Wells may require sidetracking in order to re-drill the well to a new target, sidetrack past a fish or sidetrack due to hole problems.

The main requirements in sidetracking a well is the development of a lateral force to allow the bit to cut on the side of the hole. This lateral force should be provided by the geometry of the BHA forcing the cut on the side of the hole.

The most effective BHA configuration to achieve a successful sidetrack kick off is a mudmotor with bent sub.

Kick-off Point Selection

If possible, the kick-off location should be selected where a soft or soft to medium formation is present in order to increase the chances of obtaining a successful kick-off.

However, if only medium to hard formations exist at the required sidetrack depth, a high degree of patience is required.

A controlled ROP should be maintained until confirmation of a successful kick-off is achieved.

Kick-off plugs

The general procedure for setting sidetracking cement plugs is to:

1. SET a 300 - 500 ft neat cement plug (Class G in the production hole section) at 17.0 ppg (batch mix the slurry if possible).

2. WAIT on cement for 12 hours minimum

3. DRESS OFF 20 ft , and WEIGHT TEST the plug

4.1If the plug is firm

Then DRESS OFF a further 20-30 ft comparing drillability with that of the original hole

4.2 IF the plug appears to be good

Then WAIT a further 12 hours before attempting to kick-off

4.3 IF the plug does not show signs of compressive strength

Then DRILL and WASH through sufficient cement to allow placement of a second 300 ft plug at a suitable depth for sidetracking

Casing Windows

When preparing to cut a casing window care should be taken when making the initial cut, to avoid casing collars and centralisers. The cut should be initiated a minimum of 8 ft above a casing collar.

Generally the lengths of window to facilitate an effective sidetrack are:

Typical Assemblies

A suitable assembly will be agreed between the Directional Contractor in consultation with the Drilling Supervisor.

The number of non-magnetic components can usually be reduced by applying a survey correction algorithm to survey data.

General considerations:

• the size of the bent sub will depend on the hole size, formation hardness and required deviation. Note: The geometry of the assembly should be checked to ensure there is lateral loading with the chosen motor length and bent sub for the hole size in which the assembly is run
• it is usually more economical to carry out a sidetrack with a mudmotor/bent sub combination and then trip for a more optimum BHA for the remaining section
• if the assembly is to be used to drill ahead after the kick-off, a motor bearing bit should be selected
• it is possible to run the MWD tool directly above the bent sub and utilise survey correction algorithms
• if sidetracking out of a casing window, the string should be oriented using tool face high side readings or alternatively a UBHO and steering tool above the MWD.

Sidetracking on the Low Side of the Hole

The low side sidetrack can proceed to take off rapidly. Consequently, there is a risk of creating high doglegs coming off on the low side.

It may therefore be preferable to come off low side to the right or left rather than purely low side.

Once the new hole has been cut, lateral separation should be maintained to prevent collapse of the old hole into the new hole.

Maximising Kick-off Success

In cases where external factors can reduce the chances of achieving a first time kick-off (e.g. hard formations, deep kick-offs, or restricted window lengths) the ideal assembly to run to maximise kick-off probability is:

• Mill tooth bit
• mudmotor
• bent sub
• MWD
• UBHO sub
• drill collars.