Isolation
Once a stage is fully fractured, workers isolate it from the rest of the well by inserting a plug into the well.
Isolation procedures are critical for maintaining well integrity, preventing fluid migration between geological formations, and ensuring safe operations.
Isolation is important for zonal control, allowing operators to treat multiple intervals of the formation independently. Zonal isolation specifically refers to separating different subsurface zones that may contain varying pressures, fluids, or hydrocarbons to avoid cross-contamination or blowouts. This is primarily achieved through the installation of casing strings and cementing.
The process begins with drilling the initial hole and setting the conductor casing, which isolates the wellbore from loose topsoil and surface debris to stabilize early drilling. Subsequent casings—such as surface, intermediate, and production casings—are run into the hole as drilling progresses deeper. Each casing is cemented in place by pumping cement slurry into the annulus (the space between the casing and the wellbore wall). Regulations often require cementing at least 500 feet above the casing shoe and above each zone to be isolated to create a hydraulic seal. Cement plugs may also be placed at specific intervals where porous zones are detected to further prevent fluid movement.
Isolation Hazards
- struck-by or caught-in hazards during wireline operations
- unexpected pressure release during plug setting
- exposure to high-pressure fluids or gases
- electrical hazards from wireline equipment
- slips, trips, and falls due to hoses, cables, and restricted work areas
Isolation Controls and Solutions
- workers must follow wireline safety procedures and stay clear of the line of fire
- pressure must be verified and controlled before and during plug installation
- equipment must be properly maintained and inspected before use
- communication between the wireline crew and rig personnel must be maintained at all times
- walking and working surfaces must be kept as clear as possible
Knowledge Check Choose the best answer for the question.
2-8. What procedures are performed to get the mixture of fracturing fluid and gas or oil flows back out of the well?
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