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Non-leakage sucker pump technology in lifting polymer viscoelastic fluid.

Annual oil output surpasses 10 million tons in Daqing Oilfield by using polymer flooding technology, serious eccentric wear to rod and tubing of pumping wells appears as the polymer is viscoelastic fluid. Almost 100% side wear phenomenon happens after polymer appears in polymer flooding wells, and more than 500 million RMB annual losses due to eccentric wear[1-2].

Analysis of eccentric wear mechanism [3]

During the process of sucking viscoelastic fluid, clearance between pump barrel and plunger, and rod tube flow passage lead to the increase of down resistance of the sucker rod, the resistance reduces gradually from the largest value at the bottom to the neutral point, which causes lateral force of the rod string, and results in partial wear.

Lateral force generated by the axial force, in addition to causing partial wear, also leads to the buckling of the rod string bottom that shortens the effective stroke of the pump and lowers pump and system efficiency. Normal force distributing on the whole rod string in polymer flooding well results in partial grinding, shortens the checking period and increases energy consumption.

Aiming at the problem of the above, non-leakage sucker pump is studied and designed in lifting containing polymer viscoelastic fluid to solve a big friction loss amount, extend the working life of the rod and tubing, and improve the efficiency of the pump.

Structure and principle of non-leakage pump[4-6]

Structure of non-leakage oil pump

Non-leakage oil pump is mainly made up of pump barrel, centralizer, plunger core, elastic sealing body, travelling valve and fixed valve (Figure 1), adopting composite seal mainly by hydraulic flexible seal, supplemented by wear self-liquidating, fully reducing leakage, improving the efficiency of the pump. Non-leakage oil pump's main sealing section made up of the elastic sealing body with hydraulic self- proclaimed principle make rigid gap between the ordinary pump plunger and pump barrel into the elastic gap. Sand or polymer particles between the plunger and pump barrel and the formation of the card pump trend, the elastic sealing body can produce a certain degree of elastic deformation, to avoid card pump, and to avoid the sand and polymer particles on the outer surface of the pump barrel and the seal ring damage, to extend the check period. Plunger seal segment reduced from 1200mm to 50mm to improve the effective stroke.

Disc spring centralizers are added on the both sides of non-leakage sucker pump to solve the partial abrasion between the plunger and pump barrel for the unilateral wear of sealing ring caused by the uneven force.

[FIGURE 1 OMITTED]

Working principle of non-leakage sucker pump

Working principle of non-leakage sucker pump is shown in figure 2, during the upstroke, the traveling valve is closed and the fixed valve on the bottom of the pump barrel is open, the pressure of plunger inner cavity is high, the pressure of pump barrel under the plunger is low, the outer of plunger is connected to pump barrel cavity, because of the pressure difference between inside and outside of the plunger, the elastic sealing body deforms and then swells outwards to the inside wall of pump barrel, forming good seal and making the leakage almost zero.

During the downstroke, the traveling valve opens, while the fixed valve at the bottom of the pump barrel closes, the pressures of plunger inner and outer cavity tend to be equal, the elastic sealing body gradually restitutes, causing clearance between pump barrel and plunger, making the downstroke resistance to be zero, and guaranteeing liquid lubrication to prolong the life of pump.

[FIGURE 2 OMITTED]

Mathematical model of pump operational mode

The clearance at the bottom of the plunger is [[delta].sub.1] the clearance at the top is [[delta].sub.2], which means that the clearance between pump barrel and plunger is convergent annular, the convergent cuneiform included angle is [alpha]; along the plunger length, the clearance of any point Z will be [delta] = [[delta].sub.2] - ztg[alpha] = [[delta].sub.2] - z ([[delta].sub.2] - [[delta].sub.1])/1. According to the clearance flooding theory, if the gravity is not taken into account, the speed u will be:

u = 1 / 2[mu] dp/dz ([delta] - y)y - (1 - y/[delta])[V.sub.0]

In this formula, u--fluid dynamic viscosity, Pa.s;

p--pressure of any point on the annular clearance, Pa;

[delta]--the clearance of Z along the plunger length, m;

l--the plunger length, m;

U--the average speed of plunger on the upstroke, m/s.

During the upstroke, the up and down pressure difference [DELTA]P = [P.sub.D] - [P.sub.I], the speed is U, and during the upstroke the liquid clearance leakage amount is the composition of the pressure differential flooding and shear flooding.

dq = udxdy = [[DELTA]p / 2[upsilon][rho]l ([delta]y - [y.sup.2]) - y/[delta] U]dxdy

Then the leakage amount between pump barrel and plunger is:

q = [pi]D[(1 + 3/2 [[epsilon].sup.2])[[delta].sup.3][DELTA]p/12[mu]l - U/2 [delta]]

In the above formula, q--the leakage amount, [m.sup.3]/s;

D--the diameter of plunger or pump barrel, m;

[epsilon]--relative eccentricity;

[DELTA]p--the up and down pressure difference of the plunger, Pa;

The plunger and pump barrel is concentric, e = 0; when the plunger is stable,

U = 0, then q = [pi]D [[delta].sup.3][DELTA]p/12[mu]l.

Laboratory Experiment

The leakage amount of hydraulic self-sealing plunger pump in different level of clearance under 10MPa is tested relatively by using these above experimental equipments (Figure 3-4), and then compares with the API standard of conventional pump. The testing results show (Figure 5) that under the same testing condition, along with the increase of pump leakage, the leakage amount of these two kinds of pumps and the disparity will gradually increase. Obviously, the leakage amount of hydraulic self-sealing plunger pump is lower than the conventional pump. When the leakage is between 0.1 and 0.15, the amount of leakage of non-leakage pump in lifting polymer viscoelastic fluid is many times lower than the American API SPEC 11AXBLAX standard; when the leakage is the same, the wear of the conventional plunger pump is bigger than non-leakage pump in lifting polymer viscoelastic fluid (Figure 6). The testing results show that this pump can decreases both the leakage amount and the mechanical wear.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

Field Applications

A non-leakage pump is applied in Daqing B2-P47 polymer flooding well, the concentration of polymer is 400mg/L, due to the influence of polymer adglutinate, the pump inspection cycle is just 187d, while the pump inspection cycle of non- leakage pump can be 532d, which means that the pump inspection cycle prolongs to be 345d, and the centralizer wear degree is light. Recently, compared with the conventional pump average data, the daily produced fluid increases from 134.4 t/d to 161.5 t/d; the producing fluid level increases from 207m to 296m, the pump efficiency increases from 87.45% to 89.84%, the maximum polished rod load decreases from 85.8 KN to 82.2 KN, the minimum polished rod load decreases from 29.5 KN to 25.6 KN, the systematical efficiency increases from 33.8% to 40%.

The concentration of polymer in Daqing oilfield B2-E73 well is 1127mg/L, the non-leakage pump is applied starting from November 2nd, 2010. Recently compared with the conventional pump average data, the daily produced fluid increases from 78.8 t/d to 99.4 t/d; the producing fluid level increases from 440m to 623m, the pump teoefficiency increases from 42.4% to 65.3%, the maximum polished rod load decreases from 74.2 KN to 72.3 KN, the minimum polished rod load decreases from 30.6 KN to 28.7 KN, the systematical efficiency increases from 78.3% to 87.5%, and this pump has worked for 200 days. Pump inspecting cycle of early polymer flooding testing wells is enhanced more than 200 days according to statistics, and the average pump efficiency has improved 21.2%.

[FIGURE 7 OMITTED]

Conclusions

1. Eccentric wear mechanism in polymer well is analyzed, hydraulic self-sealing non-leakage pump is designed according to hydraulic sealing theory; in order to solve the eccentric wear and original sealing efficiently, centralizer and original sealing ring are added to this pump.

2. The laboratory testing results show that compared with conventional pump, this pump reduces the leakage amount and mechanical friction.

3. Testing results in Daqing Oilfield site show that: compared with conventional oil pump, the partial wear and leakage in polymer flooding can be solved effectively, pump efficiency is improved significantly, system efficiency is enhanced greatly, and also this pump has long safety running cycle, and good market prospects.

References

[1] Demin Wang. Influence of the particularity of viscoelastic fluid on the reservoir engineering, ground engineering and production engineering[J].Jounal of Daqing Petroleum Institute 2001, 25(3):46-52.

[2] HAN Xiu-ting. Theory and application of sucker-rod pumping [M].Petroleum Industry Press, 2007:4-10.

[3] ZHENG Jun-de, LIU-He, YAN Xi-zhao, et, al. The polymer produced fluid flow in the gap of the pump[J]. Acta Petrolei Sinica, 2000,21(1) : 71-75.

[4] HAN Xiu-ting Han, WANG Xiu-ling, HOU-Yu, et al. Hydraulic self-sealing plunger pump[P]: China:200510082603.1, 2005-07-06.

[5] HAN Xiu-ting, LI Jun-liang, HAO Cheng-zhi, et al. Multi-support hydraulic self-sealing plunger pump[P]: China:200910072686.4,2009-08-07.

[6] LI Jun-liang, HAN Xiu-ting, CHENG Yuan-fang, et al. Research and application of hydraulic feedback and self-sealing efficient plunger pump.[J] Oil Drilling & Production Technology ,2008,30(6):97-99.

[7] LI Jun-liang. The Structural Optimization of Hydraulic and Self-sealing Plunger Pump[D]. Dongying : China University of Petroleum(East China), 2007.

Xu-Jinchao (1) Han-Xiuting (1,2), Li-Juhui (3) Han-mei (4) Li-Juan (1) Li- Xiaodong (1)

(1) School of Petroleum Engineering, China University of Petroleum, East China, Qingdao 266555, Shandong Province, China

(2) Research and Development Department, Daqing Oilfield Ltd. 163453, Heilongjiang Province, China

(3) Daqing Huachuang Electronics Co, Ltd. Daqing 163316, Heilongjiang Province, China

(4) Petroleum Engineering Department the University of Tulsa, Oklahoma, USA
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Author:Xu-Jinchao; Han-Xiuting; Li-Juhui; Han-mei; Li-Juan; Li-Xiaodong
Publication:International Journal of Petroleum Science and Technology
Date:Sep 1, 2012
Words:1683
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