903 Well Site Completion and Servicing Safety

Isolation

Two types of isolation are used during well development: permanent zonal isolation and temporary stage isolation.

• Permanent zonal isolation is established during well construction using casing and cement to separate underground formations, protect groundwater, and maintain well integrity throughout the life of the well.
• Temporary stage isolation is used during hydraulic fracturing by setting bridge plugs inside the casing to isolate completed stages, allowing each section of the well to be fractured safely and independently.

Permanent Zonal Isolation

Permanent zonal isolation occurs first during well construction. It separates underground formations that may contain different pressures, fluids, or hydrocarbons. Effective zonal isolation helps prevent fluid migration between formations, protects groundwater, and reduces the risk of well control problems. It is established during well construction through a series of steps before hydraulic fracturing begins:

1. Drill the initial wellbore. The well is drilled to the planned depth for the first casing string.
2. Install the conductor casing: The conductor casing stabilizes the upper portion of the wellbore and helps prevent loose soil and surface materials from collapsing into the hole.
3. Install additional casing strings: As drilling progresses, surface, intermediate, and production casing are installed to isolate deeper formations and provide structural support for the well.
4. Pump cement into the annulus: Cement slurry is pumped into the space between the casing and the wellbore wall (the annulus). The cement hardens to bond the casing to the surrounding rock and create a hydraulic seal.
5. Verify cement placement. Operators confirm that the cement provides effective isolation before drilling ahead or completing the well. Verification methods may include pressure testing, cement evaluation logs, or other well integrity tests.
6. Install cement plugs when needed: Cement plugs may be placed at selected depths during drilling, well servicing, or well abandonment to provide additional isolation and prevent fluid movement.

Temporary Stage Isolation

Temporary stage isolation is performed during the well completion phase, after the well has been drilled, cased, and cemented. Its purpose is to isolate each completed fracture stage so the next stage can be hydraulically fractured safely and independently. Unlike permanent zonal isolation, temporary stage isolation uses bridge plugs that are typically removed after all fracturing operations are complete.

Temporary stage isolation is completed in the following steps:

• Hydraulically fracture the first stage: Fracturing fluid is pumped through perforations in the production casing to create fractures in the target formation.
• Set a bridge plug: A bridge plug (frac plug) is installed inside the production casing above the completed stage to create a pressure-tight seal.
• Isolate the completed stage: The bridge plug prevents pressure and fracturing fluid from entering the previously fractured stage.
• Fracture the next stage: With the completed stage isolated, workers perforate the next interval and repeat the hydraulic fracturing process.
• Repeat the process. Additional bridge plugs are installed after each stage until all planned stages have been fractured.
• Remove the bridge plugs: After all stages are completed, the plugs are typically drilled out so oil or gas can flow through the entire wellbore to the surface.

These isolation procedures help maintain well integrity, prevent unintended fluid movement, and support safe operations throughout the life of the well.

Hazards and Best Practices

• Struck-by or caught-in hazards during wireline operations: Follow wireline safety procedures and stay out of the line of fire while tools and equipment are being deployed or retrieved.
• Unexpected pressure release during plug setting: Verify and control well pressure before and during plug installation to prevent uncontrolled releases.
• Exposure to high-pressure fluids or gases: Use approved pressure-control equipment, verify isolation barriers, and follow established well control procedures.
• Electrical hazards from wireline equipment: Inspect and maintain electrical equipment before use, and ensure equipment is operated according to manufacturer and company procedures.
• Slips, trips, and falls caused by hoses, cables, and restricted work areas: Keep walking and working surfaces as clear as possible, and route hoses and cables to minimize trip hazards.
• Poor coordination between crews: Maintain clear, continuous communication between the wireline crew and rig personnel before and throughout isolation operations.

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