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Acid Fracturing

Acid fracturing is a process in which acid is injected at a high enough rate and pressure to fracture the formation which is performed above the fracture pressure of the formation. A viscous pad (a fracturing fluid that does not contain proppant) is pumped into the formation at pressures above the fracture-initiation pressure, which fractures the rock. Then an acid stage is pumped to etch the fracture surfaces. The acid also creates conductive wormholes at or near the fracture surfaces. After stimulation, the fracture closes, but the increased conductivity between the formation and the well remains because of the etching and the creation of wormholes. This results in an uneven etching pattern which increases flow capacity to the wellbore and provides a higher PI.
There are two main reasons for performing this type of stimulation treatment:

First and foremost is low permeability, where natural production is not economical; a conductive fracture provides much more flow area for produced fluid or gas.

The second reason is to overcome damage that extends deeper than matrix acidizing can effectively reach.

To reduce or prevent leakoff (loss of treatment fluids to the formation), conventional acid fracturing treatments use multiple stages of injection of nonreactive fluids and acids. This is designed to minimize the leakoff by increasing the fluid viscosity. In addition, by use of mechanical isolation downhole tools, the pay zone is usually divided to several zones of target and acid injection is to be conducted on each zone separately. This helps to have higher conductive fractures created and leads to a better productivity index for producing wells.

Top Select stimulation team has successfully fractured above 450 wells of different type of reservoirs around the world. We appreciate the opportunity to provide you with technical proposal and looks forward to being of service to you.

Acid Fracturing-Crosslinking Acid System-TPCKA®
 

TPGA® high-temperature gelling acid system is developed to effectively viscosify 15% HCL and 25% HCL on basis of high polymer material formed by cationic unsaturated monomer and acrylamide copolymer. TPGA® high-temperature gelling acid system has excellent characteristics such as high temperature resistance, high shear resistance, sound inhibition of corrosion as well as low filtration and low friction, satisfying the requirements of acidizing the high-temperature formation of 180℃

BENEFITS

  •   TPGA® helps decrease fluid leak-off and acid/formation contact, resulting in deeper acid penetration.
  •   TPGA® can increase the viscosity of foamed live or spent acid, thus improving foam stability.
  •   TPGA® can be used to transport solids, such as 40-100 mesh sand or proppant
  •   TPGA® acid system can be used at temperatures up to 400℉(204℃).
  •   High flowback rate of reacted acid.
TECHNICAL INFORMATION
Item Indices of the system Item Indices of the system
Density,g/cm3 1.0~1.1 Static Filtration Coefficient, m/min0.5 ≤5×10-4
Apparent Viscosity, mPa.s (120℃) ≥40 Emulsion Breaking rate,% ≥95
Corrosion Rate, g/m2.h ≤0.3 Surface Tension of Gelout Fluid, mN/m ≤28.0
Retarding Rate,%(90℃,10min) ≤93 Interfacial Tension , mN/m ≤2.0
Capability of Stablizing Fe ion, mg/L ≤10000 ore Damage Rate,% ≤20
Acid Fracturing-Crosslinking Acid System-TPCKA®
 

TPCKA® uses for Acid Fracture in carbonate formation. The objective is to etch the open faces of induced fractures using an HCl treatment. When the treatment is complete and the fracture closes, the etched surfaces provide high-conductivity flow paths from the reservoir to the wellbore.

Acid is pumped into the fracture

Acid etches the fracture

Creates conductive wormhole

TPCKA® can form gel through crosslinking agent, This is designed to minimize the leakoff by increasing the fluid viscosity. By increasing the acid’s viscosity, the stimulation engineer can also slow down the rate of reaction between the acid and the formation, which helps to improve fracture geometry.

BENEFITS

  •   Controllable crosslinking delay time, low friction, resulting in low operation pump pressure.
  •   High acid viscosity (≥250mPa.s), favorable retarding effect, leading to slower acid-rock reaction speed and sound deep penetration capacity.
  •   Strong temperature resistance and shear resistance, good stability and strong proppant carrying capacity.
  •   Inhibition of clay dispersion, low filtration rate, strong capacity of initiating fracture.
  •   Controllable gelout time, complete gelout with no residue, little damage to reservoir.
  •   High viscosity of reacted acid, strong carrying capacity, facilitating the flowback of cuttings and other insoluble substance.

Itmes
Indices of the system
AF medium- temperature system ℃ AF high-temperature system
Density, g/cm3 0.97~1.03 Viscosity of gelout fluid, mPa.s ≤15.0
Retarding rate% (90℃,10min) ≥95 Emulsion breaking rate, % ≥95
Capability of stablizing Fe ion, mg/L ≥10000 Surface tension of gelout fluid, mN/m ≤28.0
Crosslinking time, s 20~240 7~240 Interfacial tension mN/m ≤2.0
Shear stability Shear time, min 60 60 - -
Apparent viscosity, mPa.s 100 50 - -
Static filtration coefficient, m/min0.5 ≤4×10-4 Core damage rate, % ≤20
Equipment Layout for Fracturing Treatment
 

Acid fracturing is a process in which acid is injected at a high enough rate and pressure to fracture the formation which is performed above the fracture pressure of the formation.

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