Near-wellbore region
- Also known as
- near-wellbore, near wellbore, near-wellbore zone
The near-wellbore region is the zone of reservoir rock immediately surrounding a well, typically extending from inches to several feet. All produced or injected fluid passes through it, so its condition has an outsized effect on well performance.
What is the near-wellbore region?
Fluids flowing through a reservoir toward a well converge on it from all directions. The closer they get, the smaller the area they must pass through, so velocities rise and much of the total pressure drop occurs in a small volume of rock right around the wellbore. That zone is the near-wellbore region.
It is also the rock most exposed to everything done in the well: drilling mud, cement, completion and workover fluids, perforating, and the fluids and solids that pass through during production or injection.
Why it matters
Because pressure drop is concentrated there, damage confined to a thin shell of near-wellbore rock can reduce a well’s productivity or injectivity far more than its size suggests. Engineers quantify this as skin. Most formation damage of practical importance is near-wellbore damage.
Common near-wellbore problems
- Invasion of drilling and completion fluids and solids.
- Water blocks and emulsion blocks.
- Paraffin and asphaltene deposition as pressure and temperature drop near the well.
- Mineral scale formed as produced water loses pressure.
- Fines migration and clay swelling.
Near-wellbore treatments
Near-wellbore problems are usually treated by placing a relatively small volume of treatment fluid directly into the affected zone: acidizing to dissolve scale and damage, solvents and dispersants to remove organic deposits, and surfactant treatments to break emulsions and water blocks. Because the damaged volume is small, these treatments can be cost-effective relative to the production they restore.
Frequently asked questions
There is no fixed boundary. It usually means the rock within inches to several feet of the wellbore, the zone where most flow restriction and most treatment effects occur.
Because all flow must pass through it and most of the pressure drop happens there, a small reduction in permeability close to the well can cause a large loss in production or injectivity.
Sources
- near-wellbore; skin, SLB Energy Glossary
- Formation damage, SPE PetroWiki