Well Stimulation
Chlorite In SS H2S Wells Spent Acid Iron Content Limestone Sandstone Lithology Low Permeability High Permeability Permeability Low Temperature High Temperature Temperature
Well Stimulation
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
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
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
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% HCLExcercise (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.
‣
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%HCLHydrofluoric 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)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 & ParticlesSprint 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.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)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 AcidsSprint Stimulation Systems
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.Sprint Stimulation Systems
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 andremaining fluids are diverted to other zones
Sprint Stimulation Systems
➡ MaxOil Acid System (MOA-L/MOA-S)
✓
MOA Max-Oil Acid is a sequence of fluids pumped tomaximize 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)Sprint Stimulation Systems
➡ Non Damaging Pill (NDP)
✓
Commonly used Pill / gel plugs are polymer based and thus they aredamaging 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 lowviscosity, 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 theSprint 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
