Swage

A swage is a machined steel adapter used to connect a circulating or kill line to a casing or tubing string of a different size or thread type. When a well requires injection of kill fluid, cement, or stimulation fluid through a connection point that does not match the available surface equipment, a swage bridges the difference. In fishing operations, a swage refers to a specialized milling tool with a hollow core that is run over the outside of a stuck fish, cutting away the exterior to allow access or retrieval. Both uses share the idea of adapting what is on surface to what exists downhole or inside the wellbore.

Key Takeaways

As an adapter fitting, a swage is a short steel nipple that transitions from one outside diameter, thread type, or connection standard to another. This is distinct from a bushing (which reduces an inside diameter) or a coupling (which joins two identical connections). Swages are used whenever surface equipment must connect to a wellhead, casing spool, or tubing hanger that has incompatible threading or dimensional specifications.
In well control and kill operations, swages allow the kill unit or mud pump to hook up to whatever circulating connection is available at the wellhead, even when that connection was not originally designed for the kill manifold. Having a swage kit onsite is a basic well control readiness requirement in most operating jurisdictions.
In fishing operations, a burn shoe or burn mill is sometimes called a swage mill. It is a hollow cylindrical milling tool sized to fit over the outside diameter of a fish (a stuck packer, plug, or tubing joint). The milling teeth on the face and inside of the shoe grind away the exterior of the fish, creating a profile that a releasing tool or overshot can then engage.
Swage fittings used in surface piping systems (pump connections, treating lines, kill lines) must be pressure-rated to at least the maximum anticipated surface treating pressure. Underrating a swage fitting is a mechanical failure risk during high-pressure operations such as hydraulic fracturing or well killing.
In completion hardware, a swage-type collet or lock ring is used to permanently secure a tubing hanger, liner hanger, or packer in a polished bore receptacle. The swage action of the collet expanding into a groove provides a permanent, non-releasable lock.

What Is a Swage in Well Operations?

Think of a swage the same way you think of a plumbing adapter in a hardware store. When a homeowner has 1/2-inch copper pipe but needs to connect to a 3/4-inch threaded iron fitting, they buy a reducing adapter. A swage in the oilfield serves exactly this function, except the pressures are much higher, the materials are alloy steel, and the consequences of failure matter a great deal more.

Surface equipment at an oil or gas well arrives with specific connection types. A cement pump may have a union connection. A kill manifold may have flanged API connections. A wellhead may have threaded casing collars. When these components need to communicate with each other and do not share a common connection standard, a swage adapter bridges the gap. For routine operations where all equipment is pre-planned, connection compatibility is engineered in advance. For emergency or contingency operations where field crews must quickly hook up kill fluid or cement, a swage kit allows fast adaptation to whatever the wellhead has.

In Alberta and British Columbia, well service companies carry standard swage kits that cover the most common wellhead configurations used in the region: 2-3/8 inch and 2-7/8 inch tubing threads, 4-1/2 and 5-1/2 inch casing threads, and hammer union connections in 1502, 1003, and 602 pressure ratings. A kill operation that would otherwise require custom fabricated pipe can proceed within minutes when the right swage is available onsite.

Fast Facts

The word "swage" comes from early metalworking, where a swage was a shaped die used to form hot metal by hammering. A blacksmith's swage block was a cast iron block with holes and grooves of various shapes cut into it, used to form round bars, tubes, and other profiles. The term entered the oilfield lexicon in the early 20th century, initially describing the forged reducers used to connect pipe of different sizes in surface flow lines. Today "swage" in a well control context almost always means a connection adapter, while in fishing it means the milling tool used to engage and recover stuck downhole hardware.

Swage Adapters in Well Control and Cementing

Well control procedures require that kill fluid can be pumped into the well through an established circulating path. For a normally equipped well with a conventional blowout preventer stack, this means the choke and kill lines plus the standpipe manifold. When any of these connections is non-standard or unavailable, a swage adapter allows the kill pumps to connect to whatever outlet is accessible.

In cementing operations, swages are used wherever the cement pump's treating line must connect to a wellhead port, a float collar circulating nipple, or a stage collar port that has different threading or diameter than the treating line. Cementing units typically carry a range of swage adapters as part of their standard toolbox, since each well completion may have a different wellhead configuration even within the same field.

Pressure rating is the critical specification when selecting a swage for a high-pressure job. A hydraulic fracturing kill line swage must be rated to the maximum treating pressure expected. For Duvernay or Montney completions in Alberta, treating pressures of 70 to 100 megapascals are common. A swage rated to 35 MPa would be a safety hazard in that environment. API and NACE standards specify material requirements for swages used in H₂S service.

Swage Mills in Fishing Operations

When a packer, plug, or other permanent downhole tool becomes stuck or needs to be removed, and the standard releasing mechanism has failed or is inaccessible, a swage mill provides an alternative path. The swage mill is a hollow cylindrical milling tool with tungsten carbide cutting inserts on its face and inner bore. It is sized to fit over the outside diameter of the fish, with clearance of a few millimetres.

When the swage mill is rotated and advanced downward, the carbide teeth cut into the exterior of the fish, removing material from the outside while the hollow bore allows the original inner diameter of the fish to be accessed. The result is a milled-over fish whose exterior has been reduced or modified enough to allow a releasing tool, an overshot, or a pulling tool to engage an interior feature such as a collet recess or packer element groove.

Swage milling is slower and more expensive than mechanical release or jarring, but it is one of the last options before the decision to sidetrack the wellbore to bypass the stuck tool entirely. On a deep Foothills well in Alberta where a sidetrack would cost CAD 8 to 15 million, a swage milling job costing CAD 150,000 to 400,000 is well worth attempting first.

A swage fitting is also called a reducer, reducing nipple, or crossover sub depending on the application. A swage mill in fishing is also called a burn shoe or burn mill. Related terms include kill line (the high-pressure line connecting the surface kill manifold to the wellbore, used to pump kill fluid to regain well control; the kill line connection at the wellhead may require a swage adapter), fishing (the process of recovering stuck or dropped downhole tools or pipe from the wellbore; swage mills are one of the tool types used when standard overshots cannot engage the fish), overshot (a fishing tool that engages the outside diameter of a fish by extending a grapple or bowl over it; complements the swage mill which modifies the fish exterior so the overshot can engage), mill (a downhole cutting tool with hard-faced carbide or diamond cutting surfaces, used to dress metal obstructions in the wellbore; swage mills are a specific sub-type used in fishing operations), and hammer union (a quick-connect, hammer-tightened pipe coupling used extensively in high-pressure oilfield service lines; swage adapters frequently convert from hammer union to threaded or flanged wellhead connections).

How a Missing Swage Adapter Delayed a Saskatchewan Well Kill for Four Hours

A well service crew was called out to kill a gas well in southeast Saskatchewan that had developed a casing-tubing annulus pressure buildup. The kill plan was straightforward: pump brine into the tubing to equalize pressure and then circulate heavy fluid to hydrostatic kill. The crew arrived at site with a pump truck rated for the job and a supply of kill fluid.

When the crew connected to the wellhead, the pump truck's treating line had a 2-inch hammer union (1002 rated). The wellhead's kill valve was a 1-inch NPT threaded port with a 2000 psi gate valve. No one on the crew had a 2-inch hammer union to 1-inch NPT female swage in the truck's toolbox. The correct fitting would have allowed the connection in minutes.

The crew spent four hours sourcing the adapter: phoning two other service companies, waiting for a truck dispatched from Weyburn, and ultimately fabricating a thread adapter at a nearby farm shop with a machinist's help. The four-hour delay allowed annular pressure to continue building. By the time the kill was completed, the wellhead had reached 14.5 megapascals annular pressure, which was within 2 MPa of the casing burst rating for the production casing string.

Post-incident review at the operating company resulted in a swage kit requirement added to the well site preparation checklist for all well intervention jobs. The kit specified: union-to-NPT adapters in 3/4 inch through 2 inch, thread type crossovers from 2-3/8 and 2-7/8 tubing threads to hammer union, and a pressure rating card matched to each adapter. The cost of the kit was CAD 1,200. The delay cost CAD 6,800 in standby time plus the risk premium that came with operating at 97 percent of casing burst rating.