a review of downhole separation technology

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SPE 94276

A Review of Downhole Separation TechnologyO.O. Ogunsina, SPE, and M.L. Wiggins, SPE, U. of Oklahoma

Copyright 2005, Society of Petroleum Engineers

This paper was prepared for presentation at the 2005 SPE Production and OperationsSymposium held in Oklahoma City, OK, U.S.A., 17 – 19 April 2005.

This paper was selected for presentation by an SPE Program Committee following review ofinformation contained in a proposal 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 a proposal of not more than 300words; illustrations may not be copied. The proposal must contain conspicuousacknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.

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Abst ractIn recent years, a technique of separating water downhole toreduce the volume of produced water and decrease the chanceof surface pollution has been developed. It is called downholeoil-water separation (DOWS) technology. This techniqueallows water to be separated in the wellbore and injected into asuitable injection zone downhole while oil with traces of wateris produced to the surface.

Subsequent to the introduction of the DOWS technologyto the oil industry in the 1990’s, several trial applications have been undertaken to test the technology. These trials allowedsignificant information to be collected on the feasibility of theDOWS technology. Through the joint efforts of Argonne National Laboratory, CH2M-Hill, and the Nebraska Oil andGas Conservation Commission, a comprehensive technicalreport was issued in January 1999 discussing this technology.Additional reports on trial applications and feasibility studieshave been presented by various study groups.

This paper reviews the status of and issues surroundingthe application of downhole separation technology. Thisreview summarizes the various papers and reports dealingwith DOWS technology and its application in the oil and gasindustry. This technology has the potential to providesignificant reductions in produced water as the technology isadopted by the industry. It can also reduce produced water

handling costs and increase oil and gas production in the rightapplication. The wide-spread adoption of DOWS technologyis dependent on improving the understanding of the processand its applications throughout the oil and gas industry.

IntroductionOne of the waste by-products of crude oil and natural gas production in the upstream industry is produced water.Produced water has been defined as the water produced to thesurface from the hydrocarbon bearing formation during theextraction of oil and gas, and can include formation water,injection water and any waste chemicals added downhole orduring the oil/water separation processes.

Conventional production processes involve producing both oil and water to the surface and then separating them athe surface. This separation occurs through the use oseparation and dehydration equipment including skimmervessels, plate coalescence, hydrocyclones, and, in some casescross-flow membrane filters to reduce the oil content in thewater phase and enhance the quality of the water prior todisposal. However, as a reservoir matures and oil and gas production peaks, there is often an associated increase in watercut and a corresponding increase in both lifting and waterdisposal costs. The increased water cut also necessitatesadditional maintenance for production equipment anddownhole treatment for corrosion, bacteria, scale, andnaturally occurring radioactive material (NORM).

Although producers still have a variety of choices ineither disposing the water or re-using it, there is a growingconcern from the public related to the handling of this waste product. Public concern about the environmental impacts o produced water disposal has therefore become a major issue inthe industry especially related to surface damage due tospillage or subsurface contamination of drinking water due to poor injection activities. Environmental regulations pertainingto produced water management are expected to become more

stringent in the future necessitating new practices andtechniques of managing produced water.

Downhole oil-water separation (DOWS) technology wasintroduced to the industry in the 1990’s and further work toassess its feasibility was sponsored by the US Department ofEnergy in 1999.1,2 “DOWS, unlike the conventional separation process, separates oil and gas from produced water at the bottom of the well and injects the separated produced waterinto another formation usually deeper than the producingformation, while the oil and gas are pumped to the surface.”2

DOWS technology has the following advantagesassociated with its application.

1. DOWS presents an economic advantage in terms of

reduction in water handling costs, as much of the produced water is not pumped to the surface, therebyreducing treatment and disposal costs.1-5

2. Reports on trial applications have shown that whenDOWS technology is used, additional oil may berecovered due to reduced water cut and waterflooding potential during re-injection.1,2,6

3. DOWS presents a viable option in surface facilitiesde-bottlenecking projects, especially in fields that arefar from processing facilities, as it provides extracapacity for the production of additional oil and gasdue to the reduced surface volume of producedwater.4-7



2 SPE 94276

4. DOWS reduces environmental impact of oil and gasoperations as it minimizes the opportunity forcontamination of the surface land and waters throughspillage and surface leaks and underground sourcesof drinking water through leaks in tubing and casingduring the surface injection process.4,5,7,8

Although the technical feasibility of DOWS was

established in some specific situations, the economicfeasibility still remains a great challenge in many fieldapplications due to quick failures in several of the applicationsand a general misapplication and misunderstanding of thetechnology. There is a need to improve the understanding onthe use of the technology and its application in order toenhance its chances for wider industry acceptability. This paper reviews the current status on the use of DOWS throughreview and analysis of the field applications carried out inseveral independent studies.

Literature ReviewThe production of subsurface water often accompanies oil and

gas production as it is present in the reservoir. Generally, thiswater production increases during the life of the reservoir as aconsequence of reservoir depletion, water influx from anadjoining reservoir, or through improved reservoir recovery processes. Oil and water, due to density differences, arenormally initially segregated in the reservoir. However, as production begins, they become mixed into emulsions as thefluids from the reservoir flow to the surface through thereservoir, perforations, tubing, chokes and pumps. Once thefluids reach the surface, they must be separated again.Proposed solutions to reduce the cost of separation and prevent the formation of emulsions have been either to preventwater from entering the wellbore or manage the water afterentry in a way that emulsions are not formed, which

sometimes involves the use of expensive chemicals.DOWS technology seeks to address both problems. First,

DOWS reduces the amount of water that is transported withthe oil from the reservoir to the surface. Second, separationcosts are reduced due to a decrease in emulsions problems asthe water phase is reduced in the production stream. Severalstudies, including laboratory experiments, simulations,modeling, feasibility analyzes, and field applications have been carried out to demonstrate the DOWS technology.1-20

DOWS consists essentially of two systems: a separationsystem and a pumping/injection system. Two basic types ofDOWS systems have been developed based on the separationsystem utilized. One type relies on gravity separation while

the second system uses hydrocyclones to separate oil andwater. A third type of separation system using membraneseparation technology is yet to be developed and applied in thefield but has been investigated through simulation studies.18

There are three basic types of pumping/injection systemsused with DOWS technology. Electric submersible pumps, progressing cavity pumps, and sucker rod pumps have beenused in combination with the hydrocyclone separation systemto reinject the water. The gravity separation system hasfocused on the use of the sucker rod pump for reinjection.Stuebinger and Elphingstone11 foresee the potential for severaldifferent combinations of fluid lift systems and injectionsystems.

Shaw et al.10 noted in their report that DOWS can also beclassified based on the relative positioning of the pump andthe separator assembly in the wellbore. If the fluid enters theseparator assembly first, the configuration is called a pulthrough system. If the produced fluid enters the pumpingsystem first, the configuration is called a push through systemBoth processes have the disadvantage of poor separation. In

the push through systems this is due to formation of a tighteremulsion created by the feed pump. The poor separation is dueto free gas or poor homogeneity of inlet mixtures in the pulthrough systems.

Gravity Separation DOWS. This type of DOWS takesadvantage of the gravity separation of oil and water thaoccurs in the tubing/casing annulus.3,9 In this process, the oil isallowed to rise upward due to density differences with the produced water. The separation process is controlled byStoke’s law.

The gravity separator systems work mainly with suckerrod pumps. There are three different types of gravity separatorsystems based on the pump type, the dual action pumpingsystem (DAPS), the triple action pumping system (TAPS) andthe Q-Sep G system.2

As reported, the most commonly used type of gravityseparator DOWS is the dual action pumping system (DAPS)which was first developed in 1994 and installed in 1995 byTexaco personnel. The pump design is shown in Fig. 1. Iincorporates dual intakes to take advantage of the gravitysegregation in the casing. The two intake ports are a criticadistinguishing feature of the gravity type DAPS. Limitationsfor the DAPS system includes a maximum fluid capacity of1200 BPD, the inability to efficiently handle natural gas orfines in the fluid, and available injection pressures. It alsorequires sufficient vertical space between the injection and

production zones to allow for sufficient gravity separationThe application must provide sufficient wellbore volume thaan appropriate resident time is provided for the oil drop size toseparate and rise from the fluid stream. Equipment allows theinstallation in 4-1/2 inch and larger casing.

The second type of gravity separator is a modified versionof the DAPS, the triple action pumping system (TAPS) shownin Fig. 2. This separation system was also introduced byTexaco and can be used when the injection formation has low permeability or requires higher injection pressures. The TAPSincludes an upper piston that operates on the upstroke and two pistons that operate on the downstroke.

The last type of gravity separator DOWS is the Q-Sep G

This system is designed to avoid the compressive strainexperienced by the sucker rod string in the DAPS systemduring the down stroke due to the required injection pressureThis system provides a dual operation of lifting thehydrocarbon and injecting the water on the upstroke while icarries out an enhanced gravity separation during the downstroke.

Hydrocyclone Separation DOWS. The separationmechanism in hydrocyclone separation DOWS is alsogoverned by Stokes law and is seen in the difference betweencentrifugal force generated by the spinning fluid and the dragforce on the moving droplet. The hydrocyclone separator has



SPE 94276 3

no moving parts. Separation is achieved through highcentrifugal forces which develop due to the geometric designof the hydrocyclone (Fig. 3).

In operation, produced fluid is introduced into the topcylindrical portion of the hydrocyclone. The swirling of thefluid mixture makes the water, the heavier fluid, to spin to theoutside of the hydrocyclone and move toward the lower outlet

while the lighter fluids (oil and gas) remain in the center of thehydrocyclone where they are drawn through a vortex finderinto the upper outlet and produced by the pump to the surface.

Perfect separation of oil and water in a hydrocyclone,however, is not possible as some oil is carried along with thewater fraction to be injected and some water is brought to thesurface with the oil and gas fraction. Multiple hydrocycloneassemblies can be connected in series to enhance the separatorefficiency or in parallel to accommodate flow rates greaterthan achievable in a single unit.17

Reports show that the hydrocyclone provides veryeffective separation of oil from high water cut fluids, the waterdisposal stream usually containing less than 200 ppm residualoil. A key parameter of hydrocyclone separation is the feedmixture viscosity. Hydrocyclone performance is viscositysensitive and inlet mixture viscosities above 5-10 cp will showreduced separation performance. The inlet viscosity is afunction of temperature, oil concentration, and purecomponent viscosities.

The disposal zone injectivity and the pressure required to produce the fluid to the surface dictates the horsepowerrequirement which in turn determines the number of pumpsthat are most appropriate. Dual pump systems allowhorsepower savings to be achieved in applications where the pressure required to dispose the water is less than the pressureneeded to produce the lower density oil stream to the surface.

The hydrocyclone DOWS separator system was

developed by C-FER Technologies Inc. Several suppliers havedeveloped different products with various tradenames for thehydrocyclone based DOWS including AQWANOT,HydroSep, and Q-Sep. The tradenames are based on the typeof pumps used: electric submersible pumps, progressing cavity pumps or rod pumps. The most common is the electricsubmersible pump DOWS (Fig. 4). It offers many advantagesin situations where the reservoirs are deep and the productionvolume is high. Because of the limited wellbore space,hydrocyclones used in DOWS are narrow and tall in designrequiring a minimum 5-1/2 inch casing size.

Membrane Separation DOWS. The existing gravity

separation and hydroclone separation DOWS technologieshave disadvantages in terms of separation efficiency, cost,complexity, frequency of failure, and control systemrequirements. A new membrane separation technology thatcan allow water free production from early production anddoes not require any mechanical moving parts is presently being investigated and has the potential to enhance the use ofDOWS in the industry.14,18

Membrane filtration is the separation of the componentsof a pressurized fluid performed by polymeric membranes.The polymeric membrane is permeable to one or morecomponents of the mixture and is impermeable to theremaining components. The openings in the membrane

matrices (pores) are so small that significant fluid pressure isrequired to drive liquid through them. The pressure required todrive the fluid through the membrane varies depending on thesize of the membrane pores. Reverse osmosis (RO)membranes have the smallest pores, while microfiltration(MF) membranes have the largest pores, and hence, requirethe least pressure.

Tweheyo et al.18

reported that the basic principle inhydrophobic oil wet membranes proposed for use in downholeoil-water separation is that the membrane maintains thecapillary entry pressure for water higher than the oil pressureThis concept presents the potential of separating oil and waterdownhole and the possibility of water free oil production“The membrane well represents the central element in a robusdownhole separation system that does not require movable parts, mechanical tools or advanced sensors.”18

The membrane device can be placed either on the production tubing or towards the reservoir wellbore. It can becombined with a water re-injection system so that theseparated water is injected into a suitable formation like otherDOWS systems. It therefore offers a viable option for futureDOWS and in the long term should be simpler than existingDOWS systems.

The challenges surrounding the process are stilnumerous. Since different wells operate in different downhole pressure regimes, it is expected that different membrane typeswill have to be designed to allow for the various capillaryentry pressures of water that will be experiencedAlternatively, if a standard membrane type is used for alwells, there will be a need to control the bottomhole pressurethrough a pressure control device. The ability to increase production as desired may be reduced to a specific range orate-pressure drawdown for the optimum performance of themembrane system. Furthermore, membranes loose their

performance effectiveness with time based on the membranetype, hydrodynamics, membrane-solute interaction, feed and process conditions.

Another concern in downhole application is related tomembrane fouling. Flux, as a measure for membrane performance, decreases due to fouling. Membrane foulingoccurs due to the deposition and accumulation of particles onthe membrane surface and within the pores of the membrane.14

The critical enabling technology needed is the development ofreliable membrane materials that can provide long-termservice without excessive fouling.

Different reservoirs may require specific experimentastudies to establish the maximum pressure range over which a

particular type of membrane may be used. Empirical studieson reducing membrane fouling can make use of standardmembranes and measure filtration flux while keeping othervariables like trans-membrane pressure, oil-water cuttemperature, and cross-flow velocity constant.

Field ApplicationsAlthough relatively more expensive, the most widely usedtype of DOWS is the hydrocyclone separation DOWStechnology. There have been some success stories with theapplication of DOWS technology; however, the confidencelevel in the technology is still low. This has limited the extentof deployment of the technology industry-wide. The low



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confidence level is mainly due to the misapplication of thetechnology in some cases which has yielded undesirableresults that have not encouraged further deployment.11,17

While the individual components of DOWS technologyare fairly simple and easy to operate, the environment inwhich they operate is complex and dynamic. This requirescareful consideration and evaluation of operating conditions

when choosing candidate wells. Other reasons for the limiteddeployment include high costs, especially for thehydrocyclone type DOWS, as well as the indirect monitoringand control required as the pumping/separator system isdownhole. Indirect monitoring may impact the separationefficiency and possesses the attendant risk of injectingsignificant amounts of oil together with the produced water.This potential production loss is a great inhibitor for theapplication of this technology.

Further deployment and trial application of thetechnology is needed in order to carry out more studies toovercome the existing challenges. The fact that most oilcompanies presently produce more water than oil and thecurrent relatively high cost of crude oil in the internationalmarket present an opportunity to encourage furtherdeployment of the DOWS technology at this present time.Some of the ways to facilitate further deployment of thetechnology includes providing proper guides in the selectionof candidate wells as well as technological improvement of the process to increase the separator/pump robustness whilelowering costs.

The DOWS technology has been applied in NorthAmerica (Canada and USA), South America, Germany,France, and China with mixed results. Several feasibilitystudies without actual field application have also been carriedout for applications in other areas including Africa (Nigeria)and the Middle East (UAE).

Some of the field applications have shown positive resultswith a significant reduction in produced water and no decreasein oil rates for a significant period of time including theapplications in the Alliance Field 3 and the LA-90 well of LacqSuperieur Field of southwest France.16 Veil et al.2,5 provides asummary analysis of thirty-seven field trials in North America.Experience from field trials indicate that as operators andvendors gain experience with the technology in a particulararea, especially in candidate well selection, that overall performance of DOWS systems improve.

Other applications of DOWS technology were notsuccessful and failed within a few days to a few months ofinstallation. The failure analysis in many cases showed

plugging of injection zones as the main cause of failure. Otherreasons included excessive solids production, corrosion ofdownhole tools, undersized pumps, etc. One field trial in EastTexas showed early promise but failed quickly due tooperational problems.12 An example of an unsuccessfulapplication of DOWS technology is an example from the LaVictoria Field in Venezuala.17

Parameters for Technical and Economic SuccessDepending on the DOWS type, typical DOWS project costs(procurement and installation) range between $120,000 and$300,000.2 Although reports show that some DOWS projectshave had payback periods as short as 2 months, the relatively

high cost suggests that the design life or time to failure is acritical factor to the success of a DOWS project. The degreeand duration of benefit that can be realized with the DOWStechnology depends on the particular characteristics of the producing well, reservoir rock and fluid properties, and therobustness of the separator/pump assembly. The factors listed below, though not in order of importance, are all relevant and

should be given careful consideration in the selection anddesign process in order to ensure the success of a DOWStechnology installation.

I. Presence of a suitable injection zone. This is perhapsthe most important technical requirement. For DOWStechnology to operate properly the injection zone mushave sufficient permeability and porosity to accepseparated produced water. The produced water shouldenter continuously into the formation so that theinjection pressure does not build up to exceed thecapability of the pump. Accurate determination of theinjection index of the target zone should never becompromised during the selection of candidate wells.

II. Location of the injection zone. It is mandatory that theinjection zone and the production zone be isolated andthat there is a significant distance between the last production perforation and the injection interval. TheStuebinger et al. report1 recommends at least 10 feet oseparation for gravity-type DOWS installations. Theinjection zone can be in the same formation as the production zone provided there is no pressurecommunication between the perforated intervalsWithout sufficient isolation between intervals, theinjected produced water can migrate back into the producing zone and then short circuit into the producing perforations, thereby recycling the producedwater and causing oil production rates to drop sharply.

III. High water-oil ratio. The economics of the applicationof DOWS is a lot better at the later stage of the producing life of a well when the water cut is above80%. At this stage most wells already require artificialift systems; a significant portion of the energy istherefore being spent in lifting the water to the surfaceIt is reported that power savings up to 50% overconventional ESP lift can be achieved when DOWStechnology is applied. Furthermore, increasing water production leads to higher chemical consumption ratesneeded to prevent corrosion, scaling, and emulsions

that ultimately leads to well abandonment due todeclining profitability. The best use of DOWS istherefore in areas with high water handling costs, i.ehigh water cut wells, operations requiring the use ofthird party facilities for water treatment or operationsrequiring long distance transportation of producedwater.

IV. Compatibility between produced water and injectionzone fluids. Incompatible fluids can cause pluggingcorrosion and scaling. This can lead to reducedinjectivity and ultimately a shutdown of the DOWSsystem.



SPE 94276 5

V. Wellbore size and geometry. It is expected that theinterval for DOWS use is fairly vertical. Substantialdeviation of the interval from the vertical may haveundesirable effects on the operation of the DOWStechnology especially when the flowrates are high.Appropriate casing diameters are also required for theinstallation of the downhole equipment.

VI. Produced fluid gravity. Gravity type DOWS are notsuitable for very heavy oils as the time required fornatural separation becomes unnecessarily lengthy. Inaddition, the difference in the density of the producedoil and water is very important to this process as fluidswith minor density differences lengthen the separationtime. Reports indicate that heavy crude/water mixturesare more likely to form water in oil emulsionsespecially when exposed to the shear induced by a pushthrough design using ESPs, thereby reducing theefficiency of the DOWS system.

VII. Unconsolidated formations. Reservoirs that are suspect

for sand production may not be suitable for DOWStechnology due to the potential of plugging within theDOWS system.

VIII. Wellbore integrity. As with any other productionoperation, especially subsurface injection, wellboreintegrity is important. Suitable zonal isolation must be provided in the injection zone through packerarrangement and cement integrity. This is required to prevent unwanted fluid movement behind pipe,minimize leakage in the DOWS system, and potentialrecirculation of injected fluids.

IX. Wellbore accessibility. The candidate well should befree of any downhole obstruction that may increase theoperational risk in installing downhole equipment andgaining access to the targeted disposal/injection zone.

The application of DOWS technology requires carefulanalysis and screening in candidate selection. It furtherrequires an appropriate evaluation and design process todetermine both economic and technical feasibility of the potential installation. An appropriate design process isnecessary to provide acceptable performance that willencourage utilization of the technology.

Blanco and Davies13 developed a decision tree orselection guide for use in determining the application of

DOWS technology. While the guide does not directly addressthe technical requirements in the design of a DOWSinstallation, it provides insight on the overall process oneshould utilize in evaluating the application of the technology.Fig. 5 reproduces their screening guide. Jokhio et al. 20 analyzed the economic parameters that affect DOWSinstallations and discussed characteristics of improved oilrecovery operations that could benefit economically from theapplication of DOWS technology. Alhoni et al.19 present anengineering feasibility study for a particular reservoir toscreen and select potential candidates well for application ofDOWS technology. Each of these examples provides insight

into the selection process for the application of DOWStechnology.

ConclusionsDOWS technology was introduced to the oil and gas industryin the 1990’s. Reports detailing the application of DOWStechnology from inception to date indicate DOWS technology

has considerable benefits despite formidable challenges.The DOWS technology applied in mature fields

producing at high water-oil ratios has established benefits inreducing water handling costs and increased oil productionwith a reduction of risk of adverse affects on the environment.

While current technology is available for successfuDOWS implementation, there are opportunities for improvingthe technology. One such opportunity is in the developmenand application of membrane technology, which mayrepresent a significant enhancement in the utilization ofDOWS technology.

The choice of candidate wells has a great impact on the potential benefits derived from the application of DOWStechnology. A major consideration in the application of thetechnology is the proper candidate well selection based uponseveral factors. These factors include the presence of asuitable injection zone, wellbore configuration, zonaisolation, and compatibility of fluids.

Data from the field trials indicate that as operators andequipment vendors gain experience in selecting candidatewells, the overall performance of this technology improves.

While proven in the field, DOWS technology still has anumber of obstacles to overcome prior to gaining wide-spreadacceptance within the oil and gas industry. The first step inthis acceptance is for the professional and technical staff togain a better understanding of the principles and applicationsof DOWS technology. The second is for field and operating

staff to gain operational experience with actual fieldinstallations that are successful. Once these two things occurand personnel become familiar and comfortable with thetechnology, then the DOWS technology will evolve and may become a widely accepted technology for produced watermanagement.

References1. Stuebinger, L. et al.: “Dual Injection and Lifting Systems: Rod

Pumps,” paper SPE 38790 presented at the 1997 SPE AnnualTechnical Conference and Exhibition, San Antonio, TX, 5-8Oct.

2. Veil J.A., Langhus, B.G. and Belieu, S.: “Feasibility Evaluationof Downhole Oil/Water Separation (DOWS) Technology,”

Technical Report for U.S. Department of Energy, Jan. 1999.3. Matthews, C.M., Chachula, R., Peachey, B.R., and Solanki

S.C.: “Application of Downhole Oil/Water Separation Systemsin the Alliance Field,” paper SPE 35817 presented at the 1996SPE International Conference on Health, Safety & Environment

New Orleans, LA, 9-12 June.4. Bowers, B.E., Brownlee, R.F., Schrenkel, P.J.: “Development of

a Downhole Oil/Water Separation and Reinjection System forOffshore Application,” SPEPF (May 2000).

5. Veil, J.A., Langhus, B.G. and Belieu, S.: “Downhole Oil/WateSeparators: An Emerging Produced Water DisposaTechnology,” paper SPE 52703 presented at the 1999 SPE/EPAExploration and Production Environmental Conference, AustinTX, 28 Feb.-3 March.



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6. Verbeek, P.H.J., Smeenk, R.G., and Jacobs, D.: “DownholeSeparator Produces Less Water and More Oil,” paper SPE50617 presented at the 1998 SPE European PetroleumConference, The Hague, The Netherlands, 20-22 October.

7. Shaw, C.: “Downhole Separation as a Strategic Water andEnvironmental Management Tool,” paper SPE 61186 presentedat the 2000 SPE International Conference on Health, Safety, andthe Environment in Oil and Gas Exploration and Production,

Stavanger, Norway, 26-28 June.8. Schrenkel, P.J.: “Joint Industry Development of the Downhole

Oil Water Separation System: Field Case Study – An Update,” paper SPE 38535 presented at the 1997 SPE ProductionOperations Symposium, Oklahoma City, OK, 9-11 March.

9. Peachey, P.R and Matthews C.M.: “Downhole Oil/WaterSeparator Development,” JCPT (Sept. 1994) 17-21.

10. Shaw, C. and Fox, M.: “Economics of Downhole Oil-WaterSeparation: A Case History and Implications for the North Sea,”

paper SPE 50618 presented at the 1998 SPE EuropeanPetroleum Conference, The Hague, The Netherlands, 20-22October.

11. Stuebinger, L.A. and Elphingstone, G.M. Jr.: “MultipurposeWells: Downhole Oil/Water Separation in the Future,” SPEPF (Aug. 2000).

12. “Analysis of Data from a Downhole Oil/Water Separator FieldTrial in East Texas,” Argonne National Laboratory and ArthurLanghus Layne, Technical Report for U.S. Department ofEnergy, Feb. 2001.

13. Blanco, A.E. and Davies, D.R.: “Technical and EconomicApplication Guidelines for Downhole Oil-Water SeparationTechnology,” paper SPE 67182 presented at the 2001 SPEProduction and Operations Symposium, Oklahoma City, OK,24-27 March.

14. Fernandez, L.G., Soria, C.O., Tourn, C.A.G., and Izquierdo,M.S.: “The Study of Oil/Water Separation in Emulsion byMembrane Technology,” paper SPE 69554 presented at the2001 SPE Latin American and Carribean Petroleum EngineeringConference, Buenos Aires, Argentina, 25-28 March.

15. Xiaoming, L. et al.: “Research of Downhole Separation andInjection Technique for Rod Pumping Well,” paper SPE 68719

presented at the 2001 SPE Asia Pacific Oil and Gas Conferenceand Exhibition, Jakarta, Indonesia, 17-19 April.

16. Gay, J-C, Minnebois, J-L, Lacourie, Y., and Lecoffre, Y.:“TotalFinaElf Experience and Strategy in DownholeProcessing,” paper SPE 78541 presented at the 2002 Abu DhabiInternational Petroleum Exhibition and Conference, Abu Dhabi,13-16 Oct.

17. Bangash, Y.K. and Reyna, M.: “Downhole Oil Water Separation(DOWS) Systems in High-Volume/High HP Application,” paperSPE 81123 presented at the 2003 SPE Latin American andCarribean Petroleum Engineering Conference, Port-of-Spain,Trinidad, West Indies, 27-30 April.

18. Tweheyo, M.T., Akervoll, I., Holt, T. and Torsaeter, O.:

“Simulations of Oil-Wet Membrane Wells for Water-Free OilProduction and Downhole Separation,” paper SPE 81189 presented at the 2003 SPE Latin American and CaribbeanPetroleum Engineering Conference, Port-of-Spain, Trinidad,West Indies, 27-30 April.

19. Alhoni, M.A., Jerbi, K.K., Drawil, T.A., and Zekri, A.Y.:Application of Downhole Oil-Water Separation: A FeasibilityStudy,” paper SPE 80485 presented at the 2003 SPE AsiaPacific Oil and Gas Conference, Jakarta, Indonesia, 9-11 Sept.

20. Jokhio, S.A., Berry, M.R., and Bangash, Y.K.: “DOWS(Downhole Oil-Water Separation) Cross-WaterfloodEconomics,” paper SPE 75273 presented at the 2002 SPE/DOEImproved Oil Recovery Symposium, Tulsa, OK, 13-17 April.

21. Wacker, H.J. et al.: “Test Proves Out Triple-Action Pump inDownhole Separation,” Oil & Gas Journal, (4 Oct. 1999) 49-55

Fig. 1. DAPS System (From Stuebinger et al.1)



SPE 94276 7

Fig 2. TAPS System. (From Wacker et al.21

)

Fig. 3. Hydrocycl one Schematic. (From Bow ers et al.4)

Fig. 4: DOWS Hydrocyc lone System.



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Yes

No

CURRENT PRODUCTION METHOD(ECONOMICAL ANALYSIS)

“BASE CASE”

Premises :1. ESP is economically moreattractive than the current productionmethod.2. DOWS is going to be evaluated since:a) Surface facilities are overloaded orb) Water handling cost are too high or

c) WC is higher than 50% ord) Drilling an injector well is too expensive3. The extra oil production may add by anadditional well being put on production orincreased oil production from this well is notconsidered.4. The profitability impairment due to thevolume of oil injected into the disposalformation is not considered

“ DOWS ECONOMICAL FEASIBILITY ANALYSIS”

ECONOMIC DATA INPUTESP& DOWS equip. reliability, water handling

cost, oil price, discount rate, power supply cost,ESP & DOWS W/O costs, etc

Select different DOWSinstallation times, i.e. ESPW/O installation times

DOWS evaluation- Maximum achievable oilrate based on operationalconstraints?- Economic limit- Cum. NPV at DOWS economiclimit

ESP economical analysis- Economic limit- Cum NPV at ESP economic limit

Sensitivity analysiswith DOWS reliability , oil price,

discount rate, water handling andpower cost at the diffe entr

installation times

DOWS reliability, oil price, water handling,discount rate and power supply cost analysis

- Minimum DOWS reliability, oil price,water handling, power cost, etc to achieve

DOWS more economic lly attractiveathan ESP

Is DOWS benefit >Extra W/O cost@ DOWS econ . limit Install DOWS

Produce untilDOWS economic limit

Evaluate anotherProduction alternative

Install DOWS whenInput conditions

are optimumfor installation

Design a plan ofDOWS installation

time depending on theDOWS reliability , oil price,water handling, power cost

and discount rate

Install ESP

Produce untilESP economic limit

Evaluate another

Production Alternative

Evaluate

“Strategy 1 or 2”

Install ESP

Produce untilESP economic limit

Evaluate anotherproductionalternative

Does DOWS extend thewell’s economic life?

Install DOWS

Produce untilDOWS economic

limit

Evaluate anotherproduction alternative

Install DOWS at fixedinstallation time

Install DOWS at ESP economic limit.

“Strategy 1”

“Strategy 2”

“Strategy 3”

Yes

No

3

2

Fig. 5. Decision tree for DOWS installation developed by Blanco and Davies.13

(From Blanco and Davies

13)

a review of downhole separation technology

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