Most Read

Latest

Fishing with Washover Strings

Washover strings can be used when:

  • the formation has bridged off and stuck the string.
  • the string has become cemented in the hole.
  • dressing the top of the fish for latching on with an overshot.
  • milling over stuck packers
  • milling over stabilisers and reamers.

Feasibility

Consideration shall be given to the cost of the washover operation as in many cases this will outweigh the loss of the fish in the hole plus possible sidetrack operations.

Shoe Selection

Select the washover strings shoe according to the following table.

 

Shoe Position

Shoe Selection

Inside casing

Hard facing only on the bottom and on the inside of the shoe, so that it does not cut on the outside diameter

In open hole

Hard facing can be on inside and outside. Washing over in open hole shall only be considered in exceptional circumstances.

Clearance is small

Use thin walled shoe. Free movement and torque shall be carefully monitored in this operation.

General Guidelines

The following general guidelines shall be used when running washover strings:

  • A safety joint and drive sub shall always (mandatory) be installed above the washover string to release the string if the washover string becomes stuck.
  • Hardbanding should have same specifications as specified for drillpipe.
  • No more than three or four joints shall be run initially, depending on the hole inclination and dogleg severity.
  • Low rpm and weight shall be used during washovers to reduce the possibility of splitting or flaring the shoe.
  • In order to monitor torque build-up and string resistance, rotation shall be stopped periodically. If torque or resistance become excessive, the washover string length shall be reduced. Each time rotation is re-established, a new cutting pattern shall be created on the washover shoe. To re-establish a new cutting pattern, the string shall be raised slowly while rotating and gently lowered back to bottom. The washover string shall be kept in motion as much as possible to prevent sticking.
  • A junk sub shall be installed above the washover string if stabiliser blades are to be washed over.
  • The mud may be “slicked up” by adding lubricants. This may help reduce friction between borehole and the washover assembly.

Procedure

1. RIH to 10 ft above TOF.

2. Circulate and washover fish while slowly lowering string. Circulate with Hi-Sweep pills. Circulation rate to be high enough especially above washover pipe where string configurations OD’s are different.

3. After washover has swallowed fish, rotate string at 30-50 rpm.

4. Check torque. If torque is too high POOH and change washover.