Tab 6 F_ Sandstone Acidizing Chem and Design

1

Sandstone AcidizingSandstone AcidizingSandstone AcidizingSandstone Acidizing

2

Matrix Stimulation Engineering Solutions

Outline

• Sandstone vs. Carbonate• Sandstone composition• Mineral surface area• Reaction of HF with silicates• Design methodology

• Fluid selection

• Mud Acid, Clay Acid and Organic Clay Acid.

• Avoid problems

2

3


Objectives• Describe the sandstone acidizing process.• List the key components in sandstones.• State the importance of mineral surface area. • Describe the primary, 2nd and tertiary reactions of mud acid

with clay.• State the major components of spent mud acid. • List the incompatible ions with spent mud acid and state why

they are incompatible.• State the problems associated with illite and chlorite.• State the purpose of the each sandstone treatment stage.• Describe the fluid selection process.• Describe when/why Mud Acid, Clay Acid and OCA are used.• Describe Mud Acid, Clay Acid and OCA treatment designs and

how they are different.• State how to avoid potential problems during a treatment.

4


Carbonate vs. Sandstone

CARBONATE

• A large fraction of the matrix is soluble (>50%)

• Dissolution of rock (wormholes)– damage bypass

• Diversion

SANDSTONE

• Dissolution of the damaging mineral

• A small fraction of the matrix is dissolved

• Potential precipitation

•Treatment of sandstone with high calcite content (>20%):

– Use carbonate design methodology

– Use sandstone diversion techniques

– Iron control may be a problem

3

5


Sandstone Constituents

QuartzQuartzQuartzQuartz

*Feldspars*Feldspars*Feldspars*Feldspars

*Chert*Chert*Chert*Chert

*Mica*Mica*Mica*Mica

SecondarySecondarySecondarySecondary

CementCementCementCement

(Carbonate Quartz)(Carbonate Quartz)(Carbonate Quartz)(Carbonate Quartz)

ClaysClaysClaysClays

(Pore lining(Pore lining(Pore lining(Pore lining

i.e., illite)i.e., illite)i.e., illite)i.e., illite)

ClaysClaysClaysClays

(Pore filling(Pore filling(Pore filling(Pore filling

i.e., Kaolinite)i.e., Kaolinite)i.e., Kaolinite)i.e., Kaolinite)

RemainingRemainingRemainingRemaining

Pore SpacePore SpacePore SpacePore Space

6


Minerals Minerals Minerals Minerals Chemical CompositionChemical CompositionChemical CompositionChemical Composition

QuartzQuartzQuartzQuartz QuartzQuartzQuartzQuartz Si0Si0Si0Si02222

Feldspars Feldspars Feldspars Feldspars OrthoclaseOrthoclaseOrthoclaseOrthoclase KAlSiKAlSiKAlSiKAlSi3333OOOO8888

MicroclineMicroclineMicroclineMicrocline KAlSiKAlSiKAlSiKAlSi3333OOOO8888

AlbiteAlbiteAlbiteAlbite NaSiNaSiNaSiNaSi3333AlOAlOAlOAlO8888

PlagioclasePlagioclasePlagioclasePlagioclase SiSiSiSi2222----3333AlAlAlAl1111----2222OOOO8888(Na,Ca)(Na,Ca)(Na,Ca)(Na,Ca)

MicasMicasMicasMicas BiotiteBiotiteBiotiteBiotite (AlSi(AlSi(AlSi(AlSi3333OOOO10101010) K(Mg, Fe)) K(Mg, Fe)) K(Mg, Fe)) K(Mg, Fe)3333(OH)(OH)(OH)(OH)2222

MuscoviteMuscoviteMuscoviteMuscovite (AlSi(AlSi(AlSi(AlSi3333OOOO10101010) K(Al)) K(Al)) K(Al)) K(Al)2222OH) OH) OH) OH) 2222

Clays Clays Clays Clays ChloriteChloriteChloriteChlorite (Mg, Fe(Mg, Fe(Mg, Fe(Mg, Fe+2+2+2+2, Fe, Fe, Fe, Fe+3+3+3+3))))6666SiSiSiSi3333AlOAlOAlOAlO10 10 10 10 (OH)(OH)(OH)(OH)8888

KaoliniteKaoliniteKaoliniteKaolinite AlAlAlAl4444(Si(Si(Si(Si4444OOOO10101010)(OH))(OH))(OH))(OH)8888

IlliteIlliteIlliteIllite SiSiSiSi3333AlOAlOAlOAlO10101010(OH)(OH)(OH)(OH)2222KAlKAlKAlKAl2222

SmectiteSmectiteSmectiteSmectite (AlSi(AlSi(AlSi(AlSi3333OOOO10101010)Mg)Mg)Mg)Mg5555(Al,Fe)(OH)(Al,Fe)(OH)(Al,Fe)(OH)(Al,Fe)(OH)8888

MixedMixedMixedMixed----LayerLayerLayerLayer Kaolinite, Illite or Chlorite with SmectiteKaolinite, Illite or Chlorite with SmectiteKaolinite, Illite or Chlorite with SmectiteKaolinite, Illite or Chlorite with Smectite

QuartzQuartzQuartzQuartz QuartzQuartzQuartzQuartz Si0Si0Si0Si02222

Feldspars Feldspars Feldspars Feldspars OrthoclaseOrthoclaseOrthoclaseOrthoclase KAlSiKAlSiKAlSiKAlSi3333OOOO8888

MicroclineMicroclineMicroclineMicrocline KAlSiKAlSiKAlSiKAlSi3333OOOO8888

AlbiteAlbiteAlbiteAlbite NaSiNaSiNaSiNaSi3333AlOAlOAlOAlO8888

PlagioclasePlagioclasePlagioclasePlagioclase SiSiSiSi2222----3333AlAlAlAl1111----2222OOOO8888(Na,Ca)(Na,Ca)(Na,Ca)(Na,Ca)

MicasMicasMicasMicas BiotiteBiotiteBiotiteBiotite (AlSi(AlSi(AlSi(AlSi3333OOOO10101010) K(Mg, Fe)) K(Mg, Fe)) K(Mg, Fe)) K(Mg, Fe)3333(OH)(OH)(OH)(OH)2222

MuscoviteMuscoviteMuscoviteMuscovite (AlSi(AlSi(AlSi(AlSi3333OOOO10101010) K(Al)) K(Al)) K(Al)) K(Al)2222OH) OH) OH) OH) 2222

Clays Clays Clays Clays ChloriteChloriteChloriteChlorite (Mg, Fe(Mg, Fe(Mg, Fe(Mg, Fe+2+2+2+2, Fe, Fe, Fe, Fe+3+3+3+3))))6666SiSiSiSi3333AlOAlOAlOAlO10 10 10 10 (OH)(OH)(OH)(OH)8888

KaoliniteKaoliniteKaoliniteKaolinite AlAlAlAl4444(Si(Si(Si(Si4444OOOO10101010)(OH))(OH))(OH))(OH)8888

IlliteIlliteIlliteIllite SiSiSiSi3333AlOAlOAlOAlO10101010(OH)(OH)(OH)(OH)2222KAlKAlKAlKAl2222

SmectiteSmectiteSmectiteSmectite (AlSi(AlSi(AlSi(AlSi3333OOOO10101010)Mg)Mg)Mg)Mg5555(Al,Fe)(OH)(Al,Fe)(OH)(Al,Fe)(OH)(Al,Fe)(OH)8888

MixedMixedMixedMixed----LayerLayerLayerLayer Kaolinite, Illite or Chlorite with SmectiteKaolinite, Illite or Chlorite with SmectiteKaolinite, Illite or Chlorite with SmectiteKaolinite, Illite or Chlorite with Smectite

Formation Minerals - Silicates

4

7


Chemical Chemical Chemical Chemical

MineralsMineralsMineralsMinerals CompositionCompositionCompositionComposition

Formation Minerals

CarbonatesCarbonatesCarbonatesCarbonates CalciteCalciteCalciteCalcite CaCOCaCOCaCOCaCO3333

DolomiteDolomiteDolomiteDolomite Ca, Mg(COCa, Mg(COCa, Mg(COCa, Mg(CO3333))))2222

AnkeriteAnkeriteAnkeriteAnkerite Ca,(Mg,Fe)(COCa,(Mg,Fe)(COCa,(Mg,Fe)(COCa,(Mg,Fe)(CO3333) ) ) ) 2222

SideriteSideriteSideriteSiderite FeCOFeCOFeCOFeCO3333

Sulfates Sulfates Sulfates Sulfates GypsumGypsumGypsumGypsum CaSOCaSOCaSOCaSO4444·2H·2H·2H·2H2222OOOO

AnhydriteAnhydriteAnhydriteAnhydrite CaSOCaSOCaSOCaSO4444

OthersOthersOthersOthers HaliteHaliteHaliteHalite NaClNaClNaClNaCl

Iron OxidesIron OxidesIron OxidesIron Oxides

8


• Mineral Composition & Surface Area

• Dominant Factor « Surface Area

• Reaction Rate: Clays > Feldspars > Quartz

Mineral Specific Area

Quartz Few cm2/g

Feldspar Few cm2/g

Clays: Kaolinite 22 m2/g

Illite 113 m2/g

Smectite 82 m2/g

Reaction Rate - Factors

5

9


Mud Acids: HCl – HF • Hydrochloric wt% + Hydrofluoric wt%

� 12 – 3, 12 – 2

� 13.5 – 1.5

� 9 –1.5, 9 – 1

� 6 –1.5, 6 - 1

� 4.5 – 0.5

• Siliceous minerals

10


Reaction of Mud Acid (HCl – HF) with Clay

PrimaryPrimaryPrimaryPrimary

(5+x) (5+x) (5+x) (5+x) HF HF HF HF + M+ M+ M+ M----AlAlAlAl----Si + (3Si + (3Si + (3Si + (3----x+1) Hx+1) Hx+1) Hx+1) H+ + + + ====

HSiFHSiFHSiFHSiF5 5 5 5 + + + + AlFAlFAlFAlFxxxx(3(3(3(3----x)+x)+x)+x)+ + M+ M+ M+ M++++ + 2H+ 2H+ 2H+ 2H2222OOOO

Spent HF

Si(OH)4

AlF2+

Si(OH)

Si(OH)Si(OH)

HF

Clay

Tertiary

AlF2+ + M-Al-Si + (3-x+1) H+ + H2O =

2AlF2+ + M+ + Si(OH)4

Secondary

X/5 HSiF5 + M-Al-Si + (3-x+1) H+ + H2O =

AlFx(3-x)+ + M+ + Si(OH)4

NaNaNaNa++++ or Kor Kor Kor K++++

6

11


Precautions to Avoid Precipitates

• Potassium fluosilicates

K2SiF6

AVOID CONTACT WITH K, Na, Ca

•Calcium fluoride

CaF2

•REMOVE CALCITE

•Aluminum fluoride

AlF3

MAINTAIN A LOW pH

12


Hydrated/Amorphous Silica: Cannot Avoid

Si(OH)4

Al

7

13


Former Site of Kaolinite Following Mud Acid Treatment

14


Design Methodology to Maximize Stimulation

8

15


Sandstone Acidizing Fluid Stages

Pre-acid Preflush:NH4Cl brine or toluene/xylene displaces water containing incompatible cations (Na+, K+, Ca++) away from the wellbore.

Preflush:HCl (or organic acid) removes CaCO3 from matrix to prevent the precipitation of CaF2.

Main Fluid:Mud acid removes silt and clay (alumino-silicate) formation damageOverflush: Displaces spent acid away from the critical matrix.Diverter:Decreases fluid flow into the thief zone/s and increases flow into other non-treated zones.

16


Sandstone Acidizing Fluid Stages

1. Pre-acid Preflush: NH4Cl brine or toluene/xylene displaces water containing incompatible cations (Na+, K+, Ca++) away from the wellbore.

2. Preflush: HCl (or organic acid) removes CaCO3 from matrix to prevent the precipitation of CaF2.

3. Main Fluid: Mud acid (HCl – HF) removes silt and clay (alumino-silicate) formation damage

4. Overflush: Displaces spent acid away from the critical matrix. 5. Diverter: Decreases fluid flow into the thief zone/s and increases

flow into other non-treated zones.

9

Sandstone Acidizing Fluid Selection Sandstone Acidizing Fluid Selection Sandstone Acidizing Fluid Selection Sandstone Acidizing Fluid Selection

18


Matrix Treatment Design Methodology

• Candidate Selection

• Establish Nature and Location of Damage

• Treating Fluid/Additive SelectionTreating Fluid/Additive SelectionTreating Fluid/Additive SelectionTreating Fluid/Additive Selection

• Determine Pressure/Injection Rate

• Establish Fluid Volumes

• Develop Pumping Schedule and Placement Strategy

• Define Shut-in/Cleanup Stages

• Economics Assess Productivity and Profitability

10

19


Fluids Available

• Hydrochloric acid

– Preflush

– Main acid component

– Overflush

• Hydrofluoric acid systems

– Mud Acid

– Organic Mud Acid

– Fluoboric Acid (Clay Acid)

– Organic Fluoboric Acid (OCA)

• Organic Acids

– Formic

– Acetic

– Citric

20


Selection Criteria

• Formation mineralogyFormation mineralogyFormation mineralogyFormation mineralogy

– Reactivity

• Chemical composition

• Surface area

– Rock Structure

• HCl solubility

• Clay distribution

– Sensitivity

• Deconsolidation

• Precipitation

• Fines release

• PermeabilityPermeabilityPermeabilityPermeability

– Type of damage

– Mobility of induced damage

• Produced FluidsProduced FluidsProduced FluidsProduced Fluids

– Oil wells: Sludge/Emulsions

– Gas wells: Water saturation

• TemperatureTemperatureTemperatureTemperature

– Corrosion

– Penetration

• Bottomhole pressureBottomhole pressureBottomhole pressureBottomhole pressure

11

21


Pre-Acid Preflush

• Ammonium chloride (NH4Cl)

• Guideline– 3 wt% (<5% Clay)

– 4 wt% (5 -10%)

– 5 wt% (10 -15%)

– 6 wt% (>15%)

• Calculated Concentration = 3% + – (% Smectite + % Mixed Layer*0.5)*0.3) +

– (% Illite+ % Mixed Layer*0.5)*0.12) +

– % Kaolinite*0.08 +

– % Chlorite*0.12 +

– % Feldspar*0.05)

Formation Brine

HCl

22


HCl Preflush/Overflush

HCl Fluid Selection Guide for All Temperatures

>100 md 20-100 md <20 md

<10% silt and <10% clay 15X 10X 7.5X

All other combinations ofsilt and clay composition 10X 7.5X 5X

<4% chlorite/glauconite, use < 20md Guidelines for HCl.4-6% chlorite/glauconite, use <20md Guidelines for HCl with 5% Acetic Acid in PF/OF>6% chlorite/glauconite, use 10% Acetic Acid PF/OF to Organic Clay Acid HT<2% Zeolite, use 10% Acetic Acid in HCl PF/OF with 5% Acetic Acid in Mud Acid 2-5% Zeolite, use 10% Acetic Acid as PF/OF with Organic Clay Acid >5% Zeolite, use 10% Acetic Acid as PF/OF with Organic Clay Acid HT

12

23


0

2

4

6

8

10

12

14

16

0 10 20 30 40Weight % of HCl in Acid Formulation

Max

Wt

% o

f H

F in

Aci

d F

orm

ula

tio

n

Ideal CaseIdeal CaseIdeal CaseIdeal Case

0% Calcite0% Calcite0% Calcite0% Calcite

3% Calcite 3% Calcite 3% Calcite 3% Calcite

6% Calcite 6% Calcite 6% Calcite 6% Calcite

*Based on AlF*Based on AlF*Based on AlF*Based on AlF3333 & CaF& CaF& CaF& CaF2222 pptpptpptppt

Increasing wt.% of calcite Increasing wt.% of calcite Increasing wt.% of calcite Increasing wt.% of calcite

undissolved by HCl Preflushundissolved by HCl Preflushundissolved by HCl Preflushundissolved by HCl Preflush

HCl/HF Ratio to Avoid AlF3 & CaF2

with CaCO3 Remaining

24


HCl Preflush Volume to Dissolve all

Calcite 2 feet Radially

13

25


Main Acid (HF) Volume

• Targeted reduction: 90% in damage skin.

• Minimum skin achievable: Total of pseudoskin

• StimCADESkiSkin

Volume

?

??

Mud Acid Systems Available

Mud Acid

Organic Mud Acid

Fluoboric Acid (Clay Acid)

Organic Clay Acid (OCA)

14

27


Mud Acid

• Nine HCI-HF formulations

• Dissolves siliceous minerals (silt and clay)

• Schlumberger (Dowell) offered the first commercial Mud

Acid Service in 1940 in the (U.S. Gulf Coast).

+

HCl

HFor

Y1

Mud Acid

28


NHNHNHNH4444 HFHFHFHF2222 ((((Y1Y1Y1Y1) + X ) + X ) + X ) + X HCl HCl HCl HCl (X (X (X (X ---- 1) HCl + 2 HF + NH 1) HCl + 2 HF + NH 1) HCl + 2 HF + NH 1) HCl + 2 HF + NH 4444 CICICICI

Mud AcidMud AcidMud AcidMud Acid

((((25% HCl + 20% HF25% HCl + 20% HF25% HCl + 20% HF25% HCl + 20% HF) + HCl + H ) + HCl + H ) + HCl + H ) + HCl + H 22220 Dilute HCl / HF0 Dilute HCl / HF0 Dilute HCl / HF0 Dilute HCl / HF

Field Generation of Mud Acid (HCl/HF)

15

29


+ A high HCI solubility can be indicative of carbonate cementation in the absence of petrographical data++ No or limited HCI preflush preferred+++ Perform a Mud Acid treatment prior to pumping acid. Use guidelines for Small Fines Migration problem to select Mud Acid System

Silts and Clays

Native During Production (fines migration)

Carbonate Cemented Sandstones+Noncarbonate Cemented Sandstones

T> 300o FNARS201

T< 300o FReg. Clay Acid ++

Small Fines Migration ProblemSevere Fines Migration Problems

Use guidelines for damage induced by completion operations.

Options: in matrix, sandstones:Noncarbonate cemented Overflush with 5% HCI containingClay Control Agents L42, L53W or L55

T> 300o FNARS201

Reg. Clay Acid+++

Organic Clay Acid

130oF <T<300oFReg. Clay Acid+++

Organic Clay Acid

T> 130o FClay Acid LT+++

Organic Clay Acid

30


Silts and Clays

Induced by Completion Operations

In Fissures, Gravel Packsor High-Permeability Matrix

In Matrix

Mud and Silt Remover Treatments+

Noncarbonate Cemented Sandstones

Mud Acid Treatments (MA)++++

Carbonate Cemented Sandstones++

Regular Clay Acid+++

+ The MSR formulation should be based on the HCI guidelines and Mud Acid guidelines. For carbonate cemented sandstones, Breakdown Acid or HCI-base MSR is recommended.

++ A high HCI solubility can be indicative of carbonate cementation in the absence of petrographical data.+++ limited HCI preflush is recommended in this case.++++ See Mud Acid Selection Guide for Native Damage

16

31


Mud Acid Selection GuideMud Acid Selection GuideMud Acid Selection GuideMud Acid Selection Guide

HCl HCl HCl HCl ---- HFHFHFHF

> 100 md 20-100 md < 20 md

< 10% silt and < 10% clay 12 - 3 8 - 2 6 - 1.5

> 10% silt and > 10% clay 13.5 - 1.5 9 - 1 4.5 - .5

> 10% silt and < 10% clay 12 - 2 9 - 1.5 6 - 1

< 10% silt and > 10% clay 12 - 2 9 - 1.5 6 - 1

32


Mud Acid Guidelines for Reservoirs with < 2% Zeolites* > 20 md < 20 md < 10% Silt and <10% Clay 8% HCl/2% HF with 5% Acetic 6% HCl/1.5% HF with 5% Acetic > 10% Silt and >10% Clay 9% HCl/1% HF with 5% Acetic 4.5% HCl/0.5% HF with 5% Acetic Other 9% HCl/1.5% HF with 5% Acetic 6% HCl/1.5% HF with 5% Acetic

Mud Acid Guidelines for Reservoirs with 2 -5% Zeolites* > 20 md < 20 md All Silt and Clay Ranges OCA OCA

Mud Acid Guidelines for Reservoirs with >5% Zeolites* > 20 md < 20 md All Silt and Clay Ranges OCA HT OCA HT *10% Acetic Acid PF/OF and use OCA when fines migration is a problem.

17

33


Mud Acid Guidelines for Reservoirs with < 3 Chlorite/Glauconite > 20 md < 20 md

< 10% Silt and <10% Clay 6% HCl/1.5% HF 6% HCl/1.5% HF

> 10% Silt and >10% Clay 4.5% HCl/0.5% HF 4.5% HCl/0.5% HF

Other 6% HCl/1% HF 6% HCl/1% HF

Mud Acid Guidelines for Reservoirs with 4 - 6% Chlorite/Glauconite > 20 md < 20 md

< 10% Silt and <10% Clay 8% HCl/2% HF with 5% Acetic 6% HCl/1.5% HF with 5% Acetic

> 10% Silt and >10% Clay 9% HCl/1% HF with 5% Acetic 4.5% HCl/0.5% HF with 5% Acetic

Other 9% HCl/1.5% HF with 5% Acetic 6% HCl/1% HF with 5% Acetic

Mud Acid Guidelines for Reservoirs with >6% Chlorite/Glauconite* > 20 md < 20 md

All Silt and Clay Ranges OCA OCA

* 10% Acetic Acid PF/OF

34


Clay Instability in HCl

MineralMineralMineralMineral

• Zeolites

• Chlorites

• Illite

• Mixed Layer

• Smectite

• Kaolinite

Max. T in HCl (deg F)Max. T in HCl (deg F)Max. T in HCl (deg F)Max. T in HCl (deg F)

75

150

190

200

200

250

Effluent From Core #640

0

5000

10000

15000

20000

1 3 5 7 9 11 13 15 17 19Sample #

Co

nce

ntr

atio

n (

mg

/L)

15 wt% HCl 12 wt% HCl - 6 wt% NH4Cl 3 wt% HF

Fe

Al

K

Si

Mg

Short Berea Core #2: 12-3 Mud Acid

0

2000

4000

6000

8000

10000

12000

14000

1 3 5 7 9 11 13 15 17 19Sample Number

Co

nce

ntr

atio

n (

mg

/L) Al

SiCaFeKMg

10 wt% Acetic Acid + 6 wt% NH4Cl

12 wt% HCl - 3 wt% HF

6 wt% NH4Cl

All clays have a temperature at which they become unstable in HCl. Unstable clays decompose quickly, consume HCl and can migrate.

Jauf Core # 710 HCl and Mud Acid Sensitivity Test @ 300oF

0

500

1000

1500

2000

2500

0.00 25.00 50.00 75.00

Cumulative Pore Volume

Del

ta P

ress

ure

(p

si)

12 wt% HCl -3 wt% HF Mud Acid

15 wt% HCl6 wt% Ammonium

Chloride

6 wt% Ammonium

Chloride

18

35


Organic Mud Acid

• Formic acid (9% L036 replaces 12% HCl)

• Less corrosive than comparable Mud Acid formulations

• Reaction rate ~ 1/4 that of Mud Acid

• Reduces sludge tendency

+

L36

(Formic)

HFor

Y1

Mud Acid

36


Retarded HF Systems• Problem

– Mud Acid (HCl-HF) spends very rapidly near the wellbore and is not effective in removing clays and other fines deep in the formation.

–Some wells show good stimulation initially, but experience a rapid production decline.

• Solution

–Retarded Mud Acid system for deep Hydrofluoric penetration.

–A system that stabilizes formation fines.

–Low HF concentrations

19

37


Retarded HF formulation using

Fluoboric Acid (HBF4)

Clay Acid

• Ammonium bifluoride + boric acid + HCl

• HBF4

+ H20 HBF

3(OH) + HF

• HF reacts with silt and clay

• HBF4

continues to generate HF slowly

38


20

39


Kaolinite Observed With SEM

40


21

41


800

600

400

200

0

0 10 20 30 40

Fluoboric/Clay Acid

12% HCl - 3%HF

1st 6 in.

Unconsolidation

1st 6 in.

Unconsolidation

Distance From Inlet (in.)Distance From Inlet (in.)Distance From Inlet (in.)Distance From Inlet (in.)

Pe

rme

ab

ilit

y, %

Ch

an

ge

Pe

rme

ab

ilit

y, %

Ch

an

ge

Pe

rme

ab

ilit

y, %

Ch

an

ge

Pe

rme

ab

ilit

y, %

Ch

an

ge

Improved Penetration with Fluoboric Acid

42


140

120

100

80

60

40

20

00 5 10 15 20 25 30

140

120

100

80

60

40

20

00 5 10 15 20 25 30

UntreatedUntreatedUntreatedUntreated TreatedTreatedTreatedTreated% of Original Permeability % of Original Permeability

Pore VolumesPore VolumesPore VolumesPore Volumes Pore VolumesPore VolumesPore VolumesPore VolumesDistilled Water

6% Sodium Chloride

Clay Acid

Water Sensitivity Test Frio Sand

22

43


*Clay Acid LT can be used to 130O F,

but is not recommended above 130O F.

BHST (BHST (BHST (BHST (°F) F) F) F) Clay Acid LTClay Acid LTClay Acid LTClay Acid LTRegular Clay AcidRegular Clay AcidRegular Clay AcidRegular Clay Acid

100 96 48110 76 38120 52 26

130 35 18140 24 *150 16 *

160 11 *170 8 *180 5 *

190 3 *225 2 *250 1 *300 0.5 *

Minimum ShutMinimum ShutMinimum ShutMinimum Shut----in Time (hrin Time (hrin Time (hrin Time (hr))))

Fluoboric Acid Shut-In Time

44


• Preflush to Mud Acid: Very acid sensitive formation

• Main Acid: Carbonate-cemented sandstones

• Overflush to Mud Acid: Enhanced fines control

• Shut-in and bring production back slowly

Clay Acid Applications

Clay Acid

100-125 gal/ft

NH4Cl w/ U66

30-60 gal/ft

Mud Acid

100-150 gal/ft

HCl or DAD

50-75 gal/ft

23

45


Publications on Clay Acid

Mobil - SPE 8399

Arco - SPE 11722

Exxon - SPE 9387

Tenneco - SPE 14820

AGIP - SPE 20623

Statoil - SPE 24991

Statoil - SPE 31077

Ashland - IPA

46


Evaluation of Fluoboric Acid Treatment in the Grand Isle

Offshore area using Multiple Flow Rate Test

• Seven case histories were presented

• A plot of (Pws2 - Pwf

2) / Qg vs. Qg (the turbulence plot) was used

as an evaluation tool.

REF: McBride, Rathbone, and Thomas, SPE 8399

∆( ) 'PQ

P PQ C D Q

g

ws wf

gL g

2 2 2

=−

= +

24

47


2

1

00 5 10 15

)/(/)( SCFDPSIQp 22∆

6 months after RMA6 months after RMA6 months after RMA6 months after RMA

After RMAAfter RMAAfter RMAAfter RMA

After Clay AcidAfter Clay AcidAfter Clay AcidAfter Clay Acid

3 years after Clay Acid3 years after Clay Acid3 years after Clay Acid3 years after Clay Acid

Q (MMCFD)Q (MMCFD)Q (MMCFD)Q (MMCFD)

48


12.0

10.0

8.0

6.0

4.0

2.0

0

-6 0 10 20 30 40 50

After After After After

MudMudMudMud

Acid Acid Acid Acid

Trt.Trt.Trt.Trt.

After Fluoboric Acid TreatmentAfter Fluoboric Acid TreatmentAfter Fluoboric Acid TreatmentAfter Fluoboric Acid Treatment

Time (Months)

Q (

MM

scf/

D)

25

49


Silicon to Aluminum ratios in HF and Fluoboric Acid effluents

Zone Sample HCL/HF Fluoboric

C(3.4) B 0.6 -C - 2.9C’ - 2.5

A(1.7) E 0.5 -F - 1.6F’ - 1.7

50


SPE 20623SPE 20623SPE 20623SPE 20623

ADVANCES IN MATRIX STIMULATION TECHNOLOGYADVANCES IN MATRIX STIMULATION TECHNOLOGYADVANCES IN MATRIX STIMULATION TECHNOLOGYADVANCES IN MATRIX STIMULATION TECHNOLOGY

G. Paccaloni and M. Tambini AGIP Spa

• Incorrect Stimulation Fluid

• Initial: 2200 BOPD 400 BOPD @ 6 months

• Reperforate: 2000 BOPD Same decline

• Mud Acid: 2000 BOPD Same decline

• Fluoboric Acid: 1900 BOPD @ 60 months

26

51


2000

1500

1000

500

0

0 0.5 1 1.5 2

Ashland Oil Well No. 3

Pro

duct

ion

(BL

PD

)

Time (Years)

Figure 8 - Production of Oil Well No. 3 showing decline after Mud Acid treatmentindicative of fines migration and sustained production after fluoboric acid treatment.

Decline after Mud Acid & Clay Control Treatment

After Fluoboric Acid Treatment

52


CONCLUSIONS• HBF4 generates HF at a slow rate thus providing deeper live-acid penetration

than is possible with ordinary HCl/HF acid.

• Treatment with HBF4 prevents silt and clay migration/swelling through fusion of platelets and reduction of CEC. This should prevent fines dispersion resulting from both ionic shock and mechanical dislodgment.

• HBF4 normally is used n combination with HCl/HF acid. The faster-reacting HCl/HF acid removes damage immediately around the wellbore, while the HBF4 penetrates deeper to remove formation damage and to stabilize clays and other fines.

• A shut-in period is required following injection of HBF4 to allow spending of the acid and stabilization of the clay.

• HBF4 is less damaging to formation integrity than HCl/HF acid.

• Fluoboric acid minimizes silica formation.

• Case history studies of the use of fluoboric acid in sandstone matrix acidizing indicate that the system is very effective in removing formation damage and stabilizing formation fines.

27

Organic Fluoboric Acid (OCA) for HCl Sensitive Sandstone Formations

54


Applications

• HCl Sensitive Formations

–Unconsolidated sandstones

–Chlorite

–Zeolite

• High Silt/Clay Content

–> 30% Silt/Clay

• HT formations

–T > 300 F

28

55


Fluid Selection Guidelines

OCA-HT OCA

Temp >300F yes

Temp < 300F yes

Zeolite <5% yes

Zeolite >5% any temp yes

Chlorite <5% yes

Chlorite >5% any temp yes

56


Experimental Methods• Sequential Acid Spending

29

57


Testing Results

• Sequential acid spending on 90% 100 mesh sand and 10% zeolite, 200oF

Sequential Reaction ----->0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4

Si C

on

cen

trat

ion

(M

ola

r)

Organic Clay Acid9/1 mud acidClay Acid3/1 mud acid

58


Core Flow Testing9/1 Mud Acid

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0

T im e (m in )

Per

mea

bili

ty (

md

)

6 % N a C lF re s h W a te r3 % N H 4 C l1 5 % H C L9 /1 M u d A c id

Potential Fine Migration after Acidizing

30

59


Core Flow TestingOCA

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

7 0 0

8 0 0

9 0 0

1 0 0 0

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0

T im e (m in )

Per

mea

bili

ty (

md

)

6 % N a C lF re s h W a te r3 % N H 4 C l1 5 % H C lO C A

Fines stabilized

60


Placement1. NH4Cl preflush (25-50 gpf)

2. 10% Acetic Acid (75-100 gpf)

3. OCA (100-200 gpf)

4. NH4Cl overflush (3-4 feet radially)

5. Diverter

6. Repeat 2-5 as required

No Shut-in Required

NH4Cl

25-50 gal/ft

OCA

100-200 gal/ft

10% Acetic Acid

75-100 gal/ft

NH4Cl w/ U66

25-50 gal/ft

31

61


DifferentiationRecomended Procedure

Low Temperature A 5% NH4Cl PreflushNon Sensitive Clays A B D H ILow Clay Content B HCl Preflush

Low Temperature C Organic Acid PreflushNon Sensitive Clays A B D E G High Clay Content D Mud Acid

Low Temperature E Clay AcidSensitive Clays A C F H IAny Clay Content F Organic Clay Acid

High Temperature G Shut InSensitive Clays A C F H IAny Clay Content H 5% NH4Cl Postflush

I Immediate Flow Back

Mud Acid

Clay Acid

OCA HT

OCA

62


Case History #1 - GOM

• Deep water turbidite sand

• 11,000’ TVD, BHST 175 F

• Frac-Pac completion

• Permeability - 400 to 1600 md

• 5% Zeolite

• Compaction - 20 - 30% perm reduction

• Increasing skins - higher drawdowns

11,592’

12,141’

11,928’

12,060’

Well #1Well #1Well #1Well #1 Well#2Well#2Well#2Well#2

BeforeBeforeBeforeBefore AfterAfterAfterAfter BeforeBeforeBeforeBefore AfterAfterAfterAfter

BOPDBOPDBOPDBOPD 775775775775 1034103410341034 218218218218 1045104510451045

MCFDMCFDMCFDMCFD 498498498498 547547547547 216216216216 837837837837

Production levels sustained for more than 1 year

32

63


220220220220 245245245245 270270270270 295295295295 320320320320 345345345345 370370370370

Job Time (Minutes)

0000

1000100010001000

2000200020002000

3000300030003000

4000400040004000

5000500050005000

Pre

ssu

re -

psi

0

10

Inje

ctio

n R

ate

In

jec

tion

Ra

te

Inje

ctio

n R

ate

In

jec

tion

Ra

te -- --

(BP

M)

(BP

M)

(BP

M)

(BP

M)

Treating Pressure - psi

Injection Rate - BPM

Pump OCA

Prime Pumps

Start PostFlush

Start Displacement

Increase Rate

End of Treatment

Acid at Perfs

4

2

6

8

Case History 1: GOMCase History 1: GOMCase History 1: GOMCase History 1: GOM

64


Case History #4- Venezuela• Temp: 140 – 235 °F

• Reservoir Pressure: 950 – 1400 psi

• Reservoir Permeability: 100 - 300 mD

• Depth: 2900 -4200 ft

• Gravel Packed with sand 20/40

Formation lithology: Quartz: 48%-56%Mica: 3%-11%K-Feldspar: 1%-3%Kaolinite: 28%-36%Smectite: 1.4%-2.3%Illite: 1%-2.5%Chlorite: 1.1%-3%%Zeolites: 1.2%

0

40

80

120

160

200

240

280

0 30 60 90 120

Time after Treatment (days)

Ave

rag

e O

il P

rod

, BO

PD

Average Before Average Expected

Average Actual M ud Acid Treatments

33

65


Case History #5- Pakistan

Lowered FWHP ~400 psi Lowered FWHP ~400 psi Lowered FWHP ~400 psi Lowered FWHP ~400 psi

Maintain production at 50 MMscfdMaintain production at 50 MMscfdMaintain production at 50 MMscfdMaintain production at 50 MMscfd

Formation lithology: Formation lithology: Formation lithology: Formation lithology:

Quartz:Quartz:Quartz:Quartz: 49%49%49%49%----60%60%60%60%

Mica:Mica:Mica:Mica: 1%1%1%1%----3%3%3%3%

Feldspar:Feldspar:Feldspar:Feldspar: 1%1%1%1%----6%6%6%6%

Smectite:Smectite:Smectite:Smectite: 1.4%1.4%1.4%1.4%----2.3%2.3%2.3%2.3%

Glauconite:Glauconite:Glauconite:Glauconite: 1%1%1%1%

Chlorite:Chlorite:Chlorite:Chlorite: 7%7%7%7%----10%10%10%10%

Siderite:Siderite:Siderite:Siderite: 7%7%7%7%----20%20%20%20%

FeFeFeFe----DolomiteDolomiteDolomiteDolomite 0%0%0%0%----7%7%7%7%

• Temp: 340 Temp: 340 Temp: 340 Temp: 340 °°°°FFFF

• Reservoir Pressure: 4300 psiReservoir Pressure: 4300 psiReservoir Pressure: 4300 psiReservoir Pressure: 4300 psi

• Reservoir Permeability: 160 mDReservoir Permeability: 160 mDReservoir Permeability: 160 mDReservoir Permeability: 160 mD

• Perfs: Perfs: Perfs: Perfs: 3318.5m to 3328.0m3318.5m to 3328.0m3318.5m to 3328.0m3318.5m to 3328.0m

• Gravel Packed with sand 20/40Gravel Packed with sand 20/40Gravel Packed with sand 20/40Gravel Packed with sand 20/40

• Acetic acid and OCA w/ VES diverterAcetic acid and OCA w/ VES diverterAcetic acid and OCA w/ VES diverterAcetic acid and OCA w/ VES diverter

Pre-Stimulation

Post-Stimulation

66


Organic Fluoboric Acid: Conclusions

• OCA provides safe stimulation of sensitive formations

– Zeolites, Chlorites and high temp formations

– High clay content

• OCA provides deeper penetration

• Undesirable precipitates are minimized

• Fines Migration is controlled

• No shut in required

34

67


Sandstone Acidizing Conclusions• Damage identification determines the types of acid and other solvents used.

• Fluid selection for a mud acid treatment is based on permeability and mineralogy.

• A knowledge of the chemical reactions involved between acids with formation minerals and connate fluids is required.

• Appropriate volumes of preflushes and overflushes help preventincompatibilities.

• The primary reaction of mud acid with silt and clay occurs very fast.

• Secondary and tertiary reactions do not contribute to damage removal.

• Hydrated silica (silica gel) is normally not a damaging precipitate.

• Retarded acid with silt and clay control properties are required in sandstone reservoirs with production declines.

• Acid sensitive sandstone reservoirs cannot be treated with a conventional mud acid treatment, i.e. they require a organic fluoboric acid system.

• Although guidelines exist for volume selection a numerical simulator is recommended to quantify acid volumes.

68


Matrix Stimulation: Sandstone

Sandstone Stages

1. Pre-acid Preflush

Fluids @ End of Treatment??

4 3 2 13. Main Treating Fluid

2. Acid Preflush

4. Overflush

5. Diverter Stage

StimCADE Demo

Documents

Tab 6 F_ Sandstone Acidizing Chem and Design