Casing Magnetization is recommended as a relief well contingency for blowout scenarios where active ranging systems have limited utility. These scenarios often consist of either a high formation resistivity region (salt) or a relief well trajectory requiring a high incidence angle approach on intersection (shallow intersections). Due to the anticipated reduction in detection range with active ranging methods, passive ranging becomes the primary method for obtaining a proximity measurement to the target well.
By pre-magnetizing the pipe prior to installation, the uncertainties in passive ranging techniques caused by unknown polarities, pole positions, and variations of field intensities from one joint to another can be eliminated. Once the pipe is magnetized, the ferromagnetic domains within the pipe are aligned in the desired orientation and the pole strength, positions, and polarities are now configured to a known measured state. The increase in pole strength from magnetization will increase the detection range significantly depending on the installation configuration and size of pipe.
Wild Well’s magnetization coil is built in different sizes, which allows it to fit over the casing diameter for the string to be magnetized. The system consists of a custom-designed coil of wire, with several thousand wraps which, when injected with a DC current, creates a large magnetic field within the coil. As the coil is passed over the joint of casing, the ferromagnetic domains within the casing align to the field of the coil. Once the applied field from the coil is removed, the pipe is left with a residual magnetic field, which is uniformly distributed and of much higher magnitude than it was prior to magnetization.
The magnetized casing installation strategy is custom designed for the relief well homing-in strategy. Pre and post magnetization results are provided for each casing joint magnetized which are then used to build an installation model. The installation model provides a visualization of the expected interference pattern and detection range capability.
Based out of Norway and the United States, the magnetization coils are portable fixtures that can be dispatched globally by regular air freight options. Typically, casing magnetization is performed at the casing storage yard, which allows the magnetization to be performed alongside other casing preparation activities prior to shipping the casing to the rig.
Depending on the installation strategy and number of joints to be magnetized, the magnetization process typically takes a team of two magnetization technicians and a forklift operator at the supply base approximately 3 to 4 days to complete
Dedicated forklift operator at the casing yard Access to mains power: 100–240 Vac, 47–63 Hz
The ranging strategy for a subsalt relief well typically consists of a combination of active and passive magnetic ranging, if it were possible to use active ranging above or below the salt region. In either scenario, the locate and follow phase may take place throughout the salt region with reduced detection range capability. To improve passive magnetic ranging performance, several sections throughout the salt region can be pre-magnetized. With casing joints of uniform magnetization, the installation pattern can be varied depending on the desired detection range ability and trajectory strategy. The optimum approach can be determined with the use of magnetostatics finite element models, which can be generated on a case-by-case basis.
Shallow reservoirs requiring relief well intervention present a challenging relief well trajectory. This is due to the limited TVD for directional drilling to take place from the kick-off point to reach the desired intersection depth and overcome the surface offset. The casing magnetization strategy for a shallow reservoir scenario attempts to create the maximum field strength possible at the shoe. This allows for a large detection range for the near orthogonal approach. The amount of pipe to magnetize may range from several joints up to 10 joints depending on the relief well strategy and overall positional uncertainty to overcome.