9
 Copyright 2001, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the SPE Permian Basin Oil and Gas Recovery Conference held in Midland, Texas, 15–16 May 2001. 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, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes 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 where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., f ax 01-972-952-9435. ABSTRACT It nitrogen injection has been proven as a competitive alternative for volatile oil reservoirs lately found in Piedemonte area of Colombia, taking into account the reservoir fluid nature and the reservoir conditions. A laboratory study was carried out by the authors in the Enhanced Oil Recovery Laboratory of Colombian Petroleum Institute. Three corefloods were carried out using Berea sandstone and volatile oil samples from the Piedemonte area and nitrogen as displacing agent. One of these corefloods was conducted in a long Coreflooding apparatus, and the other ones, in a short Coreflooding apparatus connected with a slim tube in a order to achieve miscibility conditions. The main variable studied was the flow rate, which represents three different flow regimes. The scaling criteria taken was a dimensionless group, which relates viscous and gravity forces, called gravity number. Displacement efficiencies determined were around 50%, 65% and 80% for each one the tests. The results of these corefloods were compared to determine the best scheme of nitrogen injection. Results have successfully confirmed the effectiveness of nitrogen as displacing agent for this kind of oils and the better swept efficiency given by the equilibrium between the governing forces. INTRODUCTION The volatile oil reservoirs lately found in the Piedemonte area of Colombia are quite complex not only in geology but in the fluids composition also. That is why, several analyses have been done to select the best explotation, production and commerciali zation strategy. Reservoirs in Piedemonte area are more than 15000 ft deep, with pressures and temperatures greater than 5500 psi and 250 °F. Thermodynamic and phases behavior of this reservoirs are also unique in the world. Fluids behavior have a great importance in the hydrocarbons volume estimation and therefore in the field development. There is gas reinjection in the field to keep the initial reservoir pressure, in an effurt to maintain a single phase fluid and to improve the recovery. Reinjection gas come from a first stage separator with high methane content. When observing different studies, made by investigators of world-wide recognition in the area of volatile oil deposits, that propose the nitrogen injection like an alternative able to compete with the gas reinjection in this type of deposits, since the characteristics that favor the reinjection of the gas are also propitious for the nitrogen injection, the investigation group decided to orient its efforts in the investigation with nitrogen as a new form of profitable operation. The replacement of the natural gas by nitrogen as injection gas brings advantages that are according to the plans of economic development of the country. A series of displacements were doneto investigate and to quantify the effect of phases behavior and porous media on the efficiency of sweeping with nitrogen. An overhaul about experiences of operation with nitrogen in different oil fields including the facilities required for a project of nitrogen injection, was initially done. The equipment used for the development of the tests, the followed procedure is described to obtain the SPE 70053 Evaluation of Displacement Efficiency in Volatile Oil Reservoirs under Nitrogen Injection Juan E. Rivera de la Ossa/Ecopetrol-ICP, Juan C. Correa Castro/Un iversidad Industrial de Santander, Cesar A. Mantilla Uribe/Universidad Industrial de Santander, Cesar Augusto Duarte Prada/E.O.S. Ltda

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  • Copyright 2001, Society of Petroleum Engineers Inc.

    This paper was prepared for presentation at the SPE Permian Basin Oil and Gas RecoveryConference held in Midland, Texas, 1516 May 2001.

    This paper was selected for presentation by an SPE Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the Society of Petroleum Engineers and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect anyposition of the Society of Petroleum Engineers, its officers, or members. Papers presented atSPE meetings are subject to publication review by Editorial Committees of the Society ofPetroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paperfor commercial purposes without the written consent of the Society of Petroleum Engineers isprohibited. Permission to reproduce in print is restricted to an abstract of not more than 300words; illustrations may not be copied. The abstract must contain conspicuousacknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

    ABSTRACT

    It nitrogen injection has been proven as a competitivealternative for volatile oil reservoirs lately found inPiedemonte area of Colombia, taking into account thereservoir fluid nature and the reservoir conditions. Alaboratory study was carried out by the authors in theEnhanced Oil Recovery Laboratory of Colombian PetroleumInstitute.

    Three corefloods were carried out using Berea sandstoneand volatile oil samples from the Piedemonte area andnitrogen as displacing agent. One of these corefloods wasconducted in a long Coreflooding apparatus, and the otherones, in a short Coreflooding apparatus connected with a slimtube in a order to achieve miscibility conditions. The mainvariable studied was the flow rate, which represents threedifferent flow regimes. The scaling criteria taken was adimensionless group, which relates viscous and gravity forces,called gravity number.

    Displacement efficiencies determined were around 50%,65% and 80% for each one the tests. The results of thesecorefloods were compared to determine the best scheme ofnitrogen injection. Results have successfully confirmed theeffectiveness of nitrogen as displacing agent for this kind ofoils and the better swept efficiency given by the equilibriumbetween the governing forces.

    INTRODUCTION

    The volatile oil reservoirs lately found in the Piedemontearea of Colombia are quite complex not only in geology but inthe fluids composition also. That is why, several analyses havebeen done to select the best explotation, production andcommercialization strategy.

    Reservoirs in Piedemonte area are more than 15000 ftdeep, with pressures and temperatures greater than 5500 psiand 250 F. Thermodynamic and phases behavior of thisreservoirs are also unique in the world.

    Fluids behavior have a great importance in thehydrocarbons volume estimation and therefore in the fielddevelopment. There is gas reinjection in the field to keep theinitial reservoir pressure, in an effurt to maintain a singlephase fluid and to improve the recovery. Reinjection gas comefrom a first stage separator with high methane content.

    When observing different studies, made by investigators ofworld-wide recognition in the area of volatile oil deposits, thatpropose the nitrogen injection like an alternative able tocompete with the gas reinjection in this type of deposits, sincethe characteristics that favor the reinjection of the gas are alsopropitious for the nitrogen injection, the investigation groupdecided to orient its efforts in the investigation with nitrogenas a new form of profitable operation.

    The replacement of the natural gas by nitrogen as injectiongas brings advantages that are according to the plans ofeconomic development of the country.

    A series of displacements were doneto investigate and toquantify the effect of phases behavior and porous media on theefficiency of sweeping with nitrogen. An overhaul aboutexperiences of operation with nitrogen in different oil fieldsincluding the facilities required for a project of nitrogeninjection, was initially done.

    The equipment used for the development of the tests, thefollowed procedure is described to obtain the

    SPE 70053

    Evaluation of Displacement Efficiency in Volatile Oil Reservoirs under NitrogenInjectionJuan E. Rivera de la Ossa/Ecopetrol-ICP, Juan C. Correa Castro/Universidad Industrial de Santander, Cesar A. MantillaUribe/Universidad Industrial de Santander, Cesar Augusto Duarte Prada/E.O.S. Ltda

  • 2 JUAN RIVERA, JUAN CORREA, CESAR MANTILLA, CESAR DUARTE SPE 70053

    presented/displayed results. Results are analyzed andinterpreted by using tables and graphs for their betterunderstanding and a set of conclusions and recommendationsis also given.

    APPLICATIONS OF THE NITROGEN IN IMPROVEDRECOVERY

    Nitrogen, like injection gas, has several applications suchas maintenance of pressure, inmiscible displacement, catchedoil production and miscible displacement, among others. Thepropose application in this work is the miscible volatile oildisplacement by nitrogen injection. Depending on a thepressure, amount and location, nitrogen can get to cost fromone fourth part to half of the price that is paid by the naturalgas.

    A great number of methods of oil recovery and gas thatuses nitrogen, which go from pressure maintenance to ones, asit is the miscible displacement. In Literature are six methodsthat use nitrogen, these are shown in table 1.

    SOURCES OF NITROGEN FOR THE OIL INDUSTRYIN OPERATIONS OF IMPROVED RECOVERY

    Between the advantages of nitrogen on other injection gases,like dioxide of carbon and the natural gas, it is its abundance.This advantage is due to the fact that nitrogen is in the air, andadditionally it can become an economic resource, if appropiatetechnology is used to extract it. The operator has two options,(1) to buy the equipment of nitrogen generation so that it ispart of the facilities of the field, or (2) to directly buy nitrogento a supplier. Historically the second option has been moreeconomic because it does not require initial investment ofcapital, and the suppliers have personnel to operate nitrogenplants. In each project the operator must evaluate bothalternatives.

    At the moment three processes of nitrogen generation are usedin the the industry, that turn great air volumes into nitrogen (orat least in a consistent gas of 88% N2 and something of CO2,call chimney gas).

    Nitrogen production by cryogenic separation of thecomponents of the air has been used since the beginning of thecentury, and is the most economic method to produce purenitrogen. The pioneers in this technology were thepetrochemical steel industries in which the wished productwas oxygen. The fundamental concept in cryogenic generationis to cool the air until its liquefaction and then to distill it. Inorder to reach low temperatures, a cycle of refrigeration isused that consists of an air compressor, a column ofdistillation and a section of compression.

    PHASES BEHAVIOR AND MISCIBILITY

    The final objective of the processes of miscible displacementis to recover the greater volume of hydrocarbons by natural orby artificial mechanisms, which are limited in effectiveness bythe influence of capillary and interface forces. Exist fewprocesses of miscible displacement in which reliable liquidsare used and they are known as miscible displacements, inaddition there are processes like miscible displacements gas-condensed gas. In the operations of gas reinjection, whichhave been used in gas condensed reservoirs for many years,the second case is had. This process also falls within theclassification of miscible displacement, because the injectedgas is completely miscible with the fluid of the reservoir. Therecovery, in these cases, is not affected by capillary forces,and in theory the displacement efficiency is of the onehundred percent, that is hydrocarbons which are contacted bythe miscible pocket are moved totally. The gas recovery ofcondensed gas in channels of low permeability is difficult toobtain in operations of reinjection of the gas.

    The miscible displacement of the type vaporizing gas wasphysically simulated in this research, the use of nitrogen asdisplacement fluid has been studied by several researchers, inwhich the effects of temperature, reservoir fluid composition,injection fluid composition, on the minimum miscible pressureare considered. The miscibility can be explained like thephysical condition between two fluids that allows them to bemixed in all the proportions without an interface between thematerials forms. If both fluids are not mixed in any proportion,then they are not miscible.

    SCALED PHYSICS MODELS

    Three dimensionless groups exist which are used to define theregions of flow, these are: group of relation between viscousand capillary forces; and shape factor. The analysis shows thatthe relative magnitudes of the forces involved in the systemcombined with the properties of the deposit determine theregion of flow and distribution of the fluids in the media. Thedimensionless numbers are:

    Ngv = Lkavg v / Hqo ................................................(1)

    Ncv = Lpc*k avg v / H2qo .............................................(2)

    M = w / o .................................................................(3)

    Ngv and Ncv are the relations of characteristic time so that thefluid flows in the transverse direction due to the forces ofgravity or capillary, with respect to the time of flow inhorizontal direction due to the viscous forces.

  • SPE 70053 EVALUATION OF DISPLACEMENT EFFICIENCY IN VOLATILE OIL RESERVOIRS UNDER NITROGEN INJECTION 3

    These numbers of gravity and capillary are dimensionless anddefer from the work presented/displayed by other authors likePozzi15 and others. Whereas authors like Peter, Zhou andBlunt 14 propose it like advantageous for cases in which themobility relation is unfavorable. The advantage to use Ngvand Ncv is that they represent the magnitude of the gravity andcapillarity forces in the transverse direction with respect to theviscous forces in the lenghtwise direction, including theinfluence of the shape factor.

    The term miscible displacement refers to displacements witheffects of negligible capillarity (Ncv=0), which also caninclude two phases, since the interface voltage is very low oralmost zero. When the capillary forces are despised, singleviscous and gravitational forces contribute to the flow. Themechanisms of transferences of masses as dispersions anddiffusion influence, since they affect the mixture and thedifferences of viscosity and density. Nevertheless, thedispersion usually, is the only factor that contributes indisplacements in where the hair forces and gravity are smalland the rates of injection are relatively small. After anextensive recopilacion of works done on misciblesdisplacements, Zhou constructed figure 4 with data ofdifferent investigations, among them Fayers22, Araktingi,Ingsoy, Christie and Pozzi15.

    EXPERIMENTAL EQUIPMENT AND PROCEDURESOF TEST

    In the laboratories of the Colombian Petroleum Institute threemiscibles representative volatile oil displacements werecarried out using nitrogen to determine the recoveryefficiency, at typical conditions of deposit of this area, that ispressure of 5700 psi and temperature of 244 F (39,3 Mpa and118C). One of these displacements was made in thecoreflooding equipment on an adjustment of nuclei of Berea,which contained initially saturations of crude recombined andsynthetic salt. The other two displacements were made in theequipment coreflooding for steam, connected in series withslim tube with a length sufficiently long to guaranteeing thatthe multiple contacts between the fluids take place there, andthus to have a miscible displacement in the nucleus containedin the steam equipment. Three different rates from injectionwere used, each one of which represents a region of flow inthe balance between the gravitational and viscous forces. In allthe cases, the displacement equipment was in horizontalposition.

    This way, the main factor of displacement studied was theeffect of the rate of injection on the recovery efficiency. Thescheme of the equipment is in figure 1 and 2. As much forcoreflooding, as for the steam equipment connected to theSlim tube.

    .

    RESULTS OF THE TESTS

    Because the tests can represent of the best way thereservoir conditions, the pressure was defined according tosome values of present pressure of deposit in the area ofPiedemonte. Therefore, the back pressure system was loadedto 5700 psi (39,3 Mpa), since this it represents the pressure ofproduction of the deposit. The temperature of the test is of 244F (117.8C), and also obeys to the temperature of presentdeposit. These two conditions help to promote the mechanismof displacement by multiple contacts between the fluids.

    The main suppositions to initiate the tests are: homogenousporous media, only are two phases in flow (oil and nitrogen),consider the effects of the gravity forces, viscoses and themixture mechanisms, the law of Darcy is applicable, the flowoccurs in a single dimension, and the porous media constitutedby the nuclei this water wet.

    The variable that is going away to analyze is the numberdimensionless (Ng) that describes the balance between theviscous and gravitational forces. The obtained results agreewith the behavior registered in the different articles that makereference on this subject. Figure 5 compares the recoveryfactors obtained for each value of number of gravity.

    As it is possible to be observed in figure 5, the best resultswere obtained in a regime that balances the two forces thatgovern the displacement. In the study made by Peters12 agraph with similar behavior appears, although this graph issingle qualitative but nonquantitative, it express what it ispossible to be appreciated in this work. The best recoveries arewhen the Ng is in the middle of the regions where thegravitational force and the viscous force act with greaterintensity. As the Ng depends on the rate, also we can assumethat when being the Ng in a balance between the two regionsbefore described, is going to be, also, in the middle of twoproblems that desmega the recovery, which are the digitation,and the gravitational segregation.

    The digitation happens by the high speed of the fluid injectorand discharge relation of mobilities, that when finding achannel of high permeability begins to flow that waypreferential, causing an early irruption with the consequentdiminution in the recovery.

    The gravitational segregation appears due to the low rate ofinjection of nitrogen and to the smaller density of this withrespect to the oil, causing that nitrogen mounts on the oilcausing that the gas flows preferedly by above and leaveswithout sweeping the part of down, producing a decrease inthe recovery.

  • 4 JUAN RIVERA, JUAN CORREA, CESAR MANTILLA, CESAR DUARTE SPE 70053

    CONCLUSIONS

    1. The displacements were miscibles or they were very nearto miscibility. This is deduced with base in thecorrelations found in the literature and the results of theproject evaluation of the mechanism of miscibility involatile oil reservoirs submissive the nitrogen injection.The average of the minimum pressure of miscibilitybetween the fluids for the temperature of test is of 5850psi. In addition, the high obtained factors of recoverymake be conceited that the sweeping of the displacementfront is miscible by multiple contacts.

    2. The process of nitrogen injection loses all yield after theirruption of the front. As I am observed in the tests, the oilproduction after the irruption is insignificant with respectto the amount that recovers before the irruption.

    3. The nitrogen injection has demonstrated to be analternative that is due to consider to improve the recoveryof volatile oil deposits in the obtained area recovery in thecarried out displacements in this study were of 50,05%,65,6% and 79,26% for three different rates from injection.

    4. The assembly made connected to the Slim tube in linewith the Berea nucleus it turn out quite favorable topromote the contacts within slim tube, and to increase theefficiency of the displacement. Of to have connected thissystem, the results of the displacement in a short nucleuswould have been masked, because the space is not thesufficient one to guarantee that the multiple contacts takeplace in the cores.

    5. The best form to consider the associate gas produced, isby means of the volumetric factor, which considers theconditions of deposit and the volume of oil produced toconditions standard. Other proposed methods, likebalance of mass from the injection gas, are notrecommendable to evaluate the displacement efficiencybecause they start from suppositions not absolutelycertain.

    6. As shown when comparing the three displacements, as theirruption of the gas front is delayed, the efficiency of thedisplacement is greater. This indicates that the bestsweeping delays but the arrival of the front until theproduction point, and this directly related to the regime offlow that predominates and the mixture of fluids.

    7. The best obtained result was in the second displacement,which indicates a behavior similar to the one found in theliterature. It is possible to said that the best result isbetween the regions of the viscous forces and gravity.Also a graph is had, although this is quantitative butnonqualitative.

    8. The transition zone, as a fraction of the distance run bythe sweep front, was 5% in coreflooding, in the slim tubesystem and in the steam equipment was 1%. There is ahigher sweep efficiency when the transition zone is lower.

    REFERENCIAS

    1. Ahmed, T., Menzie, D., and Crichlow, H.: Preliminaryexperimental results of high pressure nitrogen injection for EORsystems. SPE Journal 339 348, (April 1983).

    2. Buchanan, R.D, and Donohoe, C.W.: Economic evaluation ofcycling gas condensate reservoir with nitrogen. Journal ofPetroleum Technology, 263 270, (February 1981).

    3. Clancy, J.P., Gilchrist, R.E., Cheng, L., and Bywater, D.R.:Analysis of nitrogen injection projects to develop screeningguides and offshore design criteria. SPE 11902, (September1983)

    4. Clark, N.J., Scultz, W.F., Garmz, K., and Moore, J.L.: Miscibledrive its theory and application. Journal of PetroleumTechnology 11 20, (June 1958)

    5. Dindoruk, B., Orr, F.M., and Johns, R.T.: Theory of multicontactmiscible displacement with nitrogen. SPE 30771, (1995)

    6. Evison, B., and Gilchrist, R.E.: New developments in nitrogen inthe oil industry. SPE 24313, (1992)

    7. Glaso, O.S.: Miscible displacement: Recovery tests withnitrogen. SPE 17378, (1988)

    8. Hudgins, R.J. Llave, F.M., and Chung, F.T-H.: Nitrogen miscibledisplacement of light crude oil: A laboratory study. SPE 17372,(1988)

    9. Huygens, R.J., Ronde, H., and Hagoort, J.: Interfacial tension ofnitrogen/volatile oil systems. SPE 26643, (1993)

    10. Lee, S.T., Gomez, P.A., and Toczylkin, L.: An integratedapproach to interpret and quantify Cusiana hydrocarbonsystem. SPE 27029, (1994)

    11. Perkins, T.K., and Johnston, O.C.: A review of diffusion anddispersion in porous media. SPE Journal 70 84, (March 1963)

    12. Peters, B.M., Zhou, D., and Blunt, M.J.: Experimentalinvestigation of scaling factor that describe miscible floods inlayered systems, SPE 39624, (June 1998)

    13. Plata, E., and Perez, E.: Evaluacion del comportamiento de fasesen yacimientos de condensados de gas y aceite volatil sometidosa la inyeccion de gas. Universidad Industrial de Santander. 1984

    14. Pozzi, A.L., and Blackwell, R.J.: Design of laboratory models forstudy of miscible displacement. Soc. Pet. Eng. Journal 73 80,(March 1966)

    15. Rojas, G.: Scaled model studies of inmiscible carbon dioxidedisplacement of heavy oil. The University of Alberta. 1985

    16. Sayegh, S.G., Wang, S.T., and Fosti, J.E.: Recovery of crude oilusing nitrogen. Part 2. Laboratory displacement data.Petroleum Recovery Institute, Report 1986-3. Mayo 1986

    17. Sebastian, H.M., and Lawrence, D.D.: Nitrogen minimummiscibility pressures. SPE 24134, (1992)

    18. Stalkup, F.I.: Miscible displacement. Society of petroleumEngineers Monograph V8, 1992

    19. Warren, J.E., and Skiba, F.F.: Macroscopic dispersion. SPEJournal 215 230, (September 1994)

    20. Ypma, J.G.: Compositional effects in gravity dominatednitrogen displacements. SPE Reservoir Engineering, (august1988)

  • SPE 70053 EVALUATION OF DISPLACEMENT EFFICIENCY IN VOLATILE OIL RESERVOIRS UNDER NITROGEN INJECTION 5

    21. Zhou, D., Fayers, F.J., and Orr, F.M.: Scaling of multiphase flowin simple heterogeneous porous media. SPE 27833, (1994)

    22. Jefri rotating coreholder and stand operating and maintenancemanual, DB Robinson design & manufacturing Ltd. May 1993

    23. Jefri back pressure regulator operating and maintenance manual,DB Robinson design & manufacturing Ltd. May 1993

    Appendix-Scale

    The nature of the flow in the porous media is determined bythe interaction of the physics properties of the fluids andporous media, and by the forces involved in the displacementprocess. Several regions of flow in agreement with the forcesare identified that dominate the process. Three dimensionlessgroups exist that are used to define these regions of flow: theseare relation between gravitational and viscous forces, relationbetween capillary and viscous forces shape factor.

    In agreement with the analysis, the equations of balance ofmaterials for incompressible flow are:

    And the speeds of Darcy flow for two phases are given by:

    Where is the potential of flow in j phase, Uj and Vj are thespeeds of flow of phase j in the horizontal and verticaldirections, kv and kh are the permeabilities in the horizontaland vertical directions, respectively.

    Defining the dimensionless variables: x=X/L, y=Y/H,t=Tq/L, uj=Uj/q, vj=(LVj)/(qH), kv= k avgKv(x,y), kh= k avghKH(x,y), j=(krj.0)/(j), =(j.kavg)/(Lqo); y. Thedimensionless equations are obtained.

    Where H and Ls are the thickness and the length of means,kav and kah are the permeabilities averages of means in thehorizontal and vertical direction, and q is the speed of totalflow in the horizontal and vertical direction, and q is the speedof total flow in the horizontal direction. Notice that the flowpotentials j are dimensionless and it is expressed withrelation to the oil viscosity, and that dimensionless mobilitiesalso contain the viscosity of the oil like factor.

    The four dimensionless equations converge in equations14, leaving to this like a scale group. Can be regrouped like:

    This scale group relates the time that the fluid throughout a Ldistance in the horizontal direction takes, and the time thattakes the flow from the same fluid to cross a distance H in thevertical direction, to the same difference of potentialthroughout the distance. Rt also is called the effective shapefactor, and represents the relative capacity of flow withinmeans in the horizontal and vertical directions.

    Considering that the position of the cores is horizontal, theviscous forces are in the direction of longitudinal flow,whereas the gravitational and capillary forces, it is in the crossflow direction. With the purpose of identifying the flowregions, in where each force dominates the movement of thefluid in the transverse direction, the equations of Darcy foreach phase are combined.

    In order to define the relation between o and w, thedefinition of capillary pressure is used to obtain:

    )1.........(....................0 =

    +

    + A

    YV

    XU

    TS www

    )2.......(..........0)()( =+

    ++ AVV

    YUU

    X owow

    )3........(....................),(

    = AX

    kYXkU j

    j

    rjhj

    )4(..............................),(

    = AY

    kYXkV j

    j

    rjvj

    )5.(....................0 =

    +

    + A

    YV

    XU

    TS www

    )6..(..........0)()( =+

    ++ AVV

    YUU

    X owow

    )7..(....................),(

    = AX

    YXkU jjhj

    )8.......(),(2

    =

    AY

    YXkvkk

    LH j

    jvjavgv

    avgh

    )9.........(2

    ==

    =

    ATT

    qq

    HL

    Lk

    Hk

    HL

    kk

    LH

    v

    h

    h

    v

    avgh

    avgv

    avgh

    avgv

    ( ) ( ) ( ) )10...(,1

    2

    +

    =+ Ayy

    yxkvvR

    ww

    oovow

    t

    ( ) )11....(*1 += ASJLq

    kPK

    yLqgHk

    w

    o

    avghc

    vo

    avghow

  • 6 JUAN RIVERA, JUAN CORREA, CESAR MANTILLA, CESAR DUARTE SPE 70053

    If it is replaced formulates A-11 in formulates A-10, it giveslike result:

    ................................................................................(A-12)

    Where:

    Ngv and Ncv are the relations times characteristic so that thefluid flows in the transverse direction due to the gravity orcapillary forces, with respect to the time of flow in horizontaldirection due to the viscous forces.

    TABLE 1 NITROGEN APPLICATION IN E.O.R.

    APPLICATION API DEWPOINT

    BUBBLEPOINT

    P (psi) T (F) DEPTH

    Pressure MaintenanceInjection on thegas cap

    30 Above Above NR NR NR

    Inmiscible gasdrive

    30 - - NR NR NR

    Gravitationaldrainage

    25 - - NR NR NR

    Trapped oilrecovered

    25 - - NR NR NR

    MiscibleNitrogen 41 - - > 4500 NR > 7000CO2 and N2driven force

    27 - - > 1300 < 250 > 2300

    NR: No restrictions

    ( )( )( )

    +

    +

    +=

    yJ

    KNN

    MM

    Myxkvv

    yR

    v

    cvgvvo

    woot

    111,

    2

    )14.....(..............................*2 = AqHkLp

    No

    avgvccv

    )15....(........................................ = AMo

    w

    )13........(.............................. = AHq

    LkN

    o

    avgvgv

  • SPE 70053 EVALUATION OF DISPLACEMENT EFFICIENCY IN VOLATILE OIL RESERVOIRS UNDER NITROGEN INJECTION 7

    Fig. 1-Coreflooding system diagram.

    Fig. 2-Coreflooding system diagram.

  • 8 JUAN RIVERA, JUAN CORREA, CESAR MANTILLA, CESAR DUARTE SPE 70053

    Fig. 3-Slim tube and Coreflooding system diagram.

    Fig. 4 Flow regions.

  • SPE 70053 EVALUATION OF DISPLACEMENT EFFICIENCY IN VOLATILE OIL RESERVOIRS UNDER NITROGEN INJECTION 9

    Fig.5-Gravity number Vs. Recovery factor.