China's major oil fields have long suffered from theft of crude oil at the wellhead, the dismantling of wellhead equipment, and major fire accidents caused by theft of oil and gas. Although the relevant departments have taken some precautionary measures, they cannot effectively stop these phenomena. To this end, the author strives to effectively solve this problem from a technical point of view.
Through many investigations and researches, it is found that there are mainly the following situations: stealing the wellhead crude oil: one is to open the wellhead's sampling stop valve to steal crude oil; the other is to close the relevant valve on the wellhead, resulting in Rolling, fracturing the seal until the wellhead spills oil, stealing the oil on the floor; stealing the crude oil on the tanker - the thief opens the gate valve to steal the crude oil; disassembles the fasteners of the wellhead device, steals the gate valve, clamps, bolts And other parts; disassemble the valve parts: remove the valve cover, hand wheel, steal copper valve core and so on.
From the above analysis, the problem arises in fasteners and valves. The use of conventional gate valves and the removal of fasteners are convenient, and the disadvantages are also here. In order to solve the stolen crude oil, various wellhead anti-theft valves have been developed in various oil fields. In view of the actual situation of the oilfield, the author has carefully designed a highly practical nut anti-disassembly mechanism. According to this principle, a series of anti-theft products with digital passwords, such as K-inch globe valve and 25MPa gate valve, are used. In some occasions with special requirements, such as oil wells and pipelines in the field.
The mechanism analysis and the installation of the nut anti-disassembly mechanism are shown below. The following is an introduction to the key bushings and round nuts: (1) The bushings are as shown, the bushings are provided with a step in the axial direction and a belt in the radial direction. The threaded hole of the step, the small threaded shaft can be screwed in or retracted in the threaded hole, but cannot be unscrewed (some measures are taken at the end of the hole). The end face of the sleeve is equally divided and has a rotary scale mark. The small step shaft of the bushing has a small thread of 1 thread in the radial direction; 2 round nut; 3 - stud bolt; 4 - bushing (2) The outer circle of the round nut is designed as a stepped shape of a certain length, the outer circle and The bushing is a clearance fit; the inner hole of the round nut is threaded and coupled with the bolt to transmit the force; the outer circumference of the round nut is also provided with a small L, which is matched with the small diameter of the small shaft of the thread; the round nut is set on the length thereof. There is a uniform scale and length mark, and there is a “0†scale on the end face.
Assembly process: 1 threaded small shaft is mounted on the sleeve. The method is to align the small shaft of the thread with the threaded hole of the sleeve through the inner hole of the sleeve, and then screw the small shaft through a special tool until it stops rotating; 2 install the round nut in the sleeve; 3 align the scale . According to the pre-designed axial scale and radial scale, rotate and move the sleeve to align the two sets of scales; 4 Use a special tool to rotate the small shaft to screw the shaft end of the small shaft into the small hole of the round nut. 5; Use ordinary wrench or pipe wrench to screw the bushing, the torque is transmitted from the bushing to the small shaft of the thread, and then transmitted to the round nut until it is tightened; 6 revolve the small shaft and rotate and move the bushing at will, At this time, if the sleeve is rotated, no matter how much torque is used, the sleeve is idling, and the round nut does not follow the rotation, so as to achieve the purpose of not being disassembled.
Disassembly process: It can be carried out in steps 4, 5 and 6 above.
The principle of the nut anti-disassembly mechanism can be directly used to produce fasteners in the form of clamp coupling, such as nuts and bolt mechanisms, and can also be used to improve valves, such as anti-theft type shut-off valves.
Modified anti-theft type shut-off valve The sampling valve of the conventional production wellhead usually adopts an inch stop valve, which consists of a valve body, a valve cover, a compression nut, a hand wheel, a pressure wheel, a pressure sleeve, a sealing ring, etc., and rotates the hand wheel to drive the valve stem. The upward rotation or the downward rotation movement completes the switching action of the shut-off valve, and the switch is convenient and free. Its anti-theft performance is mainly manifested in two aspects: 1 the cap is unloaded, the hand wheel and the compression nut can be easily removed, so that the various parts can be disassembled; 2 the hand wheel can be easily unscrewed or tightened. valve. Such a shut-off valve is installed on the well of the production well, and the anti-theft function is not obtained at all.
The anti-theft type shut-off valve structure is as shown.
This is mainly due to the difference in the structure of the valve stem and the handwheel.
The improved stem has a graduated logo. The valve stem body is marked with a length mark in the axial direction. The front and rear ends of the logo are provided with riveting pins and cover pins. They are assembled after the hand wheel assembly is assembled, and the purpose is two points: one is to prevent the compression nut and the hand wheel. The assembly is removed from the top of the valve stem; the second is to ensure that the handwheel assembly moves between the cover pin and the rivet pin to align the code and open the shutoff valve. The "0" on the circumference of the cover pin is provided with the word "0", which corresponds to the scale on the handwheel assembly. In addition, a small hole is drilled in the valve stem to match the small shaft of the thread.
The improved hand wheel and bushing are integrated and evenly engraved with a scale mark on the end face, and the length direction is engraved with the word “0â€, which corresponds to the axial dimension of the valve stem; and the hand wheel assembly is threaded. The hole, the small threaded shaft can be screwed in or retracted inside, but as long as the shut-off valve is always installed, it is difficult for the small shaft to completely withdraw from the threaded hole. The main purpose is to prevent the small shaft of the thread from being unscrewed and to see the small hole in the valve stem from the small hole, so as to find a way to open the shut-off valve. In order to open or close the shut-off valve, only rotate and move the handwheel assembly, and correctly align one of its radial marks and the axial “0†scale word with the radial “0†scale and axial direction of the valve stem. After a certain scale is marked, the small thread can be screwed into the small hole of the valve stem by a special small tool, and then the handwheel can be turned to open or close the shut-off valve, thereby effectively preventing the shut-off valve from being opened arbitrarily.
On-site application situation In 2002, the clamp bolts of 20 oil wells with serious oil stealing in Jiangsu oilfield were modified. The modified wellhead fasteners were never disassembled and achieved initial results, but there are still sampling stop valves. The problem of stealing oil, after the sampling valve was changed to the anti-theft type shut-off valve, it was gradually modified to the remote oil wells. In the Jiangsu oil field, the oil wells in 2a were no longer stolen, and the expected results were received.
It is convenient and convenient to modify the clamps and bolts of the old wells. It only needs to be disassembled normally; however, since the sampling valve is welded on the oil pipeline, the hot fire should be strictly in accordance with the requirements of the hot fire report, so the cost of the base layer is increased. This problem does not exist if the new wellhead can be directly used with an anti-theft shut-off valve.
Summary (1) The nut anti-disassembly mechanism is mainly characterized by a digital scale password and a concealed disassembly structure, which has a good anti-disassembly and anti-theft function. It has two sets of digital codes in the axial and radial directions. These two sets of numbers are determined during the design and processing, and the user only knows (down to page 64) the flow voltage output signal. When the mass concentration of flammable gas reaches 20% of the minimum explosion range, the system will give an audible and visual alarm prompt; when the mass concentration reaches 40%, the system will automatically turn off the power supply.
The sensor measurement range is 0~99LEL linear output 4~20mA current signal, and the output signal is sent to the system control circuit in the explosion-proof controller. After the detector has been working for a long time, it will cause signal drift, and it needs to be corrected regularly with a 30LEL propane cylinder gas sample.
Test and site use situation In October 2003, Zhonghai Oilfield Services Co., Ltd. and China Classification Society on the sealing performance of positive pressure explosion-proof logging towed, automatic control of the stability and reliability of the positive pressure positive pressure equipment, and various The sensitivity and reliability of the pressure and flammable and explosive gas detection and alarm devices were tested and approved by China Classification Society.
Sealing performance test of positive pressure explosion-proof skid 121 Check the sealing performance of each electric, gas and liquid pipeline through hole as required, close the escape door, close the isolation room and the operation door after confirmation, start the positive pressure equipment, and inject into the operation room. compressed gas. When the gas pressure reaches the highest pressure set by the pressure detecting device, the intake and exhaust valves are closed. After testing, the pressure retention time in the operation room is not lower than the set time. The stability and reliability of the positive pressure equipment. Start the explosion-proof blower, open the pressure test alarm device in the operation room, adjust the displacement of the air inlet to 100Lmin and adjust at the same time. The flow rate of the exhaust port ensures the positive pressure according to the design requirements. After 8 hours of continuous working time of the whole system, the indicators and parameters are normal.
Functional tests were performed on pressure sensors, audible and visual alarms, and flammable gas sensors to test their sensitivity and stability. The test results show that the indicators and parameters are normal.
Since 2003, the company has developed and produced the first positive pressure explosion-proof logging towed for the first time. It has been used on the drilling platforms of Bohai Sea 4, 5, 78 and 10, and all the indicators are normal, meeting the expected design requirements. .
Conclusion The explosion-proof logging trailer adopts a new explosion-proof safety system with reasonable structure and reliable performance. It meets the design technical requirements and has been tested in the field. It is highly praised by users. The explosion-proof skid circuit has stable performance and can meet the logging. The requirements of complex working conditions in the process; explosion-proof logging towed has been certified by China Classification Society and deserves to be promoted.
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