The causes of tight holes include: Insufficient inhibition, Mud weight, Lubricity and Hole cleaning.

All these factors are important and comparisons should be made between wells with and without problems, to identify the critical factors.

Tight hole is mainly encountered when coming out of the hole. It occurs where sometimes a fresh hole has been drilled, or where the formation elsewhere has a tendency to squeeze during the settling process of the hole.

Tight hole may be detected by a constant or a spot-like overpull experienced in excess of the normal hole drag (as seen in deviated holes).

The overpull may be the result of balling up of stabilisers and drill collars by formation debris not removed from the hole, or from squeezing formations.

The most important factor to realise is that this situation may cause the string to stick. To prevent this situation, it is essential that free movement, rotation and circulation is maintained at all times.

Ensure that the hole, below when pulling out, or above when running in, is in good shape so as to be able to go back there to regain rotation and/or circulation.

Balling up of drill collars and stabilisers under continued high overpulls results in loss of circulation, swabbing, and finally sticking the string. In such circumstances run back to a good part of the hole and consider conditioning the mud, adding lubricants and increasing the mud weight. Advice from Base should be sought.

Hard and fast rules cannot be given for all circumstances. The following procedure is the safest for tripping in an unknown area or through a new section of hole:

Tripping Procedure (Tight Hole)

1. Establish normal drag up and down while tripping in a good section of hole.
2. When pulling into a tight spot, limit the maximum amount of overpull to 15 MT over the normal drag. Do not pull more than 1 m with this pull, but wipe the hole going down past the starting point to ensure the free movement of the string below the tight hole area at all times. Continue this procedure until past the tight section.
3. If 15 MT over normal drag is not sufficient, overpull may be built up to a maximum 80% of the BHA weight in 5 MT increments. The same procedure of pulling 1 m at a time and wiping the hole should be followed after each build up of overpull.
4. When the string is pulled past the tight spot it is mandatory to wipe past it once more before pulling to the next tight spot.
5. At each subsequent tight spot the steps 2 to 4 starting with 15 MT overpull, shall be repeated.
6. Have a lithology log, based on cutting descriptions made up by mud logger, available on the floor at all times. This helps to identify possible tight spots.
7. Where the overpull is continuous or increasing (or both) and nearing 80% of the BHA weight (including HWDP), backream (w/ top drive) or install the kelly, circulate and ream down a few singles. Condition the mud and consider adding lubrication to the system.
8. If no improvement is obtained and no progress is made then contact Base.

Do not struggle in or out over a long interval. Analyse the problem and take action in time to remedy the situation, this is always cheaper than fishing.

The ultimate responsibility on the well site is with the Senior Drilling Supervisor. He must be informed by the contractor immediately of and hole conditions that could result in a stuck pipe. the probelm should be discused with the team: Contractor, Company drilling staff, mud contractor, and if necessary, consultation with Base.

If the string stands up, or excessive drag is experienced, then immediate remedial action should be taken; backream out of the hole with top drive, and ream back.

In areas where hole problems are experienced, increase the nozzle size/annular velocity to improve solids removal (consider four nozzle bits).