Sidetracking

First of all, unless you get a perfect cement job almost every sidetrack can be considered "open hole". Read these notes with that in mind.

The higher the angle, the softer the formation the more chance of success. Low angle, hard formation; you will need a very big bend implying high dogleg severity as it kicks off. Anticipate this if possible.

Pick your spot carefully. Go to the logs and find the best formation and ROP. If possible pick a big dogleg and sidetrack the opposite way. If the old hole builds and turns left then drop and turn right. Obvious really but well planning doesn’t always see it that way. Be prepared to fight for a better spot if you can see one. Do it right and you only need to do it once.

Sidetracking easiest on low side but low/left, low/right usually not too difficult. Going for all turn without a drop is only possible in soft formations and not recommended. Turn and build almost impossible except with a perfect cement job and they are rare.

Open Hole Sidetrack - Two schools of thought – The reamers and the time drillers. Reamers pick a spot to side-track well down a stand then pick up, set a tool-face and ream slowly down to that spot. Then pick up again, not so far and ream down again and so on reducing the reamed section progressively concentrating the effort on one spot till they are sure they have a ledge. Then comes the crunch when you set gently down on the ledge and watch how things react, hopefully side-tracking fairly swiftly.

Reaming is useless where you have a high down drag and therefore a lot of compression in the string. It is impossible to be certain you are stopping at the exact same spot every time since the string may still be on the move even though you have stopped slacking off. Same problem on a semi with heave and tide adding to the uncertainty.

I am more of the time drilling school. Start above the side-track point, set a toolface and time drill. Obvious, yes? Well, a little more than that. Time drilling means you can see immediately you get a ledge of formation through small changes in differential pressure, toolface and possibly WOB. The cuttings stream also relates to what you are doing with the bit at a point and not just over a section. Time drilling allows you to take advantage if, with a little luck, you get an edge early. You are not trapped in a programme. You can react to subtle changes as they occur, slowing things down or speeding them up as appropriate. Nothing wrong with a combination of techniques. Spend some time polishing a section to aid sliding before settling down to time drilling.

And by time drilling I mean t…i……m……..e drilling. Patience is essential especially at low angle in hard formation. Rule of thumb – Time drill at
1/10 previous ROP. Sidetracking from semis on several occasions the tide has gone out faster than I have been time drilling (Important to keep track of the tide when drilling this slowly on a semi). Patience and consistency – slacking off a foot and waiting an hour is not time drilling at one foot an hour. Mark the pipe and keep the driller on schedule. The hardest part of the job is overcoming other people's impatience; the company man, the toolpusher, the driller. Many a sidetrack has been lost through pushing ahead too soon and slipping off the ledge back into soft cement or the open hole. You need to have moved the hole by at least half a diameter before you have a reliable ledge that you can begin to push on. Assuming a consistent 4°/100 dogleg then in 8½" hole you have to drill 32' to get that much displacement and in 12¼" a half diameter takes 38'. This takes time at say 5'/hr. Warn everyone before you start.

Proceed cautiously and look for every clue that the bit is digging – slight reactive torque (toolface drifting left), a little differential pressure (let it drill off), a little WOB (let that drill off too), till you are confident that you have engaged formation.

Track the cuttings and check for yourself the percentage of cement/formation. Take samples off the top screen as well. Loggers have a habit of taking only the fines and this can give an excessive percentage of cement since it shows up more in the fines. I have had geologists and loggers insist that we had 80% cement when great chunks of clay have been bouncing off the top screen.

Jump the Plug – If you find you have plenty of good quality hard cement to dress off surrounded by softer formation it is sometimes possible to "jump the plug", an involuntary sidetrack while dressing off cement. Be conscious of this and track the cutting stream to take advantage of this possibility. It can save a lot of time. Good things do sometimes happen.

Cement Plugs – Sidetracking, for the use of.

Where possible the best place to set a cement plug is on bottom. If this means pumping a few extra barrels of cement to reach kick off point then this is much simpler and better than spotting a pill. This can depend on the length of stinger available. Cementing up round the drillpipe is not a good idea and anyway leads to contaminated cement.
Either a bridge plug or spot a weighted hi-vis pill below the planned setting depth.
Temperature is very important – MWD should be able to supply – tell the cementer though he has probably checked with the mud engineer.
API density for class G cement is 15.8ppg (1.9SG) – This can be pushed to 16.8 ppg (2.0SG) with thinners which can help early strength but needs batch mixing.
Pump enough to compensate for contamination – the problem of contamination increases in deeper and smaller hole and in oil-based mud. 25% excess at least or 100’ extra.
Use highest possible flow rates – turbulent flow in spacers if possible. But remember you can shake a very thin tubing stinger to pieces by pumping too hard.
Use a diverter tool at the end of the stinger to at least direct the flow sideways and if possible up the annulus.
Check setting times – Don’t tag till at least 8 hours and 12-24 is even better


Open hole sidetrack with GeoPilot – Notes from the G-P running procedures.

Several successful open hole sidetracks have been performed in sandstone reservoirs.
Determine the sidetrack point primarily based on drillability and secondarily on geometry.
Time drill at a setting between 150 left and 150 right of highside. Monitor the ABI and determine ROP for time drilling.
Previous open hole sidetracks have taken from 2.5 to 18 hours, sometime It can be more, it’s depending of the bent/Job/formation.

If you don’t be patient during side track

- Your goldfish may die.
- A strange dog might bite you on the street.
- A friend may punch you.
- Your computer may catch fire.
- Your loved one may leave you.

Anyways it will be bad...