PEMEX wanted to stimulate production from nonproductive well

The Cardenas field, located in the southern region of Mexico, is characterized by deep, hot, mature carbonate reservoirs. Most wells are completed with multiple perforated intervals. However, not all intervals have the same density of natural fractures or vugular porosity. The dimensions of the vugs and fractures can range from centimeters across to hundreds of feet long. This creates extreme permeability contrasts that make achieving uniform acid stimulation challenging.

After PEMEX perforated and completed one particular Cardenas well, it gave no production at all. With neighboring wells producing up to 400 m3/d, the operator decided to apply a treatment to stimulate the nonproductive well. When the initial stimulation with solvent did not improve production, PEMEX ran a full spectroscopy memory log. The log revealed a vuggy thief zone with a permeability of more than 1 D in the middle interval. Core samples showed that vugular zones represented 5 to 15% of the pore volume. The fluids in the previous treatment had presumably leaked into the open cavities rather than treating the hydrocarbon-bearing zones.

MaxCO₃ Acid diverted fluid from thief zone while stimulating target zones

Schlumberger proposed MaxCO₃ Acid degradable diversion acid to help ensure treatment fluid placement into the three intervals—one hydrocarbon-bearing zone located above and below the thief zone. The MaxCO₃ Acid self-diverting stimulation system incorporates degradable fiber and nondamaging acid to stimulate target zones while temporarily diverting acid from highpermeability zones. The fibers degrade completely with time, ensuring production contribution from diverted areas post treatment.

PEMEX realized stabilized production of 175 m3/d

The acid stimulation treatment involved 12 stages, starting with a 30 m3 MaxCO₃ Acid stage to quickly minimize the impact of the fracture thief zone. The fiber-laden stage obstructed the fracture long enough to effectively stimulate the target zones. Initial production reached 111 m3/d, eventually stabilizing at 175 m3/d. A subsequent production log showed contribution from the upper interval and minor contributions from the lower intervals.