In carbonate matrix acidizing, the dominant question is not "what acid" but "at what rate". Inject too slowly and the acid spends locally, creating face dissolution or compact dissolution patterns that give almost no production benefit. Inject too quickly and acid is wasted creating uniform dissolution past the damage zone.
The optimal-rate curve isn't a constant
Buijse–Glasbergen and similar models predict an optimal injection rate that minimizes pore volumes to breakthrough (PVbt). But the curve shifts with:
- Temperature — higher temperature shifts optimal rate upward.
- Heterogeneity — natural fractures and high-perm streaks accept acid disproportionately.
- Mineralogy — dolomite reacts slower than limestone, changing the dissolution pattern.
- Acid system — emulsified, gelled and self-diverting acids alter effective Damköhler number.
Why simulation beats a single rate
Pumping at a constant rate optimized for an average permeability is a rule-of-thumb dressed up as engineering. A staged schedule with diversion targets the heterogeneous interval more honestly. See the broader matrix acidizing guide for how this fits the full design loop.
What to model
- Wormhole regime maps for each candidate acid system.
- Sensitivity of PVbt to rate, temperature and heterogeneity.
- Coverage along the interval with the planned diversion sequence.
KEMISIM's matrix acidizing software implements these models and surfaces the rate window that actually keeps you in the wormholing regime.