ACID FRACTURING

A Presentation on

Presented byHimanshu Rajawat

Submitted toDept. of Petroleum EngineeringRTU, Kota

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

Motive For Fracturing

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. www.thegasgun.co

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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.

Acid Fracturing…..

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.

Acid Fracturing…..

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.

Acid Fracturing…..

Factors effecting fracture conductivity:

Fluid leak-off

Reservoir permeability and porosity

Leak-off filtrate viscosity

Reservoir fluid compressibility

Reservoir temperature

Acid Fracturing…..

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

Etched fracture length

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

Acid fracture Simulation

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

Acid fracture Simulation

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.

Hydrochloric acid (Hcl)Acetic acid (HAc)Formic acidHydrofluoric (HF)

Acids used in fracturing……..

Surfactants Suspending Agents Anti-Sludge Agents Corrosion inhibitors Alcohol Fluid Loss Control Agents

Additives Used……

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)

Thank You