A METHOD TO EVALUATE THE DURABILITY OF SUCKER ROD PUMPS AND TO REDUCE CORROSIVE WEAR

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1 81 A METHOD TO EVALUATE THE DURABILITY OF SUCKER ROD PUMPS AND TO REDUCE CORROSIVE WEAR Razvan Geoge RIPEANU Petoleum-Gas Univesity of Ploiesti, ROMANIA apeanu@upg-ploiesti.o ABSTRACT The pape pesents expeimental tests made in stati and dynami onditions in ode to establish the wea laws fo diffeent mateials ouples at diffeent medium tempeatues and pessues. Some omplex wea laws wee obtained fo eah mateial ouple, depending on the medium tempeatue, the pessue and the omposition and the pump woking paametes, suh as the deep in well, the pumping veloity et. Beause even when it is hosen the best mateials ouple, the oosion still emains at a high value, it is pesented a method to edue the oosion wea using a galvani athodi potetion. With the wea laws obtained, it was eated an oiginal inteative ompute pogam depending on the pump type and the woking paametes, in ode to establish the pump lifetime. The esults obtained with the eated pogam wee onfimed by data fom the oil fields. Keywods: duability, od-pumps, ative anode, oosion, wea laws 1. INTRODUCTION In Romania oil-fields, the ude oil lifting is mainly made by deep-well pumping with piston od pumps. An impotant peentage of the damages of podution wells is aused by the pumps failue and the pump eliability depends on piston-ylinde and ball-valve ouple duability. Fo eamis ball-valve ouple, the pump eliability depends only on the piston-ylinde duability. The ude oil ontains an impotant quantity of highly minealized wate, ih gases with a geat peentage of CO, gains of sand fom petolifeous bed. The aveage peentage of impuities in the eovey fluid ises ontinuously in the time and epesents 60 90%, existing wells with 96 98% impuities [1]. Thus, a main failue ause of od-pumps is the abasive and oosive wea of the ouples piston-ylinde and valve age- ball. The piston slipping along the ylinde, is theoetially made, moe o less, in the pesene of a lubiating film. In fat, the film thikness is not onstant. It is possible that the piston slips dietly on the ylinde and the abasion wea is aompanied with an adhesion wea. The mateials fo piston and ylinde ae not adequate fo adhesion wea. The woking fluid also ontains sand. The quantity and the size of sand depend on the existene and the quality of the sand filte. Sand gains smalle than adial leaane pass though the piston and the ylinde and emove hips fom both sufaes. The fluids also have a stong oosive ation on the metalli mateials. The eleto-hemial eations geneate bittle and had ompounds. In stati onditions, these ompounds ealize a passivated oating. In dynami onditions, the tangential fition foe between the piston and the ylinde loally emoves the oxide oating. The oating eonstution needs time and sliding is ontinuous. The sufae without oating oxide is exposed to the oosive ation. The uent density on non-oated aeas, is muh bigge than that on the oated aeas. Unde these onditions, the oosion ate on nonoated aea is bigge. In onlusion, in the od-pumps with pistonylinde ouples, thee ae thee main wea types, namely abasive, oosive and adhesive. It esults that wea diminishing is possible by diminishing the oosive wea. In ode to edue the oosive wea, thee ae thee possible methods to apply [,, 4, 5]: - adequate mateials, with high oosion esistane; - eduing the fluid aggessiveness by oosion inhibitos; - eleto-hemial methods, suh as the athodi potetion. In ode to ise the woking life of the od pumps in abasive and oosive medium, it is eommended to use mateials with high hadness and oosion esistant as the had-homium plating steel fo the ylindes o the pistons, the abonitided and nitided

2 8 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI ylinde and the metalli abide layes type METCO fo pistons in ode to esist at heavy duty onditions. The pupose of this pape is to pesent the methodology used fo establishing wea laws in ode to pedit the piston-ylinde duability and also to pesent the athodi potetion method with ative anode. onneting-od assembly 6, moved by an eleti moto 11. The piston-ylinde system is ompletely immesed in the fomation wate kept in a tank 9. In ode to maintain the sand in suspension, thee is a punhed plate 10.. EXPERIMENTAL RESULTS The samples wee pepaed fom the eal pistons and ylindes in ode to detemine the stati oosive wea. The speimens wee immesed in hloal-alium type fomation wate [, ]. The testing onditions to detemine the oosion ate in the pesene and without the ative anode, wee: - tempeatue 0, 0, 40 and 50 0 C, espetively, - atmosphei pessue with and without CO, - pessue of CO :,, 4 and 5 MPa, espetively. Table 1 pesents the oosion ate esults fo the ouple metal spayed piston with nitated ylinde, in Fig. 1. The inemati diagam of the testing devie the absene of the ative anode []. Simila esults wee obtained fo ouples metalspayed piston ylindes made of abonitided and Fo these wea tests, it was used some fomation wate with % sand, fom the od pumps, with the had-homium plated steels [1,, ]. gain size smalle than 6 m. The wea abasion poess was investigated on a The testing onditions wee: testing mahine designed and ompleted fo that - able load, 50N; pupose. Figue 1 pesents the inemati diagam of - numbe of double stokes pe minutes, 54; the devie. On vetial od 1 is fixed the sample type - tempeatue, 0 C; piston. The sample type ylinde, slotted, is - babotage of CO ; tightened on the piston with a flexible able 4, - mateials ouple: the piston: metal spayed, the tensioned with a weight set 5. The altenative ylinde: homium plated, abonitided, nitided. movement of the piston is povided by the ank and Table 1. The oosion ate fo the ouple piston metal spayed- nitided ylinde Test onditions Mass loss, mg Coosion ate, g/(m h) Tempeatue, o C Pessue CO, MPa Time, h Piston Cylinde Piston Cylinde babotage babotage babotage babotage

3 8 Table pesents the piston-ylinde wea esults with CO babotage [1, ]. Table. The piston-ylinde wea Wea, mg Mateials ouple Piston / Cylinde Piston Cylinde 15' 0' 45' 60' Chomium 5./ / /9.5 1./10. Metal Spayed plated Cabonitided 6.4/9.4 8./ / /19. Nitided 6.1/ / /1. 9.1/14.5 In ode to have a fixed expeimental load, the pessue between the piston and the ylinde is alulated, as in the eal onditions, fo a pump and a ude oil type [6]: 90 vm N p, N/m (1) f j whee: is the dynami fluid visosity, Pa.s; v m the piston aveage speed, m/s; S n v m () 0 whee: S the piston stoke, m, n the numbe of double stokes pe minutes, f the fition oeffiient, N the load, N, j the adial leaane, m. Analyzing the oosion expeimental esults with the CuveExpet pogam a oelation between oosion ate and tempeatue, was established []: v o d p, p, t a b e, g/m h () p, p, whee: a p,, b p,, p,, d p, ae oeffiients depending on the piston ( p) and the ylinde ( ) mateials ouple and on the testing onditions []. Fo the CO pessue, it was establish a oelation suh as: 4 v a b p p d p e, g/m h (4) o p, p, p, p, p, p whee a p,, b p,, p,, d p,, e p, ae oeffiients depending on the piston ( p) and the ylinde ( ) mateials ouple and on the testing onditions []. Analyzing the oosion expeimental esults with the DataFit pogam, it was established a elation fo oosion ate as a funtion of tempeatue and of CO pessue: v o =a+b/x 1 +x +d/x 1 +ex +fx /x 1, g/m h (5) whee: a, b,, d, e, f ae oeffiients depending on the mateials ouples; x 1 the tempeatue, 0 C, x the CO pessue, ba. Figue shows the vaiation of the oosion ate vesus tempeatue and CO pessue, fo nitided ylinde in the ouple with metal-spayed piston. Fo all mateials ouples, the elation (5) leads to adequate esults. The multiple detemination oeffiient, R is geate than Analyzing the wea esults with the DataFit pogam, a elation was established: a x b (6) u p, p, p, whee u p, is the piston and ylinde wea, espetively, mg; x- time, min.; a p,, b p, - oeffiients depending on the piston ( p) and the ylinde ( ) mateials ouple and on testing onditions []. Fig.. The oosion ate vaiation vesus the tempeatue and the CO pessue, fo the nitided ylinde Figue pesents the wea vaiation vesus time fo the nitided ylinde in ouple with a metalspayed piston []. Fo this mateials ouple, the elation (6) has R = Fig.. The wea fo the nitided ylinde in ouple with a metal-spayed piston. EVALUATION OF PISTON- CYLINDER DURABILITY In ode to evaluate the piston-ylinde life time, the autho puts the ondition to obtain a minimum sufae pumping effiieny of =0.65 [6]. Taking into aount this ondition, fo example, fo a od pump type RH 7/8 x 1 ¾ x 1ft, the piston-ylinde effiieny is []: p = (7) whee: = is the stokes effiieny, sm sf

4 84 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI sm =0.746 the tavelling valve effiieny, sf = the standing valve effiieny. The pump ate leakage elation is []: 4 d N H Qp jmax, m /4h (8) l whee: is the inemati visosity, St. The umulate linea wea of the piston and the ylinde must not ovepass a etain value, h max : h max j max -j i, mm (9) whee: h max is the umulate linea wea, mm, j max the maximum leaane between the piston and the ylinde, mm, j i the initial leaane, mm. Aoding to the test ondition fo a oosive and abasive medium, the initial leaane is eommended j i =50m and thus, fom elations (7), (8), (9) it esults h max =97m. h max = h p + h, mm (10) whee: h p is linea piston wea: u p vm, p h p A v 10, mm (11) p fp p m, pex h the linea ylinde wea: u v m, p h 10, mm (1) A v f m, pex u p, u the gavimeti piston and ylinde wea, espetively, mg; p, the sufae piston and ylinde density, espetively, kg/m ; A fp, A f fition aea fo piston, ylinde, m ; v m,p the aveage pump piston speed: C n vm, p, m/s (1) 0 v m,pex aveage expeimental piston speed, simila as elation (1); C the effetive piston stoke [6]: C k C, m (14) k the oveload oeffiient, [6]:.7 H n k 1 (15) the od sting extension [6]: = H, m (16) the extension oeffiient, m/m ; H depth of pump, m; n, n ex double stoke pe. min. at pumping unit, espetive expeimental; l p piston woking length, m; C sufae stoke, m. Replaing u p and u with elation (6) in the elations (11) and (1) and notati ng a pij, b pij the oeffiients fo the piston i in the ouple with the ylinde j and a ji, b ji the oeffiients fo the ylinde j in ouple with the piston i and all the vaiables in the elation (10), fo a time life x the following elation was obtained: Cex n b ex ij d N l p pi hmax 10 bpij C n j C 1 pi l p x aji a pij j C 1 pi l p (17) In ode to onside the tempeatue and the CO pessue influene on the piston-ylinde duability, it was defined the gavimeti wea index fo the piston i, whih woks with the ylinde j, as []: K upij =v upij 10 - /A pex. (18) whee: v upij is the gavimeti wea ate fo the piston i, whih woks with the ylinde j, mg/m h; A pex. piston aea at wea tests. In the same way it was defined K uji. Taking into aount that v opij / K upij =m pij =t. and v oji / K uji =m ji =t. whee: v opij, oji is the oosion ate depending on the tempeatue and the CO pessue, the elation (5) fo the piston i that woks with the ylinde j, and espetively, fo the ylinde I, whih woks with the piston j, it was obtained the oelation between the wea ate and the oosion ate []: vopij,oji t, pco Apex,ex 10 vupij,uji (19) m 60 Beause the wea ate epesents the wea deivative with time, the a pij, ji oeffiients fom the wea law, obtained afte expeimental tests, ae: a vopij,ojit,pco Apex,ex10, mg/min. (0) m CONCLUSIONS Based on many expeimental tests in laboatoy and on the infomation fom moe than 100 diffeent wells fom Romanian oil fields, the alulus methodology ould evaluate, with an eo smalle than 1%, the od pump lifetime taking into aount the piston ylinde mateials ouples, the tempeatue, the CO pessue, the deep of the pump, the numbe of double stokes pe minute at pumping unit, the sufae stoke and the od pump type. The athodi potetion with ative anode edues the oosion ate fo all mateial ouples. The athodi potetion effet depends on the mateial ouples and on the testing onditions.

5 85 The expeimental tests establish that the wea ises with the tempeatue, see the elations () and (5). The CO pessue influenes the wea, depending on the CO pessue value and the mateials ouples, see the elations (4) and (5). Beause in the CO pessue tests, it was used only CO gas, the CO pessue value is the same as the patial pessue of CO. The maximum oosion ate was obtained fo MPa CO pessue when the ondutivity of the tested fomation wate was maximum. REFERENCES 1. Ripeanu R.G., Tudo I., 00, Reseah egading downhole pumps wea whih woks in ude oil wells with high CO atio, The Annals of Univesity Dunăea de Jos of Galaţi, Fasile VIII, Tibology, pp Ripeanu R.G., 005, Establish the eliability of pistonylinde ouple of downhole pumps, Jounal of the Balkan Tibologial Assoiation, Ed. SiBulCom. Ltd, 11 (), pp Ripeanu R.G., 006, Establish the eliability of od-pumps us at deep- dill pumping, Poeedings of the 7 th Intenational Symposium INSYCONT 06, Caow, Polish Aademy of Siene, pp Tudo I., Ripeanu R.G., 005, Galvani athodi potetion influene fo diminishing wea in ooding medium, Jounal of the Balkan Tibologial Assoiation, Ed. SiBulCom. Ltd, 11 (), pp Ripeanu R.G., Tudo I., Dinu F., 009, Reseah about the effiieny of ative anode potetion at entifugal pumps, Jounal of the Balkan Tibologial Assoiation, Ed. SiBulCom. Ltd, 15 (), pp Pete N., Chitu-Militau N., 1986, Extatia titeiului pin pompaj u pajini (in Romanian), Ed. Tehnia., Buhaest, pp