Fishing and milling tools

what are oil fishing tools?

Oil fishing is a normal term used to describe the special techniques that are employed to recover items or equipment from down-hole. These items or equipment stuck in the hole prevent the normal operation from continuing. They have to be removed as rapidly as possible. The longer the equipment remains in the hole, the more difficult it is to recover. The tools to help to remove those items are called oil fishing tools.

Why are those items or equipment stuck in the hole?

• Fatigue failures caused by excessive stress in the drill string;

• Failure of downhole equipment on account of corrosion or erosion by drilling fluids;

• Parting of drill string because of excessive pull when attempting to free equipment stuck;

• Mechanical failure of parts of drill bit;

• Accidental dropping of tools or other un-drillable objects into the hole;

• Sticking of drill pipe or casing.

List of Fishing Tools

1. Fishing Tools for Tubular Products

•    Inside fishing tools

•    Outside fishing tools

•    Hydraulic and impact tools 

•    Others

2. Miscellaneous Fishing Equipment

•    Milling tools

•    Junk basket 

•    Magnetic fishing tools 

•    Others

Standard Fishing Assembly

Overshot - Fishing bumper sub - DC - fishing jar - DC's - Accelerator - HWDP. 

This configuration may be modified to suit particular conditions. 

The number of drill collars depends on what is available and what may be already down-hole. To achieve the maximum jarring effect, the number of drill collars in the fishing assembly should equal the amount of those already down-hole. 

With an accelerator in the fishing assembly, the number of drill collars may be substantially reduced. An accelerator is recommended for all fishing. 

A safety joint shall not be run while fishing because safety joints are likely to freeze when jarred. However, a full opening safety joint (drive joint made for jarring) may be used when a wash-over string is run. This full opening safety joint is run below the standard fishing assembly so that internal cutters may be run when the wash-over string sticks and has to be backed off. 

Detailed drawings of the fishing assembly shall be made and kept before the assembly is run. Tools with restricted IDs shall not be run. 

If penetration rates were high when a twist-off occurred, circulate the hole clean before pulling out. Also, circulate as required before latching on to the fish and avoid tagging the top of the fish prematurely. 

A spiral grapple should be used whenever possible in preference to a basket grapple an overshot is run after the fish has been milled over, then always run an extension so that the grapple can catch onto the unmilled pipe. 

In a washed-out hole if a standard fishing assembly fails to locate the top of the fish, then attempts should be made using either a bent single or a wall hook.

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Milling tools

1. Milling

Milling is used to grind metal objects at the bottom of the well, trim the fish crown, and sometimes to grind shorter stuck drill collars and drill rods.

1) The role of mills

As one of the effective fishing tools, mills are used to trim and grind the top of the fish; grind stuck pipes, rods, and downhole tools. It has obvious effect on the repair andmilling of staggered fractures of casing damaged wells.

2) Classification of mills

The mills are divided into flat sole grinding shoes, concave sole grinding shoes, tapered (pear shaped) grinding shoes and guide collar eye grinding shoes.

2. Mill shoe

Mill shoe is a tool for over-milling operations and milling falling objects. It is used for drilling and removing the rock, sand, cement and other deposits around the falling fish in the well during the milling operation. It can also be used to trim the top of the fish.

Mill shoes are used for annulus milling, overmilling, and flushing of stuck process pipe strings and downhole tools to remove jamming and open channels, creating necessary conditions for fishing.

Types of mill shoes are: A, B, C, D, E, F, G, H, I, J, K, L, M, N types.