Analysis of Jump-Out Loads about Connectors of Buttress and Round Threads of Casing

Transcription

1 nalysis of Jump-Out Loads about onnectors of uttress and Round Threads of asing Lian Zhanghua, Liu Yonggang, Tang o Southwest Petroleum Institute, P.R. Of hina Han Jianzeng, Zhang Yi Shanghai aoshan Iron & Steel co. LTD, P.R. Of hina Yang Long Tubular Goods Research enter of NP, P.R. Of hina bstract The finite element models of contact problems about connectors of buttress and round threads of casing were established with the elasto-plastic EM of NSYS software. Under the three flank angles 3 0, 5 0 and 10 0 for the buttress casing connector, the curves that the jump-out loads varied with the loading process were obtained. With the three tapers 1/14, 1/16 and 1/17, for the round casing connector, the curves that the jump-out loads varied with the loading process were obtained. t the same time, the jump-out process of the buttress and round thread connectors was studied, respectively. The average jump-out force of the buttress connector is ton, and however, the average jump-out force of the round connector is ton. That is to say, under the same casing and the same casing size, the connector of the buttress thread is not so easy to jump out, but the connector of the round thread is very easy to jump out. It provides the theoretical supports for the selection of the casing connectors in the extra-deep well and complex well. Introduction The casing standards of many countries (including hina) have been using PI (merica Petroleum Institute) standard. However, PI casing standards have not adapted to the requirements of some special type wells. The non-pi casing was developed by some Oil ompanies in the world to meet the requirements of the casing strength in the some special and complex wells. ccording to the statistics, there is one-third PI casing, one-third non-pi casing and one-third non-pi Premium onnections in the world. Two cases of non-pi casing were accepted: one is the size, steel grade and wall thickness of PI casing, but the thread of connection was special thread, such as the VM connection; another is to use the Premium steel grade to prevent the corrosion and high stress problems, but the size, wall thickness and connection are also PI standard. The gas seal of the PI thread connection is poor for the deep well and extra-deep well in the west hina, the failure of the connection thread was seriously jumped out. The study of the connection of the non-pi flank angle and non-pi taper in the paper was supported by the National Natural Science oundation of hina (No ) and by NP Innovation oundation, so as to develop the non PI connection of casing to adapt to the deep well and extra-deep well drilling in the west hina. The failure of the jump-out of the oil-gas well casing thread is one of the several failure types of casing, once the jump-out accident of casing connection occurs, it will cause the well to discard as useless and the big economic loss of the oil field. The literatures which studied the thread jump-out of casing are not many, some of them just researched the round thread of casing in testing and theory, but seldom studied the buttress thread of casing, and the literature 5 has proved that the elasto-plastic EM can substitute the real testing for simulating the process of the jump-out of the casing connection. So we used NSYS software to the analysis of the jump-out loads of the connection in the paper. The main factors that influenced the jump-out of casing connection: 1. The real connection strength of the casing is not enough; the taper of the casing end thread is disqualification. 2. The short round thread connection of low strength was selected, the thread mate of connection

2 was not at adequate position. 3. The speed of running casing at up and down live casing was too fast, the casing impacted the platform, and the big impact loads caused to the connection to jump out. 4. The out thread of casing was damaged, and the buckling torque was too big, and so on. rom the view of the several factors of connection jump-out above, some outer factors of them can be avoided, but some inner factors of them are the shape of the connection thread, the non-linear properties of the material and the contact condition between the threads. We analyzed the process of the connection jump-out by EM. The oil-gas casing pipes through the connections are usually connected one by one, and then run to the well. The casing string from the wellhead to several kilometer depths was hanged, each connection of casing must sustain the weight of the casing string itself below, and so the requirement of the high tensional strength of the connections is one of the important performances. The connection of casing will jump out if the load of the application on the connection obviously exceeds the design limit load, that is to say, the connection jumps out. Generally, the jump-out properties of the connection depend on the shape of thread, material performance, such as the flank angle, height, taper of thread, and the stress-strain curve of the material. EM Modeling The size of the EM model based on the basics size of the PI buttress and round thread connection, the casing size, P mm(9 5/8 ) 11.99mm. The leakage path of the buttress and round thread and their contact mate were shown as in igure 1. The finite element mechanics models of the buttress and round of the axial symmetry are shown as in igures 2 and 3, respectively. The models were meshed with 4-node element. The mate between the surfaces of the threads is contact element, the axial load applied on the casing end, the fixed constraint applied on the connection end. The contact problem of the connection belongs to large deformation, so the stress-strain curve of the grate P110 casing material was obtained by testing, shown as in igure 4. D E onnection I J P asing G H HIJ-leakage path; DE GH-tightly contact surface; E-flank angle surface; a. uttress connection onnection D asing E P,D,E-leakage path;,de-tightly contact surface; b. Round connection igure 1. leakage path and contact surfaces of buttress and round connections of the casing

3 onnection entral line asing Local magnified igure 2. E Model of uttress thread onnection entral line asing Local magnified igure 3. E Model of Round thread

4 stress(mpa) P strain igure 4. P110 asing stress-strain test curve nalysis of jump-out loads about the buttress connection The finite element model of the buttress shown as in igure 2, the load was gradually applied on the casing so as to make the casing gradually jump out of the connection, three flank angles of thread were studied, the flank angle is the angle between the E surface and the plane which is vertical the axis of the casing, shown as in igure 1a. igure 5 is the jump-out curves of the thread which the jump-out loads three flank angles are 3, 5 and 10, respectively. The flank angle 3 is the PI standard angle lank angle 3 0 xial orce(ton) D Load step 5 0 E G igure 5. urves of the jump-out E simulation of the buttress connection The load support capability of the connection thread with the flank angle 3 is biggest, about 600 ton, then with the flank angle 5, and that of the connection with the flank angle 10 is smallest, jumped out at D point in igure 5. Three cases in igure 5, the maximum load is at, the threads will jump out if the axial load of the casing exceeds the load value at. The load curve with 3 0 mostly keeps unchanged to the point when the load is gradually increasing, and then the connection G quickly jumped out. Similarly, the load curves with 5 0 and 10 0 provided the jump-out procedure. The initial jump-out loads of the three flank angles are 3, 5 and 10 were obtained, 607ton, 599ton and 575ton, respectively. The jumpout load decreased with the increment of the flank angle. The simulating procedures are shown as igures 6-8.

5 Von Mises 应力 (MPa) S_Max =571t =606t =607.6t =587.6t =494.6t =426.0t =138.5t S_Max=802 S_Max=850 S_Max=928 S_Max=1064 S_Max=1066 S_Max=1080 S_Max=1150 (1) (2) (3) (4) (5) (6) (7) igure 6. lank angle 3 0, von Mises stress, Red-plastic zone. Jump-out E simulation of the buttress connection Von Mises 应力 (MPa) S_Max =564t =599.2t =592.3t =553.8t S_Max=804 S_Max=848 S_Max=941 S_Max=1154 (1) (2) (3) (4) igure 7. lank angle 5 0, von Mises stress, Red-plastic zone. Jump-out E simulation of the buttress connection Von Mises 应力 (MPa) S_Max =564.2t =575.5t =542.4t =394.0t =134.3t S_Max=778 S_Max=815 S_Max=1000 S_Max=1258 S_Max=888 (1) (2) (3) (4) (5) igure 8. lank angle 10 0, von Mises stress, Red-plastic zone. Jump-out E simulation of the buttress connection

6 nalysis of jump-out loads about the round connection or contrast analysis of the jump-out mechanism and load support capability between the buttress and the round, the simulation analysis of the jump-out process of the round was presented in this paper, the round thread E model is in igure 3, the axial load of the casing was gradually increased in the study, and the jump-out procedure of the round thread was directly observed and studied. Three tapers 1/14, 1/16 and 1/17 of the round thread were simulated with EM software NSYS, the taper 1/16 is PI standard, the results are shown as igure 9, the jump-out loads of the round connection were gradually decreased with the increment of the thread tapers. The jump-out loads of the tapers 1/14, 1/16 and 1/17 are about 320ton, 348ton and 359.5ton. The conclusion: under the condition of the requirement to meet the taper structure, the thread taper degrees are as less as possible Taper degree 1/17 1/16 xial orce(ton) / Load step igure 9. Three tapers 1/14,1/16 and 1/17. Jump-out E simulation of the round connection y contrast of the jump-out loads between igures 9 and 5, the average jump-out load of the buttress and the round are 594.1ton and 342.5ton, respectively. t the same structure size, the jump-out load of the buttress is more 251.6ton than that of the round, that is to say, the buttress is not much easier to jump out than the round. Hence, the buttress casing connection was suggested to the depth well, extra depth well and complex well so as to prevent the jump-out failure of the connection. or example, in the west hina oil filed, some well 5638m depth, casing 9 5 / mm P110, mud weight 1.2. When the whole well was filled with mud and no mud, the maximum axial load of the casing at the wellhead that was calculated was 326.5ton and ton, respectively, namely, the axial load of the casing at the near wellhead is the range from to ton. The round thread casing will very probably jump out, the average jump-out load is about 342.5ton in the result of the paper, but the buttress casing will not jump out because the average jump-out load is 594.1ton, which exceeds the range of the maximum load of the well. So the casing connections have not other problems, such as quality, material problem and so on, the buttress connection will not jump out in the west hina oil filed. rom the prevention of the connection jump-out mechanism, the casing of the buttress should be extensively used in the oil filed. onclusion Through the analysis of the elasto-plastic EM of the jump-out loads of the buttress and the round thread connections, the conclusion was obtained as follows:

7 1. The elasto-plastic E models of the contact problem of the buttress and the round connections are convenient to simulate the jump-out procedure of the casing connection. 2. or the buttress thread, the jump-out loads on the casing connection will decrease with the incensement of the flank angle, namely, the connection is more easily jumped out. 3. or the round thread, the jump-out loads of the round connection were gradually decreased with the increment of the thread tapers. Under the condition of the requirement to meet the taper structure, the thread taper degrees are as less as possible. 4. The average jump-out load of the buttress and the round are 594.1ton and 342.5ton, respectively. t the same structure size, the jump-out load of the buttress is more 251.6ton than that of the round, that is to say, the buttress is not much easier to jump out than the round. 5. rom the prevention of the connection jump-out mechanism, the casing of the buttress should be extensively used in the oil filed. 6. The study of the paper provided the theory supports for the selection of the casing string of the depth well, extra depth well and complex well so as to prevent its jump-out failure. References 1. Wang Li, hen Zhaoxiong, Tong Deshun. inite element simulation about the casing connection jump-out failure. eijing Science and Technology Journal. 2001, 23(2): Wang Zhiguo, Liu uqing, Tang Haoqing. Discuss of the reasonable torque about the PI round thread casing. ao Steel Technology. 2001, (2): Wang Li, Zhang Ruxin, Liu Yuwen. Mechanical property test study of the PI round thread casing. ao Steel Technology. 2000, (4): Shi Jiaoqi, Han Xinli, Zhao Kefeng. Study of the buttress thread of casing in the extra well. Petroleum Machinery. 1998, 26(11): * This paper was supported by hina National Science oundation (Project No ) and Supported by NP Innovation oundation.