SPE 153123

A Unique Electrical Submersible Reciprocating Pumping (ESRP) System Design Applied in Unconventional Oilfield Zhang Wensheng, SPE, Wang Lin, SPE, Wang Fengshan, SPE, Huang Youquan, SPE, Cao Gang, SPE, Zhang Fengwu, Ren Huaifeng, SPE, Ge Junwen,Zhang Weiping, Liu Ling, Wang Xinmin, Daqing Oilfield Co.,ltd.

Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Annual Technical Conference and Exhibition held in San Antonio, Texas, USA, 8-10 October 2012. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract In recent years, a unique electrical submersible reciprocating pumping system (ESRP) was developed and has been applied in Daqing Oilfields. The main structure of ESRP is similar with ESP, consisting of an electrical submersible motor, pump, tubing and cable. The key equipments of ESRP are the reciprocating motor and the pump. The motor is a novel permanent magnetic line motor consisting of stator and mover. The pump is a special reciprocating pump. In operation, the mover slips in the stator from one end to the other periodically controlled by surface equipment, applying the power to the plunger of the reciprocating pump. Because of its small outerdiameter, the whole system could be run into the horizontal wellbore conveniently. This unique lifting system was designed mainly for the production of satellite oilfields in Daqing Oilfield. Unlike the properties of the main blocks of Daqing Oilfield with thick pay zones, high permeability and shallow imbedded reservoir, these satellite oilfields distributed discontinuously, the layers are thin and imbedded deeply with poor permeability. The producers’ averaged production is below 35 bpd. Beam pumping system showed poor benefit due to the high investment and operating cost. PCPs and Bailing lifting systems were applied later in a larger scale. But the management was relatively complicated and still limited in horizontal wells. As the result, ESRP showed great advantages both in technical and economic respects in the production. Till the end of 2010, ESRP has been applied in more than 30 wells in Daqing Oilfield. The longest running life has reached above 400 days. It showed remarkable advantages in the production of low displacement and deep reservoir, especially for horizontal wells. With the improvement of displacement and other specifications, this unique lifting system design has great potential in the development of unconventional reservoir as well as mature oilfields. Introduction

Beam pumping system is the most popular artificial lift method in oilfields due to its maturity and high reliability after more than 100 years application around the world. Take Daqing Oilfield for example, in this largest oilfield of China, there are more than 40 thousand producers in the oilfield while 80% equipped with beam pumping systems. After 50 years development, the annual production rate of Daqing Oilfield has decreased by 20% compared with its peak rate. A group of satellite oilfields around the main blocks had to been developed in recent years in order to release the huge production pressure of the oilfield. These satellite oilfields distributed discontinuously, the pay zones are thin and imbedded deeply with poor permeability. In most cases, the averaged production is below 35 bpd per well. As the result, beam pumping system showed poor benefit due to the high investment and operating cost. PCPs and Bailing lifting systems were tried in some areas, showed obvious limits in management and operating conditions. In order meet the requirement in the development of these , From 2004, a novel Electric Submersible Reciprocating Pumping (ESRP) system was developed and in some oilfields, showing remarkable advantages in technical and economic respects as well. Principle and Features of Electrical Submersible Reciprocating Pumping (ESRP) System Operating Principles of ESRP System

The basic form of ESRP is the same as ESP. It consists of linear motor, reciprocating pump, surface control, and downhole

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tools. The power was transmitted from surface control to submersible motor by power cable attached along the tubing. See Figure 1. In operation, the linear motor mover slides inside the stator under the effect of magnetic force periodically by surface control system, driving the plunger of reciprocating pump up and down to produce the fluid from the well. Features of ESRP System

1) Eliminate tubing and rod failures in conventional beam pumping system. 2) High feasibility in complicated structure wells, such as deviated wells and horizontal wells. 3) High adaptability in low production rate wells. 4) Excellent Energy saving artificial lift system. 5) Lower investment and operating cost. 6) Simple structure and easy maintenance. Key techniques of ESRP Linear Motor

The basic principle behind the linear motor was discovered in 1895, but practical devices were not developed until 1947. It is an electric motor that has had its stator and rotor "unrolled" so that instead of producing a torque (rotation) it produces a linear force along its length. The most common mode of operation is as a Lorentz-type actuator, in which the applied force is linearly proportional to the current and the magnetic field. In a traditional electric motor, the rotor spins inside the stator. In a linear motor, the stator is unwrapped and laid out flat and the "rotor" moves past it in a straight line. Linear motors are now used in all sorts of machines that require linear motion. Due to its remarkable advantages in simple structure, fast dynamic response, high velocity and accelerated speed, high precision, and low vibration, it has been widely used in lathes, elevator, magnetic levitation, etc. In oilfield, linear motor was firstly applied on the surface in a new energy saving pumping system. It is much more difficult to employ the motor in downhole due to the limited space. In China, the most popular casing size is 5 1/2” in the oilfield which make it more difficult to design the linear motor. See Figure 2. To date, the OD of linear motor is 114mm with a 2.5 tons lifting force as well. In the design of Permanent magnetic materials were to be selected to improve the magnetic field strength and the power performance as well. In operation, the mover of linear motor endures high liquid column load which was easy to cause the bending or broken of rod. High strength alloy was applied the material of standing bar. Reciprocating Pump and downhole tools

The structure of reciprocating pump is similar with beam pump. The plunger of the pump is connected with mover of motor. In order to decrease the influence of gas and sand, anti-sand and anti-gas design are required in the structure of pump. In the process of upstroke, mover is driven upwards along the stator. The travel valve is closed, at the same time the fixed valve is opened, lifting the produced liquids to the surface. In the process of downstroke, mover slides downwards. The travel valve is opened and the fixed valve is closed, allowing produced liquid flow in to the pump. The specifications of reciprocating pump are listed as following: 1) Length of the pump barrel is 3.0m. Length of the plunger is 1.1m. 2) Plunger stroke is 1.3m. 3) Pumping speed ranges from 12 m-1 to 1min-1. 4) The minimum adjustable stage is 0.1min-1. 5) The maximum of displacement is 20m3 per day. Sand screen was applied as the border isolating the pump from produced sand. Meanwhile, a specified anti-sand pump was designed with three sand-wrapping rings and sand deposit mandrel, which allows the produced sand dropped to the bottom of the well. Surface Control System

Surface control system is the controlling center of ESRP. It takes responsibility of startup, shut off, set up, and other control functions in operation. It also has a series of protection functions including overload protection, single phase protection, short circuit protection, etc. All the operating parameters could be displayed on the control panel. Surface control system consists of main circuit and control circuit. Main circuit is composed of isolation switch, fuse, and AC contactor. Control circuit is composed of control transformer, potential transformer, current transformer, frequency changing circuit, and protection circuit. Before the operation, pumping speed and frequency should be set up on control panel. In operation, the current signal was tested by protector to protect the assembling unit from overcurrent and unbalanced current. At the same time, voltage signal was tested by main circuit to protect the assembling unit from voltage overload, unbalanced voltage.

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Experiments in Laboratory

The testing equipments mainly include two testing wells, calibrating tank, pressure gauge and surface manifold. See Figure 4. The depth of the two testing wells is 100m. One ESRP is employed in #1 well. Another 80m tubing strings are employed in #2 well, used for increasing testing volume and decreasing the pressure fluctuation of #1 well. In the process of experiment, switch 1, 4, 5 and 6 are to be opened. Pressure of gauge P1 indicates the manifold has been full of water. As the result, switch 4 is to be turned off and switch 2 is to be turned on in order to release the liquid in upper lines. When there is no water flowing from switch 2, it means the upper lines have been emptied. Then switch 2 is to be turned off. Start up ESRP system, adjust switch 1 and change the pressure of gauge P2 from 0 to 15Mpa. Then record the corresponding flowing rate. The operating status could be observed clearly from ESRP operating current curve. See Figure 5. The performance of ESRP is a periodic movement which has some similiarity with beam pumping system. The difference is that the linear motor of ESRP only operates for a short period in one pump stroke, while the motor of beam pumping system works constantly. As the result, the power consumption of ESRP is much lower than beam pumping system. In-situ Test Results

In January 2005, an ESPR system was installed in Well P49. The production rate was 9 tons per day, while oil production was 2 tons per day. Pump submergence was 450m. The production status was similar with the previous beam pumping system. Anti-paraffin treatment cycle has been prolonged from original 20 days with beam pumping system to more than 143 days with ESRP system. This ESRP system has operated for more than two years constantly. Tests showed that, compared with the original beam pumping system, the power consumption quantity of ESRP system was decreased by 44.66Kw.h. The power factor was increased by 0.644. The comprehensive electricity save rate was raised 41.1 per cent, and pump efficiency was raised by 65.1 per cent, and system efficiency raised by 9.3 per cent. All the results showed considerable power saving results. See Table 1. In this experiment, once paraffin plugging occurred, several times colliding pump barrel and so on abnormal behaviors. After developing function of software, land control system can identify automatically and respond in time these abnormal behaviors, therefore prevents pump from burning out because of overload.

Table 1. Contrast of Energy Saving Index Test Effect in Well P49

ITEMS BEAM PUMPING

SYSTEM ESRP SYSTEM DIFFERENCE

Real power/kW 4.2 2.66 -1.54

Magner/kW 11.1 0.4 -10.7

Power factor 0.345 0.989 0.644

Daily power consumption /kWh 108.79 64.13 -44.66

Comprehensive electricity save rate /％ 41.1

System efficiency /％ 14.4 23.7 9.3

Pump efficiency /％ 18.4 83.5 65.1

To date, 20 sets of ESRP systems have been applied in Daqing Oilfield including 10 vertical wells, 7 deviated wells, 3 horizontal wells. The deepest pumping depth is 2062m. The maximum of deviated well angle was 35.1°. The averaged production rate was 3.5 tons per day. The averaged operating life was above 400 days. Conclusions 1. ESRP is a novel artificial lift method integrated the advantages of both beam pumping system and electric submersible pump. 2. ESRP eliminates tubing and rod failures in conventional beam pumping system. It has higher feasibility in complicated structure wells, such as deviated wells and horizontal wells. 3. Laboratory experiments and in-situ tests showed that ESRP had an excellent energy saving performance in operation. 4. Compared with traditional beam pumping system, ESRP has lower investment and operating costs. It also has simple surface equipments and the maintenance is easy for operators. 5. Linear motor is the prime technique in ESRP system. The lifting force is the key indicatior reflecting the performance of linear motor as well as the application conditions of ESRP system. With the development of linear motor in optimal design and new materials, the lifting performance of ESRP system will be improved as well. 6. Application in Daqing Oilfield indicated that ESRP showed remarkable advantages both in technical and economic respects. It has a broad future in the development of unconventional reservoir.

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Acknowledgement Authors are very grateful for the long term contributions by the participants from Daqing Oilfield Production Institute, No.5, No.7, No.8, No.9 oil Company of Daqing Oilfield. Authors wish to acknowlegd the permission of publishing the paper and the support of the related materials by Daqing Oilfield Co., ltd. References Fu Fengli, Tang Xiaohao: Asynchronous Motor Design Manual [M].Beijing: Mechanical Industry Publishing House, 2002: 691-713. Zhang Qi: Principle and Design of Petroleum Engineering [M]. Shandong: Petroleum University Publishing House, 2001: 135-141. Xia Deqian.Automatic Control Theory [M].Beijing: Mechanical Industry Publishing House, 2001:213-221. Zhen Weisheng, Li Zhenzhi, Lin Weimin: Petroleum Engineering Technology of Comprehensive Block Oilfield in Intermediary and Later

Developing Stage [M].Beijing. Petroleum Industry Publishing House, 2001:47-54. Wu Jihui, Sun Jun,He Zhigang,et,al: Present Research Situation of Oil-well Deparaffin and Paraffin Control Technique [J], Field Land

Enginnering, 2004, 23(7):14 Chen Taoping, Hu Jingbang: Petroleum Enginnering [M].Beijing: Petroleum Industry Publishing House, 2002: 439-452. Wan Renpu: Petroleum Engineering Manual [M].Beijing: Petroleum Industry Publishing House, 2000: 489-512. Guan Xiaojing, Wang Zhiguo,Wang Zhongdong: Uncertainty Analytical Modell of Pumping Jack System Efficiency Test and Its

Application [J]. Petroleum Journal, 2005, 26(1): 113-116.

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Figure 2. Structure of Linear Motor

Casing

Pump

Linear motor

Tubing

TubingGuider

Wellhead

Liner

Control

Cable

Figure 1. Diagram of ESRPS

Stator Outer Pipe

Stator Inner Pipe

Rotor Permanent Magentic

Materials

Silicon Plate

Coil

Reservior

Plug

Tail Pipe

Tubing

Pump

Linear Motor

Casing

Cable

Connecting Rod

Reservior

Fixed

Trave

Plunger

Figure 3. Diagram of ESRP Downhole System

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P2

Pressure gauges

Cable

Tubing

1

3

2

Tubing

Casing

pump

Linear motor

Inlet

P1

4

Control Wellhead

#2 well #1 well

Figure 4. Diagram of ESRP Experiment

Tank Water inlet 5 6

Figure 5. Operating Current Curve of ESRP in Experiment

-5

0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200 250

电流

Time(s)

Current(A)