A significant share of disappointing acid treatments were never viable candidates. Skin was present, but the skin was not the kind acid can remove. Candidate selection is a diagnosis problem before it is a design problem.
Separate the components of skin
- Damage skin — fines, scale, organic deposition, drilling-mud invasion. Treatable.
- Completion skin — perforation efficiency, partial penetration, deviation. Not acid-treatable.
- Rate-dependent skin — turbulence in gas wells. Misread constantly.
- Reservoir effects — permeability contrast, faulting, depletion. Not damage at all.
Use transient data, not nodal alone
Build-up or step-rate testing separates mechanical from damage skin far better than a productivity index that has been declining for other reasons. Where transient data is unavailable, offset analogue behaviour is the next best evidence — the basis for using an analogue field database in screening.
Check that uplift is actually deliverable
Removing skin only helps if the well is not constrained downstream by tubing, artificial lift or facility backpressure. Run the nodal case with skin set to zero before committing spend.
Then design
Once the candidate qualifies, fluid system, injection rate, diversion and volumes follow from mineralogy and reservoir description — the modelling covered by our matrix acidizing design software and discussed further in what stimulation software should actually decide for you.