Review and analysis of zonal-isolation effectiveness in carbonate reservoirs using multistage stimulation systems

It is common practice to complete long carbonate intervals with multistage stimulation treatments, especially in horizontal wells. Each zone is, typically, mechanically isolated using cement or openhole packers and then acid stimulated. It is important to pump the planned acid volume to the target zone without any significant loss into adjacent zones. Zonal-isolation effectiveness is rarely evaluated because of a lack of zone-specific pressure and/or temperature data. Instead, it is judged on the basis of job pressure response or post-job production logging. In this study, zone-specific pressure and temperature gauges allowed for a more effective review of zonal isolation during stimulation treatments. In this paper, we review zonal-isolation results from a series of high-rate acid jobs conducted in wells equipped with zone-specific pressure and temperature gauges. Twenty-one acid-stimulation jobs from thirteen different wells were reviewed to investigate the effectiveness of zonal isolation during and after treatment. The examples presented in this paper cover several different completion types: cemented and uncemented, intelligent well systems (IWSs), plug-and-perforate completions, and ball-activated sliding-sleeve completions. The analysis revealed several different pressures and/or flow communication patterns. Field examples and analysis results presented in this work will help engineers design and optimize the zonal-isolation distance in cemented and uncemented wells requiring multistage stimulation in carbonate fields without losing a significant pay length.