Gelled isolation fluids are used in various applications throughout the oilfield for creating access to a specific segment of the wellbore while leaving the remaining portion of the wellbore unaffected. In single well applications, zones are isolated whereas laterals are isolated in multi-lateral completions. Gelled fluids are typically used in scenarios where isolation is not feasible or too costly to be obtained by use of a packer, plug or other downhole tool. A gelled fluid offers the benefits of being both temporary and easily cleaned up after the treatment. The objective in this application was to use a low cost gelled fluid to fully isolate existing perforations along a lateral to stimulate new zones.
The candidate well selected for re-fracturing was originally completed without being stimulated due to water zones nearby. The 4200 feet of semi-continuously perforated horizontal section did not produce as expected. In order to fracture the targeted zones, a gelled fluid was used to seal off the existing perforations and maintain zonal isolation between fracturing stages. The gelled fluid was designed and optimized in the lab for the well and treatment conditions. An inner string with sliding sleeves was placed in the horizontal section of the well. The gelled fluid was then pumped into the annular space between the original casing and an inner tubing string and allowed to setup before fracturing began.
Before the job was pumped, laboratory testing and simulation concluded that the gelled fluid would be placed within the pump time of the job and hold for the expected time frame of the fracturing operations. Due to the constraints of the wellbore tooling, completion system, and well conditions, this testing provided detailed operational guidelines on placement time, pump rate, fluid shear rate and temperature constraints before committing to pump the job. The fluid was successfully placed and maintained isolation for the duration of the 36 hours of a 9 stage stimulation treatment. Pressure on the backside of the tubing string was monitored throughout all 9 stages and remained fairly constant throughout the stimulation process indicating that zonal isolation was achieved and maintained.
The novelty of this work included the application of using a gelled fluid in conjunction with a sliding sleeve system to optimize the zones for stimulation and address a specific need of limiting flush volumes and pump downs. This unique application provides knowledge on additional options for using this type of isolation gel for these types of applications in the re-stimulation market as a cost effective option.