When equipment has been lost or is stuck in the hole, the following points shall be considered in deciding the optimum course of action:

• The type of equipment in the hole to be fished (drillpipe, collars, junk bit cones etc).
• The condition of the hole/mud. Will formation instability cause the hole to deteriorate ?
• Is the fish stuck ? If yes, what is causing it to stick ?
• Is it possible to get free ?
• The size and condition of fish.
• Can tools be run inside or outside the fish ?
• What fishing assembly should be run ?
• What was the drilling situation prior to getting stuck ?
• Consider all ways to get loose from fish.
• Will wireline tools have to be run through the fishing assembly ?
• What are the anticipated times and costs to free the fish ?
• Are there open reservoirs below the fish ?

Fishing Economics

The choiceis between two alternatives:

• The known costs that would be incurred if fishing attempts were abandoned.
• The unknown costs of continuing fishing operations.

The right decision is the one that costs the least money, and the problem is to find a strategy for minimising losses.

Alternative Method

A guide to deciding when to stop fishing attempts is to suspend fishing after a calculated number of days using the following equation:

Fishing should be abandoned after (days)        =  alternative operating cost in $

                                                                                    2 x daily fishing rig costs in $/day

Example

Estimated plug-back, sidetrack and re-drill cost           =  $ 1000,000
Total fishing rig cost                                                            =  $ 100,000 / day

Fishing should be abandoned after (days)      =  5 days

When the Fish is Located Between Communicating Reservoirs

Fishing may have to continue beyond the economic acceptable cost.

In cases where the fish is located between reservoirs (that are in communication) fishing may have to continue. In this case annular shut off could be difficult as there is no guarantee of success when cementing around the fish. Environmental constraints and tool costs might prolong fishing jobs eg., stuck radioactive logging tools.

Considerations When the Fish is Abandoned

When attempts to recover the string and regain access to the existing hole are abandoned, the following alternatives are usually available:

• Setting a cement plug and sidetracking, the costs involved are:

• the replacement value of abandoned tools
• possible calliper log materials
• cementing operator
• rig time to set plug
• WOC time and dressing plug
• tool rental for sidetracking
• deviation company charges.

• Plug back and sidetrack, costs are as above plus bits and rig time to drill to original depth.
• Plug back and abandon the hole, move the rig (usually only considered if in top hole), the costs involved are:
  • bits and rig time to drill to original depth
  • time base mud costs.
• Abandon the hole below the fish but complete the well.

Evaluation must be undertaken with a view to relative costs and the objectives of the well.