effective sandstone acidizing - best practice

F-3374R 05/97

EffectiveSandstone

AcidizingSandstone 2000TM

1Effective Sandstone Acidizing

Effective Sandstone AcidizingEffective Sandstone Acidizing

IntroductionSandstone acidizing technology has improved significantly over the last 5 yearsas a result of field analysis, fundamental research, and applied research. Oldertheories predicted that after sandstone acidization, approximately 10% HCl,approximately 3,500 mg/L of silicon, a small amount of aluminum, and apossible trace of sodium should exist in the initial undiluted returns. Thosetheories proved to be inaccurate in 1984 when samples from a Gulf coast wellwere obtained after sandstone acidization. Our analysis revealed almost no acid,no silicon, and large amounts of aluminum and sodium. Further study andresearch revealed a complex reaction process based on acid concentration,temperature, and the target formation mineralogy. Based on this research, theSandstone 2000™ Acid System was developed. Approximately 90% of the wellstreated with the Sandstone 2000 Acid System have been returned to productionwith a two- to four-fold increase in production rate. This Best Practices providesmore information about sandstone acidizing technology and how it can helpimprove your sandstone acidizing success rate.

Formation AnalysisTo perform a successful acidization treatment, operators must know the composi-tion of the formation at the treatment point. The dominant mineral component andtemperature of the target formation will determine the most effective formationconditioning system (preflush), HF/HCl treatment blend, and volumes. Thepresence of potassium feldspars, sodium feldspars, illite, carbonates, and zeolites isa primary concern since these compounds can form or contribute to formingsignificant matrix-blocking precipitates, such as sodium or potassium fluosilicatesand aluminum fluorides, during HF/HCl treatments. Water-sensitive clays alsorequire special consideration because they may swell, obstructing the formationmatrix. Precipitates and swelling can be controlled or eliminated with effectivetreatment planning. HCl-sensitive formations must be identified before treatmentso that severe precipitation of sandstone reaction products will not occur. Ifpossible, an X-ray diffraction analysis of a formation core from the target areashould be obtained. For wells without core samples, Halliburton’s Spectral GammaRay Log procedure can provide an accurate target area mineral analysis for use intreatment planning.

Formation ConditioningTreatment of a well before sandstone acidization can greatly increase the successrate of the stimulation treatment. Formation conditioning design depends on thepresence of key minerals. Proper formation conditioning before treatment withHF acids is critical to the success of the stimulation treatment. The flowcharts onPages 8 and 9 can help you design an effective conditioner for your formation.Table 1 () describes the problems that certain minerals commonly found insandstone formations can cause. Table 2 (Page 3) describes various formationconditioning systems and when they should be used.

Note

Copyright 1997, Halliburton Energy Services, Inc. All rights reserved.

2 BEST PRACTICES

Table 1—Formation Minerology

Clays

Ion exchange on clays was previously thought to be of minor consequence.However, recent work has shown that the impact of ion exchange can bedramatic for brines undergoing deep matrix invasion in sandstone with clayshaving a significant ion-exchange capacity. When ion exchange occurs, thecations naturally present on the surfaces of the clays are replaced or exchangedwith ions from the invading brine. This transformed brine must also maintaincompatibility with the formation.

NH4Cl

Recent research involving 3-ft columns packed with sand and clay has demon-strated the importance of brine compatibility both before and after ion ex-change. For example, when 3% CLAYFIX (NH4Cl) flows across an ion-ex-changing clay, the solution becomes 3.3% sodium chloride brine. This initialconcentration may be sufficient before ion exchange. However, the concentra-tion of salt after exchange is not high enough to prevent swelling of water-sensitive clays (smectite or mixed-layer clay). The result is the loss of matrixpermeability. The most effective brine for sandstone acidizing is NH4Cl.CLAYFIX 5 Conditioner provides sufficient ion exchange and maintains enoughsalt concentration to prevent clay swelling before and after ion exchange.

Mineral ProblemFeldspars Feldspars contain sodium and potassium. The major concern

is fluosilicate precipitation. K-Spars cause the most precipitation problems.

Carbonate Carbonate consumes HCl and can cause precipitation of fluosilicates and aluminum from spent acid.

Illite Illite causes fines migration problems and is ion-exchanging. It contains potassium, which can cause fluosilicate precipitation from spent acid.

Kaolinite Kaolinite causes fines migration problems. It disperses in fresh water and causes plugging.

Smectite Smectite is an ion-exchanging mineral that swells in fresh water.

Mixed-Layer Clay Mixed layer clay is ion-exchanging and swells in fresh water. It often contains potassium, which can cause fluosilicate precipitation from spent acid.

ChloriteChlorite is ion-exchanging and unstable in HCl.

Mica Mica is ion-exchanging and unstable in HCl. It contains potassium, which can cause fluosilicate precipitation from spent acid.

Zeolite Zeolite is ion-exchanging and unstable in HCl. It often contains sodium, which can cause fluosilicate precipitation from spent acid.


Table 2—Formation Conditioning Systems

HCl-Sensitivity and Clay Instability Ratings

Many formations are “HCl-sensitive;” formation minerals decompose whencontacted by HCl. During this process, metal ions such as Fe, Al, Ca, and Mg,are dissolved from the mineral, leaving an insoluble silica gel mass that can beextremely damaging. HCl-sensitive minerals include zeolites and chlorite.However, research has shown than all clays have a temperature above which theyare unstable. An instability rating for clays at various temperatures has beendetermined to address this problem. For example, if a formation contains 5 to10% illite with a BHST of 225ºF, it is considered HCl-sensitive. Figure 1 belowshows clay instability rating curves for various common clays.

Figure 1—Clay instability rating of various clays at different temperatures

Fluid System When to Use

Mud Cleanout

Mud-Flush Removes whole water-based mud losses

N-Ver-Sperse Removes whole oil-based mud losses

Wellbore Conditioning

Paragon or other organic solvents Removes asphaltene/paraffin deposits, heavy oils, pipe dope

HCl for pickling Removes iron scales and prevent them from entering the formation

Oil Well ConditioningGidley's CO2 Conditioner Helps prevent emulsion problems and terminal upsets;

improves acid penetration into oil zones

Matrix Conditioning

CLAYFIX 5 Conditioner Helps condition high ion-exchanging clays5 to 15% HCl Helps condition carbonate removal, ion exchanging, remove

polymer damage

CLAY-SAFE 5 Conditioner Helps condition carbonate removal, ion exchange for HCl-sensitive minerology

CLAY-SAFE H Conditioner Helps condition HCl-sensitive minerology, but requires removal of polymer damage (K-Max, HEC, etc…) or high carbonate levels

50 100 150 200 250 300 350

Temperature ( oF)

0

25

50

75

100

Feldspar

Inst

abili

ty R

atin

g

Ana

lcim

e

Chl

orite

Illite

Sm

ectit

eK

aolin

ite

4 BEST PRACTICES

When formation minerals have an instability rating of 0 to 25, use HCl preflushesand HCl-HF fluids. At high instability ratings of 75 to 100, use only organic,acid-based systems. This consists of the organic acid-based CLAY-SAFEconditioners followed by an organic-HF system, Volcanic Acid System. If thestability rating is from 25 to 75, use CLAY-SAFE conditioners. The HF stagecan either be an HCl-based fluid or the Volcanic Acid System. A very successfulrecommendation has been the use of CLAY-SAFE conditioners followed by theappropriate HCl-HF fluid system. HCl alone can be very damaging in thesetypes of formations, but HCl in the presence of HF is not. The HF preventsmassive silica deposition, which minimizes the effect of the clays’ HCl-sensitiv-ity. As the instability rating exceeds 50, use the Volcanic Acid Systems. Manycases exist in which HCl-based fluids worked well, and others where completelyorganic acid systems provided excellent results. Historical performance oftreatments in the area and personal experience can help you choose the appropri-ate fluid.

Acetic Acid

Despite the sensitivity of clays to HCl, they are stable in acetic acid and fairlystable in formic acid. Unfortunately, both of these acids are similar to freshwater in the presence of water-sensitive clays. Substituting acetic acid (MSA) forCLAYFIX is not a good alternative, since MSA does not exchange ions with theclays or prevent clay swelling. MSA is not an equivalent substitute for HClbecause it does not dissolve iron scales and is slow to dissolve carbonates.However, use of CLAY-SAFE conditioners should provide sufficient ion ex-change to help 1) prevent precipitates in the HF/HCl process, 2) control clayswelling, and 3) stabilize the clay to sandstone acidization.

Cation-Exchanging Minerals (CEMs)

If the CEMs (stilbite, bentonite, zeolites, smectite, illite, mixed layer clays, andchlorite) exceed 15%, use CLAYFIX 5 ahead of the preflush containing CLAY-SAFE conditioners. This combination of preflushes will provide enough ionexchange to help prevent clay swelling.

Carbonates

Sandstone formations containing greater than 5% carbonates are prone to matrixprecipitation of complex aluminum fluorides as spent HF flows across thecarbonates. The solution to this problem requires 1) deep removal of the carbon-ate with large preflushes of HCl or 2) the use of an additive that prevents pre-cipitation. For example, 50 gal/ft of 15% HCl preflush in a sandstone containingonly 5% calcite will remove the calcite in a radius of about 2 ft from the wellbore.If spent HF follows, aluminum fluoride precipitation will begin 2 ft from thewellbore. Since 150 gal/ft of spent HF would penetrate about 5 ft from thewellbore in a 20% porosity rock, several feet of matrix would be subject toprecipitation and plugging. To remove the carbonate to a distance of 5 ft, 300gal/ft of 15% HCl preflush would be required.


Laboratory tests and field studies have revealed that the addition of ALCHEK inthe sandstone acidizing treatment can help prevent precipitation of aluminumfluorides as spent HF flows across carbonate. Preventing precipitation ensuresthat the formation retains the full permeability improvement potential of thesandstone acidizing system.

Matrix Conditioning Volume

To provide adequate ion exchange, remove carbonates, and optimize sandstoneacidizing, the volume of matrix conditioner should be equal to or greater thanthe volume of the sandstone acid used in the treatment.

Many fields contain more than 20 to 40% of total ion-exchanging clays. Forthese fields, the preflush fluid volume needs to be sufficient to complete the ionexchange before the spent HF flows across the clays. Fields that contain lessthan 30% of ion-exchanging clays should be conditioned with about 100 gal/ftof HCl, 100 gal/ft of CLAYFIX 5, or a 50/50 combination of both. Fields thatcontain more than 30% of ion-exchanging clays should be treated with about150 gal/ft of matrix conditioners.

Gidley’s CO2 Conditioner

Carbon dioxide preflushes have successfully prevented terminal upsets aftersandstone acidizing treatments and have improved the HF treatment response.One operating company’s study revealed that oil-wet particulates (colloidal silicaand fines) stabilized the terminal emulsions. These particles were precipitatedfrom HF acid reacting with the formation in the presence of hydrocarbons, suchas crude oil and xylene. The solution is in Gidley’s CO

2 Conditioner, a Halliburton-

exclusive process that removes the hydrocarbons from the near-wellbore area.The carbon dioxide treatment uses 100 to 200 gal/ft of CO2 under miscibleconditions to displace the oil away from the matrix in the near-wellbore area.Displacing the hydrocarbons allows better HF invasion of the matrix and pre-vents emulsions from forming. The CO

2 can also be used throughout the acid

stages to provide enhanced energy for cleanup.

Some oils form asphaltene precipitation easily and other oils have minimalmiscibility with CO

2 under reservoir conditions. Both of these conditions can be

at least partially eliminated with a xylene preflush ahead of the Gidley’s CO2

Conditioner.

Additional Information

Brines that remain compatible both before and after ion exchange include 5%NH4Cl, 7% KCl, 5% CaCl2, and 6% NaCl. These brines are sufficient to com-plete the ion exchange in deep-matrix invasion and prevent clay-swelling. Theyshould be considered for a variety of operations including gravel-packing,sandstone acidizing treatments, killing wells, perforating, and any other opera-tions where deep-matrix invasion is expected. In fact, practices such as killing awell with seawater alone might be a source of deep-matrix damage.

6 BEST PRACTICES

TreatmentThe correct ratio of HCl to HF in an acid blend is selected based on the mineralspresent in the target area of the well. The flowchart on Page 9 is designed to helpyou determine the best acid blend for your needs. Table 3 describes the availablesandstone acid systems.

Table 3—Sandstone Acidizing Systems

HF Reactions

The three stages of matrix reactions that can affect your choice of acid systemsare described in the following paragraphs.

Primary Stage

The primary HF reaction removes matrix damage and improves permeability.Live HF reacts with sand, feldspars, and clays. The reaction results primarily insilicon fluorides with some aluminum fluorides. The HF acid provides thegreatest dissolving power during this phase while only a small amount of HCl isconsumed. The primary stage is the stage that removes skin damage.

Secondary Stage

During the secondary reaction, the silicon fluorides react with the clay andfeldspar. The reaction releases a large amount of aluminum into the solution,consumes a large amount of HCl, and forms silicon precipitates. Only thealuminum fluorides are present at the end of the secondary reaction; the siliconfluorides have vanished. The critical part of the reaction is to control how thesilicon precipitates.

Researchers have discovered that precipitation of silicon as silica gel is not asignificant problem in flow tests conducted below 250°F. Silica gel precipitationis not a problem if the fluid is in flow. If live HF is shut-in across the perfora-tions, severe and permanent damage to the matrix permeability can result fromthe silica gel precipitates. If the temperature is above 100°F, this precipitationcannot be prevented.

Fluid Name AdvantagesSandstone Completion™ Acid This acid formulation is the fluid of choice when the mineralogy is

unknown. It offers maximum dissolving power with minimum secondary precipitation and prevents aluminum precipitation.

Fines Control™ Acid This formulation is a retarded system that removes deep damage caused by fines and swelling clays. It also helps prevent fines migration.

K-Spar™ Acid This acid is compatible with formations high in feldspars and illite. It also helps prevent fines migration.

Volcanic™ Acid This organic acid system is compatible with HCl-sensitive minerals. It can also be used used in high temperature applications.

Silica Scale™ Acid This acid uses a high HF concentration to remove silica scale from geothermal wells.


The precipitation of silicon as silicon fluorides can be very damaging. Thisprecipitation of silicon can be prevented with improved fluid design. In one casein Indonesia, Silica Scale™ Acid was used on a potassium-dominant feldsparformation at 200°F. Based on previous research, silicon fluoride precipitateswould likely form. An ammonium chloride overflush was used, and the treat-ment pressure was increased. When an HCl overflush was used in other treat-ments, the treatment pressure decreased. The ammonium chloride overflushincreased the treatment pressure response because the HF was no longer active,and the fluosilicate precipitates were plugging the matrix. Pressure did notincrease with the HCl overflush because the HCl redissolved the precipitate. Thedissolved precipitate continued to react until the silicon fluorides were no longerpresent, thereby preventing the pressure increase.

Based on these observations, a pressure increase from an ammonium chlorideoverflush indicates a potential incompatibility between the acid and the forma-tion mineralogy. The success rate of sandstone acidizing depends on howeffectively the acid blend prevents silicon fluoride precipitation.

Tertiary Stage

During the tertiary reaction, the aluminum fluorides react with either clay orcarbonates until all remaining acid is consumed. The resulting solution containsspent acid and complex aluminum fluorides. If a brine source is available toraise the pH and mix with the aluminum, the aluminum will precipitate withsmall amounts of silica gel to form “alumino silicate scale.” Although theaddition of 3 to 5% acetic acid and ALCHEK in the treatment process cangreatly reduce or eliminate alumino silicate scale in the wellbore, only ALCHEKcan effectively prevent alumino silicate scale deep in the matrix.

HCl/HF Ratios

The ratio of Hcl to HF depends on the dominant minerals and temperature in theformation. Tests were conducted on sodium feldspars, potassium feldspars, andillite-dominant formations to determine the best acid blend to prevent sodiumand potassium fluosilicate precipitation at varying temperatures. The results arelisted in Tables 4 through 6 (Page 10).

The optimal ratio of HCl to HF is 9:1; the minimum ratio is 6:1. Research andfield results have shown Fines Control Acid™ (retarded HF) provides excellentcompatibility with formation minerals.

Acid Volumes

What are the guidelines for choosing lower HF volumes? Although 1.5% HF hashalf the dissolving power of 3% HF, doubling the volume of 1.5% HF will notproduce the same results, because lower HF concentrations react much moreslowly with sand. This slower reaction allows the HF to use more of its dissolv-ing power on such targeted damage sources as clays and feldspars while usingless dissolving power on sand. Table 7 shows the different HF concentrationsand volumes that will give the same performance.

8 BEST PRACTICES

AreHCI-sensitive

clays or zeolitespresent?

Yes No

No

Yes

NoYes

NoYes

AreCECs>15%?

AreCECs

freshwater-sensitive?

Iscarbonate

>5%?

Condition withCLAY-SAFE 5

Condition withHCI

Condition withCLAYFIX 5ahead of

CLAY-SAFE 5

Conditioning acidvolume =

HF treatment volume(Include ALCHEK¨ in theselected acid treatment)

Conditioning acidvolume = 75%

of HF treatmentvolume

Start

*Recent experimental results indicate that ALCHECK can successfully prevent or reduce the formationof aluminum precipitates during HF treatments in which carbonates are present.


Fines ControlTM Acidcan be used at any

temperature

Fines ControlTM Acid can be usedat any temperature

No

Yes

Present?

Feldspar

Treataccording totemperature

below

Final BlendChoose most

compatible or weakestHF blend from all

applicable categories

Start

SodiumFeldspar

°F HF Blend>175 Sandstone

CompletionTM

<175 K-SparTM

PotassiumFeldspar

°F HF Blend>250 Sandstone

CompletionTM

<250 K-SparTM

Record blend;go to Clays

Go toClays

Yes

No

HCI-sensitive?

Clays

K present?(illite)

Illite/Mixed Layer Clay

°F HF Blend>200 Sandstone CompletionTM

<200 K-SparTM

Record blend;go to Zeolites

Treat withVolcanicTM

Acid

NoYes

Treat with SandstoneCompletionTM Acid

Present?

Zeolites

NoYes

Treat withVolcanicTM

Acid

Treat withSandstone

CompletionTM

Acid

Record blend;go to

Final Blend

10 BEST PRACTICES

Organic-HF Acid

Acetic HF and formic HF fluids often are used to remove skin damage andincrease production in wells that cannot tolerate HCl-based fluids. However,these fluids can produce severe secondary precipitation of HF reaction productsand are not recommended. New organic HF acid systems can replace the use ofacetic HF and formic HF fluids in HCl-sensitive formations. An organic acid,such as ALCHEK, is blended with the HF acid to prevent the secondary precipi-tation with HCl-sensitive minerals, such as chlorite, zeolites, and clays.

Volcanic Acid, Halliburton’s new organic-HF acidizing blend, is also suited foruse in high-temperature formations and helps prevent HCl-induced sludging. Itincorporates NH4Cl to prevent swelling of water-sensitive clays and a penetrat-ing agent to help acid contact the damage. Volcanic Acid II is based on ALCHEKas the organic acid.

Temp °F HF Blend > 175 Sandstone Completion Acid < 175 K-Spar Acid

Temp °F HF Blend > 250 Sandstone Completion Acid > 200 K-Spar Acid

Temp °F HF Blend > 200 Sandstone Completion Acid > 125 K-Spar Acid

Table 4—Application to Sodium Feldspar

Table 5—Application to Potassium Feldspar

Table 6—Application to Illite

Table 7—HF Acid Volume GuidelinesHF Concentration Volume gal/ft

3% 100

1.50% 150

1% 200

Retarded HF 200


Avoiding Problems

ALCHEK

If carbonates are present in the formation, the addition of ALCHEK in theHCl/HF treatment blend successfully prevents or reduces the formation ofaluminum precipitates. Alumino-silicate is an amorphous scale containing bothaluminum and silicon. The scale forms when spent HF has lost all acid, thesilicon fluorides have completely reacted to place a large amount of aluminuminto solution, and a brine source is available to raise the pH. ALCHEK is moreeffective than acetic acid at preventing aluminum scaling and aluminum precipi-tation in the formation. ALCHEK is used in Sandstone Completion Acid,Volcanic Acid II, and in other acid systems when the formation consists of 5% ormore carbonates.

Clean Water

The use of clean water, rather than saltwater or potassium chloride water, willensure that the ammonium chloride is at its full potential to perform ion ex-change with the formation instead of the sodium or potassium in the contami-nated water. If contaminated water is used, the concentration of ammoniumchloride may be insufficient to prevent matrix plugging from fluosilicate precipi-tation or clay swelling.

Brine Compatibility

Recent studies at Halliburton Energy Services have revealed that heavy comple-tion brines are incompatible with most formation waters. In most cases, thecombination of heavy brines and formation water results in salt precipitation.Formation zones with heavy brine losses from the wellbore should be preflushedwith large volumes of CLAYFIX 5 Conditioner. The CLAYFIX 5 Conditionerwill dissolve the salt and increase the effectiveness of the acid treatment. Failureto use CLAYFIX 5 Conditioner will allow salt to precipitate in the matrix whenthe HCl preflush contacts the heavy brine.

Water-Based Mud Loss

Wells having significant mud loss across the producing interval require specialattention. If the mud lost is a normal water-based bentonite mud, use Mud-Flushto thin the mud and flow it back. Each stage should be about half the volume ofthe mud lost and should be pumped and returned to the surface. For example, ifthe zone took 100 bbl of mud, a two-stage treatment of Mud-Flush should beused. Continue to pump subsequent stages until the returns are fairly clean.

Oil-Based Mud Loss

Every producing interval drilled with an oil-based mud should be treated withN-Ver-Sperse to remove oil-wet mud solids and remove the leaked-off oil carrier.The oil-wet mud solids will not be easily attacked by HF because of the oilsurrounding them. The oil leak off can cause severe emulsion problems. If wholemud has been lost, contact with acid will cause a semipermanent substance

12 BEST PRACTICES

similar to peanut butter to form. One recent case involved a well with twounsuccessful HF treatments. An N-Ver-Sperse mud removal treatment broughtthe well in at close to the tubing-limited production rate.

Scales in Wells

For a successful HF stimulation, mechanically or chemically clean the wellborebefore treatment. Cleaning the wellbore ensures that the treatment acid will reactwith the formation instead of the wellbore contents. Cleaning also prevents scalein the wellbore from being pushed down into the formation.

Tubular Metallurgy Inhibitors

Use the Halliburton Chemical Stimulation manual to choose the correct metal-lurgy inhibitor for your location. The inhibitor and stimulation chemicals shouldbe compatible to achieve maximum acid effectiveness.

Other Sandstone Acidizing References

1. Gdanski, R.D.: “AlCl3 Retards HF Acid for More Efficient Stimulations,”Oil & Gas J. (Oct. 1985) 111-115.

2. Gdanski, R.D. and Peavy, M.A.: “Well Returns Analysis Causes Re-Evaluation of HCl Theories,” paper SPE 14825 presented at the 1986 SPESymposium on Formation Damage Control, Lafayette, Feb. 26-27.

3. Almond, S.W., Brady, J.L., and Underdown, D.R.: “Return Fluid Analysisfrom the Sadlerochit Formation, Prudhoe Bay, Alaska: Field Study - PartI,” paper SPE 18223 presented at the 1988 SPE Annual TechnicalConference and Exhibition, Houston, Oct. 2-5.

4. Shuchart, C.E. and Ali, S.A.: “Identification of Aluminum Scale with theAid of Synthetically Produced Basic Aluminum Fluoride Complexes,”SPEP& F (Nov. 1993) 291-296.

5. Gdanski, R.D.: “Fluosilicate Solubilities Impact HF Acid Compositions,”paper SPE 27404 presented at the 1994 SPE Symposium on FormationDamage Control, Lafayette, Feb. 7-10.

6. Shuchart, C.E. and Buster, D.C.: “Determination of the Chemistry of HFAcidizing with the Use of 19F NMR Spectroscopy,” paper SPE 28975presented at the 1995 SPE International Symposium on Oilfield Chemistry,San Antonio, Feb. 14-17.

7. Shuchart, C.E.: “HF Acidizing Returns Analyses Provide UnderstandingHF Reactions,” paper SPE 30099 presented at the 1995 SPE EuropeanFormation Damage Control Symposium, The Hague, The Netherlands,May 15-16.

8. Gdanski, R.D.: “Fractional Pore Volume Acidizing Flow Experiments,”paper SPE 30100 presented at the 1995 SPE European Formation DamageControl Symposium, The Hague, The Netherlands, May 15-16.


9. Gdanski, R.D. and Shuchart, C.E.: “Newly Discovered Equilibrium ControlHF Stoichiometry,” paper SPE 30456 presented at the 1995 SPE AnnualTechnical Conference and Exhibition, Dallas, Oct. 22-25.

10. Gdanski, R.D.: “Kinetics of the Tertiary Reaction of HF on Alumino-Silicates,” paper SPE 31076 presented at the 1996 SPE Formation DamageSymposium, Lafayette, Feb. 14-15.

11. Guichard, J.A. III, Allison, D., Gdanski, R.D., and Ghalambor, A.:“Modified Retarded Stimulation Treatments Improve Production FromWilcox Reservoirs,” paper SPE 31139 presented at the 1996 SPEFormation Damage Symposium, Lafayette, Feb. 14-15.

12. Shuchart, C.E., Gdanski, R.D.: “Improved Success in Acid Stimulationswith a New Organic-HF System.” SPE 36907, European PetroleumConference, Milan, Italy, October 22-24, 1996.

13. Gdanski, R.D.: “Kinetics of the Secondary Reaction of HF on Alumino-Silicates,” SPE 37214, 1997 SPE International Symposium on OilfieldChemistry, Houston, February 18-21, 1997.

14. Shuchart, C.E.: “Chemical Study of Organic-HF Blends Leads to ImprovedFluids,” SPE 37281, 1997 SPE International Symposium on OilfieldChemistry, Houston, February 18-21, 1997.

15. Gdanski, R.D.: “Kinetics of the Primary Reaction of HF on Alumino-Silicates,” SPE 37459, 1997 SPE Production Operations Symposium,Oklahoma City, March 9-11, 1997.

Notice: This publication is based on sound engineering practices, butbecause of variable well conditions and other information that must berelied upon, Halliburton makes no warranty, express or implied, as tothe accuracy of the data or of any calculations or opinions expressedherein. Halliburton shall not be liable for any loss or damage, whetherdue to negligence or otherwise, arising out of or in connection with suchdata, calculations, or opinions.

14 BEST PRACTICES

Notes


Notes

16 BEST PRACTICES

Notes

effective sandstone acidizing - best practice

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