Long, hot interval needs acid stimulation

When oil production began to decline in a carbonate well in Kazakhstan, the operator needed to stimulate production. The 366-m [1,200-ft] interval was too long to ideally stimulate in a single stage, but it was already perforated with good injectivity, eliminating the possibility of mechanical isolation. Instead, the operator asked for another means of conducting an acid fracturing treatment that would distribute the stimulation effect along the interval.

Adding to the challenge, the formation temperature of 132 degC [270 degF] would require a retarded acid to ensure deep stimulation rather than rapid face dissolution. The conventional acid system used in the area is an emulsified acid system, but the operator asked for an alternative acid system that would simplify mixing and operations—and be less likely to develop emulsions in contact with formation fluids.

As a final challenge, the well was completed with 3.5-in tubing, which raised engineering concerns about fluid friction and how to safely achieve the necessary flow rates for the fracturing operation.

OpenPath services maximize acid reach and distribution

Schlumberger engineers recommended integrating two OpenPath stimulation services.

For acid fracturing, engineers designed an OpenPath Reach service using a single-phase retarded acid system to extend fracture-face etching and stably reduce fluid friction. To ensure complete stimulation of the long lateral, engineers designed OpenPath Sequence services to sequentially isolate high-permeability zones or fractures with temporary particle-and-fiber diversion pills. The pills divert fluids to lower-permeability zones or enable new fracture creation, improving wellbore coverage. Additional diversion was designed into the treatment with VDA viscoelastic diverting acid.

Oil production triples after acid fracturing

The operation was pumped as an initial fracture followed by two diverter sequences, resulting in clear pressure signals indicating successful diversion. The single-phase retarded acid system was mixed in real-time during the job, rather than batch-mixed beforehand as is necessary with conventional emulsified acid, resulting in simpler operations.

After the stimulation operation, oil production increased from 15 m³/d [94 bbl/d] with 1,034 kPa [150 psi] of wellhead pressure to 45 m³/d [283 bbl/d] with 1,241 kPa [180 psi] of wellhead pressure.