Well Acidizing

Well Stimulation Fluid Selection Criteria

Spent Acid

H2S Wells

Iron Content

High Temperature Temperature Low Temperature

Chlorite In SS

Acid Systems

Well Stimulation

Chemicals & Compatibility

High Permeability

Sandstone Lithology Limestone

Permeability Low Permeability

Low Temperature Environment ➡ Acid reaction with formation is “Surface Reaction Limited” (low reaction rate). ➡ Use high concentration acid system for high permeability formation. ➡ Use 15%-20% HCL base fluids for limestones ➡ Use 10-13% HCl - 1.5-3% HF base fluid for sandstones if silt and clays are less then 8-10% ➡ If high clays (10% to 20%), use 1%-1.5% HF with overflush of HCL 7.5%

High Temperature Environment ➡ Very Fast Reaction between acid and formation “Mass Transfer Limited” reaction. ➡ Potential reaction by-product precipitation if ph>4 ➡ Use reduced acid concentration systems. 7.5%-15% HCL base fluids for LS and 7.5%-10% HCL-1% to 1.5% HF for SS depending on silt and clay%. ➡ Retarded Acid is recommended at very high temperatures > 250 deg F. ➡ Post flush of 7.5% HCL is required for all HF treatment

High Permeability Environment ➡ Deep Damage is expected and treatment shall cover min 2 ft depth ➡ Check permeability contrast. If contrast is high use diverter. if low end of permeability is tight use NDA-S. ➡ If perforated section is long use a batch of diverter for each 25 ft of perf height.

Low Permeability Environment

➡ Likely to have shallow damage invasion however, minor precipitation can cause a very high impairment to permeability. ➡ Ensure reaction rate is controlled and ph remain < 3 ➡ highly volatile fluid is recommended to improve cleanup ➡ Check closely emulsion and sludge creation due to Iron in Acid, surfactant and Inhibitor used. ➡ Treatment including mutual Solvent is preferred(Decrease injection P)

Sandstones and Cementitious Material ➡ Silt and Clays

✓HF concentration should not cause formation to disintegrate causing sand production

✓Formation pressure vs initial formation pressure and formation temperature should be checked

✓amount of clays and water sensitive/migrating clays (illite and kaolinite) needs to be known and acid conc. to be reduced in case of it presence.

➡ Calcareous

✓If percent is higher then 15%-18% use HCL base fluids

Excercise ➡ calculate amount of 7.5% HCL preflush per foot required to remove CaCO3 from a SS formation with 7% limestone and 15% porosity.

✓OH size 8 in ✓Acid penetration 2 feet ✓Limestone density = 22.53 lb/gal ✓1.0 lb of CaCO3 is dissolved by 1 gal of 7.5% HCL ➡ Time 10 minutes

Excercise (Continued) ➡ Vol of CaCO3 in cuft = 22/7(((2.333)^2)(0.333)^2))x0.15x0.07= 0.1759 cuft/ft ➡ Limestone density in lb/cuft = 22.53*7.48=168.52 lb/cuft ➡ Wt of CaCO3 per foot = 168.52*0.1759 = 191.944 lb/ft ➡ gallons of 7.5% HCL required = 191.944/1.0= 192 gal

SS with Fine Migration and High Clay Content ➡ If fine migration is the main impairment to the producing well, HBF Acid should be used as a main treatment at 125-150 gal/ft. A shut-in period shall always follow the placement of HBF acid ➡ 4% HBF equal approx 1% HF ➡ HBF acid has an HF acid Base with the addition of Boron H3BO3 Agent as a reaction control agent.

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A full strength HBF has 8% HBF4+0.6%HF+0.3%HCL A Half Strength HBF has 4% HBF4+0.3%HF+0.15%HCL

➡ HBF Acid can be used as a post-flush after HF acid

Hydrofluoric Acid Cleanup ➡ Flowback ✓Natural flow back ✓N2 kickoff ✓Swabing ➡ Pre Flush/Overflush

✓NH4Cl/HCl, Xylene and Mutual Solvent (Pre Flush). ✓NH4Cl/HCl or Diesel or Nitrogen (Over flush- 4 ft) ✓Mutual solvent /Surfactant (To make Water wet formation).

Sprint Stimulation Systems ➡ Silt & Particle Removal Acid System(SRA) ➡ HCl/HF Mixture (Mud Acid) ➡ Volatile Acid System (VAS) ➡ Organic Retarded Acid System (ORA) ➡ Deep Penetrating Gelled Acid (DPGA) ➡ Non Damaging Diverting Acid (NDA/NDA-s) ➡ MaxOil (MOA-L/MOA-S) ➡ Non Damaging Pill (NDP) ➡ Carbo/Sulfo Clean

Sprint Stimulation Systems ➡ Silt & Particle Removal Acid System (SRA)

✓SRA-15, SRA-7.5, SRA123 ✓Remove Drilling Damage/Formation Silt in SS ✓Restore Fracture Density ✓Restore Permeability/ Open Clogged Perforation ✓Suspending & easy flow back of Silt & Particles ✓Special Additives S281, S260

Sprint Stimulation Systems ➡ HCl/HF Mixture (Mud Acid)

✓Frequently Used in SandStone ✓Ratio 12:3, 6:1.5 (depends upon Clay %) ✓HF Partially Dissolve Siliceous Materials (Bentonite) ✓HCl Base fluid as a Pre/Post Flush. ✓HF can cause Precipitation. ✓Early flow back Required. ✓Special additive Ammonium Bi fluoride. (ABF)

Sprint Stimulation Systems ➡ Volatile Acid System (VAS)

✓Alcoholic Acid is a mixture of Methanol or Isopropanol and Hydrochloric Acid (HCI) or HCL:HF Acid

✓Lowers the surface tension, increases the vapor pressure and improves the spent acid cleanup.

✓Improve success in acidizing low- to moderate permeability Reservoir.

✓Reduce Water saturation (Gasification) ✓S2000 Volatile Agent (Use as 300gal/1000gal)

Sprint Stimulation Systems ➡ Organic Retarded Acid System (ORA)

✓High Temp. Environment above 250F ✓Preferred in Low Permeability formations ✓Deeper Penetration ✓Less Corrosive than HCl. ✓Blend with other Mineral Acids ✓9% Formic or 10% Acetic Acid

Sprint Stimulation Systems Organic Retarded Acid System (ORA)

Sprint Stimulation Systems ➡ Deep Penetrating Gelled Acid (DPGA)

✓Mainly Used for limestone. ✓For Deeper Penetration ✓Reduce wormhole effect/ Increase Acid Spending Time ✓Temp. Range 200-300F. ✓Special Additive S301 (Acid Gelling Agent)

Sprint Stimulation Systems Deep Penetrating Gelled Acid (DPGA)

Sprint Stimulation Systems ➡ Non Damaging Diverting Acid (NDA/NDA-s)

✓Self diverting acid system for stimulating Limestone and high permeability Sandstone formations.

✓Non polymer based gelling system ✓95% retained permeability ✓Excellent post job clean-out and biodegradable or in contact with Isopropanol/Hydrocarbon.

✓While pumping and under high shear, rheology is very low. Once in the formation, high gel network is created and remaining fluids are diverted to other zones

✓S1000 Special Additive.

Sprint Stimulation Systems ➡ MaxOil Acid System (MOA-L/MOA-S)

✓MOA Max-Oil Acid is a sequence of fluids pumped to maximize stimulation of oil and gas zone and minimize acid to get to water zone.

✓MOA is a non damaging fluid that temporarily divert acid of the water zone.

✓The system is fully degradable and brakes down by hydrocarbons.

✓The system works for saline water zone for both gas and oil wells.

✓Temperature up to 140 deg C. (285 deg F) ✓Recommended for formation permeability > 20 md

Sprint Stimulation Systems

Sprint Stimulation Systems ➡ Non Damaging Pill (NDP)

✓ Commonly used Pill / gel plugs are polymer based and thus they are damaging to formation. Sprint NDP pill a unique carrier which includes ZERO polymer yet very efficiently viscosifying water base fluids and brines for temperatures up to 285 deg F (148 deg C).

✓ NDP base fluid allows loading fluids with medium to coarse graded particles such as calcium carbonate / frac gravel / LCM material for different oilfield applications.

✓ The gel is non-Newtonian; under high shear rates the solution has a low viscosity, but a high viscosity gel forms rapidly under low shear rate conditions. The gel provides the fluid with good solid carrying capability.

✓ The Pill can be washed/cleaned later, meanwhile the gel entering the formation breaks at the contact with hydrocarbons producing a solid-less fluid.

Sprint Stimulation Systems ➡ Carbo/Sulfo Clean

✓High dissolution capacity for common carbonates scales (CaCO3,Ca, Ba, Sr Sulphate with Soaking Time 24 hr at 150F.

✓Non corrosive to 13%Cr and Duplex steel and Very low corrosion on N80,J55,P105 (<10mpy)

✓No re-precipitation of reaction products ✓Recommended for tubulars where HCl is not recommended ✓Can be used for the near wellbore matrix, perforations, slotted/perforated liner, gravel pack, pre-packed screen and/or open hole

✓Remove Drill-in fluid filter cake uniformly(Avoid Worm hole)

Sprint Stimulation Systems

Selection Flow Chart