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European Journal of Applied Sciences – Vol. 10, No. 5
Publication Date: October 25, 2022
DOI:10.14738/aivp.105.12881. Gareyev, A. A. (2022). Method of Periodic Operation Mode Forecasting. European Journal of Applied Sciences, 10(5). 149-156.
Services for Science and Education – United Kingdom
Method of Periodic Operation Mode Forecasting
А. А. Gareyev
Due to natural depletion of developed or new fields with poor reservoir features placed under
production, the number of wells equipped with electric centrifugal pumps (ESPs) running in
the periodic operation mode, is growing. Similar properties are intrinsic to hard-to-recover
fields, which actually the Bazhenov (shale) suites are.
Obviously, oil producers are facing the problem of providing upstream exploration and
production from low-permeable (shale) reservoirs, characterized by low flowrate (less than 15
m3/d) at dynamic fluid levels over 2,000 m. Exploitation of such fields using low-capacity ESPs
leads to MTBF drop of the latter. ESP failures occur due to salt deposition in the centrifugal
pump chamber (further referred to as “R-0”). The author came up with the solution of the first
problem [1] about 15 years ago, but - one might wonder why - it was ignored by the experts.
This paper is aimed at the search of the ways of improving the efficiency of ESP’s control
running in the auto-reclosing mode, in order to simplify the task for field production engineers,
dealing with routine operations.
Figure 1. NIZHNESORTYMSKNEFT NGDU well stock running on an intermittent basis in 2022.
Oil fields are numerated as 1,2 ... 25. The majority of wells (478) of the ESP stock running in
periodic mode, refer to the North Labatyugansk oil field.
Figure 2 shows an example of operation on the well No. 3348 of the North Labatyugansk oil
field in the periodic mode.
The well is equipped with ESP 5-30-2200 at the depth of 2,368 m and is running with a flowrate
of about 8 m3/d at the dynamic fluid level of 1,585 m. The ESP’s suction pressure changes from
78 MPa to 82 MPa. Producing water cut amounts to 36%.
178
11
55
149
109
12 9 1
56
127
11 8 4 12 21
478
2
51
2 3 5 23 18 29
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Well stock running on an intermittent basis
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 5, October-2022
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Figure 2. A copy of the “Stock Progress” report related to the well No. 33548 of the North
Labatyugansk oil field. The ESP unit suction pressure changes from 78 atm to 82 atm. Rundown
time is 30 minutes, accumulation time – 2 hours.
Fluid rundown time is 30 minutes, accumulation time – 2 hours. In general, the unit runs for 4.8
hours a day and stays in the accumulation mode for 19.2 hours.
The previous ESP 5-20-2350 with 538 days of TBF was lifted after its failure due to “R=0” of the
“cable-motor” system. Operation parameters: flowrate – 13 m3/d at the dynamic fluid level of
2,145 m; depth of the ESP installation – 2,372 m. Upon disassembly, it was discovered that the
decrease in the ESP’s electric resistance took place due to the cable-extension failure, which is
evidence of the pump’s temperature rise over 230 °С (working temperature of the cable
extension and its thermal-resistant flat portion). The ESPs of the intermittently running well
stock are equipped with thermomanometric sensors (ТМS). The data is transferred to the
control station. Figure 3 shows the graph of electric current variance, centrifugal pump’s
suction pressure variation and corresponding performance factors (cos
).
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Gareyev, A. A. (2022). Method of Periodic Operation Mode Forecasting. European Journal of Applied Sciences, 10(5). 149-156.
URL: http://dx.doi.org/10.14738/aivp.105.12881
Figure 3. Change of well operation rates during periodic operation. At present, a process
engineer is unable to analyze and make effective decisions on operation of centrifugal pumps in
order to gain the best economic outcome.
Currently there is no adequate theoretical basis for designing a periodic mode of well operation.
Therefore, the solution of the set task usually proceeds from the fact of an ESP’s failure, e.g.,
using the operational data of the previous ESP, which failed due to “R-0” after 538 days of
running (TBF). The gained TBF value is the result of combined operation, i.e., with switch-over
from the periodic mode (240 days) to continuous mode (300 days), which proves that the pump
was affected by high temperature while running. The working temperature of the cable
extension tраб = 230 °С. The ESP unit failed due to the decrease of electric resistance of the cable
extension isolation, thus, the temperature inside the running pump exceeded the working
temperature of the cable extension by 50 °С and even more. The operation parameters of the
ESP 5-20-2350 unit are as follows: at AC frequency of
47.5 Hz, the fluid flowrate Qж = 13
-16 m3/d, the dynamic fluid level Ндин – 2,105 m. Producing water cut amounted to 25%.
Electric current
variance
Pump’s suction
pressure
variation Рпр
Change of cos (f)
(performance factor)
Accumulation tнак
Pumping-out tотк
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 5, October-2022
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Figure 3. The ESP unit failed due to “R-0” of the cable line (cable extension) with the working
temperature of 2300С. The cable extension failure shows that the temperature of the pump
section exceeded 2300С. In fact, the pump temperature exceeded 3000С (the temperature of
leakage current spikes in the cable extension).
For the purpose of the ESP unit design, let’s first determine the ultimate dynamic head, at which
the pump’s temperature will rise up to 230 °С.
The parameters of the ESP unit and the reservoir required for this calculation, are shown in
Table 1.
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Gareyev, A. A. (2022). Method of Periodic Operation Mode Forecasting. European Journal of Applied Sciences, 10(5). 149-156.
URL: http://dx.doi.org/10.14738/aivp.105.12881
Table 1.
No. Data Unit of measurement Designation Value
1 ESP unit motor power W N 26,000
2 Efficiency Decimal fractions μ 0.26
3 Vertical pump-setting depth m Нв 2,319
4 Fluid flowrate m3/d Q0 17
5 Producing water cut Decimal fractions B 0.36
6 Saturation pressure MPa Рн 11.4
7 Well-productivity factor m3/(atm*d) k 0.07
8 Gas factor m3/m3 Г 92
9 Pump radius m �! 0.046
10 Thermal conductivity of the
methane insulating layer
W/(m*deg.) λиз 5
11 Average gas insulation layer
thickness on the pump surface
m δиз 0.001
12 Heat transfer coefficient W/(m2*deg.) α 2,800
13 Temperature of salt deposition deg. Тсол from the
Table
14 Head of one ESP unit apparatus atm h from the
Table
15 Gas to oil ratio Decimal fractions φ to be
calculated
16 Pump suction pressure atm Рпр from the
Table
17 Temperature at the pump suction deg. Тf to be
calculated
18 Temperature on the pump surface deg. Тw to be
calculated
19 Thermodynamic gradient deg/m γ 0.03
20 Vertical depth of the formation top m Нкр 2,530
21 Formation temperature deg. Тпл 78
22 Radius of the centrifugal pump
apparatus
m R2 0.045
23 Height of one working apparatus m z 0.034
23 Number of apparatuses in the
centrifugal pump
units of measurement n 560
23 Heat density W/m3 q0
Let us determine the centrifugal pump’s optimum suction pressure.
According to [3], the pump’s optimum suction pressure is:
Роп = Рн = 114 atm.
The expected flowrate of the unit:
�ж = 114 ∗ 0,07 = 7,98 m3/d
It’s obvious that the ESP 5-30-2200 with the flowrate of 7.98 m3/d can run only in the periodic
mode. Herewith, the ESP unit setting depth must be equal to the depth of the formation top.
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 5, October-2022
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Let’s estimate the ESP flowrate, with which the pump’s temperature is less than the
temperature of salt deposition onset [2]. The depth of the ESP installation Нсп = 2,319 m. Let’s
carry put a detailed calculation according to [1 - 3].
Step 1.
According to [1, 2,] simultaneous equations have to be solved:
�% = �& + '
()'
*!+н∗+пр∗&'∗Рат
-(()/)∗1∗Г∗ /
(
∝ + 4из
5из
0
(1)
Рсол. = f(Tw)<Рпр
where: Рсол – pump’s suction pressure. under which salt deposition starts; Tw– temperature on
the pump surface.
Step 2. Let’s calculate the gas content in the liquid-gas mixture at the pump suction, given the
pump’s suction nozzles:
� = 6!∗Г∗7()
Рпр
Рн 8∗(()В)∗ -
Рпр
6!:6!∗Г∗7()
Рпр
Рн 8∗(()В)∗ -
Рпр
(2)
Let Рпр = 50 atm according to the operation data of the well No. 3348 of the North Labatyugansk
oil field. We get:
� = 0,398
Step 3.
Let’s calculate the temperature of the gas-liquid mixture at the pump suction, based on the
geothermal gradient
Tf=Тпл - (Нкр – Нв)*γ (3)
Tf=71, 7 °С
Step 3.
Let’s calculate the heat density in the pump according to [4]:
�; = 84,525 W/m3
Step 4.
Let’s calculate the pump temperature according to (1) under the conditions of the well No. 3348
of the North Labatyugansk oil field [1, 3 ]. For this purpose, let’s assume the pump efficiency
at � = 0,398 equal to 0.15:
From which Тw =271 0C+71,7 = 342.7
Under the pressure Рпр – 50 atm according to [3] (Table П.5.), we identify the salt deposition
start temperature: Тсол = 275 °С. Then [2], during operation under such conditions, the cable
extension will fail due to R-0 and salt deposition will take place. Since the production water
content amounts to 35%, the ESP unit will fail due to the decrease of electric resistance of the
thermal-resistant flat section with the working temperature of 230 °С (342.7 °С).
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Gareyev, A. A. (2022). Method of Periodic Operation Mode Forecasting. European Journal of Applied Sciences, 10(5). 149-156.
URL: http://dx.doi.org/10.14738/aivp.105.12881
Step 4. Let’s calculate the pump suction pressure, under which the pump temperature will
become equal to 212 °С (less than 230 °С). According to (1), the pressure is 72 atm, whereas
the boiling point is 285 °С according to (3). If a pump is running in such an operation mode, no
salt deposition inside the pump will occur.
Step 5. Let us switch over to planning the periodic operation mode.
For this purpose, let’s select a “pitch” of the periodic mode. Such a pitch can be approximately
calculated based on the pump optimum operation mode and the well flowrate. For instance, the
expected well flowrate is 8 m3/d, the optimum pump delivery is 40 m3/d (due to nonuniformity
of the pump delivery let’s assume the value above 30 m3/d). Based on the proportionality of the
rundown time and the volumetric rate of the produced fluid, the total rundown time per day
tотк = 4.8 hours, hence the accumulation time is 19.2 hours.
Step 6. In order to identify the rundown time for one period, let’s compose an equation of a
centrifugal pump’s heat balance, based on the assumption that after each stop of the ESP unit,
the pump temperature comes up with the gas-liquid mixture temperature at the pump suction,
i.e., Тпр – 71.7 °С. Let’s assume the permissible pump temperature as 225 °С (less than 230 °С
to avoid damage of the flat cable).
�т = с ∗ (Тпл − Тпр) ∗ Мн = � ∗ (�нач − �кон) = � ∗ ∆�отк (3)
where: Тпр – initial rundown temperature; Тпл – permissible temperature of the flat cable is
225 °С; ∆�отк – time interval of safe rundown, free of salt deposition; N– pump thermal rating
(17,000 W); с – heat-absorption capacity of the pump hardware (880 W/kg); Мн – pump mass
(200 kg). The heat-balance equation (3) is rough, ignoring the amount of heat transferred
outside the centrifugal pump by the motor and the pumped fluid. Such approximation makes
the calculation easier and is admissible due to the small amount of heat transferred outside.
Let’s make calculations:
∆�отк = 880 ∗ 200 ∗ (225 − 72)
17,000 = 25.8 �������
Let’s find out the number of cycles per day:
�циклов = 4.8
25.8 = 288
25.8 = 11 ������
Then, the maximum and the minimum centrifugal pump suction pressure can be figured out.
Under the centrifugal pump suction pressure Рпр, the rundown time is 25.8 minutes, so there
will be totally 11 cycles per day and 1.8 hours of accumulation time.
It’s worth mentioning that the manual calculation is pretty cumbersome, time consuming and
in general is impracticable for process engineers at this point due to the lack of necessary
competence. Here we have shown just the final results of the calculation. However, the
calculation procedure can be easily programmed and installed on the engineer’s computer to
simplify the identification of process parameters of periodic (or continuous) mode of a
centrifugal pump operation.
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 5, October-2022
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References
1. Gareyev Regarding the significance of thermal condition for electric centrifugal pump. “Oborudovaniye i
tekhnologii dlya neftegazovogo kompleksa” (Equipment and Technologies for the Oil & Gas Sector), No.1,
2009, pp. 23-29
2. Gareyev A.A. et al. Centrifugal-pump suction pressure. “Neftepromyslovoye delo” (Oilfield Engineering),
No.11, 2014, pp.35-39
3. F.F. Tsvetkov, B.A. Grigoryev HEAT AND MASS TRANSFER. Moscow. MPEI (Moscow Power Engineering
Institute) publishing house. 2006. P. 547.