Hydraulic Fracture Treatments
Created by pumping above the pressure needed to fracture the rock.
To prevent closure, hydraulic fracture is propped open by pumping a slurry of sand. At greater depths high strength proppant is used.
- Substantially increases production from low permeability formations (less than 10mD).
- Bypassses skin damage over a wide range of permeabilities.
- Careful design essential or fracture may grow out of zone resulting in water and unwanted gas production.
- Only used in carbonates.
- Conductive path along fracture created by acid "etching" fracture walls.
- Etched formation must be strong enough to withstand closure forces.
Fluid pumped below the fracture pressure.
- Acid is injected to dissolve formation damage or else bypass it by dissolving the rock.
- Significant productivity increases only obtained if damage is present.
Carbonates (limestone, chalk, dolomites):
- Most carbonate reservoirs are acidized with HCl, although not suitable for high porosity (>35%) chalk.
- Acid bypasses damage and links up with nearby vugs and natural fractures.
- Careful design essential or acid may create a high conductivity path to nearby gas or water zones.
- Careful design essential or acidizing can damage the permeability of some sandstones.
- Hydrochloric acid (HCl) most easily used but formation damage must be soluble in HCl or carbonate content of reservoir must be >15%.
- Mud acid (HCl/HF) can dissolve damaging siliceous material such as clay minerals.
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