Tab 6 F - Sandstone Acidizing Chem and Design
Tab 6 F - Sandstone Acidizing Chem and Design
Tab 6 F - Sandstone Acidizing Chem and Design
Outline
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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
Matrix Stimulation Engineering Solutions
Objectives
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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.
Matrix Stimulation Engineering Solutions
Treatment of sandstone with high calcite content (>20%): Use carbonate design methodology Use sandstone diversion techniques Iron control may be a problem
Matrix Stimulation Engineering Solutions
Sandstone Constituents
Secondary Cement (Carbonate Quartz) Clays (Pore lining i.e., illite) Clays (Pore filling i.e., Kaolinite) Quartz
Chemical Composition
Si0 22 Si0 KAlSi O 33 88 KAlSi O KAlSi 3O 8 KAlSi O
3 8 2-3 1-2
Biotite Biotite Muscovite Muscovite Chlorite Chlorite Kaolinite Kaolinite Illite Illite Smectite Smectite Mixed-Layer Mixed MixedLayer Mixed
(AlSi O ) K(Mg, Fe)3(OH) 33 10 22 (AlSi O 10) K(Mg, Fe) 3(OH) (AlSi O ) K(Al) OH) 3 O 10 ) K(Al) 2 OH)2 (AlSi
3 10 2 2 +2, Fe+3 (Mg, )) Si AlO (OH)8 66 33 10 (Mg,Fe Fe+2 , Fe+3 Si AlO 10 (OH) 8 Al (Si O )(OH) 4 (Si 4 O 10 )(OH) 8 Al
10
(AlSi O )Mg5(Al,Fe)(OH) 33 10 88 (AlSi O 10)Mg 5(Al,Fe)(OH) Illite or Chlorite Kaolinite, Kaolinite, Illite or Chloritewith withSmectite Smectite
Formation Minerals
Minerals Carbonates Calcite Dolomite Ankerite Siderite Sulfates Gypsum Anhydrite Others Halite Iron Oxides Chemical Composition CaCO3 Ca, Mg(CO3)2 Ca,(Mg,Fe)(CO 3) 2 FeCO 3 CaSO42H 2O CaSO4 NaCl
Specific Area
Few cm2/g Few cm2/g 22 m2/g 113 m2/g 82 m2/g
Siliceous minerals
Matrix Stimulation Engineering Solutions
HF Clay Spent HF
Si(OH)4
Secondary X/5 HSiF5 + M-Al-Si + (3-x+1) H+ + H2O = AlFx(3-x)+ + M+ + Si(OH)4 Tertiary AlF2+ + M-Al-Si + (3-x+1) H+ + H2O = 2AlF2+ + M+ + Si(OH)4
Matrix Stimulation Engineering Solutions
AlF2+
Si(OH) Si(OH) Si(OH)
10
11
Si(OH)4
Al
12
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Pre-acid Preflush: Overflush: Displaces spent acid away from the critical matrix. Diverter: Preflush: Main Fluid: NH Cl brine or displaces water containing Decreases fluidtoluene/xylene flow into the thief zone/s and increases flow into HCl organic acid) removes CaCO matrix to prevent the Mud acid removes silt and clay (alumino-silicate) formation damage 4 (or 3 from + + ++ incompatible cations (Na , K , Ca ) away from the wellbore. other non-treated zones. precipitation of CaF . 2
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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 (aluminosilicate) 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.
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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)
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Selection Criteria
Formation mineralogy Reactivity Chemical composition Surface area Rock Structure HCl solubility Clay distribution Sensitivity Deconsolidation Precipitation Fines release Permeability Type of damage Mobility of induced damage Produced Fluids Oil wells: Sludge/Emulsions Gas wells: Water saturation Temperature Corrosion Penetration Bottomhole pressure
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10
Pre-Acid Preflush
Ammonium chloride (NH4Cl) Guideline
3 wt% (<5% Clay) 4 wt% (5 -10%) 5 wt% (10 -15%) 6 wt% (>15%) (% 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
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HCl Preflush/Overflush
HCl Fluid Selection Guide for All Temperatures
>100 md <10% silt and <10% clay All other combinations of silt and clay composition 15X 20-100 md 10X <20 md 7.5X
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
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11
14 12 10 8 6 4 2 0 0
3% Calcite 6% Calcite
40
23
24
12
Skin Ski
? Volume
Matrix Stimulation Engineering Solutions
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Mud Acid Organic Mud Acid Fluoboric Acid (Clay Acid) Organic Clay Acid (OCA)
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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
HF
or
Y1 Mud Acid
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28
14
Carbonate Cemented Sandstones+ T> 300o F NARS201 T< 300o F Reg. Clay Acid ++ Severe Fines Migration Problems T> 300o F NARS201 Reg. Clay Acid+++ Organic Clay Acid 130oF <T<300oF Reg. Clay Acid+++ Organic Clay Acid
Small Fines Migration Problem T> 130o F Clay Acid LT+++ Organic Clay Acid Use guidelines for damage induced by completion operations. Options: in matrix, sandstones: Noncarbonate cemented Overflush with 5% HCI containing Clay Control Agents L42, L53W or L55
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
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++ +++ ++++
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
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15
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*10% Acetic Acid PF/OF and use OCA when fines migration is a problem.
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16
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Max. T in HCl (deg F) Short Berea Core #2: Acid 12-3 Mud Acid Test @ 300 F Jauf Core # 710 HCl and Mud Sensitivity 2500 Effluent From Core #640 6 wt% wt% Acetic Acid 15 wt% HCl 12 12 wt% wt%HCl HCl- 66 wt% 10 + 75 wt%Cl NH Cl 15 wt% HCl 12 wt% 3 HCl - HF 6 wt% NH Ammonium wt% Ammonium 6 wt% NH Cl 3 wt% HF 20000 3 wt% HF Acid Chloride Mud Chloride 150 2000 Fe 190 Al 15000 1500 Si 200 Ca Al Fe 10000 1000 200 K Si Mg 250 500
o
14000
12000
Concentration (mg/L)
Concentration ( mg/L)
10000
8000
6000
4000
5000
Mg
2000
K
5
5 7
0
0
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0 1
0.00 1
3
17
15 17
75.00 19
19
Sample 11 #
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Sample Number
17
+ L36 (Formic)
HF
or
Y1 Mud Acid
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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
Matrix Stimulation Engineering Solutions
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Retarded HF formulation using Fluoboric Acid (HBF4) Clay Acid Ammonium bifluoride + boric acid + HCl HBF4 + H20 HBF3(OH) + HF HF reacts with silt and clay HBF4 continues to generate HF slowly
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40
20
10
20
30
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Treated
% of Original Permeability 140 120 100 80 60 40 20 0 0 5 10 15 20 25 30 Distilled Water 6% Sodium Chloride Clay Acid Pore Volumes
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21
100 110 120 130 140 150 160 170 180 190 225 250 300
*Clay Acid LT can be used to 130O F,
Matrix Engineering Solutions but is not Stimulation recommended above 130O F.
96 76 52 35 24 16 11 8 5 3 2 1 0.5
48 38 26 18 * * * * * * * * *
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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 - Pwf2) / Qg vs. Qg (the turbulence plot) was used as an evaluation tool.
2 2 ( P 2 ) Pws Pwf = = C L + D 'Q g Qg Qg
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Q (MMCFD)
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12.0 10.0
Q (MMscf/D)
Time (Months)
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24
A(1.7)
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SPE 20623 ADVANCES IN MATRIX STIMULATION TECHNOLOGY G. Paccaloni and M. Tambini AGIP Spa
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2000
500 Decline after Mud Acid & Clay Control Treatment 0 0 0.5 1 Time (Years) Figure 8 - Production of Oil Well No. 3 showing decline after Mud Acid treatment indicative of fines migration and sustained production after fluoboric acid treatment.
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1.5
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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.
Matrix Stimulation Engineering Solutions
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Applications
HCl Sensitive Formations
Unconsolidated sandstones Chlorite Zeolite
HT formations
T > 300 F
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55
Experimental Methods
Sequential Acid Spending
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Testing Results
Sequential acid spending on 90% 100 mesh sand and 10% zeolite, 200oF
0.4
Si Concentration (Molar)
0.35
Organic Clay Acid 9/1 mud acid Clay Acid 3/1 mud acid
0.3
0.25
0.2
0.15
0.1
0.05
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140
120
Permeability (md)
100
80
60 6% N aC l F re s h W a te r 3% N H 4C l 15% H C L 9 /1 M u d A c id
40
20
0 0 50
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100
150
200
250
T im e (m in )
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Permeability (md)
Fines stabilized
T im e (m i n )
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Placement
1. NH4Cl preflush 2. 10% Acetic Acid 3. OCA 4. NH4Cl overflush 5. Diverter 6. Repeat 2-5 as required No Shut-in Required (25-50 gpf) (75-100 gpf) (100-200 gpf) (3-4 feet radially)
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Differentiation
Recomended Procedure
Low Temperature Non Sensitive Clays Low Clay Content Low Temperature Non Sensitive Clays High Clay Content Low Temperature Sensitive Clays Any Clay Content High Temperature Sensitive Clays Any Clay Content A A B D H I B C A B D E G 5% NH4Cl Preflush HCl Preflush Organic Acid Preflush Mud Acid Clay Acid Organic Clay Acid Shut In 5% NH4Cl Postflush Immediate Flow Back
D E
OCA
A C F H I
F G
OCA HT
H I
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11,592
11,928
BOPD MCFD
12,141
62
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Treating Pressure - psi Injection Rate - BPM Acid at Perfs Increase Rate
10
4000
Pressure - psi
3000
Pump OCA
2000
End of Treatment
1000
0 220
245
270
295
320
345
370
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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%
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Post-Stimulation Pre-Stimulation
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OCA provides deeper penetration Undesirable precipitates are minimized Fines Migration is controlled No shut in required
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StimCADE Demo
5. Diverter Stage
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