Cut-and-Thread Fishing Technique

The cut-and-thread fishing technique is a wellbore fishing procedure used to recover a stuck tubular or workstring from a wellbore by first cutting the stuck pipe at a selected depth above the obstruction point, then threading the free (upper) section of pipe past the stuck fish — either by milling, washover, or sidetracking alongside the stuck pipe — to recover the free portion while leaving or working around the portion that remains stuck, used when the normal over-pull or jar methods cannot free the entire fish in a single operation and when the geometry of the wellbore allows the free pipe to be threaded past the stuck point.

Key Takeaways

The cut-and-thread technique is employed when a pipe string is stuck in the middle of the wellbore — typically differentially stuck (stuck to the formation by hydrostatic pressure differential) — and the string above the stuck point can be freed while the portion below and including the stuck point requires washover or milling to be removed, avoiding the well abandonment that would result from leaving the fish permanently in hole.
Cutting the pipe at the selected depth is accomplished with a string shot (explosive back-off), a chemical cutter (chemical cutting tool that erodes the pipe wall with corrosive fluid under pressure), or a mechanical cutter (rotary pipe cutter run on a workstring) — the choice depends on depth, pipe size, well conditions, and how clean a cut is required for the subsequent threading operation.
After cutting, the free upper string is pulled to surface, leaving the lower portion (the fish) in hole; the washover string or mill is then run to the top of the fish and works downward around the outside of the fish, either washing or milling through the sticking mechanism (differential pressure zone, cement, scale, or sand) while threading the workstring around the fish.
The technique is named "cut-and-thread" because the free pipe string is threaded (passed) alongside the fish during the washover operation — the workstring runs concentrically outside the fish string while working downward, maintaining the workstring on the fish string's centerline until the fish can be freed and extracted.
Success of the cut-and-thread technique requires that the wellbore have sufficient clearance between the fish string OD and the casing or open-hole wall for the washover string to be run concentrically — minimum clearance of approximately 1 inch between the fish OD and the hole diameter is needed for most washover shoe designs.

Fast Facts

Differential sticking — the most common cause of stuck pipe that leads to cut-and-thread operations — occurs when the drill string is held against a permeable formation by the pressure differential between the mud hydrostatic pressure and the formation pore pressure, with the pipe embedded in the filter cake against the formation wall. The hydrostatic pressure force acts over the area of pipe in contact with the filter cake and can create tens to hundreds of thousands of pounds of sticking force that exceeds the drill string tensile strength, preventing pull-to-free. The cut is typically made above the differential stuck zone to free the string above that point, allowing at least partial recovery and preservation of the portion of the wellbore above the stuck pipe for continued operations or sidetrack drilling.

What Is the Cut-and-Thread Fishing Technique?

Pipe stuck in a wellbore is one of the most costly and operationally disruptive events in drilling — it can require days to weeks of fishing operations, potentially result in permanent loss of the wellbore if the fish cannot be recovered, and may require sidetrack drilling at substantial cost to bypass the stuck fish and continue the well. A comprehensive set of fishing techniques exists to address different stuck-pipe scenarios, and the cut-and-thread technique addresses the specific situation where the stuck portion of the string is in the middle of the wellbore and normal extraction methods are insufficient.

The technique is applied when assessment of the sticking mechanism and fishing options indicates that the portion of the drill string above the stuck point can be freed (typically by reducing mud weight to reduce differential pressure or by jarring with a jar tool incorporated in the string), while the portion at and below the stuck point cannot be immediately freed. Rather than leaving the entire string in hole while extensive and potentially unsuccessful freeing attempts are made, the cut-and-thread approach recovers what can be recovered promptly, then executes a systematic plan to deal with the remaining fish.

The "thread" aspect of the technique refers to the operation of running a washover string concentrically outside the fish — threading the washover shoe and pipe down alongside the stuck fish string to reach the sticking point with the washover tool, which then works to free the fish through mechanical or chemical action from the outside while the fish string is continuously supported and guided.

Cut-and-Thread Procedure and Considerations

The first decision in a cut-and-thread operation is the cut point: selecting the depth at which to sever the string to maximize the free portion recovered while leaving the minimum amount of fish that still allows washover access to the stuck zone. The cut point must be above the shallowest stuck zone (to ensure the cut section above is actually free), within the reach of the cutting tool, and in a location where the pipe condition is good enough for a clean cut that will accept the washover shoe.

Pipe cutting methods have different applications. The string shot (primacord explosive tool run in the drill string and detonated at the desired cut point) uses explosive force to back off (unscrew) a threaded connection by rotating the lower string slightly, allowing the connection to unscrew rather than requiring a pipe cut — this preserves the threaded connection and allows the cut section to be re-used. Chemical cutters run on a wireline or coiled tubing and cut through the pipe wall using reactive chemicals or abrasive jets, making a clean cut at any point in the string. Mechanical rotary cutters use a rotating cutting shoe to physically cut through the pipe wall from the inside.

After cutting, the washover assembly is made up: a washover shoe (a large-OD milling tool with internal clearance to pass over the fish OD) attached to washover pipe (large-OD, thin-wall pipe that provides washover fluid circulation while concentrically surrounding the fish string). The washover assembly is run in hole over the fish, and the shoe is worked down alongside the fish by rotating and applying weight, grinding away the sticking mechanism (filter cake, formation, cement, or scale) that is holding the fish in place. Once the shoe has reached below the stuck zone, a conventional overshot or spear can be run inside the washover pipe to engage and retrieve the freed fish.

Cut-and-Thread Across International Jurisdictions

Canada (AER / WCSB): Cut-and-thread fishing operations occur in WCSB wells where differential sticking in permeable Cardium, Viking, or Mannville sands traps drill string against the borehole wall. AER well records for WCSB wells document fishing operations in well history reports, and cut-and-thread operations are noted with the cut point depth, cutting method, and outcome. WCSB directional wells with long horizontal sections are particularly susceptible to differential sticking in high-permeability zones where the mud filtrate invasion rate is high — cut-and-thread fishing in horizontal sections is more challenging than in vertical sections because the workover string must travel horizontally along the fish, requiring adequate hole cleaning and low friction to advance the washover shoe.

United States (API / BSEE): API RP 54 (Recommended Practice for Occupational Safety for Oil and Gas Well Drilling and Servicing Operations) addresses the safety requirements for fishing operations including cut-and-thread procedures. BSEE offshore regulations require that significant stuck-pipe incidents and fishing operations be documented in the well history submitted with development plan updates, as lost-in-hole pipe affects wellbore integrity assessments. Gulf of Mexico deepwater wells with open-hole sections through reactive shale formations have elevated differential sticking risk and more complex cut-and-thread operations than shallow land wells due to the narrow drilling window limiting mud weight adjustments that would help free the fish.

Norway (Sodir / NORSOK): PSA Norway requires documentation of non-productive time (NPT) causes including stuck pipe and fishing operations in the well performance reports submitted after NCS well completions. NORSOK D-010 references contingency planning for stuck-pipe scenarios in the well design process, including pre-planned cut-and-thread fishing programs for formations with known sticking risk. NCS wells frequently encounter sticky reactive shale sections in the Cretaceous Kimmeridge Clay and Jurassic Draupne formations where differential sticking and wellbore instability create stuck-pipe risk that requires pre-planned fishing contingencies.

Middle East (Saudi Aramco): Saudi Aramco's deep carbonate drilling programs encounter differential sticking risk in high-permeability vuggy carbonate and dolomite sections where the large pore openings exposed to the wellbore create conditions for rapid filter cake deposition under high differential pressure. Aramco's well engineering teams plan fishing contingencies for drilling programs that include identified high-risk sticking intervals, specifying cut points and washover tool specifications in the pre-drill contingency plan rather than improvising after the sticking event occurs.

Cut-and-thread is also called the cut and thread fishing technique or washover fishing. The cut portion of the operation may use a back-off procedure (unscrewing a connection) rather than a physical pipe cut, sometimes called a "back-off and thread" in that context. Related terms include fishing, stuck pipe, differential sticking, washover, overshot, string shot, chemical cutter, and pipe recovery. The fish is the stuck object in the wellbore that is being fished; the fishing tool is the downhole tool used to engage, free, or mill the fish.

Tip: When planning the cut point for a cut-and-thread operation, choose a depth that leaves the minimum length of fish while still ensuring the cut section above is genuinely free — do not make the cut prematurely in the hope that the short fish remaining will be easier to recover, because a short fish is often harder to washover than a longer one (less guidance length for the washover shoe and more tendency for the shoe to override the fish top and mill adjacent casing wall). Verify the free point by pull test before cutting: gradually increase the over-pull (above free-hanging weight) while monitoring strain gauge and pipe stretch, with the free point being the deepest depth at which the string shows elastic stretch response to pull force. The cut point should be 1 to 3 metres above the confirmed free point to provide a safety margin and ensure the cut section is in a stretch-responsive (free) portion of the string.

FAQ

What is the difference between cut-and-thread and a conventional washover operation?
A conventional washover runs the washover assembly directly over the top of the fish without first cutting the string — the fish is connected to the surface string at the top, and the washover assembly is run separately around the outside of the entire stuck string. In cut-and-thread, the string is first severed to isolate the fish from the surface string, then the washover assembly is run as a separate tool string over the now-disconnected fish. The cut-and-thread approach is used when the fish is too long to washover in a single operation (the washover pipe reaching from the top of the fish to the surface connection would be excessively long), or when the fish has been disconnected as part of a partial recovery strategy. Conventional washover preserves the option of pulling the entire string intact if the washover frees the sticking mechanism, while cut-and-thread commits to a two-trip recovery process.