Ch 17 - Water Production Control

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Chapter 17: Water Produ ction Contro lThe treatment of wells to prevent or control unwanted fluid production has a long history in the oil pro-duction industry. Methods of modifying channeling, gas or water coning and other reservoir problemshave resulted in a great many treatments, most of which were unsuccessful. This section describesprocedures and techniques to modify flow paths or change other reservoir characteristics near thewellbore to control unwanted production or injection of fluids.The modification of the reservoir to achieve water shutoff, redistribution of injection or other sweepimprovement in a secondary flood operation, is a poor substitute for using reservoir information to planthe location of wellbores to take advantage of the reservoir features. Unfortunately, by the time suchinformation is known about the formation, the wells have been drilled and there many not be sufficientreserves to justify new wells. With the increasing use of the technology of horizontal wells and theradial extension drilling from existing vertical wells, however, newer techniquesto improve the drain-age in established fields are available. Before extensive experimentation with the chemical andmechanical methods of changing flow paths, a study should be made o@ he possibility of using thereservoir character to improve the fluid recovery.Summary of Impo rtant PointsThe following major points illustrate the experience gained with treatment of water injection and pro-duction problems.

1. For chemical or physical permeability modifying techniques to be successful in a pattern water-flood, the treatment must be injected deep enough into the reservoir to modify the flow of thefluid in a large area of the pattern. The actual depth of injection required will depend on horizon-tal and vertical permeability and well spacing in the pattern. In waterfloods, it may be necessaryto selectively treat both injector and producer.2. If deeply penetrating, permanent permeability reducing techniques are used in a primary recov-ery zone, the residual hydrocarbons in the zone may not be available by later recovery methods.3. For near wellbore permeability reduction or water control techniques to be completely effective,there must be natural, impermeable reservoir-wide barriers between the treated zone and theproductive zone, the vertical permeability must be very low in contrast to horizontal permeability,or a pressure balance method of depletion may be used.4. Treatment of a zone to reduce water flow in a pattern waterflood, especially a very high perme-ability zone, will reduce the total fluid injected in the well. In wells that are operating just belowthe fracture extension pressure, the zones cannot take any more fluid, regardless of the avail-able volume of water. Reducing the flow capacity of a high permeability zone must be accompa-nied by a lowering of the expectation of water input. The only way to more rapidly process orsweep the formation is to drill more wells and reduce the distances between injector and pro-ducer. This is of critical importance in a low permeability reservoir.

Sou rces of WaterBefore touching on a discussion of shutoff methods, a brief description of the sources of water influx isworthwhile.20 Water may exist in solution with oil or as water mixed with gas. Water may also exist asa pore filling phase (conflate water) or itmay flow into the reservoir in response to pressure reduction.

1. Solution water exists as a mixture of water vapor in hot gas reservoirs or as a dissolved phasein the oil. The amount of water that can be dissolved in oil is small, usually less than 0.2% by vol-ume. However, more water is often contained as a micro-droplet dispersion in oil. What ever themethod of containment, the production of this type of water cannot be stopped.

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2. Connate water is a distinct phase in the pore of the formation. When production is started, someof this connate water will be produced. The amount that is mobile will depend on the irreduciblewater volume. Pore fillings that create high microporosity, such as some chlorite and illite clays,will hold higher volumes of this water. Like the solution water, this type of water cannot bestopped without stopping the oil.3. Active drive aquifers, from either bottom or edge sources, can provide pressure support forenhanced recovery from a reservoir but can also produce enormous quantities water. If perme-ability barriers exist between the water and oil zones or if the reservoir vertical permeability ismuch lower than the horizontal permeability, then water production from these sources can becontrolled in the near wellbore. S ince the water drive is an active pressure support, the waterproduction cannot be stopped completely, but with careful planning, the water movement can beused to advantage to help drive the oil.

a. Inbottom water drive applications, coning near the wellbore is the biggest problem. Stoppingconing requires information on the values of horizontal and vertical permeability. When verti-cal permeability is much less than horizontal permeability (below 50%), then near wellboretreatments to place permeability barriers can have some effect in reducing water production.If the formation is fractured, either naturally or hydraulically, matrix permeability barriers areuseless. If the vertical permeability approaches 50%or more of horizontal permeability, bar-riers are also useless, but horizontal wells may be very useful.

b. In edge water drives, the problem is from both vertical permeability and from horizontal per-meability variance or streaks of high permeability. These streaks can allow water break-through early in the project life. For successful control, the streaks must be plugged from theproduction well. Depth of plugging depends on the vertical permeability. If there are barriers(vertical perm=O), then plugging depth can be shallow. If vertical permeability is high, thebarrier must extend nearly back to the original oil/water contact ifthe water control is to besuccessful.treatment of hundreds of feet) before any water control attempt will be long lasting. Ifthefracture extends down into the water, density contrast techniques may be effective in plug-ging off just the bottom zone.

c. In the special case of fractured reservoir, the fractures must be plugged deep (radius of

4. Water injection in a flood follows the same rules as an edge water drive except that plugging canbe applied from both producing and injection wells. Barriers are critical to individual zone control.5. Entry of water from reservoir or tubular leaks may be very troublesome, but usually can be iden-tified by salinity contrast and sealed by repair treatments such as cementing squeezes.

Problem Definit io n - ReservoirBefore any treatments can logically be discussed, a definition of the problem must be presented. With-out a full understanding of what is causing the sweep problem or unwanted water production in a wellor between wells, effective treating is a very remote possibility. An analysis of fluid flow patterns and adescription of the reservoir are critical to success.There is a distinct separation of water channelling problems into near wellbore and deep reservoirbased on both effect in the reservoir and methods of treatment. In the near wellbore area of produc-tion wells, the greatest problem in producing hydrocarbon fluids from all of the pay is permeability con-trast. No formation is homogeneous, and permeability variations of 1to 2 orders of magnitude arecommon in many reservoirs. To effectively drain all of the reservoir often requires selective stimulationof the lower permeability sections, or at times, reducing the permeability of the higher permeabilityzone if a water or gas drive is active.When a reservoir contains natural fractures, the problem of rapidly and evenly producing all the reser-voir may be compounded. Open natural fractures provide a pathway with typical permeability between10 millidarcies and 1darcy. Completion of a well into a naturally fractured reservoir invariably leads to

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a state of flush production during which producing rates are very high, followed by a sharp decline inrate as the fractures empty. P roduction may fall 50 to 90% in a matter of weeks. The production stabi-lizes with flow from the matrix into the natural fracture system. This is a characteristic of the naturally-fractured formation and is not a solvable problem. Natural fracture systems are usually a positiveaspect of the reservoir, especially if the well locations are selected to take advantage of the improveddrainage that the fracture system offers. Many times, however, the natural fracture system is notextensive enough to economically serve as a conduit to the wellbore. In these cases, hydraulic fractur-ing with either acid in a carbonate formation or proppant and a fluid in either carbonates or sandstoneare very beneficial if the fracture can be contained in zone.Problem Defin i t ion - Near WellboreMechanical problems in the well are often invisible culprits which cause productivity of a well to suffer.Incorrectly sized tubing, casing, insufficient perforations or improperly designed lift systems can act asa choke on a reservoir and severely limit production. There is no cure for a mechanical problem otherthan redesigning and recompleting the well.ConingNatural and induced problems in a well include fluid coning or channeling, water or gas blockages andrelated relative permeability effects?-3 Coning of a fluid usually occurs when a oil or gas zone is bor-dered by water in a reservoir with no barriers between the pays. It also may occur as gas coning intoan oil producing interval. Coning is a response of a fluid to flow towards a pressure drop. It occurswhen only part of a fluid filled, continuous formation or series of formations is perforated. The pres-sure in the produced area of the formation is lowered through production. The fluid in the adjacentzone then moves up or down towards the pressure drop. C oning will occur in any reservoir wherethere is an absence of a permeability barrier between the produced fluid and the unwanted fluid.Coning results in an increase in the unwanted fluid and a decrease in the production of the oil. The oildecrease occurs because the water or gas in the cone occupies part of the pore space that was onceoccupied by the oil. The amount of coning is related to the amount of vertical permeability (in theabsence of a barrier), the mobility of the produced and coned fluids, and the pressure differential.A sketch of cone development is shown in F igure 17.1. At initial production, the oil and water (in thiscase) lies at the initial oillwater contact and the entire oil column is perforated. As the oil is produced,the water rises near the wellbore in the section of the reservoir that was occupied by the oil. The oper-ator often reacts to the water encroachment by squeezing off the lower perfs with cement or otherchemical barrier material. The water continues to rise in the zone with the operator squeezing and pro-ducing at the same or a higher drawdown. At abandonment of the well, there is a large amount of oilremaining in the reservoir but only a small path to the wellbore. This problem is especially acute inbottom water drive reservoirs. Controlling coning is attempted by restricting the producing rate to avalue that minimizes water rise or by chemical treatments.There are a number of mathematical models for prediction of the maximum production rates to avoidor slow the rate of coning.4* These models assume a homogeneous formation with no natural frac-tures (these are usually poor assumptions). An equation from Karp8 is given as a example method.

0.0246k,Ap (h2- D 2 )

where:kh =horizontal permeability in darcies

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...........................................................................................................................................................

Figure 17.1: A wors t case, very advanced cone that h as caused early P& A of awel l . This type of con e may occur where vert ical permeabi l i ty wasas high or higher than hor izontal permeabi l i ty as in the case oflocal ized natural fractures extendina from the hvdrocarbon zone

Ap =h =D =PO -B =re -rb =rw -

The use of an

---

into the water zone in the area near & e wel lbore. -density difference, Ibm/ft3oil-zone thickness, ftcompletion interval thickness, ftoil viscosity, cpoil FVF, RB/STBdrainage radiusradius barrier (if used), otherwise rb =rwwellbore radiusartificial barrier has been proposed by several authors to prevent or slow cone develop-ment.2*8i4These barriers are usually envisioned as thin, impermeable and pancake shaped as shownin F igure 17.2. The chemicals used for this treatment include polymers, inorganic gels, and foam. Thebasic problem with all the treatments is the diameter of the barrier. It must extend into the reservoir farenough so that the gravitational force on the water will be larger than its response toward the pressuredrop of the production well. This concept is neither affordable nor possible for most treating chemicals.Barriers rarely are a long term solution to the problem of coning and water breakthrough regularlyoccur, Figure 17.3. Additional problems with barriers are that they are seldom accurately placed in theright location and that they channel through the formation rather than moving out uniformly from thewellbore. Vertical channels often do not exactly overylay horizontal permeability channels.

The more promising methods of controlling water coning in the most severe cases are the use of hori-zontal wells, F igure 17.4, and the concept of balanced fluid withdrawal from the re ~ervo ir .~*~oningcontrol by the horizontal well are discussed in the chapter on special completions. Balanced fluid with-drawal involves the removal of both oil and water from the well. The primary method of equalizingpressure is to even the drawdown across both the water and the oil zones. This is a radical change inproduction procedure since it requires perforating the water zone, isolation at the interface with a goodcement job and a packer, and then dually completing the water zone with a dedicated lift system andsurface facility. The drawbacks in initial cost could be overcome in some projects by the savings inwater treating and disposal. Water produced in this manner should be naturally low in oil and the pro-ducer may be able to classify the water in a different manner as the water separated from oil.The procedure would obviously be most applicable where oil-water separation problems were severe,where large vertical permeability values could create rapid cones, and where legal restrictions werevery stringent. The process would be of only limited use in reservoirs with edge water drive and those

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Figure17.2: An idealized schematic of a barrier in the reservoirseparating the hydrocarbon and water zones. Barriersare probably never this uniform since they follow thesame low resistance pathways as other injected fluids.

Figure17.3: Probably results of water flow around a barrier aswater flow responds to the continued pressuredecrease in the hydrocarbon zone caused by fluidwithdrawal.under water flood. Reservoirs that depend upon the bottom water drive as the sole source of drivingenergy could still use the dual completion process by controlling the rate of upward movement of theoil-water interface. This may be accomplished by balanced fluid withdrawals at the production well-bore and water replacement in the aquifer at an injection well.Water BlockOccasionally, when a well is killed with water or when a well goes off production and fills up with pro-duced water, the water will enter the zone of gas or oil production and displace the hydrocarbons fromthe area around the wellbore. In some cases, when the well is returned to production, the hydrocar-bons will not displace the water. This behavior is usually indicative of a water block. Water blocks can-not be perfectly defined in the sense that they cannot be reliably recreated in the laboratory. However,

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I-.::: drawdown$ 0 Uses bottom water c

Figure 17.4: Useof a horizontal well to slow the rateof coning ina bot tom water drive reservoir.there are four conditions which usually occur when a severe water block is encountered: (1) anuntreated water (surface tension near 72 dyne/cm); (2) low reservoir pressure; (3) small pore throats;and (4) a gas zone (low pressure oil zones account for roughly 10to 25% of reported water blocks).Although water blocks have been known to form in oil zones, they are rarer than the water blocksreported from gas producing zones. Blockages in the oil zones may also be the result of emulsions orsludges formed from contact of oil with water or acids. Diagnosis is difficult and the major problems(emulsion) is usually prepared for with a treatment of alcohol or alcohol mixture mutual solvent thatcan penetrate deeply and remove either emulsion or water block.Water blocks are usually physical changes to relative permeability or clay equilibrium. Other relativepermeability problems are related to the presence of natural or injected surfactants which may causean oil or water wetting (a bound layer of water or oil) and in situ emulsions. Any time that the pore pas-sages are restricted by trapped fluid or high viscosity fluid, regardless of the method entrapment, flowwill be restricted.Other near wellbore problems include the formation of scale, the deposition of paraffin, and the occur-rence of migrating fines in the near wellbore area or in the reservoir. These problems and the inducedproblems of surfactant adsorption and emulsions are best described as formation damage and can becontrolled with remedial treatment and/or inhibition production techniques.Problem Definit ion - Injection WellThe injection well is a special case of flow path consideration. In the unfractured injection well, theflow is outward radial flow. Injection of fluid in the unfractured case is described by the concept ofradial darcy flow through cylindrical beds in series where the beds may be areas of different perme-ability or layers of permeability-reducing material from solids carryover. In addition, in a typical hetero-geneous formation, fractures, high permeability channels and permeability barriers (faults,permeability pinchouts, etc.) all affect the distribution of fluids at the injection well or the reservoir.Once in the reservoir, the sweep pattern between injection and production wells are directly controlledby the path of least resistance: the fluids move in the highest permeability channels to the limit of whatthe channels can carry towards an area of reduced pressure. Permeability variations and pressuredistributions through the reservoir completely control the way fluids move and the rate of their move-ment from injection well to production well.The mobility ratio, solubility of fluids within each other and the effect of injected gases on heavy endsare all very important; however, the fluids will only go where the reservoir characteristics allows them.The most basic problem, then, is how to successfully modify the reservoir character or use the reser-voir character to the best advantage for oil recovery. Because of varying operating philosophies forwater floods over the years, most injection wells have been fractured. This must be considered in jobdesign.

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Reservoir Descript ion and Modeling Necessit iesTo properly apply any lasting and effective profile modification mechanism, regardless of whether it isrelocation of the wellbore, deep matrix penetration of a permeability-reducing material or near well-bore application of a zone shutoff material, it is imperative that a good description of the reservoir beavailable. This description will likely be a combination of geologic and engineering knowledge andhopefully will be present in the form of computer simulator to save time in comparison of zone controlmechanisms. To use the reservoir simulation route, the model must be constructed with as muchdetailed reservoir description involving flow geometry as is possible. Location of natural fractures, ver-tical or horizontal permeability impairments, hydraulic fractures, thief zones and a complete descrip-tion of the driven and driving fluids are necessities. From this information, a solution giving details onhow deep to inject a permeability modification material or where to relocate the wellbores of injectionand production wells to make optimum use of the reservoir characteristics may be possible. S implistictwo-dimensional models or linear correlations are rarely adequate. Modeling is greatly aided by theinput of data gathered in monitoring of water in flu^^Treating Co nsiderationsObviously, the large volume treatment of wells with expensive chemicals will depend on the amount ofreserves remaining on a particular area of the field and the opportunities for success. The selection ofmatrix treating materials should also take into account the later plans for the reservoir in terms of stim-ulation or a tertiary flood. If a matrix or a thief zone is completely shut off by a deeply penetrating, per-meability-reducing material, the opportunities for tertiary recovery are severely diminished. Most of thewater shutoff materials are not removable because of either lack of a solvent or inability to contact theblocking material in the pores of the rock. Acid can remove most cement plugs and perforating canreach beyond those that are shallow ( r 4 ft). Fracturing is the only mechanism that can reach beyondthe deeply penetrating shutoff techniques.Mod ification of Perm eabilityRegardless of flow geometry of the reservoir, there will always be a need, usually several times in thelife of a project, for a treatment to change the permeability of a particular zone. These treatments canbe divided into two subdivisions of the two major classes: deep and shallow methods of eitherdecreasing permeability or increasing permeability. Whenever perm eabi l i ty of a zone is reduced bychem ical t reatment, the total water inject ion expectat ions to a wel l sh ould b e reduc ed or otherzones shou ld b e careful ly f ractured if possib le. Allowing indiscriminate fracturing of a well byincreasing pressure to increase injection rate should be avoided at all costs.Deep Modif ication - Permeabil i ty ReductionTo deeply reduce or plug off high permeability, a few methods are available with proven performance.The processes described in the following paragraphs are all listed in the cross-reference ofTable 17.1. Deep treating processes include silica ge11*12and lignosulfonate gel for matrix treatingand fly ash, limestone fines, or thermoset or catalyzed plastics for shallow to moderate depth pluggingof gravel packs or fractures.10112 Foam diversion is often listed as a deep matrix plugging techniquebut may be operable only in formations where matrix permeability is at least on the order of severalhundred mill ida rcie~.~ost polymer systems, including those intended for deep treatment, are usu-ally limited to shallow placement by the high viscosity of the gel or undissolved polymer buildup(fisheyes, microgels and trash) on the injection face. Crosslinked polymers may have application inplugging fractures.Deep Mo dif ication - Increasing Permeabil i tyUnfortunately, hydraulic fracturing is the only method of improving the permeability enough to influ-ence the reservoir flow behavior. Although there is very good confidence in the mechanics of fractur-ing, the direction or orientation of the fracture is controlled by the reservoir stresses, and the fractureheight growth from large fracture treatments (above and below the plane of interest) is difficult to reg-ulate, although monitoring techniques are a~ailable .~he technology of very tightly controlled fractur-

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lame i .1 :Generic Materrais ana Processes Av ailable to r Reaucin g PermeabilityProduct

Lignosulfonate GelSilica GelPolymersFoamPlasticsSelective PolymersCement"Gunk Squeeze"

Commentsdeeply penetrating, total permeability snutoffmoderately to deeply penetrating, total permeability shutoffshallow penetrating, partial to total permeability shutoffunproven except in high permeability control, may have good application insteam wellsshallow penetrating, permanent, total permeability shutoffshallow penetrating, some application where distinct separation of wateroccurs but exact zone locations are unknownface pluggingof a zone. Only effective where barriers exist or vertical perme-ability is a small fraction of horizontal permeabilitya designation for a slurry of dry cement in diesel or other oil. The mixture setsup when water is contacted. Basic application is in vuggy or naturally fracturedformations with distinct oil and water pays where the exact zone locations arenot known. Penetration is typically shallow in vugs or fractures. It producesface plugging in any matrix.

ing in small treatments, to limit length and height growth, is currently available and should beconsidered when injection rate must be increased.Shallow Modif ication - Permeabil i ty ReductionThere are many products and techniques to selectively or totally reduce the permeability in the nearwellbore area.10*15-19 o describe them, they should be separated into groups designed to accomplishthe specific tasks of: (1) total zone shutoff, (2) coning and encroachment control, and (3) selectivepermeability reduction.Total permeability shutoff can be easily accomplished by a number of products if one criteria is met:there must be an impermeable barrier between the zone being sealed and the producing zones. Ifthere is a barrier, then cement squeezes, plastics, polymers and inorganic gels will all work. If there isno barrier to flow, the problem will be the same as the coning problem addressed in the followingparagraph.Controlling coning is usually a delaying tactic and the established treatments may isolate large quanti-ties of otherwise recoverable reserves. Coning occurs when water (or less frequently, gas) takes overpart of the productive oil zone. The flow of water is a reaction to production of hydrocarbons leading toa lower pressure in the oil zone in general and the near wellbore area in particular. Squeezing off thelower perfs and completing higher in the zone may temporarily reduce water production, but waterbreakthrough will occur and oil may be trapped and production hindered in this limited completion.Eventually, in the case of an active bottom water drive, the wellbore will be completely watered outand no oil will be produced, even though substantial reserves may remain in the reservoir.Chemical companies have several products designed and sold as selective permeability reducers.These products (usually polymers) can treat a sandpack or formation core so that oil will pass throughthe pack but water will not. While the sales concept and benchtop tests are impressive, the technologyis extremely poor and will probably reduce oil production in any well where oil and water are producedfrom the same zone or in many coning applications. In any case where oil flows with water towards apressure drawdown, reducing or stopping the water will reduce or stop oil production. If there is noway of removing the water from around the wellbore then there is no method to flow oil toward the wellas long as the water is there.

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Shallow Modification- Increasing PermeabilityMost matrix methods (nonfracturing) of increasing permeability in reservoir rock are very shallow pen-etrating. F ortunately, very shallow damage removal can boost production or injection enormously andeven increases of undamaged permeability can boost production or injection several percent.Removal of damage is the most important item in consideration of methods of improving production orinjection with an inexpensive near wellbore treatment. Improving initial matrix permeability with acid orother chemical methods can assist in a small way, but most matrix methods are limited to a few feet ofpenetration at the very most. By examination of flow capacity increase available by the beds-in-seriesmodification of Darcy law, it can be demonstrated that the maximum increase available is only a fewpercent.Very small, carefully controlled fracture treatments are also useful in improving near wellbore perme-ability. The short, fat fracs of a few thousand gallons of fluid and several thousand pounds of prop-pant are very useful for improving flow. In limestones, acid breakdowns are a standard in treating andretreating both injection and production wells, both from a cleanout and stimulation viewpoint.References

1. Endean H. J ., Shelton, R. D.: Water lnitiaied P roblems in P roduction Operations, ChampionTechnologies, Inc., Houston, Texas, 1991.2. Richardson, J . G., Sangree, J . B. and Sneider, R. M.: Coning, Technology Today Series, J our-nal of P etroleum Technology, (August 1987),pp. 883-884.3. Sparlin, Derry D. and Hagen, Raymond W. J r.: Controlling Water in Producing Operations,World Oil, (April 1984),pp. 77-86.4. Woods, E. G. and Khurana, A. K.: Pseudo-functions for Water Coning in a 3-0 Reservoir Simu-lator, SPE 5525.5. Wheatley, M. J .: An Approximate Theory of OilNVater Coning, SPE 14210.6. Giger, F. M.: Analytic 2-D Models of Water Cresting Before Breakthrough for Horizontal Wells,SPE 15378.7. Chaperone, I.: Theoretical Study of Coning Toward Horizontal and Vertical Wells in AnisotropicFormations: Subcritical and Critical Rates, SPE 15377, 1986 SPE Annual Mtg. New Orleans,OCt 5-8.8. Karp, J . C., Lowe, D. K., Marusov, N.: Horizontal Barriers for Controlling Water Coning, J . Pet.Tech., (J uly 1962).9. Patton, L. Douglas: Optimize Production Through Balanced Reservoir Depletion, Part 4--1njec-tion and Water Influx Monitoring, Petroleum Engineer International, (March 1989),pp. 28-30.

10. Sparlin, Derry D. and Hagen, Raymond W. J r.: Controlling Water in Producing Operations, Part4-Grouting Materials and Techniques, World Oil, (J une 1984),pp. 149-1 52.1 1 . J urinak, J . J ., Summers, L. E. and Bennett, K. E.: Oilfield Application of Colloidal Silica Gel,SPE 18505, pp. 425-454.

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12. Smith, L. R., Fast, C. R. and Wagner, 0. R.: Development and F ield Testing of Large VolumeRemedial Treatments for Gross Water Channeling, J ournal of P etroleum Technology, (August1969), pp. 1015-1025.13. Dietz, et al.: Foam Drive Seldom Meaningful, J PT, May 1985, pp. 921 922.14. Strickland, Richard F.: Artificial Barriers May Control Water Coning-1 ,I The Oil and Gas J our-nal, (October 7, 1974), pp. 61-64.15. Carroll, J . F. and Bullen, B.: Successful Water Control Examples in Gulf of Mexico GravelPacked Gas Completions, SP E 18228, pp. 495-501.16. Burkholder, L. A. and Withington, K. C.: New G el Suppresses Water Flow in Oil Wells, Oil andGas J ournal, (September 1987), pp. 93-98.17. Hess, Patrick H., Clark, C. O., Haskin, C. A. and Hull, T. R.: Chemical Method for FormationP lugging, J ournal of Petroleum Technology, (May 1971), pp. 559-564, 153, 63-66.18. Chan, K eng Seng: Injection P rofile Modification With a New Non-Polymer Gelling System,Petroleum Society of CIM, Paper No. 89-40-46, pp. 46-1 -46-1 4.19. Rike, J . L.: Obtaining Successful Squeeze - Cementing results, SPE 4608, Las Vegas, Nev.,Sept. 30-Oct. 3, 1973.20. Chan, K. S.: Water Control Diagnostic P lots, SPE 30775, Dallas, Oct. 22-25, 1995.

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Ch 17 - Water Production Control