etc. from the shackle torque-turn number curve;

[0041] The cumulative value F of the friction factor of the shackle is calculated as follows:

[0042] F=∫TΔr

[0043] Where, T is the torque value of the ordinate in the shackle torque-turns curve, and r is the circle value of the abscissa in the shackle torque-turns curve;

[0044] S4, repeating steps S1 to S3 using the thread compound to be tested, and obtaining the make-up inflection point torques Ts21, Ts22, Ts23, ... in the make-up torque-turns curve, and the cumulative values ​​of the breakaway friction factors F21, F22, F23, ... in the breakaway torque-turns curve;

[0045] S5. Calculate the relative lubrication coefficient Fs according to the cumulative value factor weight α of the shackle friction factor and the weight β of the make-up inflection point torque factor. The relative lubrication coefficient Fs is calculated as follows:

[0046]

[0047] The weight α of the cumulative value of the friction factor of the shackle and the weight β of the torque factor of the make-up inflection point are variables, which are essentially weighted factors of the cumulative value of the friction factor and the torque factor of the make-up inflection point, depending on the actual situation, such as the type and model of the thread grease;

[0048] S6. Calculate the adjustment torque Tn and finally obtain the make-up torque Tf, which is calculated as follows:

[0049] Tn=Tf*Fs

[0050] The adjustment torque Tn is the optimal make-up torque Tf for the thread grease.

[0051] Example

[0052] Select the commonly used thread compound A as the basic thread compound, and repeat the make-up operation on a certain type of special thread joint for five times to obtain its make-up and make-out torque curves, as shown in the figure. Figure 2 As shown in the figure, the make-up torque Tf of this type of special threaded joint based on thread compound A during make-up operation is 3500Nm.

[0053] Select the thread compound B to be tested, repeat the make-up operation on this special thread joint for five times, and obtain its make-up and make-out torque curves, as shown in Figure 2. Figure 3 shown.

[0054] Respectively from Figure 2 , Figure 3 The relevant parameters Ts, F and other parameters are calculated, and the calculation results are shown in Table 1 and Table 2.

[0055] Table 1 Test data of basic thread compound A on the shackle

[0056]

[0057] Table 2 Test data of thread compound B on the unfastening test

[0058]

[0059] Taking the cumulative value of the friction factor of the shackle as 0.7, taking the weight of the torque factor of the make-up inflection point as 0.3, the relative lubrication coefficient Fs of the tested thread grease B relative to the basic thread grease A is calculated as follows:

[0060]

[0061] Considering that the make-up torque Tf of this type of special threaded joint based on thread compound A is 3500Nm, the make-up torque of this type of special threaded joint based on the thread compound B to be tested should be

[0062] Tn=Tf*Fs=3500×1.34=4690Nm.

[0063] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for evaluating the lubrication properties of thread grease, characterized in that: By quantitatively evaluating the friction coefficient of the thread grease, the relative lubrication coefficient Fs of the thread grease is obtained, and the relative lubrication coefficient Fs is applied to the setting of the make-up torque Tf of the oil casing threaded joint. The thread greases with different relative lubrication coefficients Fs are used to set the corresponding make-up torque Tf to achieve the control of the threading of the oil casing threaded joint.

2. The method for evaluating the lubrication properties of thread grease according to claim 1, characterized in that: The lubrication characteristics evaluation method specifically comprises the following steps: S1. Repeat the make-up and break-out operations on the threaded joint in sequence for multiple times according to the make-up torque Tf using basic thread compound to obtain a make-up torque-turn number curve and a break-out torque-turn number curve; S2, reading the make-up inflection point torques Ts11, Ts12, Ts13, ... from the make-up torque-turn number curve respectively; S3, respectively calculating the cumulative values ​​of the friction factors of the shackle F11, F12, F13, ... from the shackle torque-turn number curve; S4, repeating steps S1 to S3 using the thread compound to be tested, and obtaining the make-up inflection point torques Ts21, Ts22, Ts23, ... in the make-up torque-turns curve, and the cumulative values ​​of the break-out friction factors F21, F22, F23, ... in the break-out torque-turns curve; S5, calculating the relative lubrication coefficient Fs according to the cumulative value factor weight α of the shackle friction factor and the make-up inflection point torque factor weight β, wherein the sum of α and β is 1; S6. Calculate and adjust the torque Tn, and finally obtain the make-up torque Tf.

3. The method for evaluating the lubrication characteristics of thread grease according to claim 2, characterized in that: In step S3, the cumulative value F of the friction factor of the shackle is calculated as follows: F=∫TΔr Where T is the torque value of the ordinate in the shackle torque-turns curve, and r is the circle value of the abscissa in the shackle torque-turns curve.

4. The method for evaluating the lubrication characteristics of thread grease according to claim 2, characterized in that: In step S5, the relative lubrication coefficient Fs is calculated as follows:

5. The method for evaluating the lubrication characteristics of thread grease according to claim 4, characterized in that: The cumulative value factor weight α of the shackle friction factor is set to 0.7, and the make-up inflection point torque factor weight β is set to 0.

3.

6. The method for evaluating the lubrication characteristics of thread grease according to claim 2, characterized in that: In step S6, the adjustment torque Tn is calculated as follows: Tn=Tf*Fs.

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