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Copyright 2005, International Petroleum Technology Conference

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AbstractWith years of study and experiments, a complete series ofProgressive Cavity Pump (PCP) products has been developed.Sets of down-hole pumps for various rates and liftingcapacities were developed for water-flooding, polymer-flooding and ASP flooding areas according to the specifics.One of the newest techniques, a hollow rotor PC Pump, has

been applied in more than 800 wells. It has proved to be aneffective way in removing the wax build-up and reducingoperation cost. Another specially designed product was thesucker rod. By strengthening and redesigning the areasusceptible to failure, the new sucker rod prolonged therunning life of the lifting systems considerably. Also, a newtype of drive head with compact structure has been proved to

be more convenient in maintenance and more economic thanthe traditional products. By means of completed monitoringtechniques including PC Pump testing equipment anddiagnosing software, PC Pump systems can be monitored inreal time. This decreased the frequency of failures andimproved the benefits effectively.

With more than 2000 PCP wells in Daqing Oilfield, thecapital and operating costs have reduced dramatically. ThePCP system, the most effective lifting method, has great

potential for Daqing’s Oilfield.

BackgroundDaqing Oilfield lies in the center of Songliang basin in Northeast China. In the beginning stages, commingle water injectionand separate zone water injection technologies were usedwhich allowed the reservoir pressure to remain at a high level.Therefore, by natural power the oil field produced for nearlytwenty years. To maintain the output, artificial lifttechnologies were used from 1980s. Beam pumping systemwas the most popular one. Up to the end of last century, thenumber of beam pumping systems in Daqing reached over

20,000 wells. There were also about 2,000 ESP wells inoperation.

In 2000, the average water cut for the whole oilfield reachednearly 90%. Huge operation cost was the most serious

problem for beam pumping system. In 2002, the total powerconsumption of artificial lifting systems was nearly 10 billion

kW ·h, which was over one third of the whole oil field’s powerconsumption.

From 1990s, polymer flooding, APS flooding and otherEOR technologies were applied in Daqing oilfield. Therecovery of the oilfield improved considerably. On the otherhand, the failure rate for the artificial lift system increaseddramatically due to the changing properties of output. Forexample, the beam pumping system in polymer flooding areasdecreased the average running life from more than 600d downto 270d. Cost for overtime also increased by ten million RMB

per year.As for ASP flooding area, the results were even more

serious. Due to high scaling in pumps and strings, the averagerunning life of the beam pumping system was less than 60d,while the shortest running life was within a month. Artificiallifting technology has become a “bottleneck” problem forDaqing Oilfield in EOR period.

With this in mind, PCP system was chosen to be the firstalternative. It has lower investment and operation cost, higherefficiency, and a high viscosity and sandy liquid production.

PCP Technologies in Water Flooding AreaProblems in Pilot Test. At first, Daqing oilfield was regardedas the best place in China for the application of PCP liftingsystem: all vertical wells, lower lift (less than 1000m), nosand, lower oil gas ratio(less than 100), and no H 2S. But due tothe limitation of manufacturing technology, PCPs were firstused only in small production rate wells whose production wasless than 30t/d. It was expected that PCP technology would be

successfully used in water flooding area in Daqing within fiveyears. But as of 1996, there were only 10 wells in the wholeoilfield. See Figure 1. High failure rate was the killer of thisnew technology.

The main forms of the failures were pump and rod failures.In most cases, the systems’ operating current increasedquickly which resulted in rods being broken frequently. Also,upon examining the strings, they sometimes appeared to have

been twisted like a rope. Due to the severe deformation ofelastomer, pumps could not be reused after treatment.Moreover, stator’s dropping out failure was also a concern.

Improvements of Elastomer. A special laboratory was

created to research the PCP system. Experiments indicated

IPTC 10032

The Successful Application of 2000 PCP Wells in Daqing OilfieldL. He, SPE, and C. Gang, SPE, Daqing Oilfield Co. Ltd.; W. Dingmin, PetroChina; and S. Guochen, SPE,Daqing Oilfield Co. Ltd.

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that the problems mainly came from three things: (1) theformula of elastomer didn’t fit for the conditions of theoilfield. The swelling of the stators was too high to keep the

pump operating normally. (2) Bonding technology in processing the pump was not qualified and resulted in stator’sdropping out failures. (3) The design parameters of the pumpwere not the optimum. Therefore, the performance of thetechnology was limited as well.

According to the above analysis, a series of experimentswere carried out in advancing elastomer formula, improvingthe pumps’ processing technology, and optimizing the pump’sdesign parameters.

1. Advancement of elastomer’ s formu la. Theelastomer’s formula was adjusted in the following threerespects:

(1) Adjusting the vulcanization system. Through the re-selection and adjustment on sulfidizer and rubber activator, theelastomer’s heat and aging resistance were improvedeffectively.

(2) Improving the antioxidant. The major factors whichinfluence rubber’s aging time include oxygen, heat, andfatigue. When temperature rises 1 ℃, the oxidation rate will beincreased by 1 time. So it’s very important to select a properantioxidant for elastomer.

(3) Adjusting the strengthening agent to improve the physical mechanical properties of the stator.

A new elastomer formula was developed after years ofstudy. Table 1 gives the performance contrast between the

previous elastomer and the new one. It obviously shows thatthe physical mechanical properties of new formula elastomerare much better than the previous one.

2. I mprovement of processin g pump technol ogy. A

series of innovative techniques were undertaken to improvethe pump’s processing quality :(1) Improving the force plug’s centralization in the process

of elastomer injection. In the old elastomer injection process,it’s not easy to put the stator’s force plug and outer barrelexactly at the same axis, which often resulted in uneventhickness of elastomer. In that case, the pump’s operating loadwould be unstable which decreased the pump’s running lifeand was easy to cause pump failure. Thus, a centralizingtreatment was added in the elastomer injection process, whichimproved the stator’s quality effectively.

(2) Improving the bonding effect by spraying sandtechnique. High stator drop out failure rate came from the

problems in stator bonding technology. Analysis indicatedthat, there were some severe defects in stator bonding agentand bonding process. After reselecting the bonding agent andreforming bonding technology, the bonding strength increasedconsiderably.

3. Optimization of pump’ s design par ameters. PCPdesign parameters mainly include: rotor/stator minor diameter

(D), rotor pitch (t), rotor eccentricity (e), stator-rotor’s fit ( δ ),and steps(Z). And the optimization of these parameters werecarried out by the following two respects:

(1) Determining the optimization goals.a. To get a larger flowing area. In order to get a larger

flowing within a limited casing inner diameter, the design parameter should have the following relationship:

0min4 Dhe D

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by flushing lines. Wax removal treatments were carried out ina given period for different areas, depending on the waxdepositing rate in this area. It’s easy to be implemented in

beam pumping system because it doesn’t have any damage onthe lifting system as well as has no great effect on the

productivity. But as for PCP system, it’s very difficult toeffectively remove the wax deposited in tubing by means of ahigh-pressured volume of water due to the interference fit

between rotor and stator. In order to improve the effect ofwater flushing, in the past, the rotor had to been pulled outfrom the barrel of the pump before flushing, and ran the rotor

back into the pump after the treatment. The process was timeconsuming and expensive; moreover, due to rotor’s frequently

being pulled out and thrown back into the pump, the stator waseasy to be damaged which decreases PCP’s running lifeconsiderably.

A new patented technology, named hollow rotor PCP water flushing technology , solved the problem effectively. In thistechnology, the traditional solid rotor was replaced by ahollow rotor, and a flushing valve was set above the pump. Inthe process of wax removal, hot water flows downwardthrough the annular. At a higher flowing rate and pressure, theflushing liquid easily would open the valve and pass throughthe pump. See Figure 4. Moreover, PCP system could operatesduring the flushing process, thus, some flushing water wouldenter tubing with lifting liquid which would improve the waxremoval result as well.

Compared with solid rotor PCP, hollow rotor PCPtechnology has many advantages:(1) The water flushing liquid’s rate and pressure is much

higher which results in a shorter wax removal process and better results as well. See table 4.

(2) The greatest benefit is that it needn’t to pull out the rotorfrom the pump or to shut off the system during the

process. The cost is cut down considerably due to thecreative reform compared with the previous method.

(3) This technology is more helpful in protecting the pumpand could improve the operating life effectively.

(4) Combined with a set of tools (eg. Packer, etc.), flushingwater could be isolated from the producing layer and willnot do harm to the reservoir. See Figure 5.

To date, there are more than 800 hollow rotor PCPs inDaqing Oilfield.

PCP Technologies for EOR ProcessBased on the improvements of small rate wells in waterflooding areas, another test pilot for EOR production wascarried out. From the end of 1998, the test pilot’s productionrate ranges from 50 to 200t/d. The initial results were exciting:the pumps’ volume efficiency reached more than 60% onaverage and running lives were near 300d, which was muchlonger than beam pumping systems’ 30d.

With the increment of PCP number, the failure rate in highrate wells rose up quickly. It was found that, the new problemcame from the original lifting system’s inadaptability to thenew operating conditions. Hence, not only the significant of

pump needs to be adjusted, but also needs the design criteriaof the lifting system to be modified. Under the guidance of thisopinion, a series of new PCP products for EOR weredeveloped in the following years.

Two Novel Sucker Rods. Compared with beam pumpingsystem, the operating conditions of PCP string are quitedifferent. Apart from the axial load, a torque load is addedalong the string in operation. Sucker rods in PCP wells wereoriginally designed for beam pumping systems which do nottake the PCPs operating conditions into account. That means,the traditional sucker rods are used for enduring axial forcealong the string. When an extra higher torque is added, whichis periodically, the string would tend to be broken on thethread or the body. The following two novel sucker roddesigns solve this problem:

1. Jaw-Clu tch sucker rod for high rate PCP well s. Inthis design, the torque of the string is added on the jaw clutch,and the dragging force is added on the coupling’s threadseparately. Because the shearing strength of jaw clutch oncouplings is high enough as well as a hollow rod body design,the string could operate in serious working conditions, such aslifting high production rate, high viscosity liquid or sandyliquid. See Figure 6.

When designing the shape of coupling, three candidateswere brought forward, see Figure 7. The Finite ElementMethod (FEM) calculation indicated that design #2 has thehighest carrying capacity, and as the result, it was selected asthe optimum design. Stress concentration analysis is animportant part in mechanical design, so does in sucker roddesign. In the process of FEM calculation, it was found thatthe fillet radius has great influence on the special rodcouplings’ stress concentration problem. Figure 8, and 9 showthat, an optimum fillet radius exists which could get the samesafety factor for both rod body and coupling.

2. Tapered-thread sucker r od. Tapered thread is widelyused in drilling pipes due to its high strength characteristic.Tapered-thread sucker rod, with a high strength rod body,could operate in high torque conditions. See Figure 10. Thisdesign fits for small production rate wells and gives betteroperating conditions.

Up to date, there are 955 PCP wells using the both abovespecial sucker rods, which is 61.7% of the total PCP wells.The average sucker rod failure rate decreased from 20% to4%, and the operating life was prolonged considerably as well.For example, N1-6-P34 is one of the PCP wells in an ASParea. Before 1999, the rod failure rate was very high whenusing a traditional sucker rod. The averaged failure rate wasonce a month. After using jaw-clutch sucker rod, the PCPsystem operated normally for 805 days. When the pump’s was

pulled out at last, it was found that the whole rod string wasstill in good conditions and had no deformation at all.

An Environmental, High Efficiency Drive Head. In the beginning, the balanced-style drive head, showed in Figure 11,was applied successfully in small production rate PCP wells inwater flooding areas. However, when this kind of drive headwas applied in high rate PCP wells in polymer flooding areas,some problems emerged which limited the applicationseriously:(1) With the increment of rotating speed and of operating

load, the life of sealing materials decreased remarkablyfrom several months down to 1 or 2 weeks. Oil leakageon the drive head was also very severe which polluted theenvironment and increased the operating cost as well.

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(2) High-power drive head had a huge volume and higher barycenter. As a result, resonance of the drive headenhanced the fatigue break rate of polished rod.

(3) Requirements needed for maintenance was higher.The patented product, “zero leakage” drive head, see Figure

12, takes some completely new ideas to improve the efficiencyand environmental performance:(1) It combines the oil-cup structure sealing with mechanical

sealing techniques which completely diminish the oilleakage of PCPs on surface.

(2) The product also had the unique low profile design,which avoids the damage of wellhead by resonance.

(3) The wellhead’s holding and sealing system made it easierand cheaper for maintenance; it does not need a crane inrepairing the drive head any more.

(4) Modularization and standard design was used on allelements of the driving system. Every element could bereplaced by another standard one, and that helps to cutthe maintenance cost to a very low level.

Due to its remarkable advantages in the environmental, highefficiency, low operating cost, and easy maintenance, this

product has become the most popular drive head in DaqingOilfield in the past few years. Till the end of 2004, 1317 newdesign drive heads have been applied in Daqing Oilfield. Theaverage operating life is more than one and a half years; thelongest one reached more than four years.

Wireless Testing and Analyzing Technology. Due to thetotally different operating status, the traditional dynamometertesting and diagnosing technique in beam pumping systemcouldn’t be applied in PCP lifting system. For a certain years,operators analyzed PCP lifting system’s performance only by

producing rate, dynamic liquid level, and motor’s operatingcurrent. And only a very few kinds of failures could beidentified in this way. In that case, a project was carried outfrom 2000, aimed at developing a new testing technique whichcould directly get the operating status of PCP system.

After years of study, a portable wireless testing system andanalysis software for PCPs were developed and put intoapplication, see Figure 13. The new testing system consists ofsensor, transmitter, receiver and processor. The later twoelements are integrated into a portable computer. The sensor isset on the drive head permanently used for picking upobjective parameters of torque, axial load, and rotating speed.See Figure 14. Because of its close packaging design, thesensor can work in all weather. The working temperature scale

is very wide, ranging from less than -40 ℃ to above 70 ℃. Atransmitter is installed in the process of testing, transformingthe objective parameters into electronic signals andtransmitting them in form of electromagnetic wave. Thesignals are received and processed by portable computer. Thenthe system’s operating status can be identified by analyzingthe dynamic data of the lifting system, including string’sloads, dynamic liquid level, producing rate, current, etc. This

process is implemented by PCP trouble-shooting software. SeeFigure 15.

The testing system has been installed in more than 100 PCPwells. It has been proved that this technique is very effective

in diagnosing PCPs’ operating status, and it’s very helpful inimproving the lifting systems’ efficiency as well.

Ceramic Coating Rotor for ASP Flooding Areas. Scaling isthe main reason of pumping failures for beam pumpingsystems in ASP flooding areas. Due to the system’sreciprocating lifting mechanism and the discontinuous flow of

producing liquid, scaling is easy to deposit in the space between plunger and pump barrel which causes pump stuckfailures frequently. In some cases, when beam pumpingsystems stop working due to power off or other issues, the

pump cannot start again unless work over treatment was taken.Compared with beam pump and ESP, PCP has a better

performance in lifting ASP producing liquid. But, severalmonths later, scaling still will be found deposited on rotorwhich decreases the pumping efficiency. In high scaling

period in ASP area, the operating torque and current of PCPswould be unstable and varied in a larger scope. In some cases,the rod string even operates discontinuously. This unsteadystate would accelerate the rod’s fatigue and it’s very harmfulto the system. As a result, a series of anti-scaling treatmentwere carried out to improve PCPs’ operating conditions. Andceramic coating rotor PCP is one of the most effectivetechniques.

It’s well known that ceramic is a kind of inert compoundwhose surface energy is much lower than other material.Therefore, scaling is hard to deposit on the surface of ceramic.Through the experiments on 10 different ceramics, two ofthem were selected for their lower surface energy and lowerfriction coefficient under dry friction condition. Thesecharacteristics help to slow down the accumulating rate offriction heat and contact stress between coating and elastomeras well as improve the running life of PCP.

In 2004, two ceramic coating rotor PCPs were applied inASP flooding areas, and the running life all reached more thanone year. More observations are still being noted for furtheruse of this technique.

Application ResultsTill the end of October 2005, PCP lifting technology has beenused in more than 2000 wells in Daqing Oilfield. See Figure 1.In water flooding areas, the average running life reached to464d; the average pump efficiency was twenty per cent higherthan beam pumping system; and the system efficiency wasfifteen per cent higher. In polymer flooding areas, PCP wells’running life was 445d, which was 1.8 times longer than beam

pumping system’s while the longest one was more than 10times longer. In ASP flooding areas, the running life was 5times longer, while the longest one was 26 times long as the

beam pumping systems’.

Conclusion(1) Large quantity of experiments and practice indicated that,

whatever flooding area it was used in, elastomer’scompatibility to producing liquid was the prime problemto be considered for PCP lifting system.

(2) Pilot tests showed that, due to the different workingconditions, high rate PCP producers have much moredifficulties in operation than the lower ones.

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(3) Two novel sucker rod designs could ensure the PCPsystems’ operation effectively in large rate producers orother complicated working conditions.

(4) ”Zero leakage” drive head has remarkable advantages inthe environmental, high efficiency, and maintenance,which has been widely used in Daqing Oilfield.

(5) The new wireless testing and analyzing technology has been proven to be very helpful in decreasing PCPs’ failurerate and improving PCPs’ management as well.

(6) PCP lifting technology is a systematic engineering, whichneeds continuous development in every component andmatching technologies. Long terms of research anddevelopment, large sum of investment, and the continuousapplication in new techniques are the most importantexperiences for Daqing Oilfield in applying more than2000 PCP wells successfully.

AcknowledgementsThe authors wish to acknowledge the contributions ofProduction Engineering & Research Institute, No.1, No.3,

No.4 and No.6 oil companies of Daqing Oilfield Ltd., Co. for providing large quantity of experiments and pilot tests results.They would also like to thank Daqing Oilfield Ltd., Co. for

permission to publish the data in their study.

References1. Wang Yan et al: “Technology for Controlling Eccentric

Wear of Sucker Rods and Tubing in Pumping WellsLifting Fluids Containing Polymer,” paper SPE 89927

presented at the SPE Annual Technical Conference andExhibition, Houston, Texas, 26-29 September, 2004.

2. Godbey, J.K., and Dimon, C.A.: “The Automatic Liquid LevelMonitor for Pumping Wells,” SPE 6039 Journal of PetroleumTechnology (August 1977).

3. Cholet, H.: “Progressing Cavity Pumps,” Editions Technip,Paris(1997) .

4. Klein, S.T. et al: “Well Optimization Package for ProgressiveCavity Pumping Systems,” paper SPE 52162 presented at the1999 SPE Mid-Continent Operations Symposium, OklahomaCity, March 28-31.

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Table 1: The contrast of two elastomer’s physical mechanical propertiesPhysical mechanical propeties Unit Standard Elastomer#1 Elastomer#2

Shore hardness A Degree 65±5 75 69Tensile strength at break MPa ≥ 12 20.43 22.66

Elongation at rupture % 500±50 565.2 576.8300% elongation MPa ≥ 8.5 11.5 10.91

Peel strength kN/m 30 50 61.6 61.2 Abrasion wear cm 3/1.61km ≤ 0.15 0.13 0.15

Break-off strengthvariety % / -16.74 -3.49

Break elongationvariety % / -12.24 -3.68

Air aging at90℃ 24h

Hardness variety Degree / 3 4

Volume variety (#120gasline+benzene %

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Figure 2. PCP’s operating torque(T) and tilting moment(Tz)

GLB120-27 GLB500-14 GLB800-14

415.0

2853.2

5306.1

1018.4

0

2000

4000

6000

T T z ,

N . m

Tz

T

672.2

12.8021.12

25.6016.30

44.82

63.66

0

10

2030

40

50

60

70

GLB120-27 GLB500-14 GLB800-14

F c F a k N

FcFa

Figure 3. PCP’s axial force(Fa) and cross force(Fc)

8 10 54165

373

778

1283

1627

2010

0

500

1000

1500

2000

2500

1991 1996 1999 2000 2001 2002 2003 2004 2005 Year

Figure 1. PCP's Application in Daqing Oilfield

N u m

b e r

( w e l

l s )

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Figure 5. Hollow rotor PCP Water flushing tools

(a) Traditional sucker rod for BPL (b) Jaw-clutch sucker rod for PCP1-coupling 2-thread 3-tooth F-drag force T-torque

Figure 6. The loading status between a jaw-clutch sucker rods and a conventional one

FT 3

1

2F

T

(a) solid rotor PCP (b)hollow rotor PCP

Figure 4. PCP’s flushing channel

Flusing

liquid

Flusing

li uidStator

Flusing

liquidRotor

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#1 Design #2 Design #3 Design

Figure 7. Optimization of rod coupling shape

Figure 8. Fillet radius’s optimization of rod coupling

R1 R2 R3

Fillet radius

Figure 9. Tooth’s maximum stress via fillet radius

M a x

i m u m s t r e s s

( M P a )

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Figure 11. Traditional drive head Figure 12. New drive head

(a)conventional rod thread (b)tapered rod thread

Figure 10. Tapered rod thread and conventional rod thread

Figure 13. Wireless testing system

Transmitter

Sensor

Computer

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Figure 15. PCP trouble-shooting software

Figure 14. PCP rod string’s loading curves by wireless testing system

0

50

100

150

200

250300

350

400

0 1000 2000 3000 4000 5000 6000

Time(1/30s)

N . m , t , r

/ m i n

Torque Axial forceRotating speed

N . m , t ,

r p m