New Controllable Downhole Throttler Based on Virtual Computer Technology Meng-Ren WU 1, Meng-Xin Li 1, De-Wan Ding 1,Yuan Gao 1, Hou-qinZhou 1 1Chongqing University of Science & Technology, Chongqing, China Abstract During the replacement of gas nozzle, the most commonly used downhole throttler of gas wells can only be finished through the repeated fishing or tubing string lifting. The principle of the current throttler structure was analyzed in the paper and its key parts were improved. Then anew controllable downhole throttler was devised through the application of the mechanical self-locking principle and by means of simulation modeling in the computer software. And only by the fast switch of the gas nozzle accomplished by the switch of the new throttle, can the long reasonable allocation cycle of previous throttlers and the rapid switch of working systems of testing wells be solved. Keywords - Gas Well; Downhole Throttle; Adjustable Throttler; Virtual Computer Technology I. INTRODUCTION The energy of natural gas is explored in an increasing speed in recent years. And the exploited natural gas was transferred to gas hydrates in the process due to the downhole pressure and temperature changes in the gas wells. Therefore, wellbore, pipes, valves and equipment were clogged and the normal operation of natural gas exploration would be thereby affected, thus generating enormous damage to the production of gas wells. In order to prevent hydrate formation, the downhole throttling technique was applied in more gas wells. Downhole throttling process is a technique, through the installation of a throttle in the appropriate location of a wellbore, to realize the throttling and depressurization within the wellbore. By the transmission of the ground throttling process into the wellbore, the technique employs the thermal energy in the stratum to heat the low-temperature natural gas after the throttling. Therefore, the throttling pressure and temperature of hydrates can be reduced, andthe formation of hydrate plugs can be prevented. Meanwhile, the security of the gas gathering and transportation system is improved and the producing and operating costs are reduced. The existing practical throttlers at home and abroad can be roughly divided into movable and stationary types in accordance with their effects and characteristics. And the movable downhole throttler is widely used currently, whose most common types are HY-4 differential pressure throttler and CQX throttler. As a movable downhole tool, HY-4 differential pressure throttler has applied the compression force setting of the air bag. Directing at the wellhead pressure of the gas field, the compression force of the air bag can be reached 0.8 to 1.2 tons within the throttler, which is far greater than the spring force. The higher the well pressure is, the larger the compression force of the rubber packer and the tighter the setting will be. In the operation, the delivery mechanism is firstly assembled with the throttler, which is put in the design position at the normal speed of no more than 60m/min. The overshot pin of the HY-4 throttler is broken, and the throttler falls into the well easily, thus causing accidents and disabling the continuous fishing of the throttler. Hence, it needs to be put again. CQX throttler, as a new movable downhole device, has employed steel wire for putting and fishing. When the throttler is placed under the setting depth, the unlocking shaft is raised and stretched through lifting up, so that the slips could be fixated on the inner wall of the pipeline. Then the shaft is released gradually. Under the tension less than 50KG, the axis is lifted rapidly, the connecting pin is cut, and the sealed rubber packer is stretched to open the setting, thus realizing two progressive levels of packer sealing by both the spring and air-flow differential. The non-retraction is appeared in the sealed rubber packer during the fishing of CQX throttler, which continues to contact with the oil pipe wall and generate the considerable friction. Due to strict requirements for high temperature, high pressure, corrosion and other factors, the sealed rubber packer is difficult to be put into the deeper wells and the fishing line is easily broken. Stationary downhole throttlers are characterized with the effectiveness and reduced pressure demand for the tubing strings above the throttler and ground pipelines; besides, without a rubber packer and not limited by pressure, and temperature, etc., it can be put into any depth of the well. The fishing operation of the movable throttler is difficult, usually appearing fishing failure; and poor sand-proof performance results in the severe sand burial of all gas wells [1-8]. In order to solve problems of existing throttlers, the novel downhole throttler can achieve the automatic dimeter change of its gas nozzle at the wellhead, reduce the number of tubing strings operation and reduce its abrasion by means of the stratum conditions, oil casting pressure and other parameters, thus declining the cost. II. THEORY [9,10] The bevel A and object B, as shown below, are placed on the same vertical plane. Then the top of object B is exposed to pressure F, whose stress analysis is shown as Fig. 1: DOI 10.5013/IJSSST.a.16.1B.06 6.1 ISSN: 1473-804x online, 1473-8031 print
main active force has the line of action out of the friction angle, the object is impossible to be balanced however small the force Q is. The equilibrium conditions related to the friction angle rather than force amount is called self-locking conditions. Under such circumstance, the equilibrium phenomenon of an object is named as the self-locking situation. As static friction force is unable to exceed the maximum value, the line of action of the full constraining force cannot exceed the friction angle. That is to say, the constraining force must be within the friction angle. It thus can be seen that: If the resultant force acting on the main active force of the object has the line of action within the friction angle, the object is remained stationary however big the force, which is called self-locking condition. As the angle between the resultant force of the main active force and the normal force is smaller than the friction angle under such circumstance, the resultant force of the main active force must have the line of action within the friction angle, and the line of action of its full constraining force is also within this friction angle. The equilibrium conditions can be achieved by the resultant force of the main active force and the full constraining force, as shown in Fig.2. Therefore, the object is stationary. Fig.1 Analysis of Stresses Wherein, Nab = Fcosθ; Maximum frictional force of the bevel is: When A and B are about to conduct relative sliding, the bevel, compared to A, is: Namely: If <, no relative sliding would be occurred on neither A nor B regardless of the amount of axial force F. Only when >, object B would slide upward slantingly corresponding to object B. Namely, if the resultant force Q acting on the main active force of the object has the line of action within the friction angle, the force Q, however big it is, will always be balanced with a full reaction force R so as to keep the object stationary; on the contrary, if the resultant force Q of the Fig.2 Self-locking phenomenon If the resultant force of all main active forces has the line of action out of the friction angle, the object must slide however small the force Q is. As the resultant force of all main active forces has already had the line of action out of the friction angle under such circumstance, and the line of action of its full constraining force is unable to be out of the friction angle. Therefore, the equilibrium conditions can be DOI 10.5013/IJSSST.a.16.1B.06 6.2 ISSN: 1473-804x online, 1473-8031 print
achieved by these two forces, as shown in Fig.3, and the object cannot be stationary. Hence, the self-locking phenomenon can be attempted to be avoided in the application of this principle. Fig.5 upper body The upper body and gas nozzle can be found in Fig.5. The gas nozzle with four different diameters (four working systems) is presented, and an annular array of grooves and helical tooth can be seen at its edge. Fig.3 Anti-self-locking phenomenon Fig.6 valves III. TECHNICAL ANALYSIS A. Structure Concerning the structure, the new throttler is mainly made up of: upper body, helical tooth, gas nozzle, bumps, grooves, gaskets, valves and lower body, whose structure is shown in Fig.4: The valve, whose structure shown as Fig.6, can be found its duct with the inner diameter larger than the largest diameter of the gas nozzle and an annular array with raised tines corresponding to the upper body. 1- upper body; 2 - gas nozzle; 2a- helical tooth; 2b- groove II; 3- elastic gasket; 4- valve; 4a- bumps; 5- small gasket; 6- lower body Fig.4 Schematic diagram of the structure of the new throttle Fig.7 Lower body As seen in Fig.7, the inner wall regarding the lower body of the device is featured with an annular array of raised helical tooth corresponding to the valve. DOI 10.5013/IJSSST.a.16.1B.06 6.3 ISSN: 1473-804x online, 1473-8031 print
B. Material Selection [11] Compared with traditional throttlers, the new throttler is produced by more excellent materials. Its rubber packer is made by high-polymer fluorine rubber, which is resistant to high temperature and high pressure and is more suitable for the environment of natural gas and organic liquids (oil, fuel and solution). High-quality carbon steel is applied in rigid materials and alloy steel is employed in valves. Both of them have been given tempering and high-frequency surface treatment. Hence, the optimal operation requirement can be reached concerning their surface roughness and hardness. bodies are fixed. And it rotates 90 o leftwards all together in the two processes of opening and closing the valves of the gas well, so as to allow the hole on the bottom of the valve to be aligned with the holes with four different diameters on the upper body bottom, thereby reaching the diameter to control the gas nozzle. Equivalently, the downhole throttle is carried out by gas nozzles with different diameters. Hence, the diameter of the gas nozzle can be adjusted by opening and closing valves. C. Main technical indicators [12] (1) Length: 336 mm; (2) Applicable outer diameter of the pipeline: 73 mm; (3) Differential pressure of the throttler: 50 MPa; (4) Applicable inner diameter of the pipeline: 59 mm; (5) Diameter range of the gas nozzle: 1.8-10mm. IV. WORKING PROCESS When the valve of the gas well is closed, valves are separated from the constraint of the groove under the action of its own weight and elastic gaskets. Therefore, the bumps on the valve and the helical tooth on the inner wall of the lower body act. Due to the anti-self-locking phenomenon, the valve is rotated 45o leftwards in the dropping process (as Fig.8). When valves fall to the bottom, the bumps at its edges just correspond to the helical tooth of the upper body. Fig.8 Working processwiththe closed valve When the valve of the gas well is opened, it operates upwards under the effect of the upward jacking of the airflow. Therefore, bumps at its edge are contacted with the helical tooth of the upper body. Due to the un-rotating and anti-self-locking phenomenon of the upper body, the valve is rotated 45o leftwards (as Fig.9), and bumps on the valve is entered into the groove of the upper body. As bumps out of the valve are constrained by the guide groove, the movement of the valve is stopped. The valve always rotates towards one direction because oblique directions of the helical tooth in the upper and lower Fig.9 Working process with the opened valve V. CONCLUSIONS (1) The transformation of gas nozzles with different specifications can be realized by this device. For such purpose, the movement of tubing strings is not necessary. However, the demand for the downhole conditions can be satisfied by merely switching on and off the valve of the gas well. Thus, the drawback of fishing operation in previous replacement of gas nozzles is changed, the number of operations is reduced, and the production efficiency is improved, thereby realizing the stable production better. (2) Fast switch of working system can be realized by this device in line with field application. (3) Complex circuits and communications are not involved in this device. It s featured with simple structure, easy operation, low production cost and strong adaptability to different reservoir characteristics. (4) The new throttler is adequate in adapting to working conditions under different pressures and shortening the working time, which has broad application prospects. REFERENCE [1] Zhou Xingfu, Yang Gongtian, Li Chun, et al, Design Method of Downhole Throttling Process forhigh-pressure Gas Wells,Drilling & Production Technology, vol.1,pp.57-59,2007. [2] SheZhaoyi, LiChuandong, Lei Zhenzhong, et al, Applications of Downhole Throttle Process in thedevelopment of Gas Wells, Drilling & Production Technology, vol.1,pp.69-73,2014. [3] Sun Hongbing, Yan Changqing, Li Xiandong, et al, Research and Application of Multi-Functional Throttler,China Petroleum Machinery, vol.3, pp.27-28, 2003. DOI 10.5013/IJSSST.a.16.1B.06 6.4 ISSN: 1473-804x online, 1473-8031 print
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