.

SPE
SPE 9912

NITROGENFOR THE ENPANCED RECOVERYOF OIL AND GAS

by J. P. Clancy,
.-. Niject ServicesCompany;R.
..- E. Gilchrist,
Consultant;and D. E. Koll, Niject Serviws Company

ABsrRAcT ring the past four years, nitrogen has been

leotedto unhance the reaoveryof oil in fcxarteen
Nitmge% producetiby air separationand compressed ~lds. Injection rates of upwarde of 350 million
to high pmseure has many potential applicationsin mderd cubic feet per day of nitrogen will be
enhanoed oil and gae recovezy. Fossible appli- tievsdduring this year.
cations inolude u8ing nitrogen as a driving gas for
costly and limited carbon dioxide, and in some yg 3 APPLICATIONOl?NITRCGEN IN ENHANCED RECOVERY
cases for miscible displacement. The displacement
of gas cap gaee the productionof attic reservoir% 3re are a nuaber of oil and gas recovery methode
the oycling of condensate reservoirs,the mainten- Wk Lch can utilize nitrogen. They range from the
anoh of reservoir preseure and other applications Sii npleet (pressuremaintenance)process to &he most
can also be considered. Nitrogen can be produced COInplex (miscible)technique. The common fa~or in
at almost any reeervoir site using proven tech- al: L of these processes ie the use of nitrogen. SiX
nology and various energy soureas. Depending upon of these recowry methods utilizing nitrogen will
the pressure, qu?.tities? and location, nitrogen be disoussedhere.
may cost one-qwxuer (1/4) to one-half (1/2) the
price of natural gas. Using existing technology, k PRESSURE MAINTENANCE, IMMISCIBLE DISPLACEMENT
nitrogencan be separated f.~omthe produced associ- AND GRAVITY ENHANC~NT
ated natural gas.
Ferhaps one of the ,Ldest, and yet simplest
INTRODUCWCON methods of oil reo”.-ry (gas injection), is a
growing application for nitrogen. (Figure I)
The oil and gas industry, facing rising demand and For many years, natural gas produced with, and
declining production, has entered into one of the separated from# crude oil was reinfected into
most exciting and challenging periods in its 120 the reservoir as a consemmtion measure. When
year history. Increasesin the price of crude oil natural gas was plentiful and inexpensive,
and gas, coupled with an ever increasing demand, additional volumes of natural gas from gas
has made improved seoondaryand te-iary recovery a fielde or residue gas (lean natural gas) from
viable reality. gas processing p~ants was also injected into
oil reservoirs. The natural gas was injected
Enhanced recovery, a term which encompasses im- to maintain pcesaure and thereby increase the
prcved secondary and tertiary recovery, means the amount or rate of oil production.
use of production methods that will provide more
oil or gas than otherwise should be expected from The high market price and limited supply of
conventional primary and secondsw reoovary natural gas severely limits the amount of this
methods. Two of the older methods of saoondary gas which can be allooaeed for injection for
reoovery, gas injection and water flooding, are pressure maintenance. Pressure maintenancecan
being improved upon to inmease the amount of oil inolude immiscible displacement as well as
or gas thee can be recovered. Polymers, caustic enhanoed gravity drainage. An alternativegase
solutions and microemulsionsare or will increase titragen. in many cases can be substitutedfor,
the amount of oil reooveredover conventionalwater could be especially effective as, and would.
flooding. The substitutionof nitrogen for natural cost one-fourth (1/4) to one-.hird (1/3) tha
gas will improve the economies of gas injeotion, market price of natural gas. At least one prcA-
allow more fields to have gas injected and in sme jeot is ourrently underway(1) and sevaral
cases till zvsult in higher recoveries of oil or others will start injeotionwithin one year.
natural gas than would be expected from the injec-
tion of natural gea alone.
 . .
.
P CYCLING OF CONDENSATERESERVOIRS the short supply og C02. Nitrqen may be an
excellent driving gas foz C02 particularly if
Just as nitragan can replaae natural gas in it is injeatedalternatelywith water.
pressure maintenance operation, GO also is it
a substitute for natural gas in aondenaate F. WSCISbE DISPLACIWl?ZNT
WITH NXTROGEN
reservoirs. (2) If the reservoiris at or near
the bubble poii%t,the rask may not sense any There are a certain numMr of reservoirs that
difference in the molsaules being uimulated, aan be considered as candidates for a miscible
be they nitrogen or methane. Nitrogen, as well drive pLocess (7) (8) (9) with nitrogen. The
as natural gas oan be effectively reayoled controlling factors for miscibility are a suf-
through a reservoir maintaining pressure and ficiently deep resezvoir to aontain the needed
keeping condensate from being deposited around miscibility preesures, and oil “light” enough
the well bore. If th%e is correut, then only to become nisoible with the nitragen at reser-
economia considerationscame into play, when a voir preeaures and temperatures. Depths of at
candidategas La being considered. leaat 10,000 feet and reservoir oil gravities
of 4P API or higher may be required to
C. ATTXC OIL PRODUCTION
(
. achieve first aontact miscibility. AS with
most enhanced recovery applications,lah,ratory
A steeply dipping oil reeezwair with an active testing of the praaess using field fluid at
water drive and isolated pzmductios wells can reservoir conditionsis suggested.
leave quantitiesof crude oil trapped alwm the
graduation well. This til, attic oil, too deep SOURCES OF NITROGEN
and too small a quantity to justify the drill-
ing of additional high risk wells, can be pro- Air, whiah consists of approximately78% nitrogen,
duced by the injection of natural gas into a 21% oxygen and 10 other gases, is the primary
single well, by gravity displacement of the resource for nitragen. Currently, there are two
upstructure (attic) oil W the injeoted gas, proceeses for converting larqa volumes of air ilto
and finally by subsequent production of the nitrogen (or a gas consisting of mostly nitrogen -
attic oil via a single well. (3) As natutel approximately88% - and sane aarben dioxide).
gas became scarae or too expensive, nitrogen,
has been substituted for natural gas. (4) The These processes are:
ability to convert one cubia foot of natura~
gas to as many as eight cubic feet of high 1. Air Separation - A cyrogenic (air liquifaation
pressure nitrogen, may allow an operator to and distillation)process which produces a gas
stretch a limited supply of natural gas and consisting of 99.9990
.... . nitrogen
., plus argon an+
achieve increaeedoil production. “ktherinert gases.

1
D. PRODWTION OF GAS CAP GAS 2* Zne* Gas Generation - Process(s) which aon-
vetis products of combustion (nitrogen,carbon
Ckmservation, as well as good oil production dioxide, carbon monoxide, water vapor, residual
practioet restriats the production of gas cap oxygen, oxides of nitrogen) from engine exhaust
gas until oil production is ostensibly finish- or boiler flue gas into a gas consisting of
ed. At such time the Gas Cap Gas is produced. nitrogen (upward of 88%), carbon dioxide and
Said gas cap gas production may not occur for substantially reduced levels of oxides of
many Years after discovexy of the field. When nitrogen, residual oxygen, water vapor and car-
the supply of natural gas is less than demand bon monoxide.
and khe prioe of the natural gas is high, the
postponement of gas cap gas production may Using either process, nitrogen can be generated at
reduae the net present value of the gas. How- almost any location. Both bzacesses are mature
ever, ig nitrogen is injected into the reser- teahnolagies,have been practiced in industry for
voir~ displacing the gas cap gas, this associ- many years, and utilize proven equipment.
ated natural gas aan be produced earlier in the
life of the l!ield. (Figure II) The continua- In oil and gas fie:d applicationsineti gas genera-
tion of high natural gas prices, relatively low tion has been practiced for upward of fifteen
nitrogen prices, reasonable nitrogen - natural years. Many articles have been written that
gas separationcosts, and earlier production of desaribe this process, the equipment reguired, and
the gas aap gas, should yield an improved net it~ operation. Many of these articles appear in
present value. the oil and gas literature.

E. DRIWING GAS FOR C02 (I@G OR RICH) MISCISLE SLUGS Air separation was first introduced into the oil
fields only four years ago. During those four
The use of C02 is receiving considerable years, nine oil field operators have started or
attention at this dine,’as a means of enhanaed committed to using air reparation nitrogen in
raoovezy. The dilemma facing the operator is twelve fields. F?owevsr, unlike the inert gas
the availability of C02, and its ever in- generationprocess, the oil and gas literaturecon-
creasing cost. To this end, attention has been tains little informationon air separation.
direated to nitrogen driving C02 slugs. (5)
(6) As C02 projeats aontinue to grow in Sinae operators (a) are finding increased uees for
number and size, an alternative, EO injeation of nitrogen iR enhanced recovery projaats, (b) have
C02 over the entire life of the flood must be tien selaating air separation ae the source of
considered to meet eaonomia considerationsand nitrogen, and (a) have Mtited information in the
AL and gee literatureon air separation nitrogen the oxygen-riahstream is further distilled
md its campxwxu!ionto high prasaure~ the remainder &o pxoduoe the oxygen produat and a low-
~f this paper will (a) be limised to air separa- purity nitrogen stream which is than dis-
tion, (b) b~efly desariba air separation its hia- aax3ed.
:o~, teahnolagy, and eafety and (o) outline the
quipmene utilized for the compressjan and separa- S. Pm&at Compression
~ionof air and the ccmpresaionof nitrogen. Compression of the gaseous pxmduats to
their use pressure covers a wide range of
~SR SEPARATIONTECHNOLOGY appliaatione fram the typiaal 15 to 30
atmaephe.a aentrifugal oxygen compressors
of the steel and chemical industriesto the
200 to 500 atmosphere rsciproaatingnitro-
The air separation industry in the United gen compressorsused in ~R appliaat:Lons.
States had its origin in a tiny plant imported
from Europe in 1907. In the three quarters of C. Nitrogen only Air Separation for Enhanaad
a centu~ sinae that date, this industry haa Reaovary WP lications “
grown until it now has the capaaity to proaess
almost ten billion cwbic feet per day of nitro- The ayale shown in Figure 3 is typical of the
gen and oxygen and consume over ten billion titrogan-onlyplant required for an EOR appli-
ZTI’US
par hour of energy. cation. The air is acmpressed to about 6
atnmzpheres befcwe cooling to about -2SOOF ?.
n
). The Air SeparationPmaess the reversing “ieat exchanger (mix) Which
removee the water and C02. A silica gel
The cxyogeniapracess for the separationof air absorption trfin then removes any rams<,ting
into ita major components, nitrogen and oxygen, C02 and the hazardous hydroaarbns bafor(~the
can be consideredas five unit operations: air air enters the si~lgledistillationaolumn.
ccmpressione contaminant removal, heat ex-
change? cryagenic dktillat ion and produot com- Here the air is separated into an oxygen-rich
prss~ion. liquid stream whiah ia imiled in the overhead
condenser to provide reflux and a nitrogen
1. Air Compression vapor stream from the top of the column. The
The early plants requiredair at 150 to 200 oxygen-riah stream, afte9: boiling at about
atmaspheres using raeipraaating compres- -290q in the condenser, is expanaed in a
sors. .Modernplants use a low pressure (6 aryogenic turbine to produce refrigerationand
to 7 atmosphere) cycle with centrifugal or returned to the atmosphere da the RHX, return-
axial air aanpressors. ing the C02 and water to the atmosphere. The
nitrogen vapor stream is warmeclin the RRx to
2. ContaminantRemoval ambient temperature and fed to the suation of
The contaminantswhich must be ramovet f~m the pxoauat compressor at about 5 atmospheres
the air before the distillationprocess are pressure.
water vapor, aarlmn dioxide and a variety
of trace hydrocarbons. Two removal systems This is the generallypreferrecicycle for small
are in aommon use: (a) the reversing heat and medium sized EOR applications (up to
exchanger cycle whiah freezes water and perhaps 25 million cubia feet per day). The
C02 on the surface of a heat exchanger alternate cycle ueing a molecular sieve pre-
followed by absorption of lydroaarbons at purifier and double distillation columns has
aryogenic temperacura or (b) the prepuri- more application as an oxygen plant but may
fier aycle in which all contamimnts are find some use in large, over 50 million cubic
adsorbed on moleoular sieve at ambient feet per day (CF19) nitrogen appliaatione.
temperature. Both cycles are well estab-
lished and the selection depends on the D. The Cold sox
value of by-product e fram the plant, the The cryogenic portions of the air separation
aost of energy~ and the volcme of nitrogen plant (heat exchangers distillation cokmub
required. etc.) are normally of aluminum conetnaction and
are enalosed in a well-insulatedcold kx. For
3. =at ~change small to medium size EOR applicationsof up to
The heat exchangers needed to cool +Ae air about 20 million CFD, the cold box is a single
to the cxyogenia temperaturesnecessary for unit whiah is factory assembled, pretested and
distillation aru of brazed alumlnum plate shipped to the site. For larger applications?
and fin aonstruation. These specialized multiple cold @xes may be manifol~ed in the
exchamers are produced in modular sizee field to form a single train, or a multi-train
and manifolded together to prwrlde the faailitymay be preferred.
necessaryheat transfaxsurface.
E. Safety
4. Gryqer!iaDistillation
The separation of air may require one or The apeaifia safety aonoerne in the aesign,
two distillationsteps. The first diatiU- constructionand operation of an air separation
a:ion produces high purity nitrogen and an plant involve an understanding of the classic
oxygen-riah stream whiah is d.iaaardedif “fire trianglen of tmcidant,fuel and sourue of
nitrogen is the only raqufred pzuduat. If, ignition. When oxygen-enriched streams at
however, high purity oxygen is required, elevated pressures are involved, it must be
 rmognized that many aszmon materiala of aon- 1. Transportability. Dimensional and weight
struotion falminuzb aarbon ateele atainlesa limitations must be related to the raad-
eteel. etc,) are potential fue18 with Wdrta- ways, Zailwaya and/or watezwaya that will
aarbons an the sourae >S ignition. h design, be used to transport the equipment to the
it ia neaesaary to insure that all heavy hydro- sit**
aarbons are removed and not allowed to aonaen-
trate locally in the preaenae of oxygen; in 2. Inetallagion. It is nonaally advantageous
conetruation?aleaning praaeduresto remove oil to prefabriaatt~,paakage and chop teet the
and grease are requiredand in aperetion~ it is major equipment’.coqonents to the maximum
moat eseential to ensure thae oxygen-riah axtent possible. This is to minimize the
streams do not come into aontaat with lubri- need for apeaieAized craftsmen or fabrica-
cated equipment. As an example of the latter, tion equipment on the conatruationsite and
the n$tragen injeation aompreseors in an EOR to aho*en the lead time for installation
application will normally be oil-lubricated of the equipr.ient.
reaiproaatingmaahlnea with diaaharge preesures
as high as 500 atmospheres. 3. Operation sand Maintenance. The equipment
must be properly designed to both withstand
It aan be appreciated read%ly that a tnalopera- the elements and to allow maintenanceto be
tion without adequate aafeguards~ which could performed on it. Tha eqxlpmant should be
enriah the nitrogen with a few peraent og proven in previous installationsat similar
oxygen~ could havs disastrous results. These operatingconditions.
are problama whiah are well known to the major
ttesigners,conatrmtors and operators of air 4. R6movel. The major components must be
separation plants who have established an deeigned to facilitate ease of removal and
enviable reaoni for safe and reliableoperation. possible relocation to a new site at the
terminationof the Nitrogen supply aontraat.
WPARATION AND COMPWSION EQUIPMENT
5. Efficiency. The added first aost of
k. General -naiderationa installing equipment with superior effi-
ciency ratinga should be evaluated against
The oil fie~d operator or hia nitrogen supply the power savings to bs realized by utLliz-
aontractor must design a system and select ing superior equipment over the life of the
equipment to meet the specific needs of the nitrogeninjectionproject.
enhanced recovery project. In addition to ths
design factors relating to pressure, volume 6. Safety and Reliability. The selection of
(@D), temperature, and purity of nitrogen and the proper proven equipment ia one con-
the energy type (elautricity or natural gas) sideration. Another is the design of a
used for generating and mxnpreseing nitrogen, functional monitoring and control system;
the operator or his supply contractor must aon- inclusion of equipment to remove and moni-
sider the site, the life of the equipment, tor hydrocarbon in the cold box, to moni-
efficienay,and safety. tor oxygen content of the product nitrogen
stream before and during product acinpraa-
Oil and gas fields are often found in remote or sione and to provide for autmatic isola-
clifflaulkto operate loaationa (suah aa the tion of the cold box if product nitrogen is
high elevation of the overthrust araa, the contaminatedwith an unacceptableamount of
marshes and waters of the Gulf -ast area, off- oxygen. Last but not least, the human
shore, or in or near populated areaa); plants factor must be considered. Operators,
must be designed to meet site specific and trained Gnd experienced in the operation,
environmental factors. Air separation and calibration,and maintenance of air separa-
aompnwalon equipment generally haa a long Mfa tion equipment and high pressure equipment,
(15-25 years) whereas nitrogen requirementsfor have aahieved enviable safety and reLiabil-
an enhancsd reaovery project may be subatan- ity records for several nitrogen euppliers.
tially lees than the life of the equipment; it
may behoove an operator to utilize the services B. Selectionof Contractorsor Equipment
of a nitrogen supply contractor who can re-
employ the equipment in subsequent projects. A field operator is faaed with se~ral alter-
Energy aoats are rising rapidlyt since energy nate methods of obtaining a high pressure
aosts account for roughly fifty precent of the nitrogen supply. He can:
cost of high pressure nitrogen, plant effi-
ciency is very germane. 1. Select a nitrogen supply contractorto pro-
vide nitrogen at high pressure under a sup-
Finally, safe-reliable operations, to insure ply (d/&lCF) contra*Z8 The contractor
the continuity of nitrogen supply, is of para- deaigns, selects the eq@pment, installs,
mount importance; the design of the plant and owns* operates, and maintains the air
its safety systems as well as the selection and separation and compression plant. The
training of operators have a draanatiaimpac% on parameters for selection of the contractor
safety and reliability. The following is a should include proven capabilities of the
list of somo of the parameters that should be contractor in reliably and safely operating
considered by a responsible nitrogen supply and maintaining similar air separation and
aontxactoror the field operator% cmpreasion equipment, as Wsll as, the
present value of the supply contract
($/HCF)and the aost of energy.
2. Seleat a aontraator to supply a turn-key and nitrogen mmpressors will be disauesad.
plant and operate the l?aoilicywith oil c@3 boxes wers disawsed above.
field personnel. The contractor designs,
seleats the equipmentO and installs the D* Ais Ckmpreesors
plant. The field operator rearuita~
seleats, hires and trains plant operatios The most important faator in the seleotion of
and maintenance personne 1. The parameters main air eupply compressors for a cryogenia
for the aeleation of?the contractor should nitrogen plant is the need for oil free air.
inalude the contractor’s (or contractors’) The absenae of oil in the air not only prevents
experience in designing and installing air danger from presenae of oil in the cold box but
separation and compreaeion equipment. the also eliminates risks and problems of removing
inetalled aost of the unit, the present oil from the air stream.
value of the energy? labor and materials to
operate and maintain the installed units The oil free requirementplue the availability
and the on-stmsm faator. of effiaientw multi-etage,packaged centrifugal
air eaapressors to handle nitrogen plant air
3, Design the eyetem, seleat ecpipment and feed requirements (large volume-low ratio)
installation vendors. The experience of result in the choice of centrifugal type in
the vendors, and the reliability? effi- essentially a+l cases. For extremely large
cienay, and proven capability of the equip- plante involting air flows of 100,000 Cm or
ment, the installed aost and the preeent more, the axial type dynamic compressor may be
value of the energyt labor and material used.
=Wima tO operate and maintain the
in=alled unit are key parameters. Other parameters must be considered in selec-
tion and design of the main air compressor:
4. Select a variant of two or more of the
above. 1. Efficiency is a key consideration because
the air compressor oonsumes at least half
The alternate method of high pressure nitrogen the power needed to deliver high pressure
supply chosen by the field operator may be nitrogen. Power is by far the most costly
based upon several parameters. The choice of a component of operatingcosts.
nitrogen supply aontract or an oil field owned
and operatedplant usually aonsiders: 2. Turn-down Flexibility - In tiew of variable
weather condition and part load contzml,
10 Capital - Cap&tal expenditures for an air it is desirable to regulateair flow. ‘lhis
separation and ao~pression plant must com- is accomplished efficiently by means of
psse with alternative investments in ail throttle valves on most sizes of centri-
and gas graduation such as exploration and fugal caq?reesors and by guide vanes on
field development. unusally large units. Cold winter condi-
tions may need inlet flow reduction of 20%
2. Personnel E@sources - Air separation and to 30% to match cold box characteristics.
high pressure compression require sophisti- With some packaged centrifugalcompressors,
cated engineers. operators, maintenance a reduatian of 20% to 30% in flow can be
personnel and instrument technicians. Some achieved efficiently. Capacity can he
or all of these personnel may not be readi- further reduced to approximately 50% by
ly available. Recruiting training, reten- using automatic by-pass control.
tion, and back-up of these personnel is
costly and con3umes valuable management 3. Single vs. Xultiple Gxnpresso~
time. By net present value analyeis, it is not
diffioult to establish whether one full
3. Iangeh of Project - The economic life of capacity or two half capacity air compres-
the equipment may substantiallyexceed the sors are warranted. Most enhanced recovery
life of the injection project. The re- applicationsreqpire full capacity for many
employment of the assests within a reason- years with reductions needed in future
ably short time may be difficult. years. The higher operating, maintenance
and capital costs for two units versus one
Major Equipment unit, in addition to the lower efficiency
of half-sized units favor the single unit
Figure 5 illustrates the major modular compo- selectionin nearly ewry case.
nents of an air separation and compression
plant. Depicted is a aentrifcgal air E. NitrogenCompressors
compressor, cold box and a nitrogen compres- In nitrogen compression, one of the several
sor. Wk.le the illustration shows electric factore affecting compressor seleation is con-
motor drives as prime movers, gas turbines or stant, namely alean a~ 100% nitroqen gas.
engines could be utilized completely or in com- However, other faators are variable and must be
bination with electric drives. One sold %x considered in the seleation of nitrogen com-
package or more could be used in combination pressors. Some of these are ae follows:
with one or more air compressors and produob
compressors. 1* Flow or inlet volume required and ratio of
compression will determine whether a cen-
In pazagraphe D and E below, air compressors trifugal compressor is praatical. !lany
 nitrogen plant modules for enhanaed re- pxadwed gas may bn aontaminatiedby the tnjeated
covery are below 20 to 30 MMSCFB where re- nitrageno As nitrogen acmtent in praduaed gas
aip-sating types are usually maa~ aoat inareaaea~the value and salability og the natural
effeative. Even for these larger volumeB gaa may decreaee. Therefore,the field aperator ia
it ie almost always neeessazy to use a re- faaed with the added complication of aleaning up
aLpraaating campresaor in seriee with the (upgrading)the natural gas @ separating (reject-
aentrifugal for the final high pressure ing) the nitrogen from the natural gae.
campreesion. If aefitrifugaltype ie prac-
tiaal, then evaluation must be made aompar- A nitrogen rejeation praceea conaista of a pre-
ing power aosts, operating sosts, inatalla- aleanup~ NGL reaovazy, and nitrogen-methanesepara-
tion and aapital aosts as well as proven tion. The teahnolqy utilized in pre-cleanup and
reliability. NGL recovery La relativelyroutine and known to the
natural ga!sinduetzy. The nitregen-methane aepara-
2. Inlee pressure i.e. outlet from the sold Ciont however, is new ta the U.S. natural gas in-
box, can vary from eaaentially atmapheric duatry. The process technology and equipment uti-
psea~ure to nearly 100 paig depending on lized to achieve nitrogen-methane separation are
the apeaifie proaeae design. TMe hae an essenti&lly proven technology in aiv and other
important effect on inlet volume and aryagenic aeparatione appliaationa. Thus nitrogen
canpreseion ratio. Large valumee and low zajeation units can be designed with minimal teah-
ratiot3favor centrifugaltype aanpreasors. niaal risk to achieve efficient nitrogen rejection
with operatingflexibilityand reliability.
3* Discharge pressures vary with the preseure
required in the reservoir or may bs set at A. ProaaesingAppraaah
typical pipeline pzeesura (1000 psig or The primary function of any natural gaa upgrad-
1sss) for manifolding to a dietane injec- ing unit is the separation of nitzogen and
tion ccmpresaor location. t$sny enhanaed natuzal gas liquide (if deairad) from the
=covery applications require relatively methane portion of the natural gas stream.
high pnmesurea - 3000 to 8S00 paig - which These major processing steps are representedby
diatate reciprocatingoampreasors at least the Blauk Flow Diagram shown in Figure 4.
for the final campresaion.
Prior to processing in the cryogeniu unit, the
4. Nhere cooling tower make up water is avail- feed is tceated to remove the bulk of the C02
able? water cooling of r-e caapzxmor pro- present in the feed. The feed then enters an
vides considerable savings in power over adsportion prepurifier unit where water, re-
air cooling. Many loaationa in the “oil maining traces of C02, and H2S are ramovad
and ges patch” do not have appreciable prior to treatment in the crycgenia prcceasing
watar and must be air cooled. unit* In the cryagenia unit, nitrogen ia
separated from the natural gas stream. The
5. Nhen thu abava factors indicate that recip- cryogenic unit can alao be used to separateNGL
raaating campresaors should be selected, products from the remaininghydrocarbons.
them is a choiue between low speed (300 to
450 sP@!)and high speed (700 to 1000 RPM). For enhancad oil recovery application, it ie
Scme faators to aonsider in this daaision important that ehe rejection plane can perform
are: these functions over the ccmplete range of
nitrogen feed contents (5 to 90 percent) with a
a. Diechazge presau~ - for hign pressures minimum of plant equipment and/or operating
(5000 EO 8500 psig or moze), the slow modifications.
-d type has proven to give good on-
stream time And low overall operating The cryagenie processing unit can be designed
costs even though capital and installa- to achieve optimum methane recovery (0.5%
tion coat is higher. -W overall oper- methane in nitrogen rejeat stream) for all feed
at.ing costs are a funotion of the compositions. Methane reaovery of the unit
higher efflaiency and lower maintenance will depend on the amount of nitrogen in feed
coet of the low speedt heavy duty and will vary from 99.95 peraent when the feed
machine as campamad eo high speed oontaine little nitrogen to 9S peroent reaovery
matins e. when the nitrogen feed content haa risen to 90
pezaent. It is important to note that the ra-
b. Size or volume - at moderate gwesauzee jeation system muse and aan be designed to
M small sizee~ the high speed aampres- operate over the complete range of feed aaupo-
sor offers adwantagee in low inzt8Ua- aitione encountered in enhanced oil recovery
tzon and zelaoation aoats due to the applications,
uuzpletely packaged arrangement e@e-
aLally wbre air aooling applies. How- B. Perfonmsnae
ever~ on large hmsepowez units, over The praaesaing saheme shown in Figure 4 can be
1500 HP, the slow speed types should be designedto perform ~he following funotions:
examined for poss2ble long term savinge
inpowar and Operatiorh 1. Renxmsl of nitrogen from natural gas feeds
whose nitrogen aontent varies with time
NITR@EN ~mN from 5 to 90 puaent without addition of
equipment.
~ several & the applications~epicted above, the
.!. -

2. Economic nitxogen rejeoeion for application

where rejeated nitrogen is required at low RH’ZRENCES
pwmre (vwmed t~ atmosphere) or at high
pre mum (for reinj ection). (1) “Sawkins Xne* Gas Plant: Design and Early
Operation”, by H. G. Kuahu, SPE Paper No. 6793,
3. Rmovery of heaVY hydroaarbcn liquid pro- Fall Meeting, Denver, 1977.
dust (NGL).
(2) “Economic Evaluation of Cycling Ges-@ndensake
COWLUSmN Reservoirs”, by c. w. Donohoe and R. D.
Buahennmb SPE Paper No. 7494, Fall hlaeti~,
Them are at least eix or more applications for Fioueton,1978.
titmgen in the enhanoed recovery of oil end gas.
In most of the Sppliaationetnitrogen is a substi- (3) “Gas ~ j.ectionfor UPstructiveDrainage”,G. D.
Lute for natural gas or carbon dioxide. subetitu- Combs and R. B. Knezek, JPT~ Marc?l,1971.
kion oacurs because nitrogen is more available and
less coetly than natural g~s or aarbon dioxide. (4) “Inert Gas Helps Recover Attic,Oilm, ~ F. S.
Godbold, O 5 G J, April 19, Z91j5.
The ultimatfasou=e ef nitrogen &a air. Cryogenic
air separation or combustion gas Glean-up (inert (5) “Nitrogen Driven C02 Slugs Reduce Cos+.:s”,
by
gas generation) are the primary prooe88ef3for J. P. Leary et al, Petroleum Engineer, May,
generating nitrogen. Twelve of the fourteen nitro- 1979.
gen projects sta*ed or aammitted to in the last
four years use air separationnitrogen. (6) “Nitrogen Use in Enhanced Reaovery Could Solve
Oil Produoera Problems”, by P. B. Crawford,
While new to the oil and gas production industry, American Oil Gas Reporter,Suly, 1978.
air separationtechnology is over 75 years old and
results in the generationof ten billion cubic feet (7) ‘E?ighPreseure Nitrogen or Air MSy Be Used for
per day of nitrogen and oxygen. Ths existing pro- Wiscible Displacement In Deep Hot Oil Reser-
cese end the equipment for air separation is quite voirsm, ~ M. D. Rushing et al, SPE Paper No.
applicableto oil field nitrogen needs. 642S Deep Drilling and Production Sympoeium,
aprile L977.
M oil field operator aan select the contract
(d-l purchase of nitrogen from a supplier or the (8) “Mieaible Displacementsof Reservoir Oil Using
purohase, ownership and operation of the e@p- Flue Gas”, Trans AIZME 213, 195S.
ment. Reliabilityof supply, safety, present value 1
cost of labr? materialv contract purohase (q,\MCI”)i (9) “Unique Enhanced Oil and Gas Recovery Project
price and energy, capital inveetment~ and avaLZ- For Very High Pressure Wilcox Sands Using
ability of qualified personnel are key parar.a’cex:s C%yogenic Nitrogen and Methane Mixtureti,by
in the selectionof a nitrogen supply contractor or Wesley W. Eakles, Jr. et al, SPE Paper No.
an equipment vendor (if oil field ownership and 9415, Fall Meeting, Dallas, 1980.
operationsare an’ciaipated).

Nitrogen rejection capability may be required in a

field in which nitrogen is injeoted. Prove!ltech-
nology is available for nitrogen-methaneaeparatim
as well as NGL recovery.
 . ...*

w
I J
Figure 1
1

Ill L

Figure 2

Figure 5

Figure 3