The document discusses acid fracturing, which involves injecting acid at pressures greater than the reservoir's fracture pressure. This connects the wellbore to the natural fracture system and improves production from low permeability reservoirs. Acid fracturing is mostly used in carbonate reservoirs, where fractures are initiated using a fracturing fluid pad followed by acid. Conductivity is achieved through etching of rock minerals on the fracture faces. Factors like fluid leak-off, reaction rate, and temperature affect the etched fracture length. Simulation tools can be used to design treatment schedules to optimize fracture conductivity and length based on reservoir properties and fluid characteristics. Acid fracturing faces challenges like fracture closure and requires proper additive selection. It is widely applied in deep, hard carbon

1. A Presentation on
Presented by
Himanshu Rajawat
Submitted to
Dept. of Petroleum Engineering
RTU, Kota

2. Enhance production from low permeability reservoirs
Connect wellbore to natural fracture system in reservoir
More uniform depletion in layered reservoir
Reduce sand control problems
Mitigate drilling/cementing induced formation damage

3. What is acid fracturing..?
1. It is a type of acidizing, in
which injecting pressure is
greater then fracture pressure
of reservoir.
2. The success of acid fracturing
depends upon heterogeneous
dissolution among fractures
faces.
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4. Mostly used in carbonate reservoirs.
Fracture is initiated with fracturing fluid (gel) called pad.
Suitable acid solution is injected followed by the pad.
Generally less complicated because of no propping agent is
used.

6. Conductivity achieved by etching of rock minerals on the
fracture faces.
Effective length of an acidized fracture is limited by the
distance travel by the acid along the fracture before
spending.
At high temperature this limit is a greater problem.

7. Etched fracture penetration and conductivity:
 Conductivity achieved by fracture acidizing is excessive due to
the high reaction rate.
 Conductivity increases considerably when acid forms a deep
channel.

8. Factors effecting fracture conductivity:
Fluid leak-off
Reservoir permeability and porosity
Leak-off filtrate viscosity
Reservoir fluid compressibility
Reservoir temperature

9. Factors effecting etched fracture length:
 Fluid leak-off
 Reaction rate
 Reservoir temperature
 Free gas present in the formation
 Above bubble point ------ High etched fracture length
 Below bubble point ------ Low etched fracture length

10. Aim
To design a treatment schedule for achieving optimum etched
fracture length
A simulator predicts a fracture model based on the
◦ Surface kinetics
◦ Flow and temperature
◦ Fluid loss into fracture faces

11. A design simulator asks for the following data:
◦ Completion details of the well
◦ Reservoir lithology and petrophysical properties
◦ Reservoir pressure and temperature
◦ Reservoir fluid details
◦ Pad type and volume
◦ Acid volume and concentration
◦ Acid Injection rate
◦ Treatment schedule

12. The Challenge
 Acids fractures may close
 Are they limited to closing stresses lesser than 5000 psi?
 Reservoir depletion might accelerate acid fracture collapse
 Propped fracturing stimulation is not an easy task in deep
hard carbonates.
 Undissolved fines can significantly reduce fracture flow
capacity if not remove with spent acid.
 Emulsions can block the etched fracture.

13. Hydrochloric acid (Hcl)
Acetic acid (HAc)
Formic acid
Hydrofluoric (HF)
 Surfactants
 Suspending Agents
 Anti-Sludge Agents
 Corrosion inhibitors
 Alcohol
 Fluid Loss Control Agents
Additives Used……

14. Applications
 It is widely cited that sixty percent of the world’s oil and forty
percent of the world’s gas reserves are held in carbonate
reservoirs
 Many world-class reservoirs are deep (TVD > 10000 ft)
and hard carbonates (E > 4 ×106psi)