Kuliah 14 Kuliah-14 C b Carbonate t Acidizing A idi i
Dosen : Ir. D I Andry A d Halim, H li MM Universitas Trisakti - Jakarta 2012
Objective/Sasaran j • Konsep Dasar Carbonate Acidizing • Dan penerapannya p p y
Daftar Pustaka • Allen S.O. and Robert A.P. ”Production Operation”, Vol. I Oil and Gas C Consultant lt t International I t ti l Inc. I • Peter E. Clark,”Well Completions : Stimulation and Work Over”. • Pertamina Hulu,” Teknik Produksi”, Jakarta, 2003 • Unocal Completion Course Presentation • BJ presentation, 2003 • Semua buku perihal Komplesi dan uji Sumur • Semua Jurnal tentang Komplesi dan uji Sumur
BJ Services Carbonate Formations & Matrix Acidizing g
Carbonates
Topics 1. 2. 3. 4 4. 5.
Types of Formation Mineralogy Acid Types T Treatment Design D i Summary
Carbonates
1. Types of Formation
Carbonates
Types of Formation Limestone Comprised mainly of Calcium Carbonate but may also contain Calcium Magnesium Carbonate and Iron Carbonate 3 Types:-
Carbonates
Types of Formation Organic Limestones F Formed d from f the th Skeletal Sk l t l Residues R id of Marine Life Relatively high porosity and high level of Impurities
Carbonates
Types of Formation Precipitated Limestones Usually formed as Evapourites Low Porosity
Carbonates
Types of Formation Clastic Limestones Formed as Secondary Sedimentary epos ts Deposits
Carbonates
Types of Formation Chalk T Type off Fine-Grained Fi G i d Limestone Li t Rocks Tend to be p pure re White and Soft M l Calcium Mostly C l i Carbonate C b
Carbonates
Types of Formation Dolomite Calcium Magnesium Carbonate Generally Harder and Less Permeable than Limestones Often with Natural Fractures
Carbonates
Types of Formation Marble M t Metamorphic hi Limestone Li t / Dolomite D l it V Very Hard, H d very Low L Permeability P bilit Natural Fractures
Carbonates
2. Mineralogy
Carbonates
Mineralogy Calcite C l i Calcium Carbonate C b t (CaCO (C CO3) Easily dissolved by Acid Main constituent of most Carbonates Usually y organic g in Origin g
Carbonates
Mineralogy Calcite C CO3 + 2HCl CaCO
C CaCl Cl2 + CO2 + H2O
Carbon Dioxide (CO2) stays in Solution Downhole, But will Cause Foaming g as the Acid is Flowed Back to Surface
Carbonates
Mineralogy Dolomite Calcium Magnesium Carbonate CaMg(CO3)2
Very soluble in Acid
Carbonates
Mineralogy Dolomite C M (CO3)2 + 4HCl CaMg(CO C Cl2 + M CaCl MgCl Cl2 + 2CO2 + 2H2O Dolomite D l it Requires R i more Acid A id per ft3 off Rock than Limestone or Chalk
Carbonates
Mineralogy Siderite Iron Carbonate (FeCO3) Usually found as minor consituent of Limestones and Chalks Easily dissolved by Acid, but can result in Iron Hydroxide precipitates
Carbonates
Mineralogy Siderite F CO3 + 2HCl FeCO
F FeCl Cl2 + CO2 + H2O
Ferrous Chloride can cause Ferrous Hydroxide Precipitates if the Acid is Neutralised
Carbonates
Mineralogy Ankerite I Iron-rich i h Dolomite D l it - Ca(FeMg)(CO C (F M )(CO3)2 Usually found as minor constituent of Dolomites Very soluble in Acid, but can result in Iron Hydroxide precipitates
Carbonates
Mineralogy Quartz Silica - SiO2 Not Sol Soluble ble in Acid Can result in Production of Fines
Carbonates
3. Acid Types
Carbonates
Acid Types Hydrochloric Acid HCl - also known as Muriatic Acid Very reactive Very cheap and readily Available Main Acid for 80% of Matrix Treatments in Carbonates
Carbonates
Acid Types Acetic Acid CH3COOH - Also called Ethanoic Acid Mildly reactive Expensive - used as alternative to HCl in High Temperatures Al used Also d to t control t l Iron I Precipitates
Carbonates
Acid Types Formic Acid HCOOH - Also called Methanoic Acid Mildly reactive (stronger than Acetic) Expensive - used as alternative to HCl in High g Temperatures p
Carbonates
Acid Types Citric Acid C 6H 8O 7 Will form Calcium Citrate precipitate if reacted with Calcite Mainly used in combination with Acetic Acid for Iron control. Never used on its own.
Carbonates
4. Treatment Design • Acid type and Strength • Corrosion Inhibitor • Iron I Control C t l • Surfactant, Non Emulsifier • Special Additive
Carbonates
Treatment Design Acid Type Use HCl Unless you have a Good Reason to Use another Acid Type At very High Temperatures, Acetic and/or Formic Acid is Used because of Slower Reaction Rate Choice of Acid Depends on Cost Cost, Availability, Storage and Function
Carbonates
Treatment Design Acid Type On very Water-Sensitive O W t S iti Formations F ti 99% Acetic Acid can be Used, as thi is this i Essentially E ti ll Water W t Free. F Remember R b that h Organic O i Acids A id are Generally Weaker than HCl and will R Require i more Tank T k Volume V l
Carbonates
Treatment Design Acid Strength Strong A St Acids id dissolve di l more Rock R k per Gallon, Require less Storage Volume and Less Mi Mix Water Weak Acids Require Less Corrosion Inhibitor and Get Further from the Wellbore
Carbonates
Treatment Design Acid Strength Choice Ch i off Acid A id Strength St th Depends D d upon BH Temperature, Available Storage Vol me and Treatment Objectives Volume Objecti es Typical HCl Strengths:7.5%, 15%, 28%
Carbonates
Treatment Design Corrosion Inhibitors Corrosion Inhibitors reduce the rate at which the Acid Attacks the Completion ((and the BJ Equipment) q p ) BJ Standard for Corrosion Protection is 0 0.05 05 lbs/sq ft Metal Loss or Less BJ Standard for Coiled Tubing Protection is 0.02 lbs/sq ft Metal Loss or Less
Carbonates
Treatment Design Corrosion Inhibitors Inhibitor Intensifiers are used at Higher Temperatures to Boost the Effectiveness of the Inhibitors Corrosion C i IInhibitors hibit are Expensive E i and highly Toxic
Carbonates
Treatment Design Corrosion Inhibitors Inhibitor Loading taken from Charts, Charts or Job-Specific Testing:• • • • • •
BH T Temperature t Exposure Time Completion Material (eg N-80, N-80 Cr-13) CO2 and/or H2S Level Mutual Solvent Loading g Acid Type and Strength
Carbonates
Treatment Design Pumping Rate For Near F N W Wellbore llb Damage D Removal, R l LCM Removal or Gravel Pack Cleanouts, pump att 0.5 0 5 to t 1.5 15b bpm. The Idea is to Keep the Live Acid in the Near Wellbore Area. Deep Penetration is Generally Not Required
Carbonates
Treatment Design Pumping Rate For Matrix F M t i Stimulation, Sti l ti Pump P att Maximum M i Possible Rates, Staying below 80% of th Frac the F Gradient G di t It is possible to Create “Wormholes” Wormholes through the formation if the rate is High Enough
Carbonates
Treatment Design Pumping Rate y Treatments Involve Paccaloni-StyleMatrix Increasing the Rate, as the Acid Stimulates the Formation These Treatments can start at 2 - 3 bpm & Finish s at 40 0 + bp bpm Paccaloni treatments,, with diversion,, Provide the Best possible stimulation
ACIDIZING
Dasar Acid Frac • Acid diinjeksikan melebihi kondisi fracture • Diaplikasikan pada reservoir Limestone dan Dolomite • Permukaan fracture (fracture face) terlarut oleh asam yang menyebabkan terbentuknya conductive channel • Panjang dari fracture ditentukan oleh jenis acid, volume, vo u e, kekuatan e ua a ac acid, d, parameter pa a e e leakoff, ea o , da dan kecepatan reaksi
Kandidat Acid Frac • Clean formasi limestone dan Dolomite – Harus memiliki fracture containment/barrier yang cukup untuk mendapatkan panjang (Xf) • Batuan dirty carbonate (< 70% kelarutan pada HCl) adalah kandidat yang jelek – Material i l tidak id k terlarut l oleh l h HCl Cl yang terlepas l bisa bi menutup fracture f ataupun masuk ke wellbore yang bisa menyebabkan perforasi tertutup (sandfill) • Formasi Chalk tidak terlalu cocok – Lunak, sehingga tidak bisa menjaga conductivity setelah fracture menutup • Tidak cocok untuk formasi sandstone – HCl, bahkan HF tidak cukup untuk melarutkan permukaan fracture – Material yang terlepas karena terlarutnya batuan akan menutup fracture yang ada
GENERAL PRINCIPLES The primary purposes of any acidizing treatment is to dissolve either the formation rock or materials, natural or induced, within the pore spaces of the rock. There are two primary requirements that an acid must meet to be acceptable as treating fluid : 1 1. It must react with carbonates or other minerals to form soluble products 2. It must capable of being inhibited to prevent excessive reaction with metal goods in the well Other important consideration are cost, availability, and safety in handling. Major types of acid in well treatment : 1. Hydrochloric Acid 2. Hydrofluoric Acid 3 Acetic 3. A i Acid A id 4. Formic Acid
Perbandingan Acid Frac dan P Proppant t Frac F Acid Fracturing
Propped Fracturing
•
Unit Frac
Sederhana
Komplit
•
Proppant Flowback
Tidak Ada
Bisa Terjadi
•
Fluid Loss Control
Jelek
Bagus
•
Kandidat
Karbonat
Sandstone + Karbonat + Shale + Batubara (CBM)
•
Residual Damage
Tidak Ada
Ada
•
Fracture Length
Pendek
Panjang
HYDROCHLORIC ACID (HCl) Used in the field is normally 15% by weight HCl; however, acid concentration may vary between 5% and about 35%. 35% HCl will dissolve limestone, limestone chalk, dolomite, and most other carbonates. Chemical reaction equation : 2HCl + CaCO3
CaCl2 + H2O + CO2
1000 gallons HCl of will dissolve approximately 10.8 cu ft (1,840 lbm) of limestone. It will liberate approximately 7,000 7 000 cu ft of CO2, and produce 2,042.4 lbm of calcium chloride (dissolved in the original water of the acid solution), plus 38.75 gal of water formed during the reaction.
Acetic and Formic Acid Acetic acid (CH3COOH) and Formic acid (HCOOH) are weakly ionized, slow reacting, organic acids. They are used much less f frequently l than h HCl and d are suitable i bl primarily i il fro f wells ll with i h high hi h bottom hole temperatures (> 250oF) or were prolonged reaction times are desired. The reaction of these acids with limestone is described by the following equation : 2HOrg + CaCO3
CaOrg2 + H2O + CO2
For field use, HAc and HCOOH solutions normally are diluted to 15% and 10%, respectively. Above this concentration will p precipitate p CaOrg g2 from its ‘spent p acid’ solution because of its limited solubility. HCl sometimes mixed with HCOOH or HAc to increase dissolving power per gallon of acid also will provide extended reaction times.
HYDROFLUORIC ACID (HF) Used in combination with HCl and has been referred to as ‘intensified acid’ or mud removal acid Depending on the formation and use. acid. use HF is used primarily to remove clay-particle damage in sandstone formations, to improve permeability of clay-containing formations, to increase solubility of dolomitic formations. Chemical reaction equation : 2HF + SiO2
SiF4 +2H2O And
2HF + SiF4
H2SiF6
ACID REACTION RATES A knowledge of the factors affecting the reaction rate of acids is important for several reasons. reasons 1. Guide for a selection Acid type and volume. 2. Determine how far a given formulation can penetrate t t into i t formation f ti b f before spending di (f t (factors govern spending time). Many factor govern the reaction time of an acid : 1. Pressure 2 Temperature 2. 3. Flow Velocity 4. Acid Concentration 5 Area/Volume 5. A /V l R ti Ratio 6. Formation Composition
ACID ADDITIVES
1. 2. 3. 4. 5. 6. 7. 8.
Corrosion Inhibitors Surfactants Silicate-Control Agent Iron-Control Agents Alcohols Gelling and Fluid Loss Agents Liquefied Gases Retarded Acid
ACIDIZING TECHNIQUES Three Fundamental techniques used in acidizing treatment : 1. Wellbore Cleanup 1 This entails fill-up and soak of acid in the wellbore. Fluid movement is at minimum unless some mechanical means of agitation is used. 2. Matrix Aciding This is done by injecting acid into the matrix pore structure of the formation,, below the fracturing g p pressure. Flow p pattern is essentially through the natural permeability structure. 3. Acid Fracturing This is injection into formation above fracturing pressure. pressure Flow pattern is essentially through hydraulic fracture; however, much of the fluid does leak off into matrix along the fracture face.
Fundamental Desain Pada Acid Fracturing i • Mendapatkan p ppenetrasi acid fracture yyang g diinginkan • Memaksimalkan acid fracture length -
BHST < 200°F, gunakan acid langsung dan leakoff rendah BHST > 200°F, tambahkan cooling down fluid + retarder untuk acid
• Fracture length harus dibatasi ¾ Jika tidak ada barrier yang membuat fracture tumbuh ke lapisan atas/bawah ¾ Untuk menjaga tidak terjadi komunikasi dengan lapisan yang tidak diinginkan
• Memaksimalkan injection rate Penetrasi yang lebih dalam Dibatasi oleh kekuatan maksimum wellhead/tubing 50
Factor Yang Mempengaruhi Fracture L th & Conductivity Length C d ti it • Jenis J i Acid, A id strength t th dan d volume l – Berpengaruh pada lebar dan panjangnyafracture lengths • Acid leakoff – Berpengaruh pada terbentuknya wormhole • Viskositas Acid – Mempengaruhi fracture width dan proses transportasi sepanjang fracture • Injection rate – Mempengaruhi panjang/tinggi fracture • Formation type – Mineralogy, temperature 51
Mekanisme Yang Terjadi Dalam Acid Frac Acid Transport
A id Reaction Acid R ti
Acid Leakoff
52
Optimasi Conductivity & Etched F t Fracture L Length th • • No N th theoretical ti l limitation li it ti off conductivity d ti it value •
- A matter of pumping more acid to widen the etched width
• • Maximum stimulation ratio achieved •
- Corresponds to the case of infinite conductivity fracture
• • Optimum acid fracture penetration kw x ≈ 50 k f
f
Contoh Program g Acid Frac • DataFRAC* Service, consisting of: – Mini Fall Off using 2% KCl brine – Step Rate Test using 2% KCl brine – Calibration Test usingg 2% KCl brine • Main Acid Fracturing Treatment, consisting of: – Solvent Preflush (10% mutual solvent) – Spacer (15% HCL) – Diverter Stage (viscoelastic fluid, etc) – Main M i A Acid id System S t (emulsi ( l i acid) id) – Solvent Postflush (10% mutual solvent) – Tubing Displacement (2% KCl brine)
Contoh Program g Acid Frac Job Execution Stage Name
Stage Fluid Volume (gal)
Cum. Fluid Volume (gal)
Stage Time (min)
Cum. Time (min)
DIVERTER
1200.0
1200
2.0
2.0
SPACER
210.0
1410
0.4
2.4
ACID
800.0
2210
1.4
3.8
SPACER
210.0
2420
0.4
4.1
DIVERTER
1200.0
3620
2.0
6.2
SPACER
210.0
3830
0.4
6.5
ACID
800.0
4630
1.4
7.9
SPACER
210.0
4840
0.4
8.2
DIVERTER
1000.0
5840
1.7
9.9
SPACER
210 0 210.0
6050
04 0.4
10 3 10.3
ACID
600.0
6650
1.0
11.3
SPACER
210.0
6860
0.4
11.7
FLUSH
2815.7
9676
4.8
16.5
Contoh Program Acid Frac
Initial Fracture Top p TVD Initial Fracture Bottom TVD Etched Fracture Half-Length Average Etched Width Average Conductivity Average Fcd Net Pressure EOJ Efficiency
7411.4 ft 7422.8 ft 60.1 ft 0.212 in 34127 md.ft 126 2 126.2 74 psi 0.092
Carbonates
Summary Matrix Acidizing in Carbonates is Usually Relatively Easy. Iff you Pump Acid into a Carbonate, you should get an I Increase i Production in P d i The Specifics of the Treatment Depend upon the Temperature, the Formation Type and Mineralogy, Mineralogy and the Objectives
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