Fishing Neck

Key Takeaways

• Overshot fishing tools that engage the fishing neck from the outside require that the fishing neck outer diameter be sized to fit within the bore of the overshot, with the overshot's internal grapple (typically a basket grapple with hard-cut teeth or a spiral grapple with helical teeth) contracting around the fishing neck OD as the overshot is lowered over the neck and then gripping the neck when an upward pull is applied: the fishing neck outer diameter must be within the engagement range of the available overshot sizes, which are manufactured in nominal OD series matching the API tubing and drill pipe OD standard series (1.90 inch, 2-3/8 inch, 2-7/8 inch, 3-1/2 inch, 4-1/2 inch) and must be at least 1/8 to 1/4 inch smaller than the smallest restriction in the wellbore above the fish to allow the overshot to be run over the top of the fish and down to the fishing neck; the fishing neck length must be sufficient for the overshot grapple to seat and engage before the overshot shoulder contacts the body of the fish below the neck, which would prevent the grapple from contracting around the neck; in complex fishing situations where the top of the fish cannot be confirmed by gauging (running a drift or impression block to the top of the fish to confirm its shape and dimensions), the fishing neck geometry from the service provider's tool specification is used to select the appropriate overshot and guide shoe configuration for the fishing attempt.
• Spear fishing tools that engage the fishing neck from the inside (by being inserted into a bore or pocket at the top of the stuck component) require a different fishing neck design than overshot fishing, typically a smooth internal bore of defined diameter and depth into which the spear's external grapple can be inserted and then expanded to grip the internal surface: internal fishing necks (used with spear tools) are machined as a smooth cylindrical bore at the top of the fish, with the bore diameter selected to accept the spear's OD in its retracted position while providing adequate wall thickness for the spear's grapple teeth to grip; the spear is inserted into the internal fishing neck bore, then either rotated (for rotational grapple spears) or pulled upward (for slip-type grapple spears) to cause the grapple to expand against the bore wall; internal fishing necks are preferred in applications where the OD of the fish is too large for the available overshot to pass over (for example, retrieving a large bore safety valve from inside a casing string where the only access to the fish is through its central bore), and are also used in slickline fishing applications where a small-OD pulling tool must engage a well component through the tubing bore without requiring the tool to pass over the outside of the fish.
• Fishing neck design for wireline logging tools follows API RP 67 and the individual service company fishing tool standards that define the neck diameter, upset length, and neck length for each tool OD class, ensuring interoperability between fishing necks from different tool manufacturers and fishing tools from different wireline service providers: the standardized wireline fishing neck allows a Schlumberger logging tool that has gotten stuck in a Baker Hughes-cased well to be fished using Halliburton's standard wireline fishing tools, because all three companies' tools and fishing equipment conform to the same API neck dimensions for each tool OD class; the API wireline fishing neck standard specifies the maximum fishing neck OD (equal to the nominal tool OD minus a clearance allowance for the overshot bore), the minimum fishing neck length (sufficient for the overshot grapple to engage), and the minimum upset diameter (providing the shoulder for the overshot to pull against); departures from the API standard fishing neck (custom profiles for specialty tools) must be documented in the tool specification and communicated to the fishing crew before the tool is deployed, so that the correct non-standard fishing tool can be selected if fishing becomes necessary; in practice, many operators require that all downhole tools run in wells on their acreage conform to the operator's fishing neck specification, which may be more conservative (larger upset, longer neck, heavier material) than the service company's standard design, to improve the probability of successful fishing if a tool is lost.
• Fishing neck condition assessment before a fishing operation requires determining whether the top of the fish is accessible, undamaged, and in the correct orientation for the planned fishing tool, because a bent, collapsed, or debris-covered fishing neck cannot be reliably engaged by the fishing tool and may require preparatory operations (junk basket cleanout, neck dressing with a mill, or impression block assessment) before the fishing attempt: the impression block (a soft lead or brass disk run on the bottom of a drillpipe string to the top of the fish) takes an impression of the fish top that, when retrieved to surface, reveals the shape, dimensions, and orientation of the top of the fish including the fishing neck OD, the center axis alignment, and any debris or damage present; if the impression block shows that the fishing neck is accessible and undamaged, the appropriate overshot can be selected and run directly; if the impression shows damage, debris, or misalignment, the preparatory operation (junk basket run, mill dress, or junk shot) must precede the fishing attempt; the fishing neck OD measured from the impression block caliper (the diameter of the circular contact ring left by the fishing neck on the impression block face) is compared against the tool specification to confirm that the correct overshot has been selected and that the neck has not collapsed or swelled from wellbore pressure or temperature effects that might change its OD outside the engagement range of the planned overshot.
• Fishing neck integration with other retrieval features (J-slots, shear-pin designs, and mechanical release profiles) in retrievable downhole tools provides multiple independent methods for tool retrieval that are attempted in sequence if the primary retrieval method fails: retrievable bridge plugs and retrievable packers are designed with a running and retrieval tool that first attempts to shear the setting pins and release the tool mechanically (by weight-down, rotation, or a combination), and the fishing neck is the backup retrieval feature used if the mechanical release fails; the fishing neck on a retrievable packer must be designed to withstand the tensile forces required to retrieve the packer after the mechanical release has failed, including the full overpull force needed to pull the packer elements and slips free of the casing wall after a potentially years-long period of set at high differential pressure and temperature; in wireline-retrievable flow control equipment (subsurface safety valves, landing nipple plugs, wireline safety valves), the fishing neck is the standard retrieval interface for the pulling tool that latches onto the neck and applies upward force to release and retrieve the component, and the integrity of the fishing neck surface is critical for reliable retrieval because a corroded, scaled, or damaged fishing neck surface may not provide adequate grip for the pulling tool's locking dog to hold during the tensile retrieval pull.