SOCIETY OF PETROLEUMENGINEERS OF AIME6200 North Central Expressway X~RWE 2751Dallas, Texas 75206

THIS IS A PRJ3PRINT--- SUBJECT TO CORRECTION

New Diverting Techniques for Acidizingand Fracturing

By

Charles L. Smith, James L. Anderson and P. G. Roberts,Member AIME, Byron Jackson Inc.

@ Copyright 1969American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the 40th Annual CaliforniaRegional Meeting of the Society ofPetroleum Engineersof AIME, to be held in San Francisco,Ca.lif.,Nov. 6-7, 1969. Permissiontocopy is restrictedto a.nabstractof not more than 300 words. Illustrationsmay not be copied.The abstract should contain conspicuousacknowledgmentof where and by whom the paper is presentedPublicationelsewhereafter publicationin the JOURNAL OF PETROLEUM TECHNOLOGYor the SOCIETY OFPETROLEUMENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriatejournalprovided agreementto give proper credit is made.

DiscussionGf tkls =Ur..namer is invited. Three copies of any discussion shouldbe sent to theSociety of PetroleumEngineersoffice. Such discussionmay be presented at khs above !neetingand,with the paper, may be consideredfor publication in one of the two SPE magazines.

ABSTRACT interestcontains at leastone sectionwithpermeability thatis markedly differentfrom

Diverting materials and techniques are dis- the remaining sections;or the formation iscussed in thispaper from the standpointof comprised of a series of zones, each differinglaboratory evaluation,fieldapplicationand job from the other in reservoir pressure aswellresults. A briefreview is given on the con- as permeability. For these reasons, someventionalmaterials used for fluid diversion. method of fluid diversion is necessary toThese include naphthalene, rock salt, para- obtain maximum stimulation from any of the

formaldehyde and a wax-polymer. various types of pressure treatments.

A more detailed discussion is presented ona Many techniques and materials have been

new solid diverting agent that is completely utilized in attempting to control the placement

soluble in both water and oil. Laboratory and of fluids into the formation. These include

field data indicate that this material, due to its mechanical devices such as bridge plugs,

high degree of thermal stability and volubility packers and perforation ball sealers. Com-

properties canbe applied Lna larger number binations of bridge plugs and packers have

of wells than the solids mentioned previously. been used successfully in many areas;however, their use is limitedto cased holes

Foamhas demonstrated the abilityto be used and they are expensive to use. Likewise,

as a Fluid diverter in many wells where other perforation baii seaiers cafibe applied only

diverting systems are ineffective. Properties -1-+~~ with ra~ing.in welu3 eo~mp~=b=u .. . ... --L They often

of foam are discussed along with unique field necessitate high pump rate, and the optimum

applications and results of jobs utilizing the number for a given job is difficult to

foam diverting system. determine,

INTRODUCTION. ~+hnt-1 nf fll]id injectionutiliZeSfinoiherm.bL.u= -. ...pressure build-up across perforations, due

When stimulating formation, it m of con- to the velocity of fluid in the perforations, to

siderable importance that the treating fluid be breakdown additional sections of a formation.

distributed into each intervalof productionor Because of horsepower requirements, this

injection. Quite often the formationof technique becomes inadequate when treating

SFE 2751

~tremely long intervals or in shorter~tervals which contain a high number oferforations per foot. A lSO, in many acid

.1 - J ..~~~k treatments, Lt is desirablena cnermca~ ~~e,.J keep treating pressures below themmation fracturing pressure.

erhaps the most widely used method of fluidiverting is by employment of solid particles] create a restriction across the portions offormation which accept fluid most readily.

hese solid materials include rock salt,

aphthalene, paraforrnalde@@, sulf arniccid and a wax-polymer. Each of these~aterials have solubilit y and temperature eimitations. This paper discusses a newolid diverting material which has lessolubility and temperature restrictions.

n addition, a new technique utilizing foam asdiverting agent is presented.

)lL SOLUBLE -WATER SOLUBLE;RANUMR ORGANIC DIVERTING AGENTS

~aboratory Development

practically all diverting agents availablevill dissolve in either oil or water, but theyVill not dissolve in both. A laboratory

nvestigation was undertaken to find aliverting agent that was soluble in both media.preliminary screening tests were run toletermine if the material was completely~oluble in oil and water. In addition todetermining if a material was soluble, theate of volubility was also determined. A. .llverting m.at.erial m.-..11~t be SIOWly soluble in

)rder to remain a solid during the entire~timulation treatment. The diverting

material should also dissolve in a reasonable~mount of time so that a well may be:eturned to production or injection withouti long delay for the diverting agent toiissolve.

Jynamic volubility tests were run toietermiine the effective life of a diverting

material under treating conditions. Many

materials have an extremely slow volubilityrate under static conditions, because the;luid immediately surrounding a particle ofiiverting material becomes saturated andwill not dissolve additional material.Dynamic solubilit y tests were run by placing100 grams of material in a heated cell and

flowing liquid through the cell at a rate of100 ml/min. Results of the dynamicvolubility tests are reported in Table I as thetime required to dissolve one-half of the

original weight of diverting agents

Table I

Temperature (oF) Half-Life (hr:min)

130 4:16

140 3:45

180 2:10

212 1:10

Filtration tests were run on core plugs toassure that the diverting material would notcause formation damage.

Laboratory tests were conducted to determinethe effectiveness of this material in creatinga block across an O. 1 inch simulated fractureand a 3/8 inch perforation. A pressuredifferential of 400 psi could be maintainedacross both the fracture and the perforationwith negligible leak-off.

Physical properties of the oil soluble-water

soluble, organic diverting agent are shownin Table 11.

Table II

Heat Stability Stable at 266F

Volubility gr/ 100 85F 175

Water .44 2.72

Kerosene 2.76 7.83

Specific Gravity 1.26

Field Application and Results

The following is a typical treatment for thedeep Ellenburger in West Texas, utilizingthis new diverting agent.

First Stage

1. 6, 000 gallonsspearhead.

gelled brine

2. 12, 000 gallons acid - 90?0byvolume 15% HC1, 107o byvolume Formic .

3. 6, 000 gallons gelled brineoverflush.

4. 500 pounds diverting agent.

Second StaKe

Same as first stage.

Third Sta~e

Same as first stage, except100 pounds of diverting agentwas used.

Fourth StaPe

Same as first stage, exceptwell was flushed in Step 3.

The first stage of diverting material resulted~.-. +-=.++tiu nres~ure buildup fromm a surldue u =G....= ~. .

6, 000 psi to 8, 400 psi. The second stageproduced a pressure buildup from 6, 100 psito 9, 000 psi. On the third, and final stage,the surface treating pressure built up from6, 200 psi to 9, 000 psi. These increasesin pressure held throughout each subsequentacid stage.

Itis interestingto compare thistreatmentwith a similar one utilizingparaformaldehydeas a blocking material. In deep Ellenburgertreatments, normally 3, 000 pounds ofparaformaldehyde is used for diverting each

stage. The quantity of paraformaldehyderequired to block effectively exceeds that ofthe new diverting agent, because paraformal-dehyde has a faster volubility rate. In thesedeep wells, most of the paraformaldehydeis dissolved on the way down the tresting

~~Th~+material is left to block isString. VV 1.-, . -----then rapidly destroyed when the acid stagereaches the formation. Paraformaldehydehas an extremely short life in acidicsoiutions; ~-liereas, thisnew diverting agentexhibits a slower volubility rate at low pHthan it does in neutral solutions.

This new oil and water soluble divertingagent has been used successfully in wellswith bottom hole temperatures from 110Fto 250F and in open hole and in perforations.

Fifty pounds of this new diverting agentsuccessfully blocked the bottom two feet ina 13 foot zone where temperature surveysindicated previous acid treatments had gone.This 50 pounds resulted in a 1400 psi surfacepressure increase prior to the second acidtreatment. A subsequent temperature

survey indicated this second acid treatmentwas diverted into the upper 11 feet of thisinterval.

This new material offers the industry aneffective diverting agent that can be used incomparatively small quantities over avariety of well conditions and temperatureranges. The material also has the addedadvantage of being both oil and water soluble.

FOAM DIVERTING

Discussion

Formations containing a zone or zones, with. .

varying permeablllt y, or zones whie~~....~a(7Ddifferent formatioii pressures, requirespecial consideration when being stimulated.Unless some form of diverting is used, theformation will accept fluid only at the mostpermeable portion. A foam diverting systemwhich will enable the entire interval to betreated, regardless of the type of formationor type of completion, can be employed byusing

1)

2)

3)

4)

the following injection procedure:

A portion of the acid treatment isinjected into the formation as in

conventional acidizing.The acid is followed with a pre -calculated volume of an aqueous

solution of a foam producingsurfactant.The foam producing solution isdisplaced into the formation witha compressed gas such as nitrogen.The above steps are repeated asmany times as necessary.

It is expected that the initial stage of acidw1ll enter the most permeable se-.. -..-+inn of the

formation; likewise, the aqueous foamingsolution. A portion of the foaming solution

adheres to the rock surfaces both within thematrix of the rock and on the fracture faces.A foam is created when this retained

solution is agitated by and co-mingled withthe following stream of nitrogen. Asadditional foam is generated, its resistanceto movement through fractures and rockmatrix increases until the pressure requiredfor further flow exceeds the pressurerequired to break down other sections of theformation. As the limit of complete blocking

is approached, the rate of injection into the

most permeable section that accepted thefirst acid volume decreases and another~ectian. ~f ~e~ser permeability is opened to

accept the next volume of acid. This pro-cedure is repeated as many times asnecessary to stimulate the entire interval.Injection rates should be kept low at the timefoam is being generated so that a uniformgas to liquid ratio can be obtained.

Laboratory R e suits

An apparatus was constructed to closely

simulate the downhole conditions that existduring a stimulation treatment whenemploying the foam diverting system. Twohorizontally mounted sand packed columnsdiffering in permeability were manifoldedtogether and connected to a reservoircomplex which allows the injection of acid,foaming solution and compressed nitrogen.A back pressure regulator can be connectedto either of the columns so that a differencein zone pressure can be simulated.

The ability of foam to create an effectiveblock may be demonstrated by arranging theapparatus so that conditions for acceptingfluid are much more favorable in onecolumn than in the other. This wasaccomplished by packing column one with20-40 mesh sand and column two with 40-60mesh sand. The permeability ratio, K 1/K2,is approximately 20 under no load. A backpressure regulator was attached to columntwo and a pressure of 200 psi was applied.Without diverting, the entire volume of fluidwas accepted into column one. However,by using the injection sequence, describedabove, flow into the more permeable lowerpressure column could be reduced to lessthan 170of the total volume. Over 99!70wasdiverted into the lower permeability, higherpressure column.

Tests were run with a single sand packedcylinder to determine the maximum pressuregradients that could be created and main-

tained by the foam blocking system forvarious mesh sizes of sand. A volume offoaming solution equal to 1/5 the porevolume of the sand was injected into thepacked cylinder. Nitrogen was injectedbehind the foaming solution with the injectionpressure increased until foam was extruded

from the column. Table 111lists the pressure

SPE 2751

required to extrude foam from the variousmesh sizes of sand.

Table 111

Mesh Size Extrusion Pressureof Sand Pressure, psi Gradient,psi/ft

8-12 680 13610-20 775 15520-40 950 19040-60 1200 240

Foam Stability

Foam is a dispersion of a gas in a liquidwithgas being the non-continuous phase and liquidthe continuous phase. Its stabilityis largelyaffectedby the nature of the fluidthat itcontacts. A liquidpenetrates a foam bymoving through the continuous liquidphase ofthe foam. As the liquidcontentof foamincreases, the foam quality,or the gas-liquidratio, decreases; thus, weakening the blockingabilityof foam. While a foam-liquid contactunder pressure eventuallyresuitsin thedestructionof the foam, the foams stabilitytime is sufficientfor itsuse in the proposedapplication. The followingtestresuitsshowthe time required for 1510HC1 to penetratea 60 inch sand column that had been previouslyblocked with the foam diverting material.

Temp.F

90125150

9090

Table IV

Mesh Size Pressure Timeof Sand Gradient, psi /ft hr:mir

40-60 50 6:33

40-60 50 4:4740-60 50 3:2140-60 80 4:5340-60 100 4:07

Gas movement through a permeable medium+W -= frnm liquid movementfilled with foaml d~,~e. . . . ...

in that the gas phase is non-continuous andany movement of gas involves breaking theliquid film surrounding the entrapped gas.Gas propagates through a foam by continuallybreaking and reforming the foam bubbles.

Although gas does not destroy foam as

rapidly as liquids, several factors combineto make foam a temporary blocking materialagainst a gaseous medium. One reason is the

continuous loss of the liquid to the gaseousphase by evaporation. Loss of liquid from thefilm reduces the amount of available liquid forp~~mAforming which in turn leads to a fewer

number of liquid-gas interfaces.

Selection of Surfactants

Special consideration was given to theselection of the surfactant used in the foamdiverting system. In any well treatment,there are a number of ways in which thefoaming solution can be contaminated.Therefore, the selected surfactant must offera high degree of tolerance to each of thepossible contaminants.

One of the most important requirements ofthe surfactant is that the presence of commonsalt ions, such as sodium, calcium, mag -nesium and chlorine, do not greatly hinder its

effectiveness as a foamer. Since many

formations contain water sensitive clays, thefoaming solution must often be prepared fromfield brine, synthetic brine or acid. Also,spent acid contains large amounts of dissolvedcalcium, magnesium and carbonates whichcould alter the foaming ability of the selectedsurfactant.

Another requirement is that the foamer becompatible with all surfactants and inhibitorsused in any part of the treatment. Eventhough the se ingredients are placed in differentsegments of the treatment, they combine inthe formation either by co-mingling fluids orby adsorption-desorption of surfactants.

Other factors that were considered whenselecting the foamer included the effects of(i) hydrocarbons, (2) acids, and (3) drilling

muds. Of all the surfactants tested, thefoamer selected for the foam diverting systemshowed the highest degree of tolerance for allthe contaminants discussed.

The foam diverting system can be appliedwhen well conditions are such that otherdiverting techniques are incompetent. Forinstance, the presence of high permeabilitystreaks or thief zones, in unfractured sand-stones or unconsolidated sands, necessitatethe use of a diverter for acid or chemicalwash treatments. While the permeability of+hi = ~ection to the treating solution must be.... b-.

5

reduced so that other zones may be brokendown and treated, any long -lasting orpermanent damage to the formation should beavoided. It is imperative that any solidmaterial introduced into the formation ordeposited on the formation face, be removed

-I-.-+.=1 means or by dissolutioneitherby meull~.,.~-........intothe produced fluids. The most widelyused method of divertingemploys the use ofsolidparticlesin conjunctionwith gelled orhigh viscosityfluidsas a carrying agent.Although these solidparticlesare normallycompletely solublein eitheroilor water, lackof adequate contactand agitationoften preventthe divertingmaterial from completelydissolvingand solidsare leftin the formation.

The foam diverting system is applied byinjecting into the formation a thin aqueoussolution followed by gaseous nitrogen. Sincethe system is solids free, formation damagedue to undissolved particles cannot occur.

In wells completed with gravel packed liners,

proper treatment distribution has often proveddifficult. Mechanical devices and solidblocking materials are of little help becausethe restriction which they create is easilybypassed by fluid movement through thepermeable pack. The re suits being that themost permeable parts of the formation acceptthe majority of the treatment. Gravel packs,however, are easily penetrated by the foamforming fluids, and foam is created within theformation, This portion of the formationthen becomes impermeable and any additionaltreatment is diverted elsewhere.

Single zone formations containing a large

number of verticai fractures and multi-zoneformations, with two or more communicatingzones, offer similar problems as those by agravel pack. In each situation, there is a

need for an in-formation diverter.

Field Results

To date, six jobs have been performedutilizing the foam diverting tectmiqw. These

jobs were performed in an area where theformation consisted of a highly verticalfractured dolomite, approximately 100 feet inlength. The completions were open hole.Each well was treated with 10, 000 gallons2870 hydrochloric acid containing an inhibitor,proper surfactants and a silt suspending agent.The acid was injected in 5 stages of 2000 gals

6 SPE 2751

each. Each of the first four stages of acidwas followed with 400 gallons of an aqueoussolution of the foaming agent. This in turnwas followed with 18, 000 std. cu. ft. of

%. ~ h~nck. After themtrogen t.o create a ~W-.A. - -.final stage of acid was displaced into theformation, a temperature survey was run todetermine what portions of the formationaccepted the acid treatment. Previoustreatment records for wells in this area showthat without any form of diverting agents thelower thirty feet of formation normally wouldaccept the entire treatment, leaving 70 feetof formation unstimulated. The use of solidblocking materials ha-d also proven unsuccess -ful in many cases because of the formationshigh vertical permeability y. Solid particlesare ineffective in this type of formation,because they bridge they form is normallyacross fractures or perforations at the wellbore. These types of blocks, due to thenature of their formation, offer resistance tofluid propagation in the radial direction only.This leaves the possibility of fluid bypassingthe block by entering the formation at anunobstructed point and moving verticallythrough the fractures. With the foam biock,the fractures are packed with foam underpressure; therefore, liquid cannot channelbehind the restriction without first deeplypenetrating the formation.

Temperature surveys indicated that in eachof the six treatments performed, goodcoverage of the entire interval with acid wasaccomplished. This was achieved atinjection rates not exceeding 5 BPM withmaximum surface treating pressures around2100 psi. The average depth of the six wellstreated is 5, 055 feet.

Table V

BOPD Avg. BOPD BOPDBefore After 6 mos. after

Well Treatment Treatment Treatment

1 53 61 662 48 58 623 25 123 1234 52 94 93~ 28 76 28*

6 24 52 55

*Flood front reached this well in fifth

month after treatment.

CONCLUSION

1.

2.

3.

4.

5.

6.

7.

8.

Both laboratory and field tests indicatethat the foam diverting system may beapplied in wells with any normal type of

completion, i, e., epen holej perforatedcasing or liner, gravel packed liner, etc.It can be used in all familiar formationsas an acid diverting material.

Creates an in-formation block. Since foamis generated within the formation, a blockof permeability and flow channels existsdeep in the formation.

Foam blocking contains no solid materialnor does it utilize a gelled carrying agentthat could damage the formationpermeability y.

Foam expansion, while flowing well back,helps clean well of insoluble fines, sludge,and other matter which tend to damage theformation.

Foam blocks can be used over a widetemLFeratlJre range, can be applied in wells

with temperatures up to 250F, and givesrapid clean-up at low temperatures (90F).

An organic diverting agent was developedthat is slowly and completely soluble inboth oil and water.

Field tests have shown that the oil soluble -

water soluble diverting agent can be usedin water injection wells and producing wells

Successful diverting with the oil soluble-water soluble diverting agent has beenaccomplished between 110?F and 250F.

ACKNOWLEDGMENT

The authors wish to express their appreciationto the management of Byron Jackson Inc. forpermission to publish this paper.

SPE 2751 71REFERENCES

1. Gallus, J. P. and Pye, D. S. , DeformableDiverting Agent Improves WellStimulation, J. Pet. Tech. (April, 1969).

2. White, Garland L., The Use of

Temporary Blocking Agents in Fracturingand Acidizing Operations, API Drilling

and Production Practice (19 %3).

3. Howard, G. C. and Scott, P. P., AnAnalysis and the Control of LostCirculation, Trans. , AIME ( 1951) 171.

4. Bernard, George C. and Jacobs, w. L. ,Effect of Foams on Trapped GasSaturation and on Permeability of PorousMedia to Water, Trans. , AIME (1965)

295.

BackPressure

Regulator

Packed Tube

K2

Packed Tube

Pressure

Regulator

Nitrogen

Fig. 1 - Foarfi Test@ A.pparatus

6each. Each of the first four stages of acidwas followed with 400 gallons of an aqueoussolution of the foaming agent. This in turnwas followed with 18, 000 std. cu. ft. ofnitrogen to create a foam block. After thefinal stage of acid was displaced into theformation, a temperature survey was run todetermine what portions of the formationaccepted the acid treatment. Previoustreatment records for wells in this area showthat without any form of diverting agents the

lower thirty feet of formation normaiiy wouMaccept the entire treatment, leaving 70 feet

,. --+,-,,ln+=~of forma~lon UI1=bhl.u.~.- -. The use of solidL1-.nl.;m~LuLN,Lg W.~~~~~~lS l-la-dalso proven unsuccess-

ful in many cases because of the formationshigh vertical permeability y. Solid particlesare ineffective in this type of formation,because they bridge they form is normallyacross fractures or perforations at the wellbore. These types of blocks, due to thenature of their formation, offer resistance tofluid propagation in the ra~ial direction only.This leaves the POs sibility of fluid bypassingthe block by entering the formation at anunobstructed point and moving verticallythrough the fractures. With the foam block,the fractures are packed with foam underpressure; therefore, liquid cannot channelbehind the restriction without first deeplypenetrating the formation.

Temperature surveys indicated that in each-c +1., . ~ t~~atments performed> goodU1 LL1e A- . . -- . .

coverage of the entire interval with acid wasaccomplished. This was achieved atinjection rates not exceeding 5 BPM withmaximum2100 psi.treated is

surf ace treating pressures aroundThe average depth of the six wells

5, 055 feet. -

Table V

BOPD Avg. BOPD BOPDBefore After 6 mos. after

Well Treatment Treatment Treatment

1 53 61 662 48 58 623 25 123 123~ 52 94 935 28 76 28*

6 24 52 55

*Flood front reached this well in fifth

month after treatment.

CONCLUSION

1.

2.

3.

4.

5.

6,

7.

8.

Both laboratorythat the foamapplied in wellscompletion, i.casing or linerIt can be usedas an acid dive

Creates an in-is generated w

of permeabilitydeep in the for

Foam. Mockingnor does it utithat could dampermeability y.

Foam expansionhelps clean weand other mattformation,

Foam blockstemperature rwith temperaturrapid clean-up

An organic dthat is slowlyboth oil and w

Field tests ~~y

water solublein water inject

Successful div-water~o~l~b~

accompli shed

ACKNOWLEDGMENT

The authors wishto the managementpermission to pu