gas+lift+with+nitrogen+injection+generated+in+situ

5/21/2018 GAS+LIFT+WITH+NITROGEN+INJECTION+GENERATED+IN+SITU

Copyright 2000, Society of Petroleum Engineers Inc.

This paper was prepared for presentation at the 2000 SPE International Petroleum Conferenceand Exhibition in Mexico held in Villahermosa, Mexico, 13 February 2000.

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ABSTRACT

Gas lift is a feasible option as an artificial lift system in a

depleted field. In the Bellota field there is no substructure

means to install any type of artificial lift system, therefore

the use of nitrogen as a gas lift source is necessary to

keep the Bellota wells producing. After evaluating

different options we implemented a nitrogen generatedin situ project using the membrane technology.

This paper analyzed the gas lift process design by using

nodal analysis and optimum allocation of nitrogen in

each well. Special emphasis and consideration was

given to this project from an economical, operational,

technical and environmental points of view. It is olso

compares this option with differents alternatives

including the traditional gas lift method using natural gas

as a source as well as the use of stored nitrogen fromstorage trucks (Tanks). Our evaluation of results

obtained from the different options investigated in this

study clearly indicates that this method is a good option

in this particular situation.

Nitrogen injection generated in situ with membr

technology can be a feasible and profitable altern

source of gas lift as shown in this study.

INTRODUCTION

Bellota Chinchorro is one of the seven producing ar

in the Southern Region of Mexico. The curr

production of this field is 105 000 STB/D of oil and

MMSCF/D of gas produced from dolomite formatio

belonging to Jurassic and Cretaceous age.

The objective of this study are the wells drilled in

Bellota field. Initial production of the bellota field sta

in 1982 reaching a peak production of 44 000 STB/D

1995. Current production is at 20 000 STB/D, ma

attributed to natural depletion. Year- to- date produc

from this field is estimated at 140 MMSTB, and

expected to produce another 50 MMSTB from calcula

total reserves.

This field is divided in two different sections. The w

that will be discussed in this gas lift application belon

the north section. These wells are currently deple

below saturation pressure. It is presumed that a gas

has been already formed in the top of the reservsince GOR has been decreasing gradually. In addit

the reservoir pressure has decline drastically makin

necessary to provide some form of artificial

assistance to keep the wells producing.

Those wells that have been converted to gas lift,

deep wells, which have so many disadvantages for

SPE 59028

GAS LIFT WITH NITROGEN INJECTION GENERATED IN SITUMiguel A. Lozada Aguilar, M.del Remedios Arredondo Monarrez, SPE, Pemex, PEP.


2 MIGUEL A. LOZADA AGUILAR, M.DEL REMEDIOS ARREDONDO MONARREZ SPE 59

artificial lift system. Some electric submergible pumps

have been tested before with poor results, and then, a

gas lift system by using nitrogen as source was installed,

since no facilities were available to handle natural gas as

a source for gas lift.

In the very beginning, storage trucks were used to

deliver nitrogen, but since this method was so

expensive, an in situ nitrogen generation project was

implemented, using the membrane technology. In this

way, it was possible to reduce 50% the total costs in

three gas lift wells.

In March 21 of 1998, gas lift started in wells Bellota 136,

138 and 158-D using nitrogen generated in situ with

membrane technology as a source.

PRINCIPIA OF MEMBRANE EQUIPMENT FOR

NITROGEN GENERATION

Nitrogen generation through membrane equipment is

carried out by pumping an air current into membrane,

which due to its especial material design let the air to be

separated into nitrogen and oxygen mainly. This is

achieved basically because the oxygen flows faster than

nitrogen through it, being expulsed to the atmosphere,

as long as the nitrogen is absorbed into the membrane

to be delivered to the next compression stage. Before

the separation process, air composition is 78% of

nitrogen, 21% of oxygen and 1% of rear gases;

Neverdeless just after the separation process, gas

mixture will be expulsed into the atmosphere with 40% of

oxygen content, and the one that has been absorbed

into the membrane has from 95% to 98% of nitrogencontent.

Membranes are built up from a polymeric thin cap, which

has special physical properties that make the separation

efficiency to have a variation base on: pressure,

temperature, permeability, membrane aria and

selectivity. Since 1987, when they have been reported

for its use in petroleum industry, they have evolved u

now, having 60% of better permeability and 30%

better selectivity, besides, a significant reduction

consumption energy has been achieved (Figure No.1

Equipment to be installed on location together w

membrane unit is the following: two air compress

pack, an air nitrogen compressor pack, flow meter

and additional equipment. A brief functional descrip

for each component is given next to it.

a).- Two air compressor pack.

This pack has the function of comprise the air, wh

comes from the atmosphere to be deliver into the n

compression stage. Air pressure is increased fr

atmosphere pressure to 200 PSIG. Those

compressors handle 5.6 MMSCF/D with 1100 HP

potency.

b).- Air nitrogen compressor pack.

This pack has the function to raise the air pressure t

comes from the previous stage to be deliver into

membrane unit at 400 PSIG, and it has also the func

to increase the pressure of nitrogen which comes f

membrane unit in two stages, one of them from 4

PSIG to 900 PSIG and the other one from 900 PSIG

2000 PSIG, to be deliver into the gas line for gas

purpose.

c).- Membrane unit.

This pack has the function of separate 5.6 MMSCF/D

air to obtain 2 MMSCF/D of nitrogen with 95% to 98%

quality. This unit is built up of 36 cylinders, the ones

the membrane element inside of them.

d).- Flow meter unit.

This unit has the function of measure the amountnitrogen that is deliver into the gas line for gas lift.

e).- Additional equipment.

This equipment helps in order to let the main equipm

accomplish its function. Some of the most import

devices are: filter system, coolers, start on compres

energy plant and fuel storage.


SPE 59028 GAS LIFT WITH NITROGEN INJECTION GENERATED IN SITU

GAS LIFT NETWORK AND WELLS CONVERSION

Those three wells, which will be converted from natural

flow to gas lift, were drilled in the same location, thereby

gas lift line construction was cheap and quickly, as

distance from each well was no longer tan 500 FT. It

was also necessary to install flow meter and regulation

valves for each well. The nitrogen generation equipment

was installed in the same location (figure No. 2).

In the other hand, in order to make the wells conversion

cheaper, it was concluded that no workover rigs should

be necessary, as operation conditions for each well

permitted start the wells on production just by injecting

gas in one point, that means not to use any upper

injection valve. In this way a puncher charge was shot,

taking in account the equivalent diameter for an specific

drop drown from casing pressure to tubing pressure.

This was achieved basically, because a high pressure

was available in the gas line (2000 PSIG).

EQUIPMENT DESIGN

In order to design the equipment dimensions, it was

necessary to use three different software: nodal

analysis, gas lift design and equal slope method to

allocate the amount of gas for each well.

Based on the results getting from the equal slope

method and gas lift design software, it was concluded

that 2 MMSCF/D of N2 will be necessary to be injected

in those three wells, and 1600 PSIG will be required on

surface pressure; thereby, according to manufacture

specifications, one equipment for 2 MMSCF/D and 2000PSIG was selected for this purpose (figure 3 and 4).

Gas lift design criteria was to find out the deepest

injection point, thereby, with static conditions was

possible to start the wells on production with 2000

PSIG of surface pressure. Injection points were

located just above of packers, due basically, that

reservoir pressure was low enough, end in the o

hand, wells productivity index were high enough

reach dynamic conditions with only one gas injec

point. Thanks to those conditions mentioned befo

it was possible to shoot the tubing by using punc

charges, rather than use workover rigs to pul

tubing string and put it back with gas lift valves.

Due basically, that there wasnt any availa

surface control valve for high pressure, it w

necessary to install chocks in order to allocate

optima amount of gas for each well; thereby it w

necessary to design the right diameter for each

of them, using Bernulli equation.

ECONOMICAL ANALYSIS

a) Assumptions for different scenarios

In order to asses the feasibility of this project, th

scenarios were madein a period of time of five years:

1) build up a gas lift network in order to use natural

as a source, installing compressors in the locatio

increase gas pressure to that one which

necessary for each well.

2) Inject nitrogen as a gas lift source by using stor

trucks.

3) Inject nitrogen as a gas lift source, by generatin

with membrane technology, with leasing option.

4) Inject nitrogen as a gas lift source, by generatin

with membrane technology, with purchase option

Those assumptions used for this analysis are referee

July, 1998 (table No.1).

The economical premises are defined as following:

Oil price: It is refereed to July 1998.

Production race: For comparison purpose, accord

to allocation of gas for each well, getting from eq

slope method, it was possible to increase 3



STB/D by injecting 2 MMSCF/D of nitrogen, and

4125 STB/D by injecting 2 MMSCF/D of natural gas.

Discount rate: It was used that one from Pemex

projects, which is 10%.

Initial investment: Initial investment was considered

in this way:

For gas lift network option, it was considered to

built up 13 miles of gas lift line of 6 in. and 3 in..

For membranes leasing option, it was

considered to invest on nitrogen line from

membrane equipment to each well.

For membrane purchase option, it was

considered to invest on nitrogen line from

membrane equipment to each well.

For storage trucks option for nitrogen injection,

there wasnt any investment.

Operational costs: In order to obtain those costs, it

was considered the production increase for each

option, as well as the total operational costs for each

option, getting, in this way the cost for each

produced barrel.

Operational costs for that to build up gas lift

network, is an addition of: differential costbetween to buy 2 MMSCF/D of natural gas and

to sell the same amount of sour gas; leasing of

compressors to increase gas pressure from gas

line pressure to that which is required to inject in

to the well; and comprising costs to inject sour

gas toward sweeter station; which yield

657.8+48+184.2 = 1249 USD/D.

Operational cost for that to leasing storage

trucks for injecting 2 MMSCF/D of nitrogen is

equal to 18,650 USD/D.

Operational cost for leasing membranes to

generate 2 MMSCF/D of nitrogen is equal to 11,

275 USD/D

Operational cost for membrane purchase is a

to that of comprising costs in gas lift netw

option, which is equal to 184.2 USD/STB.

Field depletion: it was taken that one w

represents field performance.

b) Interpretation of economical indicators.

Some of the indicators shown here are quite far good

any petroleum project, basically because the h

production rate to be expected (table 2). So

comments are summarized as following:

- Giving the risk approach form internal rate of re

all of the four option are excellent, as it is unlikel

reach the same value for discount rate in any ban

- Regarding to investment efficiency all the values

quite high, so it means that all the four options

profitable.

- Pay back period is very short for every option

cash flow will be available since the early stages.

- Net present value could be the indicator to

considered for making a good decision, since op

1 and 4 represent the highest values, and they a

represent an important difference between

others options.

- As net present value for option 1 and 4 are q

similar, best option should be that which has so

else benefits; whether environmental, technica

operational aspects concerns.

TECHNICAL, OPERATIONAL AND ENVIRONMENT

ISSUES

Technical comparisons:

According to equal slope method, figure 6 sh

how injecting the same amount of gas, whet

nitrogen or gas at the same depth, it is possible

obtain 400 STB/D more injecting natural gas t

nitrogen. The explanation of this is because nitro



is heavier than natural gas, thereby getting a higher

gradient all along the tubing; therefore, the higher

flowing bottom hole pressure, the lower liquid rate

based on productivity index ecuation. For this

specific case a 10% production rate increase could

be achieved (figure 5).

In the other hand, shows how the higher nitrogen

weigth in the annulus, the surface requirements

pressure is lower from that with natural gas injection,

therefore less potency is required. For this particular

case it is expecting to reduce 10% of total costs due

to potency reduction (figure 6).

Operational and environmental comparisons:

Nitrogen is an unfinished source available in the

atmosphere, thereby its use doesnt have to deal

with hydrocarbon exploitation.

Nitrogen plants can be installed in the most

convenient place, as they dont need natural gas

supply.

As nitrogen is an inert gas, safety problems are

reduced enormously.

Petrochemical plants can only handle 3% of impurityas a total amount of gas, thereby nitrogen uses as a

gas lift source is constrained by the total processed

gas. For this particular case the impurity percentage

was no higher than 0.5%.

As it is known nitrogen generated with membrane

technology has from 5 to 2% of impurities, mainly

oxygen. Somewhere during membrane operation,

there were some corrosion problems in the process

facilities, but unfortunately by that time it was

necessary to stop membrane operation for budget

reasons, without giving the chance to evaluate

oxygen impact on this problem, specially because

sour gas is produced in those wells. So this is a big

concern as this technology is a good option for this

particular case, anyway, if it was true, it is poss

to use chemical products to avoid this phenomen

CONCLUSIONS

Nitrogen injection as a gas lift source is feasible

it is an unfinished and available source in

atmosphere.

Nitrogen injection as a gas lift source has a sim

profitability as that with natural gas injection.

At this moment with the current conditions on

leasing contract, it is more profitable for PEMEX

buy and install its own plant.

It is possible to save 10% of potency injec

nitrogen rather than natural gas.

There is a significant reduction on risks, as nitro

is an inert gas, besides of that a significant reduc

of gas line mileage is achieved.

Reduction of 10% of production rate is expected

a result of inject nitrogen rather than natural gas.

Further investigation will be needed to evaluate

nitrogen impurities on corrosion problems.

The amount of nitrogen used for gas liftconstrained by the total gas handled

petrochemical plant, which shouldnt be no hig

than 3%.

REFERENCES

- Nodal analysis software, PIPESIM, Baker Jard

and Associates Limited.

- The technology of artificial lift methods volume

kermit Brown.

- Gas lift optimitation and design software GL

Cealc.

- Temas selectos sobre bombeo neumtico contin

Colegio de Ingenieros Petroleros de Mxico.



- Optimizacin de la distribucin de gas en la red de

bombeo neumtico del campo Cunduacn

Oxiacaque, AIPM, Miguel Angel Lozada Aguilar y

Maria del Remedios Arredondo M.

- Technical and operational manual of membrane

plants.



Figure 1

Figure 2

MEMBRANE DIAGRAM

FIBER

NITROGEN

AIR FEED

WASTE OXYGEN VENTWASTE OXYGEN VENT

FIELD MEMBRANE DIAGRAM

BELLOTA 158-D

WELL

BELLOTA 138

WELL

BELLOTA 136

WELL

MEMBRANE EQUIPMENTGAS METER

M

EM

BRAN

E

COMPRESSOR

COMPRESSOR

COMPRESSOR

FLOW LINE

NITROGEN LINE

PROCESS

FACILITIES



Figure 3

Figure 4

WELL PERFORMANCE WITH NITROGEN INJECTION

0

20 0

40 0

60 0

80 0

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1

NITROGEN INJECTION RATE(MMSCF/D )

LIQ

UIDR

ATE(

STB/D)

BELLOTA 13 6

BELLOTA 138

BELLOTA 158-D

Iny.P.=1437 PSIG

Iny. P.=1380 PSIG

Iny.P.=1671PSIG

EQUAL SLOPE METHOD

CHARACATERISTIC CURVE FOR THREE WELLS WITH NITROGEN INJECTION

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

Nitrogen injection rate (MM SCF/D)

Liquidrate(STB/D)

41004100



Figure 5

Figure 6

E Q U A L S L O P E M E T H O D

N A T U R A L G A S V S . N I T R O G E N I N J E C T I O N C O M P A R I S O N

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

3 0 0 0

3 5 0 0

4 0 0 0

4 5 0 05 0 0 0

0 0.25 0.5 0 .75 1 1.25 1.5 1 .75 2 2. 25 2.5

G A S I N J E C T I O N R A T E ( M M S C F / D )

LIQUIDR

ATE

(STB/D)

4 1 0 04 5 0 0

N A T U R A L G A S

N I T R O G E N

S U R F A C E R E Q U I R E M E N T S P R E S S U R E

N A T U R A L G A S V S . N I T R O G E N C O M P A R I S O N

1 5 0 0

2 0 0 0

2 5 0 0

3 0 0 0

3 5 0 0

4 0 0 0

4 5 0 0

5 0 0 0

5 5 0 0

7 0 0 9 5 0 1 2 0 0 1 4 5 0 1 7 0 0 1 9 5 0

P r e s s u r e ( P s i)

Depth(m

)

N I T R O G E N N A T U R A L G A S



Table 1

Table 2

BASIS FOR ECONOMICAL ANALYSIS

OPTIONOPTION CONCEPTCONCEPT PRICE PERPRICE PER

BARRELBARREL

(USD)(USD)

PRODUCTIONPRODUCTION

INCREASEINCREASE

(STB/D)(STB/D)

DISCOUNTDISCOUNT

RATE (%)RATE (%)

CAPITALCAPITAL

INVESTMENTINVESTMENT

(USD)(USD)

OPERATIONALOPERATIONAL

COSTS (USD/STB)COSTS (USD/STB)

FIELDFIELD

DEPLETIDEPLETI

ON (%)ON (%)

GAS LIFTGAS LIFT

NETWORKNETWORK

NITROGENNITROGEN

INJ. WITHINJ. WITH

STORAGESTORAGE

TRUCKSTRUCKS

MEMBRANEMEMBRANE

LEASINGLEASING

MEMBRANEMEMBRANE

PURCHASEPURCHASE

22

33

44

11 1010

1010

1010

1010

41254125

37253725

37253725

37253725

1010

1010

1010

1010

1010

1010

1010

1010

0.30280.3028

5.00065.0006

3.0273.027

0.0490.049

1253,0001253,000

150,000150,000

1710,9601710,960

00

PROFITABILITY INDICATORS

OPTIONOPTION CONCEPTCONCEPT NET PRESENTNET PRESENT

VALUE (DLS)VALUE (DLS)

INVESTMENTINVESTMENT

EFFICIENCYEFFICIENCY

EFFICIENCYEFFICIENCY

RATE (%)RATE (%)

INTERNALINTERNALRATE OFRATE OF

RETURN (%)RETURN (%)

PROFITABILI-PROFITABILI-

TY RATETY RATE

(%)(% )

PAY OUTPAY OUT

TIMETIME

(YEARS)(YEARS)

GAS LIFTGAS LIFT

NETWORKNETWORK

NITROGENNITROGEN

INJECTIONINJECTION

WITHWITH

STORAGESSTORAGES

TRUCKSTRUCKS

MEMBRANEMEMBRANE

LEASINGLEASING

MEMBRANEMEMBRANE

PURCHASEPURCHASE

22

33

44

11 44380,05844380,058

29,481,60729,481,607

40575,59240575,592

3636

10,00010,000

19 819 8

2525

8282

34 734 7

11 611 6

7474

0.08650.0865

0. 01580. 0158

0.12810.1281

90 090 0

539353,083539353,083

49954995

0.030.03

11551155

63106310

78 078 0

678996,700678996,70021221,89021221,890 1.47 x 101.47 x 10

-7-7

gas+lift+with+nitrogen+injection+generated+in+situ

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