paper nis nafagas intermittent gas lift

8/13/2019 Paper NIS NAFAGAS Intermittent Gas Lift

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February, 2004. Prepared by: Slavoljub Stojanovic 1

ASME/API/ISO Spring 2004 Gas-Lift WorkshopSofitel Hotel, Houst on , Texas, USA February 10-11, 2004

Inc rease Eff iciency o f Interm ittent Gas-Lif t

By Use of Plung er l i f t

PREPARED BY

Slavoljub Stojanovic, NIS NAFTAGAS, SERBIA & MONTENEGROPredrag Radanovic, NIS NAFTAGAS, SERBIA & MONTENEGRO


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Increase Efficiency of Intermittent Gas-LiftBy use of Plunger lift

Abstract

Gas lift method (continual and intermittent) has been the most widely applied a

recovery method, and a number of wells, almost 70% have been recovered by thismethod. In initial phase, immediately after the flowing period, continual gas lift wasapplied. But as the time went by, some changes of conditions occurs in a reservoirsuch as: (reservoir pressure draw down, water content increase, near well zonedamage, fluid inflow decrease), and because of a permanent increase of specific gasconsumption (from 250m3/m3 to 1100m3/m3) the continual gas lift method becameinefficient. A detailed analysis has been performed afterwards, and the continual gaslift method was replaced with the intermittent on more than 70% of the wells. Theintention was to decrease gas consumption and increase the total energy efficiency ofthe system. The realized results, after the intermittent gas-lift method had beenapplied, appeared to be good for economical work of the system. As the reservoirconditions kept changing, the intermittent gas lift system has reached the phase of nooptimal performance from the point of view of hydrodynamic conditions in the wellsand in the injection system, and from the standpoint of energy, the system hasreached the phase of performing in inefficient and uneconomic manner.

In process of finding a solution of high specific gas consumption and non-efficiency of an intermittent gas-lift, because of the increased fall back, we tried withuse of a Plunger lift. This paper discusses the use of a plunger lift in wells whereintermittent gas lift has been applied.An analysis of a Plunger lift has been shower both before and after its usage.

Key words: Gas lift, Intermittent, Optimization

In t roduct ion

With the aim to increase the oil and gas production in order to decrease its costs,the efficiency of a plunger lift method has occupied a special attention.A plunger lift system is based on the free plunger, moving inside of existing tubing stringusing differences in pressure above and below the plunger. The main characteristic ofplunger lift is to decrease effects of fluid fall back and to lift it on the surface.The use of a plunger lift is possible if there are satisfying amounts of gas for lifting ofaccumulated fluid slug, when the amount of needed gas is not on satisfying level (GLR)than it is necessary to inject a gas from an outer source. But, when we are deprived ofsuch conditions a plunger lift use is not possible.

It is known that a plunger lift could be used in the following occasions:a) Removal of Liquids from Gas wellsb) Hi-Ratio Oil Well productionc) Paraffin and Hydrate Controld) Increased Efficiency of intermittent Gas Lift Wells

This paper will only discuss a field of increasing work efficiency of the system forIntermittent Gas lift method.


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Appl ica t ions

The main problems which have mostly influenced on work of intermittent gas liftare liquid fall back, as well as an intensive paraffin deposition. Well fluid is lifted in theform of a slug, and efficiency of lifting depends on several factors. An importantcondition for normal functioning of this system is a proper inner tubing diameter thatgoes by the whole length of tubing. As fluids move to the surface a certain friction

appears, which as a consequence has slower speed of a slug, irregular shape of the topof fluid slug, as well as more intensive fall back of fluids by the inner wall of tubing. Atthe comes to the point of its more intensive break through the fluid, by which the fallback has been significantly increased.

A plunger installed in the intermittent gas lift system works as a mechanicalseparator between liquid slug and gas, and in such a way makes work more efficient.

A bumper spring is installed above operating gas lift valve. By opening of the gaslift valve injection of gas under the slug is done, and starts its traveling to the surface bycontemporal lifting of accumulated fluid slug above a plunger. The valve on injectionflow line is closed by the automatic controller, casing pressure decreases, a plungeralso decreases on a bumper spring, and after that it is ready for a next cycles.


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SUB-SURFACE EQUIPMENT FOR THE PLUNGER LIFT WELLS


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WELL Mk-75

The well belongs to the category of low productivity, with the average production of7.75 bbl/day before the plunger lift was built in.

The complete data about the well, reservoir and gas lift system are shown in table 1.

Initial reservoir pressure (Pri): 3045 [psi]

Current reservoir pressure (Pr): 1886 [psi]

Current Reservoir temperature (Tr): 230 [F]

Well completion type: Cased hole

Middle perforation depth (Hf): 6942.3 [ft]

Perforations number (np): 24 [hole/ft]

Well depth (HB): 6971.8 [ft]

Packer depth (Hpa k): 6689.6 [ft]

Static fluid gradient (Gs): 0.371343 [psi/ft]

Outside casing diameter (Doc): 7 [in]

Inside casing diameter (Dic): 6.26 [in]

Outside tubing diameter (Dot): 2.87 [in]

Inside tubing diameter (Dit): 2.44 [in]

Wellhead tubing pressure (Pwh): 101.5 [psi]

Wellhead temperature (Twh): 59 [F]

Porosity (): 0.192 [fr]Bubble point Pressure (Pb): 2973.3 [psi]

Flow line pressure (Pn): 50.8 [psi]

Separator pressure (Ps): 43.5 [psi]

Casing pressure (Pc): 58 [psi]

Oil specific gravity (qo): 32 [oAPI]

Well and reservoir data


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Mk-75

TECHNICAL WELL DATA

WELL

CHRISTMAS TREE

CASING

CASING

CASING

Diameter

( in )

depth

( ft )

Depth

(ft)EQUIPMENT

PRODUCTION DEPARTMENT

Design

DATE

30 Jan, 2004

"CANADA"

95/8

J-55 2624.7

7 J-55 7024.3

2624.7 ft

7024.3 ft

PERFORATED

INTERVAL

6952 ft

6932.4 ft

6971.8 ft

6886.5 ft

6889.8 ft

6896.3 ft

ISOLATION

INTERVAL

6830.7 ft

6817.6 ft

ISOLATION

INTERVAL

6807.7 ft

6794.6 ft

6689.6 ft

6382.1 ft

6381.2 ft

4858.9 ft

3244.8 ft

1

2

3

4

5

6

7

8

PERFORATED INTERVAL 6952-6932.4

6830.7-6817.6

6807.7-6794.6

RESERVOIR PRESSURE (psi) 1886

RESERVOIR TEMPERATURE (F) 230

DESIGN FLUID PRODUCTION (bbl/day) 63

WATER CUT (%) 65

Slavoljub Stojanovi,

Artificial Lift & Well Completion Engineer

L1 J-202. 3244.8

L3 J-203. 6381.2

L2 J-20 4858.9

1. 6896.3

4. 6384.5

5. N-1 Packer 6689.6

6.

7.

6886.5

8.

6889.8

Tubing Dt=27/8in EU, J-55

Gaslift valve

Gaslift valve

Operating Gaslift valve

"D" NIPLE with bumper spring

"P. L." Packer

"D" NIPLE

Bottom hole 6971.8

ISOLATED INTERVAL

(ft)

NIS-NAFTAGAS

Serbia & Montenegro

40

lb/ft

23

95/8 x 7 x 27/

8 for 3000 psi

ISOLATED INTERVAL


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Production Rate History (after the last workover)

0

2

4

6

8

10

12

14

16

18

20

22

24

26

maj.77

nov.7

7

maj.78

nov.7

8

maj.79

nov.7

9

maj.80

nov.8

0

maj.81

nov.8

1

maj.82

nov.8

2

maj.83

nov.8

3

maj.84

nov.8

4

maj.85

nov.8

5

maj.86

nov.8

6

maj.87

nov.8

7

maj.88

nov.8

8

maj.89

nov.8

9

maj.90

nov.9

0

maj.91

nov.9

1

maj.92

nov.9

2

maj.93

nov.9

3

maj.94

nov.9

4

maj.95

nov.9

5

maj.96

nov.9

6

maj.97

nov.9

7

maj.98

nov.9

8

maj.99

nov.9

9

maj.00

nov.0

0

maj.01

nov.0

1

maj.02

nov.0

2

maj.03

nov.0

3

Year

FluidProduction

Qfm3/dan

Qf

Workover

ROB-l (UKL)

(20.11.2000.)


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DateWorkover

TypeReasons for Workover and

Short Description of Workover Operation (WO)Notes

19.05.31.05.19781.

NO1

Interval 70086995 ft was perforated with 12 bullets. After unloading ofWell, it started

produc ing oi l wi th

height water cut 80

%.

01.06.08.06.1981.

NO2

Immediately after initial natural flow was obtained, the well stoppedproducing. Two more trays of unloading didn't result in fluid naturalflow, so it was decided to close the existing interval and to perforatenew one at shallow depth of the same reservoir.The existing interval was isolated with setting d ri l lable cement

retainer at 6924 ft. Interv al 6952-6933 ft w as perfor ated wit h 12

bullets/m'.

After unloading of

Well, it started

produc ing oi l wi th

natural flow.

06.11.11.11.1994.

DO +UGL

During the period after the last workover, the well was producing fluidwith natural flow after which started the increase of water cut anddecrease of operating pressure. Those were the reasons why the wellstopped producing.Previous interval, 6952-6933 ft, was re-perforated with 12

bullets/m' Reservoir pressure couldn't establish fluid natural flow andartificial lift method should have been designed.Well was equippedwith 4 gas-l i f t valves

19.10.20.11.2000.

ROB-L (UKL)

Well had been producing fluid due to intermittent gas-lift from the lastworkover (1994.) to the year of 2000. During that period productionrate had permanent slope from beginning point of 50.3 bbl/day to lastmeasured data that was 11.3 bbl/day.Well was equipped w ith 3 gas-l i f t valves (operating valve at

6381.2 ft) and bum per sp ring at 6384.5 ft.

There was a try of installing a Plunger lift in order to dissolve aproblem of a big fall back, accumulated paraffin in column of tubing.

First instal lations of

Plunger lif t in the

well with Intermittent

Gas lift.

No. Depth[ft]

Type NamePort InsideDiameter

[in]R=Ap/Ab

1. 3244.8 NITROGEN J-20m 0.25 0.067

2. 4858.9 NITROGEN J-20m 0.25 0.067

3. 6381.2 NITROGEN J-20m 0.375 0.067

Injection Gas Composition and Characteristics:

Component C1 C2 C3 nC4 iC4 nC5

% 86.47 5.09 2.42 0.88 0.85 0.27

iC5 C6 C7+ CO2 N2 H2S

0.33 0.10 0.01 / 2.08 1.50

Kick-off Injection Gas Pressure (Pko): 870 [psi]

Operating Injection Gas Pressure (Pin j): 812 [psi]

Injection Gas Specific Gravity (g) air=1: 0.65Available Injection Gas Rate (Qginj): unl imited [scf/day]

Test Rack Opening Pressure (Tsh): 59 [F

Workover and stimulation history

Gas-lift Valve and Gas Injection System Characteristics


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ANALYSIS OF WELL WORK BEFORE THE INSTALATION OF PLUNGER LIFT

Date: 19.08.2000

Valve Closing Pressure (Pvc): 609.2 [psi]

Valve Opening Pressure (Pov): 623.7 [psi]

Tubing Maximum Pressure (Pwhmax): 159.5 [psi]

Tubing Minimum Pressure (Pwhmin): 58.1 [psi]

Duration of Lift Period (tl i f t): 420 [sec.]

Number of Cycles (nc): 24 [cyc/day]

Duration of Gas Injection Period (tin j): 240 [sec.]

Date: 19.08.2000.

Fluid Production Rate (Qf): 7.8 [bbl/day]

Water Cut (WC): 65.00 [%]

Injection Gas Rate (Qgu): 63.56 [Mscf/day]

Specific Injection Gas Consumption (GORin j): 260 [bbl/ft3]

Production Test Data

Two Pen Chart Data


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Figure 3. Casing and Tubing Pressure Diagram (Date: 19.08.2000)


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Date: 19.08.2000.

WELL TYPE: Low product iv it y Qf= 7.75 bb l/day ; WC= 65 %MAIN OPERATINGPROPERTIES:

- Intermittent gas-l i f t well. Au tomatic cyc les con trol ler

1. Tubing Pressure Curve: a) Unequal peaks of pressure show that some ofcycles are empty or that a realizedproduct ion by a cycle is too smal l .

Date of analysis: 19.08.2000.

The entering data for the model application are divided into three groups. The first groupcontains the data concerning well completion, and reservoir and fluid characteristics, the secondgroup concerns specification, gas lift valve input depth, and gas injection system characteristic.The data obtained from the two-pen pressure and production measuring diagram chart are inthe third group. The data on well bore pressure and temperature measuring, and on the valvedepths, are graphically shown as the final results. All the data are directly taken from theprogram (Solea,M., Cvetianin, S.:"POVLIFT - Computer program for designing and optimizingintermittent gas lift The sixth SPE Computer conference, June, 1991. Dallas, Proceedings, Pg. 68-

88 SPE Paper No. 22296.).

Model application results:

Date:GAS-LIFT VALVES OPERATING PARAMETERS

No. PVC[psi]

TRO[psi]

TVL[F]

PTL[psi]

1 609.2 609.2 131 174.1

2. Casing Pressure Curve: a) Accord ing to the shape of casing pressurecurve (round and low peaks) i t could be

conclud ed that the t ime of gas in ject ion is too

high, and that because of a sm al l range of

valve affect insuf f ic ient gas amo unt is in jected.

Two Pen Chart Visual Analysis

Two Pen Chart Computer Analysis

Quantitative Casing & Tubing pressure Diagram Analysis

By using the new Model


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Operating Valve Depth (L ov): 2943 [ft]

Tubing Pressure at Operating Valve Depth (Ptl): 392 [psi]

Fluid Production Rate per Cycle (Qfc ik): 0.322 [bbl/cyc]

Initial Liquid Slug Length (hsl i): 781 [in]

Surface Liquid Slug Length (hsl p): 53 [in]

Initial Liquid Slug Volume (Vs li): 4.53 [bbl3]

Liquid Fallback (FB): 69.8 [%]

As it can be seen from the shown results, the operating valve is 2943 ft depth, which meansthat the designed injection point was not reached, and that the well was not relieved.The conditions of well performance have been simulated based on these data (Figure 4).

Figure 4. Operating valve depth determination and well performance conditions simulation

Solea,M., Cvetianin, S.:"POVLIFT - Computer program for designing and optimizing intermittent gas lift

The sixth SPE Computer conference, June, 1991. Dallas, Proceedings, Pg. 68-88 SPE Paper No. 22296.


13/19


According to the results of the two-pen surface pressure qualitative analysis, as

well as to quantitative analysis with the POVLIFT, better working conditions of the wellperformance ( first of all, consumption) can be expected, if the following recommendationsare realized.

Provide the gas injection point be dislocated to the last valve (6396.1 ft).

Solve the emulsion problem by demulgator injection through bend tubing, andafter that make the detailed pressure measuring.

If the results are not satisfying, perform the well workover with the new valveschedule and testing.

The reverse inflow high value (FB=69.8 %), as well as the paraffin problem, are

the facts which could make the use of plunger successful.

Analyzed date (production rate history, reservoir and fluid characteristics) have beenused in computers programmed POVLIFT and GKLIP in order to get a projectedparameter, and also a suggestion of well equipment.

Date: 18.10.2000

WELL NAME: M-75

Inside Valve

Temper

ature Bellows Test RackNo Valve Valve Port Closing pressure at Charge Opening

Depth Name Diameter at Surface at Valve DepthValveDepth

Pressure Pressure

[ft] [in] [psi] [psi] [F] [psi] [psi]

1 3244.8 J-20m 0.25 754.2 816.8 139 702.6 750.6

2 4858.9 J-20m 0.25 740 828.5 178.4 610.89 710.5

3 6381.2 J-20m 0.375 667.2 751.3 215.2 567 665.3

Designed production rate 56.6 bbl/day

Depth of down hole Stop Assembly 6382.1 ft

RECOMMENDATIONS FOR FUTURE WORKS

Gas-l i f t Design


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ANALYSIS OF WELL WORK AFTER THE INSTALATION OF PLUNGER LIFT

Date: 15.01.2001

Valve Closing Pressure (Pvc): 639.6 [psi]

Valve Opening Pressure (Pov): 699.1 [psi]

Tubing Maximum Pressure (Pwhmax): 382.9 [psi]

Tubing Minimum Pressure (Pwhmin): 60.9 [psi]

Duration of Lift Period (tl i f t): 320 [sec.]

Number of Cycles (nc): 24 [cyc/day]

Duration of Gas Injection Period (tin j): 540 [sec.]

Date: 15.01.2001

Fluid Production Rate (Qf): 64.1 [bbl/day]

Water Cut (WC): 65 [%]

Injection Gas Rate (Qgu): 57.5 [Mscf/day]

Specific Injection Gas Consumption (GORin j): 29.4 [bbl/ft3]

Production Test Data

Two Pen Chart Data


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Figure 5. Casing and Tubing Pressure Diagram (Date: 15.01.2001)


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Date.15.01.2001

WELL TYPE:Product ion inc rease to Qf= 64.1 bb l/day ; WC= 65 %,

Speci f ic Gas Consum pt ion is decreased to 29.4 bbl /scf

MAIN OPERATINGPROPERTIES:

- Intermittent gas-l i f t well. Au tomatic cyc les con trol ler

1. Tubing Pressure Curve: a) Stabil ized, insu ff iciently s harp and ro undpeaks of maximum tubing p ressure show that

an excessive amount of gas has been in jected

Date of analysis: 15.01.2001.

Model application results:

GAS-LIFT VALVES OPERATING PARAMETERS

No. PVC[psi]

TRO[psi]

TVL[F]

PTL[psi]

1 667.2 667.2 210.2 317.6

Operating Valve Depth (L ov): 6381.2 [ft]

Tubing Pressure at Operating Valve Depth (Ptl): 532.5 [psi]

Fluid Production Rate per Cycle (Qfc ik): 2.58 [bbl/cyc]

Initial Liquid Slug Length (hsl i): 1140.3 [in]

Surface Liquid Slug Length (hsl p): 445.9 [in]

Initial Liquid Slug Volume (Vs li): 6.5 [bbl3]

Liquid Fallback (FB): 14.8 [%]

2. Casing Pressure Curve: a) Character is t ic shops of casing pressure risewith roun d peaks and two typ ical decliv i t ies

both on the r is ing port , and on reduct ion of

pressure which indicates moments of the

motor valve opening, as w el l as opening and

closing of operat ing valve. Pract ica l ly al l

peaks are simi lar what sho ws a regular work

of the system.

Two Pen Chart Visual Analysis

Two Pen Chart Computer Analysis

Quantitative Casing & Tubing pressure Diagram Analysis

Using the new Model


17/19


As it can be seen from the shown results, the operating valve is 6381.2 ft depth,which means that the designed injection point was reached, and the injection is donethrough the Operating Gas lift valveThe conditions of well performance have been simulated based on these data (Figure 6).

Figure 6. Operating valve depth determination and well performance conditions simulation

Solea,M., Cvetianin, S.:"POVLIFT - Computer program for designing and optimizing intermittent gas lift

The sixth SPE Computer conference, June, 1991. Dallas, Proceedings, Pg. 68-88 SPE Paper No. 22296.


18/19


CONCLUSION

A number of wells in the oil field MZ in which a gas lift method has beenapplied, are in use for more over than 20 years.

Negative factors noticed in those wells:

1. Decrease of a reservoir pressure: from 3045 psi to 2030-1305 psi

2. Increase of water cut over 60-80 %

Wells with an intermittent gas lift method comes into a period when specificgas consumption is high, and production becomes non efficient. In such conditionsone of the possible methods to decrease specific gas consumption in wells withintermittent gas lift was a use of a Plunger lift.

According to the received results of the analyzed well Mk-75, a Plunger liftmethod showed to be successfully carried out after which we started with a seriousutilization of this method.

Main characteristics of the Plunger lift use in the oilgas field MZ:

1. Specific gas consumption is much lower then in case of intermittent gas lift.

2. fall back of liquids have been decreased after the use of Plunger lift

3. A problem of paraffin deposition is permanently drawn down after the use ofPlunger lift method.

The utilization of Plunger lift method is very attractive to use concerning thefinancial aspect, because of its simple equipment as well as maintenance.

It should be expected that a development of technology and new methodswould provide some new models possible to create in the nearest future. And, alsofind a solution if not for all existing problems than for a bigger part of them.


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References:

1. Beauregard, E., Ferguson P.I.:"Introduction to Plunger Lift: Applications, Advantages andLimitations", Presented at the Sauthwestern Petroleum Short Course, 1981.

2. Brown, K.E.: The Technology of Artificial Lift Methods, Vol. 2A, Tulsa, Oklahoma, 19803. Chacin.J. Schmidt.Z. Doty.D: Modeling and Optimization of Plunger Lift Assisted

Intermittent Gas Lift Installations,SPE. 23683

4. Solea, M. - Intermittent and plunger lift optimization, Training school material, Novi Sad,1995.

5. Solea.M. uri.S. Miljkovi.M. Iveti.Z : Analysis of Intermittent Gaslift application onField MZ, Feasibility study, 1993.

6. Solea,M., Damjanov, J., Miljkovi, M., amber, D., uri, S.:" Work Study of the Plungerlift applied in the well Mk-125", NIS Naftagas, Novi Sad, 1999.

7. Solea,M., Cvetianin, S.:" POVLIFT - Computer program for designing and optimizingintermittent gas lift The sixth SPE Computer conference, June, 1991. Dallas, Proceedings,Pg. 68-88 SPE Paper No. 22296.

8. Slavoljub,S.: "The possibility of Plunger lift Use for Exploitation of Gas Wells with liquidloading problems", Final exam work paper at University, Belgrade, 2000.

9. Slavoljub,S.: "Optimization of Oil Production in the MZ by the use of the Plunger liftmethod", Kikinda, July 2001.

10. Slavoljub, S.: "Utilization of the Mechanical method in Oil Exploitation by the use of aPlunger Lift in the Wells with Intermittent Gas lifts ", Novi Sad, November 2002.

11. Technical documentation, NIS Naftagas, Serbia & Montenegro

paper nis nafagas intermittent gas lift

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