In matrix acidizing, chemical divertants increase the chances of proper acid distribution in the production zones. Viscoelastic surfactants (VESs) are common diverting agents due to easy removal. VES-based acid effectiveness is influenced by pH, shear rate, concentration, and type of VES. Additives such as corrosion inhibitors (CIs) and iron control agents (ICAs) affect VES-based acid performance. This study analyzes a new viscoelastic zwitterionic surfactant’s diversion efficiency via rheology measurements and coreflooding experiments.

The study aimed to optimize a diverting fluid by examining its rheological behavior at pH 4 with surfactant concentrations of 4, 6, and 8 vol% while considering the presence of additives and also explored the effects of CIs and ICAs. Single coreflooding tests determined the injection rate with the lowest PVbt (IRLPVbt) for the diverting fluid and regular acid. By parallel coreflooding tests, utilizing periodic injection method and shut-in time assessed diversion efficiency on carbonate cores with permeability contrasts ranging from 3 to 27. Post-injection computed tomography (CT)-scan images were used to monitor the development of wormholes in the cores.

The rheology analysis showed that the desired VES displayed dominant elastic properties, resembling an elastic solid. The 6 vol% VES exhibited the most favorable rheological behavior, making it the optimal choice for effective diversion. The presence of CI and ICA additives together at concentrations of 1 and 0.5 vol%, respectively, not only had no negative effects but also enhanced the rheological behavior. Through the periodic injection method, injecting the VES-based diverting fluid equivalent to 0.5 pore volume (PV) of the high-permeability core (PVHP), followed by a shut-in time, and subsequent regular acid injection in parallel cores, showed the highest diversion efficiency. The study found that within a permeability contrast range of 3–5, the diversion efficiency was infinite, indicating highly effective diversion, while it measured at 95.9% for a permeability contrast of 32. Increasing the injection volume of the VES-based diverting fluid above 0.5 PVHP decreased the diversion efficiency. This study suggests a new carbonate rock acidizing procedure that could enhance well stimulation efficiency.

Keywords:
fluid dynamics, carbonate reservoir, geologist, complex reservoir, diversion efficiency, enhanced recovery, high-permeability core, injection rate, ve-based acid, flow in porous media
Subjects:
Acidizing, Carbonate reservoirs, Flow in porous media, Improved and Enhanced Recovery, Reservoir Fluid Dynamics, Unconventional and Complex Reservoirs, Well Operations, Optimization and Stimulation
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